From Cosmos to Confession: - DataSpace at Princeton University

FAR FROM EVERY STRIFE:
KEPLER’S SEARCH FOR HARMONY IN AN AGE OF DISCORD
Aviva Tova Rothman
A DISSERTATION
PRESENTED TO THE FACULTY
OF PRINCETON UNIVERSITY
IN CANDIDACY FOR THE DEGREE
OF DOCTOR OF PHILOSOPHY
RECOMMENDED FOR ACCEPTANCE
BY THE DEPARTMENT OF HISTORY
Adviser: Anthony Grafton
January 2012

© Copyright by Aviva Tova Rothman, 2011. All rights reserved.

Abstract
This dissertation focuses on Johannes Kepler‘s all-encompassing notion of harmony. By
exploring Kepler‘s place within different kinds of communities—astronomical, religious, and
political—it highlights his efforts both to reveal the harmony in nature and to work toward a
worldly harmony that might follow from it. The project situates Kepler alongside the varying
ways to imagine community in early modern Europe, from religious utopianism to irenicism, and
from the scholarly Republic of Letters to the nascent scientific society. In so doing, it not only
illuminates Kepler‘s larger context and goals, but also the broad relationship between science,
religion, and politics in the sixteenth and seventeenth centuries.
Chapter 1 focuses on Kepler‘s conception of himself as a Lutheran and his relationship to
the Lutheran Church, from his days as a student at Tübingen University to the final statement of
his excommunication in 1619. In particular, I trace Kepler‘s relationship with Matthias
Hafenreffer, the theology professor who loved Kepler dearly, but who eventually fully concurred
with those who sought to excommunicate him. This relationship, I argue, illuminates not only
Kepler‘s own conception of the church and his place within it, but also larger sixteenth- and
seventeenth-century debates about the proper relationship between science and religion, the
nature and scope of the church, and the appropriate disciplinary divisions between mathematics,
natural philosophy, and theology.
Chapter 2 considers Kepler‘s relationship with the Catholic Church, a church which
many of his fellow Lutherans saw as a direct embodiment of the Antichrist. I focus specifically
on Kepler‘s relationship with his patron, Herwart von Hohenburg, with Jesuit Paul Guldin, and
with the larger Jesuit Order. These relationships, I argue, highlight Kepler‘s unique approach to
religious community and his hopes for the future of the church, understood in very broad terms.
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At the same time, they broaden our understanding of the multi-faceted relationship between
Kepler‘s astronomical and religious pursuits.
Chapter 3 explores Kepler‘s attempt to construct a community of Copernicans, through a
focus on the relationship of Kepler and Galileo from 1597 to 1610. I highlight in particular
Kepler's use of various rhetorical techniques in his Copernican campaign, and argue that Kepler
conceived his efforts toward a Copernican community in distinctly religious terms. At the same
time, Kepler tried to model that community on the ideals of the Republic of Letters, and in so
doing he articulated a notion of the ideal man of science that differed from that of Galileo and
others.
Chapter 4 further explores Kepler‘s efforts to create a community of Copernicans by
focusing on the changing target audience of his Epitome of Copernican Astronomy. Though
initially framed as a textbook for schoolchildren, Kepler eventually came to describe the Epitome
as a book specifically intended for expert or powerful readers. This change, I argue, was
impelled specifically by two events which occurred in the middle of the printing—the banning of
the first three books of the Epitome and the start of the Thirty Years‘ War. Kepler‘s changing
attitude toward the Epitome, I contend, sheds further light on his understanding of what it meant
to be a Copernican, and on how Copernicans might best seek to enlarge their communal ranks.
Chapter 5 turns to Kepler‘s conception of politics. I first focus Kepler‘s understanding of
the political resonances of astrology and argue that Kepler drew much from the ideas of the neo-
Tacitists, who emphasized political experience and personal discretion. I then consider Kepler‘s
discussions of political harmony in his Harmonice Mundi, focusing in particular on the ―political
digression‖ at the center of the book. Kepler, I argue, believed that the mathematical harmony
of nature could, and should, provide a general blueprint for political harmony. At the same time,
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he emphasized the subjective nature of politics, a field too complex and subjective to be
grounded directly on the certain truths of geometry.
Chapter 6 offers an account of Kepler‘s evolving approach to the reform of the Julian
calendar. I focus in particular on an unpublished dialogue Kepler wrote in 1604 which proposed
not the adoption of the Gregorian calendar, but rather a differently reformed Julian calendar. I
argue that Kepler used the issue of calendar reform both to suggest the manner in which the
divided church could be reunited, and also to offer a specific model for a churchly harmony that
embraced diversity. He also used the issue of calendar reform to articulate his conception of the
proper political and social role of the mathematician, portraying him as an ideal mediator of the
controversies which led to disharmony in church and state.
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Table of Contents
Abstract ......................................................................................................................................... iii
Acknowledgements ..................................................................................................................... vii
Introduction: “Far From Every Strife” ...................................................................................... 1
Chapter 1: “Matters of Conscience”: Kepler and the Lutheran Church .............................. 24
Chapter 2: “Of God and His Community”: Kepler and the Catholic Church ..................... 91
Chapter 3: “An Ally in the Search for Truth”: Kepler and Galileo .................................... 146
Chapter 4: “Your Copernican Book”: The Targets of Kepler’s Epitome .......................... 196
Chapter 5: A “Political Digression”: Kepler and the Politics of Harmony ......................... 244
Chapter 6: “The Christian Resolution of the Calendar”: Kepler and Calendar Reform 297
Bibliography .............................................................................................................................. 354
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Acknowledgements
My greatest thanks go to my advisor, Anthony Grafton. He encouraged my interest in
Kepler from the start, willingly shared his time, knowledge, encouragement, and advice, and
taught me not only a great deal about Kepler and the process of dissertation writing, but also
about what it really means to be a historian and a humanist.
I have also been extremely lucky to have three readers who have each contributed greatly
to my intellectual development. Matthew Jones was the very first to introduce me to the
discipline of history of science, with an undergraduate lecture course on the Scientific
Revolution. He encouraged my new-found interest over ten years ago and has continued to read
and support my work in the years since. Eileen Reeves has read drafts of all of my chapters
throughout my six years at Princeton, and has always offered insightful suggestions and fresh
perspectives which have greatly benefited this dissertation. When I served as his preceptor, Yair
Mintkzer both guided me through the process of undergraduate teaching and provided me with
an example to which I can only aspire.
Michael Mahoney was a wonderful teacher and mentor, who provided me with a great
deal of support and guidance during my first years at Princeton. He read some of my first work
on this dissertation, and his vision lies at the heart of the finished product in many ways. The
members of Princeton‘s History of Science Program have also shaped this dissertation from the
prospectus through the various chapter drafts, with the many helpful comments and suggestions
they‘ve provided at each step of the way. In particular, I‘d like to thank Daniel Garber, who
helped me pursue my interest in science and religion even before I began this project, and who
helped steer the project itself in always better directions. The comments of James Byrne, Nick
Popper, Renee Raphael, and Jeff Schwegman have all enriched this dissertation in important
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ways. Catherine Abou-Nemeh has been there with me from start to finish, and my time at
Princeton was greatly enhanced by her support, ideas, and friendship. Margaret Schotte has also
been both friend and insightful reader, and it has been wonderful having someone with whom to
share the ups and downs of both dissertation-writing and motherhood.
Patrick Boner, fellow Kepler disciple, has shared with me his knowledge, guidance, and
support. Our Kepler ―road trip‖ through southern Germany will always be one of the highlights
of my time as a graduate student. Daniel Di Liscia welcomed me into the archives of the Kepler
Kommission in Munich, and I am grateful both for his expert advice and his kindness.
This dissertation has also benefited from the comments and questions of the participants
at various conferences in which I presented early versions of some of my arguments, among
them the History of Science Society‘s annual conferences, the Three Societies conference, the
annual Harvard-Princeton Graduate Conference in Early Modern History, and a 2009 conference
at Johns Hopkins University entitled ―Cosmological Continuity and the Conception of Modern
Science.‖ Finally, sections of this dissertation have been previously published in both the
Journal for the History of Astronomy (40.4, 2009) and Change and Continuity in Early Modern
Cosmology, ed. Patrick J. Boner, Archimedes Series, 27 (Springer, 2011).
My parents have always allowed me to pursue my own path and have supported me along
the way. They have shared with me not only their love but also the integrity and selflessness that
imbues everything they do; I hope to try and follow their examples as I raise my own child over
the coming years.
I have asked myself numerous times over the past ten years how I came to deserve a
husband like Elliot Gardner. His love, his friendship, his support, and his devotion to our son
Jack have all been unwavering and unparalleled. I dedicate this dissertation to him.
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Introduction:
“Far From Every Strife”
In a letter of 1610 to an anonymous recipient, Johannes Kepler (1571-1630) encapsulated
his vision of his work and his hopes for the future. He wrote,
If it has pleased the mind to contemplate what God makes, it should also please it to do
what that same God instructs. As soon as this is achieved by all, then there will be
nothing more for humankind to desire than for everyone throughout the whole world to
inhabit one city, and in turn to delight in one another, far from every strife, as we hope
will be the case in the future. 1
Kepler believed that the study of the heavens would reveal clear guidelines for proper behavior
on earth. In a war-torn Europe, he hoped that in explicating the harmonious vision behind God‘s
creation, he might point the way toward harmony of church and state. If people truly recognized
the patterns of harmony that God had imprinted throughout the cosmos, Kepler believed, they
would finally resolve their differences and live together in peace, ―far from every strife.‖ The
divisions of confession, of political allegiance, and of competing philosophical worldviews
would melt away, in this utopian image, in favor of one large world community whose shared
values stemmed directly from the divine archetypal harmony. This dissertation explores
Kepler‘s efforts both to reveal that harmony in nature and to work toward a worldly harmony
that might follow from it.
There are not many biographies of Kepler available, and none that rivals the masterful
effort of Max Caspar in 1948. This is in part because, like that of Leibniz, Kepler‘s corpus is
vast and its complexity daunting. Kepler wrote on an extensive array of subjects ranging from
1 Kepler Gesammelte Werke [heretofore KGW], eds. Max Caspar et al. (Munich: C.H. Beck,
1937-), 16:600: ―Si collibuit animo, quae Deus facit, contemplari, collibuit et quae idem Deus
praecepit facere: quod unum si ab omnibus tam posset impetrari, quam tu ultro praestas: nihil
magis humano generi fuerit optandum, quam ut omnes per totum terrarum orbem, unam urbem
inhabitarent, invicemque etiam in hoc seculo sic fruerentur omni lite remota, uti futurum
speramus in futuro.‖
1

astronomy and astrology to optics and mathematics and from theology and politics to music and
chronology. He also exchanged letters with a large range of correspondents throughout Europe
over the course of his lifetime. The critical edition of his collected works, begun by Caspar and
others in the Bavarian Academy of Sciences in 1935, numbers twenty-two enormous volumes,
including six volumes of correspondence. ―Those macaronic monuments, half Latin and half
German, half mathematical and half unintelligible, to the folly and grandeur of the German
baroque mind,‖ 2 have proved daunting to even the most diligent of readers. Likewise, Kepler
himself seemed to straddle so many divides that it has been difficult even to place him in a
particular communal context. A committed Lutheran excommunicated from his own Church, a
friend to Catholics and Calvinists alike, a layman who called himself a ―priest of God,‖ a
Copernican in a world of where Ptolemy still reigned, an astronomer who spoke about physical
causes, a teacher who both disdained the masses and strove to convert them to his worldview, a
consummate politician and a neutral mediator, a man who argued at the same time for the
superiority of one truth and for the need for many truths to coexist—Kepler does not fit easily
into any box we might construct for him.
Though no recent scholar has attempted to tackle Kepler‘s oeuvre as a whole, there have
been a number of recent studies on Kepler that have greatly enriched our picture of his life and
work, along with a number of recent translations that have made his books accessible to a much
broader audience. 3
Still, there are areas that have been remarkably understudied, particularly
given their centrality to Kepler‘s larger project. One such area is Kepler‘s theology. The best
book on the subject is still Jürgen Hübner‘s Die Theologie Johannes Keplers zwischen
2 Anthony Grafton, ―Kepler as Reader,‖ Journal of the History of Ideas 53.4 (1992): 561-572, at
563.
3 For a summary of this work, see Owen Gingerich, ―Kepler Then and Now,‖ Perspectives on
Science 10.2 (2002): 228-240.
2

Orthodoxie und Naturwissenschaft of 1975. Charlotte Methuen‘s study of Kepler‘s years in
Tübingen offers us a window into Kepler‘s early years and theological education, 4 and Peter
Barker‘s articles have helpfully focused our attention on the importance of the Lutheran tradition
to Kepler‘s worldview. 5
Yet given the extent to which Kepler pursued questions of theology and
the degree to which theological disputes affected his own personal life, much work remains to be
done, and this dissertation hopes to contribute to that larger effort. In particular, aside from
Caspar and Hübner, few scholars have focused on Kepler‘s efforts toward churchly reunification,
of central importance to him throughout his life. 6
Second, Kepler‘s political role has received
remarkably little attention, particularly in light of the eleven years he spent in Prague as Imperial
mathematician, while the explicit political discussion he included in his Harmonice Mundi has
received next to none. 7
The study of Kepler‘s political role in this dissertation is consequently
intended both to highlight some of the meanings that politics held for Kepler, while underscoring
at the same time how much remains to be done. Finally, though Kepler‘s Copernican
arguments—particularly in their physical and mathematical formulations—have received
extended analysis, his broader Copernican campaign has only recently begun to receive sustained
4 Charlotte Methuen, Kepler's Tübingen: Stimulus to a Theological Mathematic (Aldershot:
Ashgate,1998).
5 See, for example, Peter Barker, ―The Role of Religion in the Lutheran Response to
Copernicus,‖ in Margaret Osler, Rethinking the Scientific Revolution (Cambridge: Cambridge
University Press, 2000) and Peter Barker and Bernard R. Goldstein, ―Theological Foundations of
Kepler's Astronomy,‖ Osiris 16: Science in Theistic Contexts: Cognitive Dimensions (2001): 88-
113.
6 A noteworthy exception here is Maximilian Lanzinner, ―Johannes Kepler: A Man without
Confession in the Age of Confessionalization?‖ Central European History. 36.4 (2003): 531-
545.
7 Notable exceptions once again are Barbara Bauer, ―Die Rolle des Hofastrologen und
Hofmathematicus als fürstlicher Berater,‖ in Hoefischer Humanismus, ed. A. Buck (Weinheim:
VCH, 1989), pp. 93-117 and August Nitschke, ―Keplers Staats- und Rechtslehre,‖in
Internationales Kepler-Symposium, Band I, Weil der Stadt, 1971, (Hildesheim: HA Gerstenberg,
1973): 409-424.
3

attention. 8
And his Epitome of Copernican Astronomy, in particular, has rarely been studied at
all. 9
This dissertation hopes to fill some of those lacunae, while offering a more unified
picture of Kepler‘s larger project of harmony—a project which I argue he pursued consistently
throughout his lifetime. Still, I do not intend to offer a comprehensive intellectual biography of
Kepler, nor will I focus on the technical details of his work, which have thus far received the
most scholarly attention. Rather, I focus on Kepler‘s own conception of different sorts of
communities. I consider both the ways that Kepler sought to belong to existing communities—
and to reshape them into his ideal image—and the visions that he put forward of new ideal
communities. In crafting these communal visions, moreover, Kepler at the same time articulated
his conception of his own identity within them. This dissertation, then, is in many ways a
simultaneous study of Kepler‘s efforts at self- and community-fashioning. 10
Those efforts, as we
shall see, were often far from successful. Though Kepler aimed for a world ―far from every
strife,‖ his own life was indelibly colored by conflict and opposition on both a personal and a
8 Noteworthy here are James Voelkel‘s account of Kepler‘s persuasive tactics in his The
Composition of Kepler‘s Astronomia Nova (Princeton: Princeton University Press, 2001), Patrick
Boner‘s article on ―Kepler‘s Copernican Campaign and the New Star of 1604,‖ in Change and
Continuity in Early Modern Cosmology, ed. Patrick J. Boner, Archimedes Vol. 27 (Dordrecht:
Springer, 2010): 93-114, and the newly released book by Robert Westman on the larger
Copernican Question (Berkeley: The University of California Press, 2011).
9 Bruce Stephenson considers the physical theories of the Epitome in Kepler‘s Physical
Astronomy (Princeton: Princeton University Press, 1994), and Isabelle Pantin focuses primarily
on the text‘s images in ―Kepler‘s Epitome: New Images for an Innovative Book,‖ Transmitting
Knowledge: Words, Images, and Instruments in Early Modern Europe, eds. Sachiko Kusukawa
and Ian Maclean (Oxford: Oxford University Press, 2006): 217-237.
10 On self-fashioning, see Stephen Greenblatt, Renaissance Self-Fashioning: from More to
Shakespeare (Chicago: University of Chicago Press, 2005). See also Lisa Jardine, Erasmus,
Man of Letters: The Construction of Charisma in Print (Princeton: Princeton University Press,
1994) and Mario Biagioli, Galileo, Courtier: The Practice of Science in the Culture of
Absolutism (Chicago, University of Chicago Press, 1994).
4

communal level. I focus as well on this discrepancy, between Kepler‘s vision of an ideal world
and the real world that so harshly contradicted that vision.
Of course, the term ―community‖ itself, as Peter Burke has noted, is ―at once an
indispensable…and a dangerous one.‖ 11
Kepler himself more often used terms of either
friendship or familial ties, of amicitia or fraternitas. He spoke this way too of his relationship to
Germany, which he called his vaterland. While the term ―harmony‖ could mean many things to
him, he frequently used it as a substitute for an idealized conception of community, and thus
spoke of his desire to create a harmonia Ecclesiae in the sense of a new and unified churchly
community. Likewise, he referred to the general ―public‖ he hoped to reach, and in particular to
the bonum publicum, the public good. The idea of ―community‖ usefully encompasses all of
these formulations, particularly given the rich historical literature on the term that helps to situate
Kepler‘s own efforts. David Seabean has emphasized the messiness of early modern communal
definition, and the continual negotiation between conflict and coherence by which such
communities were constituted. 12
For Kepler, too, what it really meant to be part of a
community—particularly of a religious community—was a contentious matter, one which he and
Matthias Hafenreffer, his theology professor, debated at length in their letters.
Likewise, the nineteenth-century German sociologist Georg Simmel has argued that
communities are best understood as ―overlapping entities or circles that meet one another at
points of common interest, dispute, or compromise.‖ 13
It is at those moments of intersection, he
11 Peter Burke, Languages and Communities in Early Modern Europe (Cambridge: Cambridge
University Press, 2004), 5.
12 David Sabean, Power in the Blood: Popular Culture and Village Discourse in Early Modern
Germany (Cambridge: Cambridge University Press, 1984).
13 See the general discussion and citation in M. J. Halvorson and K. E. Spierling, Defining
Community in Early Modern Europe, (Aldershot: Ashgate, 2008), 7. See also Georg Simmel,
5

has noted, that community definitions are worked out in clearest relief. Kepler, like so many
others of his time, moved back and forth between multiple kinds of communities which often
came into conflict with one another, and whose competing tensions he struggled to resolve. At
the same time, Benedict Anderson has famously described the nation as an ―imagined
community‖; though most of its members never know one another, they still view their ties ―as a
deep, horizontal comradeship,‖ so much so that they will willingly die for them. 14
The
communities that Kepler struggled to create were in many ways imagined communities of this
nature—ideal, though with real consequences to which Kepler passionately devoted his life‘s
work.
Kepler did not, of course, develop his conception of community in a vacuum. Two
specific and very different sorts of polities deeply influenced his worldview. One was the Holy
Roman Empire of the German Nation itself, a polity characterized by either great diversity or
great fragmentation, depending on one‘s perspective. 15
By the sixteenth century, the Holy
Roman Empire encompassed a wide range of territories and political systems in central Europe,
from the free Imperial cities who owed allegiance only to the emperor and the small
principalities eager to protect their own privileges to the larger territories ruled by powerful
princes. At the same time, there were significant regional differences between north and south
and east and west, as well as differences of language and dialect throughout the Empire. Even
more importantly, from the Peace of Augsburg in 1555, the Empire was divided into two legally
Conflict and the Web of Group Affiliations, trans. Kurt H. Wolff and Reinhard Bendix (New
York: Simon and Schuster, 1964).
14 Benedict Anderson, Imagined Communities: Reflections on the Origin and Spread of
Nationalism (London: Verso, 1983), 7.
15 On the Holy Roman Empire at this time, see Thomas A. Brady, German Histories in the Age
of Reformations, 1400-1650 (Berkeley, University of California Press, 2009) and Michael
Hughes, Early Modern Germany, 1477-1806 (Philadelphia: University of Pennsylvania Press,
1992).
6

ecognized confessions, Catholics and Protestants, and a third, unrecognized confession,
Calvinists. Moreover, from 1555 until the start of the Thirty Years‘ War in 1618—what has
been called the ―confessional age‖—all sides typically grew more entrenched in their own
orthodoxies, and more opposed to one another.
The Empire therefore found itself divided culturally, politically, and confessionally, and
these divisions—and the fear that they would only worsen over time—served as an impetus for
many in central Europe to pursue projects of unification. Many of those projects centered
specifically around the unifying power of the sciences, and of the occult sciences in particular.
Tara Nummedal and Bruce Moran have both described the prominence of alchemy in the Holy
Roman Empire in this context. The alchemical worldview was so powerful, Nummedal writes,
because it posited ―a single, universal, natural order that linked the entire cosmos without regard
for nation or confession, offering a worldview strikingly different from the divided European
reality.‖ 16
Likewise, Moran describes ―the occult vision of unity and universality...as an
intellectual balsam for religious and political confusion.‖ 17
Though Kepler did not embrace the
alchemical worldview, his own emphasis on the harmony of nature stemmed as well from the
fear of ever-growing division in the Empire, and the conflicts with which he was all too familiar
as a Protestant in Catholic territory on the eve of the Thirty Years‘ War.
If Kepler was motivated to imagine a unified community in the face of the divided
realities of the Holy Roman Empire, he was motivated as well by the vision of another, very
16 Tara Nummedal, Alchemy and Authority in the Holy Roman Empire (Chicago: University of
Chicago Press, 2007), 74.
17 Bruce Moran, The Alchemical World of the German Court: Occult Philosophy and Chemical
Medicine in the Circle of Moritz of Hessen, 1572-1632 (Stuttgart, Franz Steiner, 1991).
7

different kind of polity—the Respublica Literarum, or Republic of Letters. 18
The term referred
to an imagined republic of scholars, one without the borders and hierarchies that characterized
the real states in which its members lived. With Latin as their main tool of communication,
those scholars who spoke of the Republic described a united community where everybody was
equal, and where the divisions of church and state were subsumed to the interests of scholarship
and camaraderie. At least in theory, members of this community would leave their own biases
and preconceptions at the door, and would consider one another‘s views with an open and
willing mind. With its members spread across Europe, the Republic was undergirded by an
emphasis on civil communication; the writing of letters both allowed members of this
community to exchange information and to reinforce their communal bonds. And it was
sustained by scholars who were interested in a wide array of subjects and disciplines, and who
viewed their engagement with the work of both their contemporaries and their ancient
predecessors as conversations that might enable them to achieve real communal progress over
time. Kepler‘s own extensive correspondence, his friendships with men of varied political and
confessional allegiances, and his commitment to the communal project of scholarly progress
over time all drew much from this ideal. Likewise, his vision of harmony as a kind of unified
diversity was very much tied to the notion of a community that, though encompassing many
18 On the Republic of Letters, see, for example Ann Goldgar, Impolite Learning: Conduct and
Community in the Republic of Letters (New Haven: Yale University Press, 1995); Hans Bots and
Francoise Waquet, La Republique des Lettres (Paris: Belin De Boeck, 1997); Brian Ogilvie, The
Science of Describing: Natural History in Renaissance Europe (Chicago: University of Chicago
Press, 2006); and Anthony Grafton, ―A Sketch Map of a Lost Republic: The Republic of
Letters,‖ in Worlds Made by Words: Scholarship and Community in the Modern West
(Cambridge: Harvard University Press, 2009): 9-34.
8

allegiances and perspectives, was ―one world, international and nondenominational, rising above
the petty concerns of church and state.‖ 19
While the confessional age in which Kepler lived was beset by division and conflict, the
scholars of the occult and the members of the Republic of Letters were far from the only ones
engaged in unifying projects. Indeed, though the hardening orthodoxies of each of the three
confessions tended to reinforce the fractures in the post-Reformation Church, there were many
men who sought to find ways to reconcile the competing confessions and reunify the church
once more. The confessional age was thus, as Howard Louthan has argued, characterized not
only by radicalization and dogmatism, but also by a widespread irenicism. 20
This term, which
referred to the attempt to peacefully reconcile the disputes of the competing confessional parties,
originated with the Christian humanism of Erasmus, and allowed its adherents to speak above the
particularities of their own orthodoxies and in favor of the commonalities that united all
Christians. Those adherents included emperors like Maximilian II, whose court played host to a
number of prominent irenicists like Hugo Blotius (1533-1608), the Calvinist curator of the
Imperial library, and Johannes Crato von Krafftheim (1519-1585), the Lutheran Imperial
physician. Both men tried to cultivate a deliberate confessional ambiguity and to embrace a
vision of the church that was ―profoundly pious but confessionally neutral.‖ 21
Other important
irenicists of the period included Georg Cassander (1513-1566), a Catholic theologian who tried
to propose methods by which Catholics and Protestants might resolve their differences, and
Georg Calixt (1586-1656), a Lutheran theologian who focused on reconciling Lutherans and
Calvinists, but also tried to add a reformed Catholicism into the mix.
19 Goldgar 3.
20 Howard Louthan, The Quest for Compromise: Peacemakers in Counter-Reformation Vienna
(Cambridge: Cambridge University Press, 1997).
21 Ibid. 65.
9

Kepler himself deeply embraced this irenical vision, and struggled to articulate ways in
which the competing confessions might resolve their differences and the larger church might
reunite. In many ways, his efforts dovetailed with irenicists like Blotius, Crato, Cassander, and
Calixt. Yet there were also ways in which Kepler was unique. For as Howard Hotson has
argued, 22 from the late sixteenth century until the end of the Thirty Years‘ War, very few irenical
efforts focused on unifying Catholics and Protestants. With the success of the Catholic
Reformation in the Empire, Catholics typically came to feel that compromise was unnecessary,
as they could solidify their own ranks without it. Calvinists, due to their own uneasy position in
the Empire, did continue to propose ideas for a larger Protestant reconciliation—indeed,
irenicists in this period were almost entirely Calvinists—but those ideas were routinely ignored
by Lutherans, whose position in the Empire was far more secure. Georg Calixt was distinctive
among Lutherans in his wide-ranging irenicism and his vision of a church that embraced
Catholics, Lutherans, and Calvinists alike, and Kepler‘s own irenicism most closely resembled
his.
While Kepler may not have drawn directly on a strong Lutheran tradition of
reconciliation, he did draw on the irenicism that characterized his immediate environment—the
Imperial court of Rudolf II in Prague. R.J.W. Evans has described how the Rudolfine court
included a cohort of cosmopolitan scholars engaged in the effort to ―preserve the mental and
political unity of Christendom, to avoid religious schism, uphold peace at home, and deliver
22 Howard Hotson, ―Irencisim in the Confessional Age: The Holy Roman Empire, 1563-1648,‖
in Conciliation and Confession: the Struggle for Unity in the Age of Reform, 1415-1648, eds.
Howard Louthan and Randall C. Zachman (Notre Dame: University of Notre Dame Press, 2004):
228-285.
10

Europe from the Ottoman menace.‖ 23
These beliefs lent themselves to a particular engagement
with the occult arts, as described by Moran and others, but also with the investigation of art,
music, and nature more broadly. And this environment provided a haven from which Kepler
could pursue his own investigations into the mysteries of cosmic harmony and the problems of
confessional divide. While in Prague, Kepler remained relatively sheltered from the censure of
orthodox theologians who looked harshly on irenicists, men whom, as the theologians accused,
―by hopping from side to side, want…to teach both parties to walk straight.‖ 24
Kepler thus drew on an irenical tradition that flourished in central Europe in the sixteenth
and early seventeenth centuries, and at the Imperial courts of Maximilian II in Vienna and later
Rudolf II in Prague. This tradition was largely a practical one, focused on the question of real
religious reconciliation, even if only provisional or partial. At the same time, another, more
ambitious tradition flourished alongside it, particularly in Protestant Europe—namely, religious
utopianism. Also in response to the many conflicts that characterized early seventeenth-century
Europe—a period which Hugh Trevor-Roper and many others have famously described as one of
―general crisis‖ 25 —many intellectuals articulated visions of ideal societies, in which reformed
religion and reformed science went hand in hand to point the way toward a new Eden on earth.
23 R. J. Evans, Rudolf II and his World: A Study in Intellectual History, 1576–1612 (Oxford:
Oxford University Press, 1984), 3. On Rudolfine Prague, see also Jaroslava Hausenblasová, Der
Hof Kaiser Rudolfs II.: eine Edition der Hofstaatsverzeichnisse, 1576-1612 (Praha: Artefactum,
2002) and Peter Marshall, The Magic Circle of Rudolf II: Alchemy and Astrology in Renaissance
Prague (New York: Bloomsbury Publishing USA, 2006).
24 Said by Calvinist theologian Theodore Beza about the conciliatory work of Jean de Serres, as
cited in Howard Louthan and Randall C. Zachman, ―Introduction,‖ Conciliation and Confession,
1.
25 Hugh Trevor-Roper, ―The General Crisis of the 17th Century,‖ Past & Present 16 (1959): 31-
64. See also Crisis in Europe, 1560-1660: Essays from Past and Present. Ed. Trevor Henry
Aston (London: Routledge, 1965) ; The General Crisis of the Seventeenth Century. Eds.
Geoffrey Parker and Lesley M. Smith (London: Routledge, 1985); and Theodore K. Rabb, The
Struggle for Stability in Early Modern Europe (Oxford: Oxford University Press, 1975).
11

Charles Webster has described Samuel Hartlib‘s millenarian impulse to create a Protestant
scientific utopia, 26 and Trevor-Roper has linked the utopian visions of Hartlib, Jan Comenius,
and Jon Dury to the particular climate of seventeenth-century England. 27
Yet these efforts were
not limited to England; on the contrary, the efforts of Hartlib and his allies emerged directly from
the central European context, and in particular from the work of Johann Valentin Andreae.
Andreae was a product of the very same Tübingen context as Kepler, and that context did much
to shape his particular utopian worldview. 28
Like Kepler, he formed a close bond with theology
professor Matthias Hafenreffer, whom he referred to as a ―second father.‖ 29
And like Kepler, he
and his peers both strongly identified with the Lutheran Church and at the same time criticized
what they saw as its growing lethargy and rigidity. Moreover, many of them were interested not
only in theology but also in mathematics, astronomy, and alchemy, and their vision of a second
reformation, as articulated in the Rosicrucian texts that Andreae helped author, encompassed
both religion and the sciences. In fact, in his list of the ideal members of his own ideal society,
Christianopolis, Andreae even mentioned Kepler by name. 30
Kepler clearly drew on this utopian tradition; he too advanced a vision of an ideal society,
one in which church and science worked hand in hand toward the betterment of both. Yet in
26 Charles Webster, The Great Instauration: Science, Medicine and Reform, 1626-1660 (New
York: Holmes and Meier Publishers, 1976).
27 Hugh Trevor-Roper, ―Three Foreigners: The Philosophers of the Puritan Revolution,‖ in
Religion, the Reformation, and Social Change (London: Macmillan, 1976).
28 On utopian brotherhoods generally and Andreae specifically, see Donald R. Dickson, The
Tessera of Antilia: Utopian Brotherhoods & Secret Societies in the Early Seventeenth Century
(Leiden: Brill, 1998); Richard van Dülmen, Die Utopie einer christlichen Gesellschaft: Johann
Valentin Andreae (1586–1654) (Stuttgart: Frommann-Holzboog, 1978); and Donald R. Dickson,
―Johann Valentin Andreae's Utopian Brotherhoods,‖ Renaissance Quarterly 49 (1996): 760–802.
29 Dickson, Tessera of Antilia, 38.
30 See Johann Valentin Andreae: Gesammelte Schriften, ed. Wilhelm Schmidt-Biggemann
(Stuttgart: Frommann-holzboog, 1995), 2:474: ―Cui ordini jam Tubingae Wilhelmus
Schiccardus, Argentinae Matthias Bernegerus, Linzii, Jo. Kepplerus, Altorphi, Daniel
Schwenterus, alii alibi, meo & Christophori Besoldi conductu, nomina dedissent….‖
12

some ways Kepler stands apart from Andreae and his followers. For one, Andreae‘s society, like
those of many others who put forth similar plans, was grounded in a particular confessional
context—Andreae‘s was a society of Lutherans, and of German Lutherans at that. Kepler‘s view
was clearly broader than this. In fact, though Andreae clearly saw Kepler as someone who
shared his vision, in the list of the ideal members of his society he included not only Kepler but
Daniel Hitzler, the orthodox Lutheran pastor who had—clearly unbeknownst to Andreae—
recently excommunicated Kepler from the Lutheran Church for his unorthodox theological
views. Likewise, while Andreae maintained that a reformed and harmonious religion would lead
to a reformed and harmonious science, Kepler often argued that the arrow of reform ran in the
other direction. He voiced his agreement with Plato, who emphasized that geometry led ―from
ambition and other forms of greed, out of which wars and other evils arise, to the love of peace
and to moderation in all things,‖ and hoped that ―my mathematics would always be ready to
propose…pleasures certainly not unworthy of a Christian man.‖ 31
Kepler‘s science, then—specifically, his astronomical work—featured centrally in his
larger harmonic vision. He emphasized that it was in his role as astronomer that he could claim
the clearest access to the divine vision: ―as astronomers,‖ he wrote, ―we are priests of the Lord
most high with respect to the book of nature.‖ 32
Indeed, the community to which Kepler devoted
perhaps the most of his energies and persuasive talents was the incipient community of
Copernicans. Kepler was, of course, not the first to try and craft a community of men of science,
31 See KGW 8:11, 27–35; 12, 3–7: ―Utinam vero etiam nunc…locus super sit illi Platonis
oraculo…si se ad Geometriam caeteraque, philosophica studia Graeci conuertissent: quia haec
studia animos ab ambitione & reliquis cupiditatibus, ex quibus bella & caetera mala existent, ad
amorem pacis & moderationem in omnibus rebus adducerent…Quibus votis si Deus annuat, non
equidem indignas homine Christiano voluptates…Mathematice mea…proponere paterata
semper erit.‖
32 KGW 13:91: ―Ego vero sic censeo, cum Astronomj, sacerdotes dej altissimj ex parte librj
Naturae simus.‖
13

nor was he the last. The story of early modern science is, in many ways, the very story of the
ways that such communities came into being. The scientific society, the scientific academy, and
the scientific journal were all products of the seventeenth century, and the themes of civility,
sociability, and credibility were central to the development of modern science as we know it. 33
Though some of these themes run through Kepler‘s own articulation of the ideal community of
science, he was not interested in establishing a formal institution, nor did he want to name a
select group of men as members. Kepler‘s efforts to create a community of Copernicans were in
many ways more similar to the efforts of Tycho Brahe and the other participants of the sixteenthcentury
astronomical community described by Adam Mosley. 34
That community, like the
Republic of Letters, was not bound by a particular location, but constituted via letters; it
embraced a variety of nations and confessions, but focused specifically on specialized questions
of astronomy.
Kepler‘s own efforts to create an astronomical community were both narrower and
broader than those described by Mosley. On the one hand, he aimed specifically at a community
whose members engaged not with astronomy in general, but with Copernican astronomy in
particular. He certainly was a member of the larger astronomical community as well, but he
33 See, for example, Marie Boas Hall, ―Oldenburg and the Art of Scientific Communication.,‖
British Journal of the History of Science 2 (1965): 277–290; Martha Ornstein, The Role of
Scientific Societies in the Seventeenth Century (New York: N.P., 1913); Harcourt Brown,
Scientific Organizations in Seventeenth Century France, 1620-1680 (New York: Russell and
Russel, 1967); Peter Dear, ―Totius in Verba: Rhetoric and Authority in the Early Royal
Society,‖ Isis 76 (1985): 145-161; Roger Hahn, The Anatomy of a Scientific Institution: The
Paris Academy of Sciences, 1666-1803 (Berkeley: University of California Press, 1971); Alice
Stroup, A Company of Scientists: Botany, Patronage, and Community at the Seventeenth-Century
Parisian Royal Academy of Sciences (Berkeley: University of California Press, 1990); and
Steven Shapin and Simon Schaffer, Leviathan and the Air Pump: Hobbes, Boyle, and the
Experimental Life (Princeton: Princeton University Press, 1985).
34 Adam Mosley, Bearing the Heavens: Tycho Brahe and the Astronomical Community of the
Late Sixteenth Century (Cambridge: Cambridge University Press, 1997).
14

focused his energies on crafting and strengthening the new Copernican movement, and he
envisioned (and strategized ways that he might help bring about) a time when everybody was a
Copernican. And here he targeted not just astronomical specialists, or those with a moderate
level of astronomical understanding, or even those artisans who supported them, but the world at
large. Though he spoke disdainfully at times of the unlearned crowd, he hoped that even they
would come to associate with the Copernican worldview. And he was not averse to using
deceptive techniques in order to sway both this vulgus and those moderately learned men who
did not count themselves as practicing mathematicians and astronomers.
Kepler‘s utter conviction in the truth of Copernican theory was relatively unique for his
time. Though many scholars—particularly Lutheran scholars of the Wittenberg school—relied
upon heliocentric theory as an important technical tool, there were few who believed that the
earth actually moved around the sun. 35
One person who did believe this was Kepler‘s own
teacher of astronomy and mathematics, Michael Maestlin. Yet even Maestlin urged Kepler not
to mix astronomy and natural philosophy by discussing the physical causes of Copernican
theory; though a Copernican, Maestlin still hoped to leave the disciplinary divisions of the
university intact. Galileo was another Copernican who believed in the truth of the theory, yet at
the start he was reluctant to speak out for the Copernican cause, despite Kepler‘s urging. And
35 See, for example, Robert Westman, ―The Melanchthon Circle, Rheticus, and the Wittenberg
Interpretation of the Copernican Theory,‖ Isis 66.2 (1975): 165-193 and Peter Barker,
―Constructing Copernicus,‖ Perspectives on Science 10.2 (2002): 208-227. For the early
reception of Copernicus more generally, along with Robert Westman‘s recent Copernican
Question, see Robert S. Westman, ―Three Responses to the Copernican Theory: Johannes
Praetorius, Tycho Brahe, and Michael Maestlin,‖ in The Copernican Achievement, ed. Robert S.
Westman (Berkeley: University of California Press, 1975): 285-345; Stillman Drake, ―Galileo's
Steps to Full Copernicanism and Back,‖ Studies in History and Philosophy of Science 18 (1987):
93-105; and Maurice A. Finocchiaro, ―Galileo's Copernicanism and the Acceptability of Guiding
Assumptions,‖ in Scrutinizing Science: Empirical Studies of Scientific Change, ed. Arthur
Donovan, Larry Laudan, and Rachel Laudan (Dordrecht: Kluwer, 1988): 49-67.
15

later Galileo was as much—perhaps even more—concerned with claiming credit for his
discoveries and guarding his secrets from others as he was in reaching out to others who shared
his views. 36
Kepler‘s efforts to create as broad a community of Copernicans as possible, and his firm
belief in the utter truth of Copernican theory, both stemmed from his larger project of harmony.
To Kepler, the harmony of the heavens would necessarily point the way to harmony on earth.
And that harmony was at its root a Copernican one. He supported the ideas of Copernicus at the
outset, he wrote in his Mysterium Cosmographicum, because they showed just how perfectly
God had structured his universe in accordance with his harmonic blueprint. He explained that
―these hypotheses of Copernicus not only do not sin against the Nature of things, but greatly
assist it. [Nature] loves simplicity, it loves unity.‖ 37
Likewise, Kepler believed that he had
demonstrated that the ideas of Copernicus could be explained by recourse to physical causes,
further proof of their clear claim to truth. To be sure, Kepler modified the views in his
Mysterium Cosmographicum over time, particularly when the observations proved trickier to
integrate into the theory than he had initially thought. Yet from the initial idea of the platonic
solids in his Mysterium Cosmographicum to the theories of musical harmony in his Harmonice
Mundi, Kepler continued to believe that Copernican theory—as explicated and clarified by
Kepler himself, of course—provided as a clear a window as possible into the mind of God.
Crafting a community of Copernicans was thus one way to craft a community of believers; those
who recognized what God had done in the heavens would surely be better able to find their way
to undertaking God‘s will on earth.
36 See Mario Biagioli, Galileo‘s Instruments of Credit (Chicago: University of Chicago Press,
2006).
37 KGW 8.32, 41-42: ―Hae Copernici hypotheses non solum in Naturam rerum non peccant, sed
illam multo magis iuuant. Amat illa simplicitatem, amat vnitatem.‖
16

Kepler‘s Harmonice Mundi, the book he saw as his masterpiece, was the place where he
discussed his notion of harmony in greatest depth. There, he devoted the various sections of the
text to harmony understood mathematically, musically, astrologically, and astronomically,
ultimately concluding with a discussion of the harmonies produced by the motions of the planets.
He linked all these ideas to the larger unifying theme of harmony because he felt that they were
all specific forms of the one harmonic archetype, which he understood as the geometrical
relations between physical quantities. 38
Yet Kepler intended the musical valences of the
metaphor to carry over as well. He knew well that the linkage between music and astronomy had
ancient roots. The Pythagoreans had first articulated the concept of the ―music of the spheres,‖
and Plato‘s Timaeus had also described a musically and mathematically ordered cosmos. 39
Ptolemy, with whom Kepler most closely associated his own work, had also discussed music,
astrology, and astronomy as larger expressions of a universal mathematical harmony. The
linkage between music and mathematics was so strong in the ancient and medieval world that
music was included in the quadrivium of the liberal arts, along with arithmetic, geometry, and
astronomy. Moreover, Kepler was not the first to link this cosmic musical metaphor to the world
of men; Plato, too, had used the notion of harmony to describe worldly peace and concord, as
had a host of thinkers after him, including many in Kepler‘s own time. 40
Kepler clearly drew on the larger discourses of universal harmony in his own work. Yet
when he spoke of the ways that harmony in nature should lead to harmony on earth, he used the
38 See Bruce Stephenson, Music of the Heavens: Kepler‘s Harmonic Astronomy (Princeton:
Princeton University Press, 1994).
39 See Christiane L. Joost-Gaugier, Measuring Heaven: Pythagoras and His Influence on
Thought and Art in Antiquity and the Middle Ages (Ithaca: Cornell University Press, 2007).
40 See Kate van Orden, Music, Discipline, and Arms in Early Modern France (Chicago:
University of Chicago Press, 2005). See in particular Chapter 2: ―Juste Proportion: Music as the
Measure of All Things,‖ 37-80.
17

word very deliberately, with its full musical meaning intact. He explained in his Harmonice
Mundi that
just as…individual consonances considered separately are pleasing on account of the fact
that they are plainly not identical notes, but in a way figured and different notes…in the
same way…the harmonious singing of parts…without any variety in them ceases to be
pleasing altogether. 41
Harmony, to Kepler, implied not a one-dimensional unity, but rather a unified diversity. Just as
music was only harmonious if it contained many different notes, so too, Kepler believed, earthly
communities needed to create a kind of cohesiveness that embraced difference, rather than one
that sought to do away with it. Though Kepler identified as a Lutheran throughout his life, the
reunified Christendom he hoped to create was thus not to be identified with any one confession,
even his own. Rather, it was to embrace them all; to offer some common ground on which all
could agree, and then to allow for the fact that nobody would be able to agree on everything,
particularly when it came to questions of theology. After all, Kepler wrote in his 1623
Confession of Faith, ―Christ the Lord who spoke this word…neither was nor is Lutheran, nor
Calvinist, nor Papist.‖ 42
Kepler endeavored to try and highlight those points of commonality
around which the different confessions might unite, and hoped that his vision of heavenly
harmony might provide the church with a true model to follow. But that model was one of unity
within diversity, not without it.
This attitude was precisely what made it so difficult for Kepler to find a place for himself
within the existing communities of his time. In the struggle to find common ground, Kepler
necessarily placed himself outside the orthodoxies of any one group. For this reason he was
41 The Harmony of the World, trans. and eds. E. J. Aiton et al. (Philadelphia: The American
Philosophical Society, 1997), 252.
42 KGW 12:29.17–19: ―Aber Gott lob das Christus der Herr, welcher diese Wort
aussgesprochen, auff diesen ihren schalg, weder Lutehrisch noch Calvinisch, noch Papistisch
gewest, noch ist.‖
18

accused of arrogance, of pride, and of setting himself apart from others, even while all he wanted
was to bring everybody together. ―I do not like to be looked upon as a man apart,‖ he insisted.
―It hurts me in my heart that the three great factions have amongst them torn the truth so badly
that I must gather it piecemeal where I can find it.‖ 43
Accordingly, he tried to align himself not
only with the Lutherans, but also with the Catholics or Calvinists when he felt that specific
positions of theirs had merit. And he put forward a larger vision of the mathematician as a
mediator, a man whose interest in the truth made him uniquely suited to point the way toward
compromise without bias. In the confessional disputes over the reform of the Julian calendar, in
particular, Kepler offered not only a vision of the mathematician as an ideal confessional
mediator, but also a specific model by which the mathematician might use his expertise in order
to arrive at a harmonious solution that embraced diversity, rather than one that excluded it.
In trying to position the mathematician as a mediating figure, Kepler capitalized on his
own political role as Imperial mathematician. And while Kepler focused on questions of science
and theology, he understood himself as well as a politicus, and addressed problems of the state
alongside problems of the heavens and the church. When it came to the political sphere, too,
Kepler was guided by the ideal of harmony, and in particular by the neo-Stoic ideal of the
―public good.‖ His science, he argued, might point the way to that public good, but only when
wielded carefully and wisely. When it came to his own role as Imperial mathematician, a role
that was fundamentally astrological, Kepler knew well that in the wrong hands astrology could
as easily lead to discord as to harmony. His larger harmonic vision could therefore as easily
43 KGW 12: ―Aber ich bezeug es mit Gott, das ich mich dessen nicht frewe, noch auch mir
drinner wolgefalle, oder gern gesehn werde, als einer der etwas sonders habe. ES thut mir im
hertzen wehe, dass die drey gorsse factiones die Warheit under sich also elendiglich zurissen
haben, das ich sie stucksweise zusamen suchen muss, wa ich deren ein stuck finde.‖
19

prompt him to deemphasize his science when it threatened the public good as it could encourage
him to emphasize it when it supported the public good.
Kepler‘s theological concerns, his astronomical program, and his political vision were all
linked, then, by the larger goal of harmony that was the guiding principle of his life‘s work.
And his efforts to craft new communities, or reshape existing ones, stemmed as well from his
desire to implement the principle of harmony on a very practical level in the real world. In many
ways, Kepler‘s story thus resonates most closely with those of Descartes, Pascal, and Leibniz, as
described recently by Matthew Jones. 44
Those men firmly believed that mathematics and natural
philosophy pointed the way toward the good life, and they tried to popularize their vision and
spread it to a larger public whom they hoped to perfect. Leibniz, in particular, had much in
common with Kepler. He too articulated a broad vision of harmony understood as ―diversity
compensated by unity,‖ 45 and he worked to create ―new natural and metaphysical grounds to
secure and to improve the political, theological, and ecclesiastical order.‖ 46
For Leibniz, the
good life, and the possibility of self-perfection, could never be simply about the individual.
Rather, Leibniz believed, ―truly perfecting the self meant becoming impelled to help
others….loving God meant truly knowing, and therefore loving, his creation.‖ 47
Kepler‘s own
self-fashioning was likewise never just about himself alone, but was always linked to his
struggles to fashion a community characterized by a harmonious unity.
This dissertation is divided into six chapters, which roughly break down into three
sections. The first two chapters focus on questions of religion, the next two chapters focus on
44 Matthew L. Jones, The Good Life in the Scientific Revolution: Descartes, Pascal, Leibniz and
the Cultivation of Virtue (Chicago: University of Chicago Press, 2006).
45 Ibid. 177.
46 Ibid. 231.
47 Ibid. 253.
20

questions of astronomy—specifically, of Copernicanism—and the final two focus on questions
of politics. Of course, as should be immediately apparent from the discussion above, these three
spheres were inextricably intertwined in Kepler‘s worldview. Consequently each section
necessarily overlaps with the others; Kepler‘s discussions on the Eucharist in Chapter 1 were
colored by his geometrical understanding of the Copernican cosmos, and his Copernican
campaign in Chapter 3 was guided by religious notions of accommodation and dissimulation;
likewise, his conception of political harmony was included in a cosmological text, and it
deliberately embraced not only a diversity of political perspectives but also of confessional ones.
Finally, his role in the debate over the Gregorian calendar reforms highlighted perhaps best of all
the ways that all three spheres—the religious, the mathematical, and the political—went hand in
hand in Kepler‘s mind. Only a mathematician could resolve a thorny confessional question like
the calendar, and he could do so best by embracing his political role.
Kepler‘s attempts at community-building were, like those of Leibniz, intended in large
part for the benefit of others. He hoped to share the wisdom that his work on harmony had made
so very clear, and to help steer Europe away from the course to which it seemed so disastrously
inclined. Yet in the end, those attempts were also, very simply, attempts to find a place where he
himself might belong. As Kepler wrote to Maestlin in 1616, he hoped there might be ―some
consolation in agreement, in this most quarrelsome time when humankind is divided into so
many opposing pursuits.‖ 48
Despite his best efforts, and despite even the remarkable trajectory
of his career, which took him from the small town of Weil der Stadt to the Imperial court itself,
Kepler never did truly find a place where he belonged. In the literature, too, he often seems the
odd man out—less celebrated than Galileo, less familiar than Newton, referred to either as the
48 KGW 17:750: ―… quod si qua est consolatio in consensu, hoc litigiosissimo saeculo, genere
humano in tot studia diversissima diviso...‖
21

end of one era or the start of a new one. This dissertation hopes in part to remedy that, by
highlighting the rich context out of which Kepler‘s work emerged, and emphasizing the extent to
which his project had an internal coherence, a single motivating principle that guided it all.
Kepler was not a man who stood outside his time, but rather very much a product of central
Europe during the confessional age. And his theory of universal harmony colored everything in
those twenty-two large volumes that now represent his life‘s work. He knew that the questions
he posed would likely not be answered in his lifetime, and that the solutions he put forward
might not solve the problems that seemed poised to overwhelm his world. Yet he hoped that he
might at least be one voice in a larger effort devoted to achieving world harmony. He thus left
his legacy ―to posterity, if, indeed, it should please God to vouchsafe the human race a length of
time in this world sufficient to work though such remaining questions thoroughly.‖ 49
A Note on Translations
In general, I have provided my own translations of Kepler‘s original words, and have included
the Latin or German originals in the footnotes. The primary exceptions are the Harmonice
Mundi, where I‘ve relied on the translation put out by the American Philosophical Society in
1997, and the Astronomia Nova, where I‘ve relied on the translation by William H. Donahe of
1992.
49 New Astronomy, trans. William H.Donahue (Cambridge: Cambridge University Press, 1992),
p. 640.
22

Chapter 1:
“Matters of Conscience”: Kepler and the Lutheran Church
In a letter of 1598, Johannes Kepler articulated his own vision of his proper role. ―I truly
believe,‖ he wrote, ―that as astronomers we are priests of the Lord most high with respect to the
Book of Nature: it is not fitting [for us] to seek praise of our mental prowess, 1 but only the
special glory of the Creator.‖ 2
By 1619, however, the theologians at Tübingen—headed by
Matthias Hafenreffer, Kepler‘s old friend and mentor—had quite a different view of Kepler.
―Since all your mental prowess was not subordinated to the sacred mysteries of worship,‖
Hafenreffer wrote, ―it has thrown you into a pitiable sort of confusion: for which reason neither I
nor my colleages can approve your absurd and blasphemous fantasies.‖ 3 Along with this
message, Hafenreffer conveyed to Kepler the news that his exclusion from the Lutheran
communion, first decreed seven years earlier, could not and would not be revoked.
In this chapter, I focus on Kepler‘s conception of himself as a Lutheran and his
relationship to the Lutheran Church, from his days as a student at Tübingen University to the
final statement of his excommunication in 1619. In some ways, this is the story behind that
excommunication. 4
But more than that, it is the story of Kepler‘s relationship with one man:
Matthias Hafenreffer, who loved and respected Kepler dearly, but who eventually fully
1 The word Hafenreffer used, ―ingenium,‖ can be translated in a variety of ways. In some cases
it can connote the more formal faculties of imagination or reason, while in others it can mean
natural talent or skill, or even wit. I have typically translated as ―mental prowess,‖ which seems
to be the sense in which Hafenreffer and Kepler refer to it.
2 KGW 13:91: ―Ego vero sic censeo, cum Astronomj, sacerdotes dej altissimj ex parte librj
Naturae simus: decere non ingenij laudem, sed Creatoris praecipue gloriam spectare.‖
3 KGW 17:847: ―…quae res totum ingenium tuum, rerum sacrarum adorandis mysterijs non
subditum, miserandum in modum perturbat: Eam ob causam neque Ego, neque Dominj collegae
et fratres mei, absurdas et blasphemas imaginationes tuas approbare possumus.‖
4 For a far more detailed account of Kepler‘s excommunication and the specifics of his
theological views, see Jürgen Hübner, Die Theologie Johannes Keplers Zwischen Orthodoxie
und Naturwissenschaft (Tübingen: Mohr, 1975).
24

concurred with those who sought to excommunicate him. This relationship, I argue, reveals
much not only about Kepler‘s own sense of self and community, but also about the world he
inhabited. In particular, it illuminates larger sixteenth- and seventeenth-century debates about
the proper relationship between science and religion, the nature and scope of the church, and the
appropriate disciplinary divisions between mathematics, natural philosophy, and theology. Over
the course of his dispute with the Lutheran Church, Kepler continued to identify as a Lutheran,
yet he came to articulate a conception of the church that was far broader than that of Hafenreffer
or his colleagues. God‘s church, Kepler argued, could not be identified with any one confession
alone, and the purpose of those who served it ought to be to guide it toward greater unity. At the
start of his career, Kepler hoped to use his mathematical prowess in the service of this unity;
geometry, he felt, might be the means by which disputing parties could come to agreement. As
his own disagreements with the Lutheran Church became more pronounced and his vision of its
theologians more cynical, Kepler‘s goals became more modest; if unity could not be achieved,
harmony might still be possible. In both his own life and the life of the church, Kepler came to
emphasize the importance of personal conscience and the possibility that disagreement might
still have a place in the larger church—harmony need not imply absolute agreement, and faith
need not imply absolute compliance with all the doctrinal positions of one confession.
Haferenreffer, by contrast, insisted that in matters of conscience absolute adherence to the
doctrines of the church was essential; it was unity, not harmony, that guided his conception of
the church and its members, and this unity was limited to the Lutheran confession alone.
At the same time that Kepler and Hafenreffer struggled with these questions, they
struggled over the proper distinction between theologians and laymen, and the relevance that
mathematics might have for both. While Hafenreffer urged Kepler to embrace his identity as a
25

mathematician when it came to the question of Copernicanism, he insisted that Kepler discard
that identity when it came to questions of theology; ―Remember,‖ Hafenreffer often insisted to
Kepler, ―my Christian distinction between you the mathematician and you the theologian.‖ 5
Kepler‘s conception of mathematics, however, was intricately entwined with his understanding
of God; he could never truly separate his mathematical self from his theological one, however
much he tried at the end. Similarly, Keplers own struggles to assert himself as a layman fell flat
against Hafenreffer‘s understanding of the term. Kepler had wanted to be a theologian from his
earliest days, and he could never fully stop thinking as one, even when it caused him grief.
Ultimately, I argue, the guiding ideal throughout Kepler‘s life was that of harmony—among
disciplines, among individuals, among confessions, and in his own life. Yet as Kepler noted
when it came to the harmony of the music and the harmony of the cosmos, ―for some sensible
harmony to exist and for its essence to be possible, there must be, in addition to two sensible
terms, a soul as well which compares them.‖ 6
Harmony, in other words, was dependent on
something or someone external to appreciate it. For Kepler, sadly, that someone was lacking; he
could never achieve the personal or confessional harmony that he so desperately sought. In the
end, he hoped his books might achieve what he in life could not: ―See, I cast the die, and I write
the book,‖ he wrote. ―Whether it is to be read by the people of the present or of the future makes
no difference: let it await its reader for a hundred years, if God Himself has stood ready for six
thousand years for one to study him.‖ 7
5 KGW 17:829: ―Tu interim sis memor, quod per Christum et salutem tuam te oro, Christinae
meae distinctionis inter Mathematicum, et te Theologum.‖
6 The Harmony of the World. Ed. E.J. Aiton, J.V. Field, and A.M. Duncan. (Philadelphia:
American Philosophical Society, 1997), 291.
7 Ibid. 391.
26

Initial Tübingen Responses to the Mysterium Cosmographicum
In October of 1595, Johannes Kepler, teacher of mathematics and district mathematician
in the Styrian city of Graz, wrote a jubilant letter to Michael Maestlin, his former professor of
mathematics at the university in Tübingen. Kepler had just made a remarkable cosmological
discovery, one which did much to brighten the drudgery of the previous months away from his
place of greatest comfort, the university, and his preferred subject of study, theology. He
documented his discovery and sent a copy of the manuscript to Maestlin, which he titled
Prodromus Dissertationum Cosmographicarum continens Mysterium Cosmographicum. 8 ―I truly
desire,‖ Kepler wrote to Maestlin,
that these things are published as quickly as possible for the glory of God, who
wants to be known from the Book of Nature….I wanted to be a theologian; for a
long time I was distressed: behold God is now celebrated too in my astronomical
work. 9
Unable to devote himself to the Book of Scripture directly, 10 Kepler had turned his focus to
God‘s other book—the Book of Nature—which, he believed, also revealed God‘s providential
plan. The astronomer who unfolded and clarified this plan, argued Kepler, performed a task
analogous to the theologian—one illuminated God‘s words, while the other illuminated God‘s
things. 11
8 Literally, ―Forerunner of a cosmographic discussion containing the secret of the universe.‖
Kepler often refers to the text as his Prodromus, but I will henceforth refer to it as it is
commonly known today, the Mysterium Cosmographicum.
9 KGW 13:23: ―Ego vero studeo, ut haec ad Dej gloriam, qui vult ex libro Naturae agnoscj,
quam maturrime vulgentur…Theologus esse volebam: diu angebar: Deus ecce mea opera etiam
in astronomia celebratur.‖
10 Though Kepler had hoped that his university years would culminate in a career in theology, he
was directed instead to a post as district mathematician in Graz. Though his unorthodox
theological views—which we shall discuss in greater depth below—may have contributed to this
decision, it may have been inspired simply by his clear mathematical aptitude.
11 For a discussion on the trope of ―God‘s two books‖ in early modern science, with a particular
focus on the issue of Copernicanism, see Kenneth J. Howell, God‘s Two Books : Copernican
27

In the Mysterium Cosmographicum, Kepler believed he had done this by demonstrating the
fundamental geometric structure underpinning the cosmos. A convinced Copernican, Kepler had long
sought the reasons for the precise number of the planets and the distances between them. His
solution, described in the Mysterium Cosmographicum, rested on the five platonic solids
(dodecahedron, tetrahedron, cube, icosahedron, octahedron). Kepler demonstrated that by nesting the
platonic solids one inside the other, and then circumscribing circles around each one to represent the
planetary orbits, one could arrive at the distances between the planets, ordered according to
Copernican theory.
And because there were only five platonic solids, it was clear that there would
be precisely six planets. Kepler further argued that the structuring of the cosmos according to the
Platonic solids made perfect sense, for geometry was the tool with which God had created the
universe and all things in it. To be intelligible was to be geometrical, Kepler contended, because
the human mind was imprinted with the very geometrical archetypes that also structured the
cosmos, and was thus uniquely suited to understand God‘s creations. 12
Michael Maestlin, Kepler‘s mathematics teacher and a fellow Copernican, responded to
the Mysterium Cosmographicum with effusive praise. He delighted in the fact that Kepler had
bolstered the theories of Copernicus, and particularly that he had done so by deriving them a
priori, via his deductive reasoning about the geometrical structure of the cosmos, rather than a
posteriori, via observations, as Copernicus himself had done. Maestlin not only praised the
book privately to Kepler, he repeated his praise in an official endorsement of the manuscript
written to Matthias Hafenreffer, Professor of Theology and Prorector of Tübingen. ―I have read
the work of the most learned master teacher Kepler,‖ he wrote,
Cosmology and Biblical Interpretation in Early Modern Science (Notre Dame: University of
Notre Dame Press, 1992). See in particular Chapter 3, ―Kepler, Cosmology, and the Bible.‖
12 See J. V. Field, Kepler‘s Geometrical Cosmology (Chicago: University of Chicago Press,
1988).
28

and I ask you to accept my judgment of it kindly. For whoever dared to think, much less
to attempt, to teach the number, order, magnitude, and motion of the heavenly spheres,
either according to the standard [approach], or according to any other hypotheses a priori
to explain them, and thus to produce them as though from the secret plan of God the
creator?‖ 13
Maestlin noted two additional positive outcomes of Kepler‘s work. First, by arriving at the
Copernican theory a priori, Kepler had challenged the popular approach taken to Copernicanism
by Lutheran astronomers. This approach, first expressed in Osiander‗s introduction to
Copernicus‘s De Revolutionibus and later articulated more strongly by Philip Melanchthon and
others, construed all motions in the Copernican theory (particularly the motion of the earth)
strictly hypothetically. Proponents of this approach maintained that although Copernicanism—or
heliocentrism—was a false theory, it was a useful tool for technical astronomy, and true results
about the positions of heavenly bodies could be obtained from it. 14 Maestlin indicated his
contempt for ―the absurdity of the hypothesis…that the true can follow from the false. For
13 KGW 13:43: ―Scriptum Doctissimi Dominj Magistri Keleri legi. Judicium meum de eo V. M.
beneuole accipias, rogo. Materia et res ipsa ut noua est, et quae nullius unquam mentem subijt:
ita profecto ingeniosissima est, et publicatu, quae in doctorum hominum manus deueniat,
dignissima. Quis enim unquam cogitare, nedum tentare ausus fuit, se Sphaerarum Mundi
numerum, ordinem, magnitudinem, motum, siue secundum vsitatas, siue alias quascunque
hypotheses, a priore docere, rationem reddere, adeoque quasi ex arcano Dei creatoris consilio
depromere posse‖
14 This position was dubbed the ―Wittenberg interpretation‖ in Robert Westman‘s seminal article
―The Melanchthon Circle, Rheticus, and the Wittenberg Interpretation of the Copernican
Theory,‖ Isis 66.2 (1975): 165-193. It allowed for the study and spread of Copernicanism by
avoiding the physical (Aristotelian) and religious (Scriptural) objections to Copernican theory,
since it adopted only the technical innovations while discarding their physical implications.
Erasmus Reinhold, professor of mathematics at the University of Wittenberg from 1536 to 1553,
used Copernicus‘s technical innovations to construct a new set of astronomical tables, the
Prutenic Tables, which were widely used. Yet Reinhold and his successor, Caspar Peucer,
argued against the theory that the earth moved. See also Peter Barker, ―Constructing
Copernicus,‖ Perspectives on Science, 10.2 (2002): 208-227 and Peter Barker, ―The Role of
Religion in the Lutheran Response to Copernicus,‖ in Margaret Osler, Rethinking the Scientific
Revolution (Cambridge: Cambridge University Press, 2000).
29

although it can happen, it only does so by chance, and rarely at that.‖ 15 Yet this aspect of the text
was hardly likely to ingratiate it with the majority of the faculty at Tübingen, who adhered to the
Wittenberg interpretation along with other Lutheran universities. Therefore Maestlin primarily
emphasized the text‘s utility for the technical practice of astronomy itself. ―There is no doubt that
those who collect observations are going to find these foundations, given a priori, of the greatest
help in the reformation of the motion of the heavenly bodies.‖ 16
Along with his praise, Maestlin included some suggestions for revision of the text before
its publication. In particular, he proposed that Kepler make it more clear and accessible to the
popular reader. Kepler had assumed that all readers were already familiar with geometry and
with the technical details of Copernicus‘s astronomical theory, but Maestlin wanted it to reach an
even wider audience. To accomplish this, he suggested that Kepler devote more space to an
explanation of the properties of the regular geometric solids, the details of the Copernican theory,
and the order and dimensions of the heavenly spheres that follow from it. ―For the attentive
reader,‖ Maestlin wrote, ―must not be stopped short by obscurity and enigmas, but must be
excited and encouraged by clarity and a plain and open discussion.‖ 17
Luckily for Kepler, Matthias Hafenreffer, with whom the decision for publication largely
rested, was a sympathetic friend. Though a professor of theology, he was only ten years older
than Kepler, and had a reputation as an insightful scholar and an understanding mentor, one who
15 KGW 13:43: ―Nec est, ut quis absurditate hypothesium, de qua Copernicus a multis accusatur,
offendatur, existimans, quod ex falso verum quoque sequi possit, etc. Nam etsi id fiat, per
accidens tamen, et raro tantum fit.‖
16 Ibid.: ―Hoc ergo ceu fundamento a priorj dato, dubium non est, quin qui Obseruationes
colligunt, voti sui ad reformandos motus corporum coelestium, maximum adiumentum sint
habiturj.‖
17 Ibid.: ―Lector enim attentus obscuritate et perplexitate non offendendus est, sed perspicuitate
et plana atque aperta tractatione, excitandus, et inuitandus est.‖
30

was conciliatory and tolerant rather than harsh and doctrinaire. 18
He was also skilled in
mathematics himself, and thus able to appreciate Kepler‘s broader interests and skills. 19
He and
Kepler formed a close bond in Kepler‘s years at Tübingen, and they remained in contact long
after Kepler had left the halls of the university. Upon receipt of Maestlin‗s letter, Hafenreffer,
representing the faculty of the university, accepted Maestlin‘s endorsement and praised Kepler‘s
manuscript. The university Senate, he wrote to Kepler, ―finds this discovery of yours to be as
admirable as it is useful to all readers.‖ 20 He did, however, agree with Maestlin‘s suggestions for
improvement of the text, and relayed to Kepler the Senate‘s order that he ―set out as a preface
both the hypotheses of Copernicus and the dimensions of regular bodies according to the
recommendations of Maestlin…and remove all obscurity when possible.‖ 21
As to the means by which Kepler was to explain Copernican theory and remove all
obscurity, Maestlin and Hafenreffer disagreed. Maestlin suggested that Kepler preface the
manuscript with the Narratio Prima, the short synopsis of Copernican theory published by
fellow Lutheran Georg Joachim Rheticus in 1540, three years before the publication of the De
Revolutionibus. As he explained later, doing this would not only clearly set forth the details of
Copernican theory, it would also situate the work more appropriately in the minds of his readers,
providing them with a textual context within which to understand Kepler‗s work: ―by this
means,‖ he asserted, ―the interests of the mathematical republic of letters will be served better.‖ 22
18 See Max Caspar, Kepler. Trans. and Ed. C. Doris Hellman (New York: Dover, 1993), 49-50.
19 See Karin Reich and Eberhard Knobloch, ―Die Kreisquadratur Matthias Hafenreffers,‖ Acta
Historica Astronomiae 17 (2002): 157-183.
20 KGW 13:44: ―Quam admirabile est autem hoc nouum inuentum tuum tamen utile esse
omnibus Lectoribus, idem amplissimus Senatus expotat.‖
21 Ibid.: ―Jubet itaque ut secundum admonitiones Maestlini et Copernicj hypotheses et corporum
Regularium dimensiones, quasi praefationis loco praemittas, et alibi quibuscunque locis opus
fuerit, pro posse, omnem obscuritatem tollas.‖
22 KGW 13.58 ―Nam crede mihi, hoc modo Literariae Mathematicae Reip. melius consulitur.‖
31

By contrast, Hafenreffer requested that Kepler explain both the geometry of the Mysterium and
the ideas of Copernicanism in his own words in a short preface. The Narratio of Rheticus would
be a poor substitute, wrote Hafenreffer, since it ―is lengthier and contains certain things foreign
to your Prodromus.‖ 23 Though Hafenreffer did not say so explicitly at this juncture, his likely
objection centered on the realist stance of the Narratio. Unlike other prominent Lutherans,
Rheticus openly emphasized the physical reality of Copernicus‘s cosmos, and argued for the
beauty of the Copernican theory as a physical system, one characterized by unity and harmony. 24
So long as Kepler summarized Copernican theory in his own words, it could perhaps be read as a
continuation of the accepted tradition that Copernicanism was simply hypothetical. Yet the
addition of the Narratio of Rheticus would alert readers even more strongly to the fact that
something more was intended—possibly the very reason why Maestlin recommended its
inclusion.
The Scriptural Implications of the Mysterium Cosmographicum
Like Rheticus and Maestlin, Kepler believed strongly that the Copernican system
represented a true picture of the workings of the heavens. 25 Moreover, he conceived of his work
23 KGW 13:48 ―Collatis Sententijs, placet posterius tuum consilium, ita tamen, ut pro Rheticj
Narratione (quae et prolixior est, et quaedam ab hoc tuo Prodromo aliena habet, et in
quibusdam deficit) breuissimam Expositionem et proportionem Corporum, cum Schemate
generalj, post praefationem ad Lectorem interseras: quae tanquam clauis erunt ad Mysterium
Prodromj.‖
24 See Westman, ―The Melanchthon Circle,‖ 181-186.
25 He, too, argued both in letters and in the Mysterium Cosmographicum itself that the true could
not follow from the false. He addresses this issue most fully in his Apologia for Tycho against
Ursus. See Nicholas Jardine, The Birth of History and Philosophy of Science: Kepler‘s A
Defence of Tycho against Ursus, with Essays on its Provenance and Significance (Cambridge:
Cambridge University Press, 1984). See also Nicholas Jardine, ―The Forging of Modern
Realism: Clavius and Kepler against the Sceptics.‖ Studies in History and Philosophy of Science
10 (1979): 141–173.
32

in the Mysterium Cosmographicum in fundamentally religious terms, arguing that through his
discovery he had revealed God‘s hand through the Book of Nature. He felt that it was important
to reconcile his belief in the truth of Copernicanism with his belief in the truth of Scripture
(particularly those Scriptural passages which seemed, on the surface, to imply the motion of the
sun and the earth‘s immobility). He planned to do so explicitly within the Mysterium
Cosmographcum itself. As he wrote to Maestlin when he first revealed his plans for the book, ―In
the beginning I work with some theses about the Scriptures: and I show how their authority may
be preserved, and yet Copernicus, if he says things that are proper in other respects, can‘t be
refuted by them.‖ 26
That is, he intended to show Scriptural descriptions of the cosmos could be
reconciled to the theories of Copernicus, while at the same time arguing that even if the two
appeared to be at odds, natural phenomena proven to be true could not be disproved merely by
reference to Scriptural citations. 27
At the start, however, neither Kepler nor Maestlin mentioned Kepler‘s plans for this
section of the book in their correspondence with Hafenreffer and the university Senate, but
merely outlined the dominant themes of the text, its Copernican premises, and the reasons why
the discovery was a noteworthy one. Kepler evidently feared that the outspoken Copernicanism
26 KGW 13:23: ―Initio aliquot thesibus de Sacris literis ago: et demonstro, quomodo simul et illis
sua authoritas constet, et tamen Copernicus, si aliter consentanea dicat, ex illis refutarj non
possit.‖
27 This may seem like a highly unorthodox position, in its preference for demonstrated scientific
truth over accepted scriptural traditional. Yet in point of fact it is not that different from the
arguments of Cardinal Bellarmine, representative of the Catholic Church, in his discussion of
Galileo‘s own attempts to reconcile scripture and nature. Bellarmine argued, like proponents of
the Wittenberg interpretation, that Copernicanism be approached hypothetically. Yet he did
concede that if any principle of science were to be demonstrated with certainty, Scripture would
have to be reinterpreted accordingly. He asserted, however, that Copernicanism had not yet
reached that level of certainty. See Richard J. Blackwell, Galileo, Bellarmine, and the Bible
(Notre Dame: University of Notre Dame Press, 1991). Kepler here argues that his a priori
derivation of Copernican theory has raised it to this kind of certainty, where even ostensible
scriptural refutations would not be enough to contradict it.
33

of the text would be enough to elicit objections from the Tübingen faculty; when no objections
were raised at the outset, and Hafenreffer approved the text for publication, Kepler wrote to
Maestlin, relieved that ―no difficulty was put before my little book by the protectors of the Holy
Scripture, as I had feared.‖ 28
Yet over the next few months, after the book had gone to press, it became clear that
Kepler‘s relief was a bit premature. As Maestlin wrote to Kepler, his book
…somewhat offends our theologians…Doctor Hafenreffer time and again has assailed
me (at least jokingly, although they seem to be serious [comments] mixed with jokes). He
wants to dispute with me, all the while defending his Bible, etc. Likewise, not long ago at
a public evening sermon, in the explanation of 1. Genesis, [he said that] God did not hang
the sun in the middle of the world like a lantern in the middle of a room. Indeed, I am
accustomed to opposing these jokes with jokes, while they are jokes; if the matter had to
be treated seriously, I would respond differently. The same Doctor Hafenreffer
acknowledges [the Mysterium Cosmographicum] to be an excellent idea and skilled
discovery, but thinks that it is simply and totally opposed to sacred Scripture and to truth
itself. Indeed, with those who do not sufficiently grasp the principles of these matters (but
who are otherwise most erudite and great men) it is preferable to act jokingly, as long as
they accept jokes. 29
Clearly, this description represents a shift from Hafenreffer‘s initial response to the book, in
which he not only embraced Kepler‘s discovery wholeheartedly but also urged him to explain
Copernican theory even more fully. In this description, by contrast, Hafenreffer appears
28 KGW 13:64: ―…nec interea temporis ulla libello meo difficultas a scripturae sacrae
defensoribus, quod metuebam, objecta fuit.‖
29 KGW 13:80: ―Idem (quod tamen tibi hic concreditum velim) nostros Thelogos etiam nonnihil
offendit…D. D. Hafenrefferus semel atque iterum (iocose quidem, licet iocis seria etiam
intermixta videantur) me adortus est. Er well mit mir disputieren all die weil sein Bibel weeret,
etc. item haud ita pridem in publica vespertina Concione, in explicatione 1. Cap. Geneseos, Gott
hab die [sun] nit mitten in die Welt, wie ein laternen, mitten in einen Saal, gehencket, etc. Verum
iocis illis iocosa opponere soleo, dum ioci sunt, si serio res agenda esset, aliter responsurus et
ego essem. Pro egregia Phantasia et erudito inuento idem D. Doctor Hafenrefferus agnoscit, sed
S. Scripturae et ipsi veritati contrariari omnino et simpliciter putat. Verum cum istis, qui
principia harum rerum non sufficienter tentent (caeteroquin viris magnis et eruditissimis) satius
est similiter iocose agere, dum icos accipiunt.‖ This story is recounted as well in Thomas
Wilhelmi, Die griechischen Handschriften der Universit tsbibliothek T bingen: Sonderband
Martin Crusius : Handschriftenverzeichnis und Bibliographie (Wiesbaden : O. Harassowitz,
2002), along with the text of Hafenreffer‘s sermon and Martin Crusius‘s Greek summary of it.
34

threatened by the Copernican contents of the book; he speaks against Copernicanism in public
sermons and argues that it flatly contradicts the words of Scripture. What caused this change of
mindset in Hafenreffer? Why the move from endorsement and encouragement to the contention
that the discovery was ―simply and totally opposed to sacred scripture and to truth itself?‖
Hafenreffer‘s move to distance himself from Kepler‘s book was first spurred by a
discussion Kepler appears to have had with Hafenreffer when he visited Tübingen to set the
stage for the printing of his manuscript. At that point, Kepler had apparently disclosed his plan to
explicitly reconcile Copernican theory with Scripture within the Mysterium Cosmographicum,
and had asked for Hafenreffer‘s advice. Hafenreffer‘s written reply, composed not in his official
role as Tübingen theologian but instead in his role as Kepler‘s friend and mentor, was lengthy
and heartfelt. Hafenfeffer recounted Kepler‘s request for advice and noted that as ―you desire my
brotherly advice…I will clearly and candidly disclose to you, a most illustrious man and a most
dear brother, what I think.‖ 30
He recalled Kepler‘s training at Tübingen, where he had surely
been taught that the Copernican ideas were only hypothetical, and ought not to be confused with
the true sayings of Scripture. He wrote,
From the moment that I first became aware of those hypotheses I have always felt it to be
beyond doubt that one must distinguish openly between them and Sacred Scripture,
which you observed when you were with us and even now you can rightly remember. 31
For this reason, Hafenreffer continued, he recommended, in both his own name and that of his
30 KGW 13:92: ―Quod denique subiungis, aliquos tuos illos conatus, in nouis demonstrationibus
mirarj, prouidi te dubium esse, quid hac in parte agendum, utrum sc. silentio res praetereunda,
an vero in id enitendum, ut omnibus pateat, tuas illas hypotheses per omnia scripturae sacrae,
consentaneas esse, atque ea in parte, ut ego quidem accepj Epistolam tuam, haud obscure,
fraternum meum consilium expetis. Ea in re, quid sentiam, clarissime vir, et frater charissime,
candide et aperte tibj aperiam.‖
31 Ibid: ―Inter hypotheses nimirum illas, et sacram Scripturam, aperte distinguendum esse, quod
me constanter sensisse, etiam ab initio conspectarum hypothses[grek] procul dubio, et cum
nobiscum esses animaduertere, et etiamnum probe meminisse potes.‖
35

colleagues that the proposed chapter on the reconciliation of Scripture and Copernican theory
―must be omitted… except for some brief mention of the matter which is made immediately at
the beginning.‖ 32
Hafenreffer argued that rather than include the proposed reconciliation (operating from
the standpoint that as Copernicanism was physically true, it had to be reconciled to Scripture),
Kepler ought to adopt the standard Lutheran approach to Copernican theory, which firmly
emphasized the Aristotelian disciplinary divisions between mathematics (and astronomy, one of
the mixed mathematical sciences), physics, or natural philosophy, and theology. 33
He wrote:
If there is some place for my council (as I firmly hope), you will act as a mathematician
alone, unconcerned about whether [your objects of study] correspond to existing things or
not. For I believe that a mathematician achieves his goal if he presents hypotheses to
which the phenomena correspond as accurately as possible: and I think that you yourself
would yield to someone who could offer better [hypotheses]. Nor does it follow that the
truth of things conforms immediately to the hypotheses devised by each expert. I do not
want to mention the irrefutable [proofs] which I could produce from the Sacred
Scriptures. For I think that what is needed here is not debate but brotherly advice. And if
you heed it (as I certainly am confident you will) and act as an abstract mathematician, I
have no doubt that your thoughts will be judged very agreeable by many (as they
certainly are for me). 34
The division between the disciplines of physics and mathematics would protect Kepler and
32 Ibid.: ―Hinc enim factum est, ut non tam meo, quam DD. Collegarum meorum nomine, Caput
Tractatus (puto quintum numero fuisse) quod istam concilationem attingebat, ommitendum esse
monuj, ne illae ipsae disputationes inde exorirj possint. Quod etiam omissum est, nisi quod ab
initio statim, aliqua, sed breuissima ejus rej fit mentio.‖
33 See James A. Weisheipl, ―The Nature, Scope, and Classification of the Sciences,‖ in Science
in the Middle Ages, Ed. David C. Lindberg (Chicago: University of Chicago Press, 1978).
34 KGW 13:92: ―Proinde si fraterno meo consilio (vti firmiter spero) locus aliquis est; porro in
ejusmodj demonstrandis Hypothesibus, nudum Mathematicum ages, nihil sollicutus vtrum rebus
creatis ita respondeant an secus. Mathematicum enim, finem suum consequutum arbitror, si tales
exhibeat hypotheses, quibus [greek] quam exactissime respondeant: et teipsum puto cessurum
esse illj, qui proferre posset meliores. Nec tamen consequitur, vuniuscujusque Artificis Meditatis
hypothesibus, rerum veritatem confestim conformarj. Nolo attingere, quae ex sacris inuicta
possem depromere. Non enim disputationibus, sed fraternis monitis opus esse judico. Quibus si
tu (utj certo confido) parueris, et abstractum Mathematicum egeris, nihil dubito, quin
cogitationes tuae, plurimis (uti certe mihi quoque sunt) jucundissimae sint futurae.‖
36

prevent him from overstepping the boundaries of orthodoxy, Hafenreffer maintained. Since
natural philosophers alone could discourse on the true nature of the heavens, while astronomers,
practitioners of a mathematical discipline, could only describe the positions of heavenly bodies,
Kepler‘s use of Copernican theory, from the standpoint of a mathematician, would not be viewed
as dangerous or particularly controversial. Operating from the standpoint that the true could
follow from the false, many of Kepler‘s conclusions could be utilized in order to improve
astronomical calculations, while the basic Copernican premise could be discounted as a useful
fiction. 35
The Theological and Communal Implications of the Mysterium Cosmographicum
Though Hafenreffer urged Kepler to act as an abstract mathematician and ignore the
relationship between Copernicanism and Scripture, Kepler was strongly committed to the
physical truth of the Copernican system. If Hafenreffer‘s appeal had ended here, then, it could
only have worked had Kepler been worried enough about his overstepping of theological bounds.
Hafenreffer, however, went one step further, and argued for the omission of the proposed chapter
on grounds that would have appealed much more strongly to Kepler. He urged Kepler to
consider the cohesive bonds of community, rather than simply the strict bounds of doctrine. His
concern, he wrote, was not merely that Kepler himself would be contravening an accepted truth
of the church, but rather that since many Lutherans would perceive Kepler‘s actions that way,
and since some might even agree with him, Kepler‘s actions could only increase the strife and
35 Hafenreffer‘s description of these disciplinary distinctions was, of course, an overly simplified
one, which did not account for the fact that the status of these disciplines had already evolved
long before Kepler‘s time. For a more nuanced account of the place of astronomy and its
evolution over the early modern period, see William Donahue, ―Astronomy,‖ The Cambridge
History of Science, Volume 3: Early Modern Science, eds. Katharine Park and Lorraine Daston
(Cambridge: Cambridge University Press, 2006): 562–595.
37

disagreement in an already contentious and fractured Lutheran Church. Hafenreffer implored
Kepler
as a brother, that you not attempt to propound or fight for that stated harmonization
publicly, for thus many good men would be offended, and not unjustly, and the whole
business could either be impeded, or tainted with the grave stain of dissension. 36
With this plea, Hafenreffer appealed not to Kepler‘s sense of orthodoxy, but rather to Kepler‘s
desire for harmony in the church. Hafenreffer‘s own desire for churchly harmony was so
important to him, he wrote, that potential harm to the church—by which he meant the Lutheran
Church in particular—would totally invalidate any good that might have come from Kepler‘s
discovery:
But if (and may God, in his greatness, avert this) you want to publicly harmonize those
hypotheses of yours with the sacred Scripture and to fight for them, I fear that it is certain
that this matter of yours may erupt in dissension and battle. In which case I wish that I
had never seen those thoughts of yours, which in themselves and considered
mathematically are splendid and noble. As it is, already in the church of God there has
been more contention than is advisable for the weak. 37
Hafenreffer concluded his letter by assuring Kepler of his ―most dear and sincere brotherly love‖
and urging him to ―act as a strict mathematician and constantly foster tranquility in the church, as
I know was agreeable to you in the past.‖ 38
36 KGW 13:93: ―Sed rebus sic iam stantibus, fraterne consulo et moneo, ne dictam illam
conciliationem publice uel proponere, et propugnare coneris, sic enim multj bonj, non immerito
offensj, et totum negotium uel impedirj, uel graui dissensionum macula adspergj posset.‖
37 Ibid.: ―Sin (quod maximus et optimus auertat Deus) publice istas hypotheses cum scriptura
sacra conciliare velles, et propugnare, certum metuo, ut in dissensiones et neruum res isthaec
erumpat: quo casu velim ego, me istas cogitationes tuas, in se quidem, et Mathematice
consideratas, praeclaras et nobiles, nunquam vidisse: Jam dudum enim in Ecclesia Dominj, plus
contentionis est, quam infirmis expediat.‖
38 Ibid.: ―Sed nescio quo me abripiat stylus: uel potius fraternus meus in te amor: qui nisj talis in
te esset, qualis est, ardentissimus nimirum et candidissimus, tam liberam stylo licentiam non
permisissem. Sed hic idem amor, duo abs te postulat, ut nimirum, strenuum nobis agas
Mathematicum: et quam antea tibj commendatam esse scio, Ecclesiae tranquillitatem, constanter
foueas.‖
38

Hafenreffer‘s own position makes a great deal of sense given his post as a theologian at
Tübingen. The Tübingen theologians had played a central role in shaping the post-Reformation
theological climate, and in fashioning the Lutheran movement into a strong and unified
confession. 39
Jakob Andreae, Tübingen Chancellor from 1561 to 1590, was a pivotal figure in
the attempt to create doctrinal accord between the different branches of Lutheranism. As
Württemberg, the province in which Tübingen was located, was straddled by Catholic Bavaria
and the Calvinist Palatinate, the need for Lutheran unity was pressing. Andreae had argued that
the best way to achieve confessional unity was to create a simple list of articles of faith with
which the majority of theologians could agree. He was instrumental in drafting the Formula of
Concord, which enumerated these articles and sharply distinguished between Lutherans and their
Catholic and Calvinist adversaries. 40 After its completion in 1577, the Formula of Concord was
adopted by two-thirds of Lutheran Germany, including the province of Württemberg, where all
government and clerical officials, as well as all teachers and university professors, were required
to sign their assent. 41
39 See Charlotte Methuen, Kepler‘s T bingen: Stimulus to a Theological Mathematics
(Aldershot: Ashgate, 1998), 41–46.
40 See Lowell C. Green, The Formula of Concord: An Historiographical and Bibliographical
Guide (St. Louis: Center for Reformation Research, 1977).
41 In summarizing the situation for Kepler and his environs, I‘ve simplified a story that was
neither this uncomplicated nor this uniform. First, while the Formula of Concord did take
seriously some concerns of both Philippists and Gnesio-Lutherans (or Flacians), it largely
followed the more uncompromising Gnesio-Lutheran approach. Moreover, while in some areas,
like Württemberg, it received overwhelming support, there were others, like Sweden and
Denmark, where Philippism continued to flourish. Finally, there were specific issues in the
39

The Formula of Concord was therefore the symbol of the quest for Lutheran unity, a
quest which emanated directly out of Württemberg and Tübingen University and which drew its
strength from the perceived need for stability and agreement in the face of threats from Catholics
and Calvinists, the enemies of the Lutheran Church. In light of this, it is clear that Hafenreffer‘s
plea that Kepler not disturb Lutheran unity by raising the contentious issue of Scripture and
Copernicanism stemmed directly from a theological environment which prized Lutheran unity—
and the particular doctrinal orthodoxy that undergirded it—above all else. Yet Hafenreffer
focused not on the orthodox doctrines themselves, but rather on the importance of unity, hoping
that this alone would sway Kepler as no doctrinal arguments could.
As it turns out, Hafenreffer was right to assume that this plea for unity would appeal to
Kepler, for whom harmony of both church and nature was preeminent. Interestingly, however,
Kepler argued for a strong and explicit emphasis on religion and the physical truth of
Copernicanism in his Mysterium cosmographicum, for precisely the reasons that Hafenreffer had
argued for their exclusion—the goal of strengthening a divided church. When Kepler had earlier
described his book to Michael Maestlin, he had asserted that he hoped it would serve to
strengthen its readers‘ faith in God. This strengthening of the faith, he clarified in a letter of
1597, would be achieved by the book‘s emphasis on geometry as the basic tool with which God
had created the universe and all things in it. Kepler argued that his book had illuminated the way
that God had fashioned humans in his image, by making them uniquely capable of recognizing
and understanding geometrical forms, and in turn the structure of the natural world. He wrote,
For as the eye was fashioned for understanding colors and the ear for understanding
sounds, thus the mind of man was fashioned not for understanding anything whatsoever,
but [specifically] for understanding quantities. And the closer something is to bare
Formula of Concord that continue to be disputed over time—one of which (the doctrine of
ubiquity) concerned Kepler directly, as we shall see below.
40

quantities—as it were, to its own origin—the more properly the mind perceives it; the
farther it recedes from this, the more obscurity and errors there are. For our mind carries
its notions about its own nature, built upon the category of quantity, with it toward the
study of divine things: if it is deprived of them, it is able to assert nothing except by mere
negations. 42
Kepler here contrasted ―quantities‖ with ―numbers‖—the latter he understood to be abstract and
mathematical, while the former were concrete and geometrical. 43
Kepler argued that mankind
was specifically created to appreciate and understand geometrical quantities on a very
fundamental level. Thus by demonstrating that the underlying structure of the universe was
geometrical, Kepler believed he had increased man‘s ability to understand and speak about God
and his creation. 44
42 KGW 13:64: ―Nam ut oculus ad colores auris ad sonos, ita mens hominis non ad quaevis, sed
ad QUANTA intelligenda condita est, remque quamlibet tanto rectius percipit, quanto illa
propior est nudis quantitatibus, ceu suae originj: ab his quo longius quidlibet recedit, tanto plus
tenebrarum et errorum existit. Affert enim mens nostra suapte natura secum ad divinarum rerum
studia notiones suas in praedicamento quantitatis extructas: quibus si spolietur, nihil nisi meris
negationibus definire potest.‖
43 See KGW 13:23: ―We see that God created the worldly bodies in accordance with a fixed
number. Moreover, number is an accident of quantity, meaning worldly number. For before the
world there was no number, except for the trinity, which is God himself. Therefore if the world
was fashioned to the measure of numbers, it must have been to the measure of quantities. But
neither in a line nor a surface is there number, but only but infinity. Therefore it is in bodies.‖
(Videmus, deum creasse corpora mundana ad certum numerum. Numerus autem est quantitatis
accidens, numerus inquam in mundo. Nam ante mundum nullus erat numerus, praeter
Trinitatem, quae est ipse deus. Quare si ad numerorum mensuram est conditus mundus, ergo ad
quantitatum mensuram. At in linea nullus numerus nec in superficie, sed infinitas. In corporibus
igitur.) The importance of the trinity, of course, is itself the starting point for the Mysterium
Cosmographicum: Kepler uses it to justify both the centrality of the sphere and the truth of the
Copernican system, since the Son, Father, and Holy Spirit correspond, in Kepler‘s view, to the
fixed stars, the sun, and the ether, and to the circumference, center, and volume of the sphere
itself. See Rhonda Martens, Kepler‘s Philosophy and the New Astronomy (Princeton: Princeton
University Press, 2000), 39-44.
44 Kepler here was also responding directly to a tradition of negative theology, in which God
could only be defined via negation—a tradition espoused by Nicholas of Cusa, whom Kepler
greatly admired. See for example, Clyde Lee Miller, Reading Cusanus: Metaphor and Dialectic
in a Conjectural Universe (Washington, D.C.: Catholic University of America Press, 2002), 12–
67. Kepler‘s suggestion is that quantity, and geometry more broadly, can enable people to speak
directly about the divine, not merely through negation.
41

But Kepler did not end his argument here. Rather, he argued for a much more explicit
continuity between his idea of the heavens and the religious conflicts on earth, one which, he
believed, could have immediate and wide-ranging effects. Specifically, he believed that the
central motif of the Mysterium cosmographicum clarified an objection of the Calvinists against
the Lutheran doctrine of ―illocal presence,‖ central to the Lutheran understanding of the
Eucharist. 45
Luther had argued that Christ‘s statement ―hoc est corpus meum‖ implied his real
presence in the Eucharist, and that this presence could not be understood in only a spiritual sense.
Christ‘s body was actually present in the bread and the wine. Yet the presence of Christ‘s body
was not restricted to the bread and the wine at the moment of Mass. According to Luther,
Because we believe that Christ is God and man, and the two natures are one person, so
that this person cannot be divided in two...it must follow that he…is and can be wherever
God is, and that everything is full of Christ through and through, also according to his
humanity—not according to the first, corporeal, limited manner, but according to the
supernatural, divine manner. 46
This doctrine, known as ubiquity, implied that as God was omnipresent, so too was Christ‘s body
to be found everywhere throughout the universe.
By extension, Luther did not assert a miraculous change of the substance of the bread and
the wine into the body and blood, for Christ‘s body and blood were already there, as they were
everywhere. The Mass was a powerful testament that Christ left behind for his followers, not a
particular, localized miracle or transformation. Moreover, Luther argued that believers needed to
45 What follows is a brief summary of the Lutheran position at this time. For a more complete
explanation of the various debates about the Eucharist, see Lee Palmer Wandel, The Eucharist in
the Reformation: Incarnation and Liturgy (Cambridge: Cambridge University Press, 2006).
46 ―Vom Abendmahl Christi Bekenntnis,‖ D. Martin Luthers Werke, Weimarer Ausgabe
(Weimar, 1883–1929), Schriften, 26, 332b: ―Weil unser glaube helt, das Christus Gott und
mensch ist, und die zwo naturn eine person ist, also das die selbige person nicht mag zurtrennet
werden...so mus folgen, das er…sey und sein muege allenthalben, wo Gott ist, und alles durch
und durch vol Christus sey auch nach der menscheit, nicht nach der ersten leiblichen
begreifflichen weise, sondern nach der ubernatuerlichen goettlichen weise.‖
42

efine their understanding of Christ‘s body, and what its presence actually implied. Rather than a
kind of pantheism to which the doctrine of ubiquity steered dangerously close, Luther maintained
that Christ‘s body was not corporeal in the usual sense, and was not subject to any physical or
natural limitations. Christ‘s body, according to Luther, was really present everywhere, but not
locally so. The Eucharist did not link the body of Christ directly to the physical world, for it was
divine, and the presence of Christ‘s body in the Eucharist could only be understood in a nonmaterial
and non-corporeal sense.
Kepler referred the doctrine of ubiquity, and in particular the notion of ―illocal presence‖
in his 1597 letter to Maestlin, arguing for the theological value of his Mysterium
Cosmographicum. He maintained that his book made the Calvinist objection to the doctrine of
―illocal presence‖ understandable, and indeed, persuasive. The Calvinists argued against the
idea of a physical presence in the Eucharist—though God‘s presence was real, it should be
understood only spiritually. Kepler had shown in his book, he noted, that everything in the
physical world could only be understood through geometric quantities—that is, corporeally. The
idea that Christ‘s body was a body in any sense of the word and yet was not subject to natural
and material limitations, as the Lutherans maintained, was therefore meaningless, much as the
Calvinists insisted. To speak of a presence that was both real and illocal was to speak
incoherently and obscurely, and ―to assert nothing except mere negations.‖ As Kepler explained,
From here comes that agitation of the Calvinists toward the phrase ―illocal presence.‖ For
both the expression (presence) and the thing understood behind the expression were
chosen from the creation of this world, which exists in space and time, and they indicate
[the idea of] quantities, even to those who are most cautious. If anyone at all were to take
the opportunity to carefully assess these and similar things selected from my little book, I
think that the factions differing in religion would come one step closer together. 47
47 KGW 13:64, 113-119, 9 April 1597: ―Hinc illa Calvinistarum [greek] ad nomen
PRAESENTIAE ILLOCALIS. Nam et vox (praesentia) et res intellecta sub voce, desumpta est ex
conditione hujus seculj, loco et tempore constantis, digitumque vel cautissimis ad quantitates
43

In other words, by forcefully demonstrating the centrality of geometry to the entire physical
world in his Mysterium cosmographicum, Kepler believed that he was clarifying, and, he hoped,
helping to eliminate a point of tension between the Lutherans and the Calvinists. In so doing, he
believed he was helping to repair some of the breaches in the church, and uniting the factions
that were at war.
Kepler and Hafenreffer, then, each made their cases with the same goal in mind. Kepler
believed that emphasizing the physical and religious aspects of his book would bolster the unity
of the church, by helping the hostile confessions better understand one another, and perhaps
resolve their differences. Hafenreffer argued that those emphases would further divide the
church by creating more disagreement, and that eliminating the chapter on Scripture and
Copernicanism would far better preserve the unity of the church. It is clear, however, that
Kepler and Hafenreffer had two separate notions of ―the church‖ in mind. For Hafenreffer, the
church whose unity he hoped to preserve was the Lutheran Church. As a theologian at
Tübingen, a mainstay of Lutheran orthodoxy, Hafenreffer saw Lutheran unity as preeminent.
The inter-confessional doctrinal debates among Lutherans, Catholics, and Calvinists needed to
occupy the full energy of the church. The church could not afford to worry about debates within
its ranks, if ultimately it hoped to maintain its integrity in the face of external opposition.
For Kepler, however, the ―divided‖ church that needed repair was the whole of
Christendom, not merely the Lutheran confession. The struggles within the Lutheran Church
were real, but they paled in comparison to the debates dividing the church understood in a more
universal sense. While some believed that those inter-confessional debates were irreconcilable,
intendit. Haec et similia si quilibet occasione ex meo libello despumpta secum perpenderet:
opinor, uno gradu propius conventuras partes in religione dissidentes.‖
44

and indeed that such reconciliation was undesirable (for only one particular confession
represented the true church), Kepler‘s ultimate goal was a united Christendom, and he believed
that reconciliation of the confessions was indeed possible. Moreover, Kepler not only felt that
reconciliation of the church was a priority, he also felt that his cosmological work was an
important tool in the enterprise of reconciliation. He argued that the truths of astronomy,
demonstrated a priori in his book, showed that some of the debates dividing the confessions, like
the nature of the Eucharist, could be definitively decided. His mathematical work, that is, could
be mobilized to settle some of the sharpest confessional disputes, in ways that would brook no
dissent. For how could one argue with certain knowledge, demonstrated a priori, of the very
fabric of the heavens? Of course, Kepler had demonstrated a truth that contradicted the beliefs
of his own Lutheran Church—one that, as we shall soon see, caused him a great deal of trouble.
Yet though Kepler considered himself a devout Lutheran, the unified church he envisioned
contained elements of all the confessions—for, as he later wrote, ―Christ the Lord who spoke this
word…neither was nor is Lutheran, Calvinist, Papist.‖ 48
Despite Kepler‘s belief in the importance of his discovery, Kepler evidently found
Hafenreffer‘s arguments persuasive—or, perhaps, still felt too closely bound to his Tübingen
roots to defy the advice of his mentor, particularly on so contentious an issue. In a letter to
Maestlin, Kepler reiterated Hafenreffer‘s request ―that I refrain from mention of the Sacred
Scriptures in public. It would give offense to many good men…Meanwhile he orders me to
48 KGW 12:29.17–19: ―Aber Gott lob das Christus der Herr, welcher diese Wort
aussgesprochen, auff diesen ihren schalg, weder Lutehrisch noch Calvinisch, noch Papistisch
gewest, noch ist.‖
45

proceed actively with these hypotheses, to the extent that they are helpful to astronomy.‖ 49
Kepler confided to Maestlin that he would follow Hafenreffer‘s advice and omit the chapter in
question, because of the possibility of creating unnecessary conflict. ―What are we to do?‖ he
asked. ―The whole of astronomy is not worth one of Christ‘s little ones being offended.‖ 50
Yet
Kepler took pains to note that he did this out of respect for unity, and not because he felt that
there was anything objectionable about the material he wanted to include. Moreover, he argued
to Maestlin that the same was true for Hafenreffer himself. Hafenreffer, he noted, had
―eloquently praised the discovery,‖ understanding full well its Copernican import. And though
Hafenreffer pretended to find the idea of heliocentrism problematic, Kepler wrote,
I truly cannot believe that he is averse to this opinion. He pretends, in order that he may
reconcile his colleagues, whom perhaps he offends with the promotion of my book. And
this must be conceded to him. For peace with his colleagues is more important to him
than with me. 51
Kepler could not accept the possibility that a close mentor and friend, one whom he so respected,
could have read his book and not been persuaded by the arguments he had so clearly outlined. 52
He reiterated this point in a later letter, claiming that Hafenreffer was ―not opposed to
49 KGW 13:99: ―Quo consilio ad D. Hafenrefferum scripserim, nosti. Respondit, summa
literarum haec est: abstineam a mentione sacrarum literarum in publico. Offensum irj multos
bonos…Interea jubet me strenue pergere in his hypothesibus, quatenus ad astronmia faciunt.‖
50 Ibid: ―Quid agemus? Tota astronomia tantj non est, ut unus ex pusillis Christj offendatur.‖
51 KGW 13:85: ―Quod si quid harum rerum ad te perfertur, id quaeso ne me celes. D.
Hafenreffero authore mutavi initium operis. Ille est typi promotor, ille copiosus inventj
laudator…Et vere credere non possum, ipsum ab hac sententia abhorrere. Simulat, ut reconciliet
collegas, quos fortasse promotione mei libellj offendit. Et hoc illi concedendum est. Prestat enim
ipsi pacem cum collegis esse, quam mecum.‖
52 Kepler‘s conviction in the utter persuasiveness of his argument, and the clarity with which he
believed he had made his points, stands in marked contrast to his more cautious approach, and
his attentiveness to the possibility of disagreement, in the Astronomia Nova. James Voelkel
describes Kepler‘s keen awareness of ―the negative response his physical reformation of
astronomical theory faced from within the astronomical community‖ and his calculated attempts
throughout the book ―to convince his readers of the necessity of his approach and to lead them
through difficult and contentious material.‖ See The Composition of Kepler‘s Astronomia Nova
(Princeton: Princeton University Press, 2001), 2.
46

Copernicus, but must necessarily stand among the other theologians for the authority (as they
think) of Scripture. Therefore he does not explain to me his genuine opinion.‖ 53
Yet he accepted
Hafenreffer‘s seeming opposition, for peace and unity, he believed, should be the ultimate guides
for the behavior of all those who cared for the church, from the followers of established church
doctrine all the way up to those who established it.
This did not mean, however, that Kepler was prepared to adopt the explicit position that
Copernicanism was hypothetical, or even to avoid the issue entirely. Rather, he explained to
Maestlin, he would merely allude to his true beliefs obscurely, following the tradition of the
Pythagoreans. Those who were schooled and interested enough could ascertain his true
intentions; others would be happy in their ignorance. He would recommend ―the silence of
Pythagoras and the riddles of Plato.‖ 54
―Privately if someone approaches us, let us communicate
to him candidly our opinion,‖ he wrote. ―Publicly let us be silent.‖ 55
He conveyed to Hafenreffer
his willingness to eliminate the offending chapter from the manuscript, and Hafenreffer appeared
satisfied. Kepler‘s letter had filled him with joy, replied Hafenreffer, ―for from it I understood
that you esteem the tranquility of the church more than any noble and beloved products of your
own mental prowess….[Therefore] let the pious and holy tranquility of the church live and
flourish.‖ 56
53 KGW 13:99: ―Enimivero quod antea censui, jam multo magis credo: non esse alienum a
Copernico hominem, sed inter theologos caeteros necessario standum ipsi pro authoritate (ut
putant) scripturae. Ideoque suam genuinam sententiam mihi non explicat.‖
54 KGW 13:85: ―Ipse jam sero incipio laudare silentium Pythagoricum, et aenigmata Platonica.‖
55 KGW 13:99: ―Cum itaque pars maxima doctorum etiam, ad hanc astronomiae (ut vulgo
videtur) sublimitatem intellectu suo non ascendat: age Pythagoraeos vel tandem etiam institutis
imitemur. Privatim nos quis adit, communicemus illi candide nostram sententiam. Publice
taceamus.‖
56 KGW 13: 102: ―Quanquam amice et frater charissime, omnes, quae a te mihj perferuntur
literae, jucundissimae sunt: proximae tamen singularj quadam et cumulata suauitate totum me
repleuerunt. Ex ijs enim intellexj, te pluris facere Ecclesiae tranquillitatem, quam quoscunque
47

While Kepler omitted the chapter on Copernicanism and Scripture, as he promised, he
did include a brief discussion of the issue at the very opening of the Mysterium Cosmographicum
(which Hafenreffer had indicated would be acceptable). He opened by sharply distinguishing
between Copernican theory and Scriptural truth, and coming down very strongly on the side of
Scripture. He wrote,
Although it is pious to consider immediately at the start of this discussion of nature
whether anything is said contrary to Sacred Scripture, nevertheless I believe it to be
untimely to disturb this controversy here, before I am challenged. I promise this
generally, that I will say nothing which might do injury to the Sacred Scripture, and that
if Copernicus is found guilty with me I will deem him worthless. And this was always
my intention, from when I first became acquainted with the books of Copernicus‘s
Revolutions. 57
Kepler here left open the possibility that nature and Scripture could, in theory, contradict one
another, and that in this case the faithful Christian would have to come down on the side of
Scripture—a possibility that he had denied earlier in private letters, and would explicitly deny
years later. 58
ingeniorum nobilissimos et charissimos foetus. Et quamuis de Thesium veritate adhuc quidem
dissideamus, eo quod uterque nostrum suis fundamentis nititur: quia tamen propter tuam, qua
fruj tibj uideris, sensus abundantiam, non quicquam succenseo: sic multo minus tu mihj poteris
indignarj, qui firmioribus suffultus rationibus libere dissentio: interim tamen Mathematicas
contemplationes, perpetua admiratione venerans. Sed viuat et vigeat Ecclesiae pia sanctaque
tranquillitas.‖
57 KGW 8.31, 1-11: ―Etsi pium est, statim ab initio huius de Natura disputationis videre, an nihil
Sacris Literis contrarium dicatur: intempestiuum tamen existimo, eam controuersiam hic
mouere, prius atque solliciter. Illud in genere promitto, nihil me dictirum, quod in Sacras
Literas iniurium sit, et si cuius Copernicus mecum conuincatur, pro nullo habiturum. Atque ea
mens mihi semper fuit, inde a quo Copernici Revolutionum libros cognoscere coepi.‖
58 Years later, in 1621, Kepler released the second edition of the Mysterium Cosmographicum,
complete with an extensive set of newly added footnotes. This was after the publication of the
Astronomia Nova, in which Kepler had published an extensive introduction on the relationship
between Copernicanism and Scripture, and after the publication of the Epitome of Copernican
Astronomy, in which he had also addressed this issue directly. As a footnote to this contention
about the primacy of Scripture over nature, Kepler clarified that nature and Scripture necessarily
agreed with one another, and that therefore there could never actually be a disagreement between
the theories of Copernicus and the words of Scripture. He explained that ―certainly God has a
48

Though Kepler hewed close to orthodoxy when it came to the relationship between
scripture and science, he was more unequivocal in his challenge to the common Lutheran
approach to Copernican theory. Hafenreffer had urged Kepler to speak only as an abstract
mathematician, without regard to the physical truth of Copernicanism. His discovery would then
be widely hailed as useful to astronomy, Hafenreffer claimed, even by those who denied that
Copernicanism was true. Kepler argued explicitly against this approach in the book, and asserted
that
I could never agree with those who rely on a model of accidental demonstration, which
infers something true from false premises by the rule of the syllogism. These men
contend, relying on this model, that it is possible for something to be false, as they deem
the Copernican hypotheses, and nevertheless for true phenomena to follow from it, as
from geuine principles. But the model does not fit. For that conclusion from false
premises is accidental, and the false nature of it appears as soon as it is applied to some
related matter: unless you freely permit that arguer to take up infinite other false
propositions, and never in this back and forth to agree with himself. 59
tongue, but he also has a finger.‖ The finger of God was clearly evident in nature, which Kepler
believed he had proven to operate according to the theories of Copernicus. Scripture, by contrast,
God had adjusted based on the ―common tongue of men‖—a reference hermeneutical principle
of accommodation. ―Therefore,‖ Kepler concluded, ―in matters which are quite plain, everyone
with strong religious scruples will take the greatest care not to twist the tongue of God so that it
refutes the finger of God in Nature…Let him debate with himself whether sufficiently sound,
sufficiently prolific reasons have been discovered for reconciling the tongue and the finger of
God; or whether he will repudiate that reconciliation and hasten to suppress with censorship the
renown of the immeasurable splendor of the works of God. That this renown should come to be
known to the common people, nay rather, to the generality of the even superficially educated,
could never be brought about by order. Ignorance refuses to respect authority; it resorts
spontaneously to combat, relying on numbers and on the shield of habit, which is impenetrable to
the weapons of truth.‖ Mysterium Cosmographicum (1596, second edition 1621): The Secret of
the Universe, tr. A. M. Duncan (New York: Abaris Books, 1981), 85.
59 KGW 8.31, 24-33: ―Atque hoc loco nunquam assentiri potui illis, qui freti exemplo
accidentariae demonstrationis, quae ex falsis praemissis necessitate Syllogistica verum aliquid
infert. Qui, inquam, hoc exemplo freti contendebant, fieri posse, vt falsae sint, quae Copernico
placent hypotheses, et tamen ex illis vera phenomena tanquam ex genuinis pricipiis sequantur.
Exemplum enim non quadrat. Nam ista sequela ex falsis praemissis fortuita est, et quae falsi
natura est, primum atque alii rei cognatae accommodatur, seipsam prodit: nisi sponte concedas
argumentatori illi, vt infinitas alias falsas propositiones assumat, nec vnquam in progressu
regressuque sibiipsi constet.‖
49

In addition to denying the possibility that the true can follow from the false, Kepler argued in the
Mysterium Cosmographicum for the physical truth of Copernicanism on its own grounds.
Ptolemaic theory was incomplete, and Copernicanism far superior, for ―the old hypotheses
simply do not account at all for a number of outstanding features,‖ such as the number of
spheres, the times of orbit, and the reason for their placement. ―On all these points,‖ Kepler
wrote, ―as a magnificent order is shown by Copernicus, the cause must necessarily be found in
it….Copernicus's postulate cannot be false, when so reliable an explanation of the appearances—
an explanation unknown to the ancients—is given by them.‖ 60
Kepler appealed to the argument that Copernicus himself had made in his preface—that
the beauty and symmetry of Copernicanism were themselves grounds for assent. 61 ―These
hypotheses of Copernicus not only do not sin against the Nature of things, but greatly assist it,‖
he wrote. ―It loves simplicity, it loves unity. Nothing exists in it which is idle or superfluous,
but more often one cause is designed for many effects.‖ 62
Copernicus had united the cosmos into
one simple system, and had ―freed nature from that oppressive and useless paraphernelia of so
many immense orbs.‖ 63 Finally, Kepler argued that his own arrival at Copernican theory a priori
was a further truth of its veracity, and was so unassailable that from his discovery Copernican
60 Ibid. 32, 9-11; 30-32: ―Quibus omnibus in rebus, cum apud Copernicum ordo pulcherrimus
appareat, causam etiam inesse necesse est… Non posse falsa esse Copernici principia, ex quibus
tam constans plurimorum [greek: phenomena] ratio, ignota veteribus, reddatur, quatenus ex illis
redditur.‖
61 See Robert Westman, ―Proof, Poetics, and Patronage: Copernicus's Preface to De
Revolutionibus,‖ in Reappraisals of the Scientific Revolution, Eds. David Lindberg and Robert
Westman (Cambridge: Cambridge University Press, 1990).
62 KGW 8.32, 42-8.33, 4: ―Hae Coeprnici hypotheses non solum in Naturam rerum non peccant,
sed illam multo magis iuuant. Amat illa simplicitatem, amat vnitatem. Nunquam in ipsa
quicquam otiosum aut superfluum extitit: at saepius vna res multis ab illa destinatur effectibus.‖
63 Ibid. 33, 8-9: ―Atque sic Vir iste non tantum naturam onerosa illa et inutili supellectili tot
immensorum orbium liberauit.‖
50

theory iIt could be demonstrated with no ambiguities for anyone, even Aristotle himself, if he
were alive.‖ 64
It is evident, therefore, that Kepler followed Hafenreffer‘s advice, but only up to a point.
He eliminated the attempt to reconcile Scripture and Copernican theory, and did so on the
grounds that it was not worth damaging the integrity of the church. Yet he remained firm in his
explicit belief that Copernican theory was a physically true description of the cosmos. Given this
stance, the elimination of the attempted reconciliation amounted at best to an evasion of the
issue, not exactly the approach Hafenreffer had recommended. If Copernicanism were true, and
so incontrovertibly true that even Aristotle would agree, then it must, by extension, agree with
Scripture—or Scripture itself was wrong, a position which was unthinkable, even to Kepler.
Kepler had claimed that he would dismiss Copernicanism if it were shown to disagree with
Scripture, yet it was clear to the discerning reader that this was not a position he viewed as
possible.
Maestlin also clearly stood on Kepler‘s side of the fence. Kepler had entrusted him with
the coordination of the printing, and—against Hafenreffer‘s advice to Kepler, and without
consulting Kepler first—Maestlin prefaced the manuscript with the full text of Rheticus‘s
Narratio, which opposed the traditional Lutheran approach to Copernican theory and argued for
its physical truth. Maestlin added a brief letter to the beginning of his text, where he urged
readers to approach the texts of both Rheticus and Kepler without preconceptions, and to keep in
mind that even in the works of the ancients ―the question of the place and lasting rest of the earth
64 Ibid. 33, 12-15: ―Neque dubito affirmare, quicquid a posteriori Copernicus collegit, et visu
demonstrauit, mediantibus Geometricis axiomatis, id omne vel ipso Aristotele teste, si viueret
(quod frequenter optat Rheticus) a priori nullis ambagibus demonstrari posse.‖
51

is not at all clear.‖ 65 He further noted that Kepler had demonstrated Copernicus‘s claims ―as
genuinely and particularly drawn out from the nature of things as from geometry, due to which
they cannot be contradicted.‖ 66 Rheticus‗s Narratio, Maestlin‗s own preface, and Kepler‗s
comments all made it clear that Kepler did not speak as an abstract mathematician. Even though
Kepler removed the section on Scripture and Copernicanism, Hafenreffer could not have been
thrilled with the final product. Still, Maestlin noted that Hafenreffer‗s criticisms were all veiled,
and that he tended to address the issue with jokes. And Kepler remained in Hafenreffer‘s good
graces, still a beloved friend and disciple despite their disagreements.
Kepler’s Exclusion from the Lutheran Communion
Kepler‘s Copernicanism, then, was not at the root of any real trouble between him and
the Lutheran Church. He conceded to Hafenreffer‘s requests, at least in large part, before the
publication of the Mysterium Cosmographicum. And even after the publication of his
Astronomia Nova in 1609, which did explicitly address some of the scriptural interpretations he
had agreed to leave out of the Mysterium Cosmographicum, Kepler was not subjected to any
censure or reprimand by the Tübingen theologians. 67
Instead, Kepler‘s real confrontation with
the Lutheran Church stemmed not from astronomy but from theology more directly—
65 KOO I:26: ―Is quaeso prius rem cognoscat, & examinet, quam praecoci praeiudicio
sententiam ferat; Is legat, quae Copernicus lib. I. cap. V. & quinq; sequentibus, item quae
Keplerus noster cap. I. sui Prodromi scribit: Nec non quae Rheticus sequente Narratione habet,
ubi principales rationes enumera, quare a veterum Astronomorum hypothesibus recedendum
fuerit. Et videbit: Questionem de loco & perpetua quietate Terrae nequaquam liquidam esse.‖
66 Ibid.: ―Atque hanc sententiam ipse non ligicis, nec leuibus aut dubijs, vel anilibus, multo minus
alienis, atque ad propositum suum violenter adactis coniecturis, sed genuinis, proprijssimis, tam
ex rerum Natura, quam ex Geometria depromptis, quibus contradici non potest, ratiocinijs
confirmat.‖
67 This may, in part, have been because he was by then out of their ambit of authority, already
ensconced in Prague as Imperial Mathematician.
52

specifically, from Kepler‘s unorthodox views about the theological doctrine of ubiquity. As
Kepler had made clear as early as 1597, he believed that Christ‘s body was not omnipresent in a
physical sense, and that even the presence of Christ in the Mass should not be understood
physically—a position that seemed to have far more in common with the Calvinist Church than
with Kepler‘s own.
In 1597, he had linked this position closely to the arguments of his Mysterium
Cosmographicum—geometry itself, he had then claimed, made it clear that the Lutheran doctrine
of ubiquity was an untenable one. Yet over the years, he began to offer instead other, more
traditionally theological reasons for his disagreements with the doctrine, and to deemphasize the
geometrical angle. Scripture itself and the ancient church Fathers, he emphasized time and
again, were quite clearly opposed to the notion; he insisted that he necessarily opposed any
doctrine that was so obviously a modern innovation. ―I feel the force of antiquity deep within
my heart,‖ he wrote to Matthias Hafenreffer in 1610, attempting to justify his reservations about
ubiquity. ―I am wrongly suspected by you of Calvinist belief when it comes to the person of
Christ. There is nothing in Calvinism that is agreeable to me that is new—[I believe] only that of
which antiquity convinces me.‖ 68
His disagreements with his Lutheran brethren, Kepler claimed,
revolved only around ―that which Luther first invented and Jacob Andreae and others elaborated
concerning the ubiquity of God and his union with the flesh, [leading toward] the omnipresence
of the flesh.‖ 69
68 KGW 16:586: ―Sensi vim antiquitatis intus in pectore. Itaque admonitus inde dico vobis,
frustra vos me circa Personam Christi de studio Calvini suspectum habere (ut audio fieri); nihil
in Calvini, qui novus est, gratiam fieret, nisi antiquitas persuaderet.‖
69 Ibid.: ―Tunc autem persuadet antiquitas, cum vos mussatis, erraverit hic et ille Pater necne,
cum haec et illa scriberet, et cum verba ejus a communi usu abducitis et scum sensui, qui Jesuitis
et Calvinianis servit, nihil opponitis, nisi illam a Luthero ano 26. primum inventam et a Jacobo
53

Though Kepler‘s position certainly contradicted the Lutheran Church‘s stance on the
presence of Christ in the Eucharist, it was, in fact, less radical than it may seem at the outset, for
it was only the Tübingen theologians who so strongly insisted on the physical omnipresence of
Christ‘s body. Indeed, the proper Lutheran approach to the doctrine of ubiquity was hotly
debated within the ranks of the confession itself, and not even the drafting of the Formula of
Concord conclusively settled this debate. 70
Even at the start of the movement, Melanchthon had
disagreed with Luther and adhered to a more Calvinist understanding of the presence of Christ‘s
body, and his views had at first dominated the movement; indeed, in the Consensus Dresdensis
of 1571 the faculty at Wittenberg and Leipzig had openly rejected the strict form of the ubiquity
doctrine. Martin Chemnitz, a follower of Melanchthon and one of the foremost Lutheran
theologians of his day, advocated a milder form of ―relative ubiquity,‖ which stressed the
omnipresence of God‘s will, rather than his body. It was primarily in Württemberg that Luther‘s
strong notion of absolute physical ubiquity held sway, mostly through the influence of Johannes
Brenz, another leading Lutheran theologian—born, by chance, in the same town as Kepler—who
feared that ―'the devil intended through Calvinism to smuggle heathenism, Talmudism, and
Mohammedanism into the church.‖ 71
The Württemberg Confession of 1559, drawn up by Brenz,
was the first document to officially endorse this understanding of ubiquity.
With the Formula of Concord, Lutherans attempted to solidify some kind of confessional
unity, as noted earlier. The notion of ubiquity proved a particularly tricky one to resolve; in the
Andreae et ceteris amplificatam ratiocinationem ab ubiquitate Dei et unione cum carne ad
omnipraesentiam carnis.‖
70 For a more detailed summary of the Lutheran stance on ubiquity, see Philip Schaff,
Bibliotheca Symbolica Ecclesiae Universalis, Volume I (New York: Harper and Brothers, 1878),
from which I‘ve excerpted the above summary. See particularly the section on ―The Formula of
Concord. AD 1577,‖ 258-340, and more specifically, ―Part VII: The Christological or
Ubiquitarian Controversy,‖ 285-296.
71 Cited in ibid. 282.
54

end, the document tried to effect a compromise between the absolute and relative approaches, but
leaned toward the more absolute one, given the prominent role the Württemberg theologians
played in drafting it. Martin Chemnitz, also one of the document‘s drafters, reluctantly signed
the Formula for the sake of peace, despite his reservations about the doctrine of ubiquity. Even
so, the controversy continued; it was carried on in particular between the theologians of Giessen,
who adhered to Chemnitz‘s relative view, and the theologians of Tübingen, who followed the
absolute view of Brenz. Matthias Hafenreffer himself was one of the key Tübingen figures in
this controversy. 72
There were, in fact, many Lutherans who shared Kepler‘s reservations about
ubiquity, just not in Tübingen. Kepler could not have picked a worse place to voice his concerns
and still hope for acceptance.
Though Kepler did express his disagreements with the doctrine of ubiquity from time to
time over the years, until 1612 he encountered no strong opposition from the guardians of
orthodoxy in Tübingen. After the expulsion of Lutherans from Catholic Graz in 1600, Kepler
had made his way to Prague, a cosmopolitan city of many beliefs and confessions. This
diversity, along with Kepler‘s own position as Imperial mathematician to Rudolf II, likely
shielded him from the censure of the theologians in the more conservative Würrtemberg. Yet as
the political situation in Prague became increasingly fraught, Kepler came to feel that he would
be better off in Würrtemberg, his ―vaterland,‖ as he often referred to it. He still saw his old
university, Tübingen, as a place of refuge and tranquility, despite any disagreements he may
have had with some of the faculty there. He thus wrote to Duke Johann Friederich of
Würrtemberg in the spring of 1609 requesting a position for himself at Tübingen, either as a
professor of mathematics or of some other discipline which the duke thought worthy of him.
72 The controversy eventually fizzled out over the course of the Thirty Years‘ War, and the
milder form of ubiquity, following Chemnitz, predominated.
55

The duke referred the request to his council, who noted that Michael Maestlin, the current
professor of mathematics at Tübingen, was getting older, and that Kepler, a famous
mathematician in his own right, would potentially make a good replacement. However, they
directed him to turn down the request at present; Tübingen did not yet need to replace Maestlin.
As a token of goodwill, however, the duke sent Kepler a goblet worth 12 to 15 florins.
Encouraged by what he took as a sign of the duke‘s favor, Kepler quickly replied to the
duke, thanking him and reiterating his interest in the position. Kepler then devoted the rest of his
letter to a summary of his position on the issue of the Eucharist and on confessional disputes
more generally. Recognizing, perhaps, that his theological objections to the Formula of Concord
might prevent him from obtaining a job at Tübingen, Kepler hastened to explain those objections
to the duke and convince him that they presented no impediment either to his own status as a true
Lutheran or to his potential employment at the university. Perhaps because the duke himself was
no theologian, Kepler chose not to descend into the nitty-gritty of theological minutiae in this
letter, and instead focused on the question of religious unity, an issue always at the forefront of
his mind. In his opinion, he wrote, when it came to contentious issues like the Lord‘s Supper or
the question of predestination, each side ought to ―reach out a hand‖ to the other and try to find
common ground. 73
The Formula of Concord, however, took the opposite approach, by pointing
an accusatory finger at the Calvinists and only increasing the divide in the church. For this
reason, he would sign the Formula ―only conditionally,‖ 74 and he would continue to believe that
even someone who adhered to the Calvinist doctrines should be deemed ―our brother in
73 KGW 16:528: ―…ich deren gentzlichen mainung bin, wan man etliche articulos, als de coena
Dominj etc beseitz setzete, und biss auff ein andermahl auffsparete, darneben jnen in
vorerwehneten articulis de praedestinatione etc. die hand raichete.‖
74 Ibid.: ―Als hab jch zu mehrer befuerderung einer sollichen hoffnung bey meiner person, mir
einmahl und zwar gewissens halben fuergenommen, der formulae Concordiae nit anderst als
conditionaliter.‖
56

Christ.‖ 75
He hoped that this conditional subscription could still allow him to serve at the
University (which did require a subscription from all its faculty). He added that it could even
lead to increased peace in the church, by demonstrating to others with specific objections that
there was still a place for them within the Lutheran Confession. 76
The duke did not reply, and two years later, with no offer of a position at Tübingen yet
forthcoming, Kepler put pen to paper once again and asked the duke if a post might now be
found for him in the province to which he so longed to return. This time, the duke‘s advisors
seemed inclined to grant the request; they once again reported to the duke that Kepler was a
reputable mathematician who himself had studied under Maestlin, and who could clearly fill the
job of mathematics professor with great skill. The final word, however, went to the theological
consistory at Stuttgart, to whom Kepler‘s request was also forwarded. The consistory responded
a few days letter with a resounding negative—Kepler should certainly not be offered a post at
Tübingen. Reviewing Kepler‘s correspondence, and in particular the letter he had sent to the
duke two years earlier explaining his opposition to the Formula of Concord, the consistory
75 Ibid.: ―…ainer der Calvinischen mainung beygethan…von diser ungleichen mainung wegen
nit solte unser Bruder in Christo genennet oder gehalten warden.‖
76 Because of Kepler‘s insistence that he would sign the Formula of Concord ―only
conditionally‖—an insistence that got him into a great deal of trouble—scholars have
traditionally assumed that he never signed the Formula of Concord at all. This assumption has
recently been challenged. In 2009, a manuscript was discovered which contained Kepler‘s
signature and his subscription to the Formula of Concord in Graz in 1594 (see Volker Schäfer,
18 June 2009, Blätter für Württembergische Kirchengeschichte, 437-438). Though this has only
begun to receive analysis, it should not dramatically change our perception of Kepler‘s stance
toward the Formula of Concord. In 1594 Kepler was 23 years old, and had only just left the halls
of Tübingen for a new job in Graz. He was still three years away from publishing his first book,
and had only begun to work out his own understanding of his place vis-à-vis the Lutheran
Church. As Kepler himself never mentioned any subscription to the Formula of Concord in all
his letters, as his refusal to subscribe led to his excommunication, and as he strove to regain the
right to take the Communion while still refusing to subscribe, we can regard this signature from
1594 at most as the indiscretion of a youth only recently come to a new place and still unsure of
himself or his beliefs.
57

deemed him a ―sly Calvinist‖ who would taint the students with his unorthodox theological
views. Likewise, he had proven himself to be an ―opinionist in philosophy,‖ one who would
cause a great deal of unrest at the university. 77
Since the statues of the university clearly required
unconditional acceptance of the Formula, the duke should deny Kepler‘s request on these
grounds alone, and avoid bringing a troublemaker into the halls of Tübingen.
This is the first clear instance where Kepler‘s unorthodox theological beliefs brought him
into conflict with his own church, though it would not be the last. While at first his refusal to
sign the Formula of Concord prevented his employment at Tübingen, it did not affect his
personal relationship with his local church in Prague. This changed when Kepler moved to Linz
in 1612, shortly after the death of Rudolf II (though he retained his position as Imperial
mathematician to Rudolf‘s successor, Matthias). In Linz, Kepler met Daniel Hitzler, who had
assumed the position of the head of the church there in 1611, shortly before Kepler‘s arrival.
Kepler may have heard of Hitzler even before arriving in Linz; both had studied at Tübingen,
though Kepler preceded Hitzler by five years. Though Hitzler had a reputation as an orthodox
Lutheran, in keeping with his training in Württemberg, he also had a reputation as a ―welcome
and loving [man, and] a theologian of eloquence and a sincere heart.‖ 78
Moreover, he had wideranging
interests that would have appealed to Kepler. A pamphlet of 1660 memorializing Hitzler
spoke of his passion for the study of both music and astronomy; according to Tobias Wagner, the
Tübingen theologian who wrote the memorial, Hitzler had not only studied both fields but had
77 KGW 16:610 : ―…auff welcher erclaerung leichtlich abzunemmen, dass er ein verschlagener
Calvinist seyn muoss, und da er zu einer profession verordnet, nit allein solch Calvinische gifft
der Jugendt nach und nach eingiessen, sonder andere mehr er in consequentiam ziehen, undt
ebener massen zu subscribiren sich understehen, auch bey der Universitaet, weiln er in
philosophia ein opinionist, vil Unrueh erwecken moechte.‖
78 See David Cristoph Seybold, Selbstbiographie Joh. Valentin Andrea's 2 (1799), 52.
58

also composed his own musical arrangements and invented his own mathematical and magnetic
instruments. 79
Given their shared backgrounds and interests, Kepler likely felt fairly comfortable when
he approached Hitzler to discuss his theological views, despite Hitzler‘s own reputation as an
orthodox thinker. After all, Kepler continued to self-identify as a Lutheran, and wanted only to
make clear that he objected to one—in his view unsubstantiated—aspect of the Lutheran
approach to the Eucharist. He hoped to continue to partake in all the church‘s activities, and
would even sign the Formula of Concord so long as his objection on this one point was duly
noted. Hitzler‘s response, however, was certainly far more extreme than Kepler anticipated. Not
only did Hitzler emphatically disagree with Kepler‘s approach, he insisted that with this
approach Kepler had firmly placed himself outside of the acceptable bounds of Lutheran belief—
and consequently he refused to allow Kepler to participate in the Communion.
Stunned and grieving, Kepler immediately appealed Hitzler‘s decision to the consistory
in Stuttgart—he did not know, of course, about their negative assessment of his theological
views to the duke from the previous year. He argued that his disagreement with Hitzler was a
matter of personal conscience, and that Hitzler had no authority to exclude him from the
Communion on that basis. The consistory replied to Kepler‘s petition in September of 1612. ―If
someone,‖ they wrote,
openly expresses in speech that he considers himself a true member of the evangelical
religion, but says that not all of its religious articles are correct, and rather distances
79 Tobias Wagner, ―Memoria Rediviva, Viri admodum Reverendi & Amplissimi, Dn. Danielis
Hitzleri,‖ (Tübingen, 1660), 4 Diss. 575, Staatsbibliothek Muenchen. Interestingly, the only
mention the document makes of Kepler is in reference to Hitzler‘s astronomical pursuits;
Wagner writes that it signifies no disrespect to Aristotle to note that the optical instruments of
modern times have allowed astronomers to far outstrip the knowledge of the ancients, and notes
that Kepler, too, discusses this issue in his discussion with the Siderius Nuncius. Wagner either
is unaware of, or chooses not to mention, Hitzler‘s role in Kepler‘s excommunication.
59

himself from true doctrine, and with uncertain and dubious opinions and outrageous
speculations obscures true doctrine for himself, or even involves others with him, and
deludes himself with his own thoughts in matters of faith and divine mysteries, and does
not base himself on any certain form of pure doctrine by subscribing to the Formula of
Concord, which is the symbol of public orthodoxy of our times and which is grounded in
the divine holy Scriptures, but rather contradicts it himself, in one or more articles: [in
such a case] a minister of the church, who is a true guardian of the mysteries of God, does
rightly when he does not admit such a one to communion…so long as he does not give up
his erroneous opinions and unite himself with our church in agreement with its doctrine. 80
Kepler had clearly distanced himself from the Lutheran Church with his beliefs about the
ubiquity of Christ, they maintained, and they could only affirm the rightness of Hitzler‘s
decision. Kepler‘s problem was that ―in contentious religious matters he bases his faith and
opinion not on the holy, prophetic and apostolic writings but rather on his own mental
prowess.‖ 81
But the mysteries of Christ were intended not just for those with great subtlety of
thought, but for everyone, the simple and the wise alike. And in most cases, the simple were far
better able to receive those mysteries; Kepler‘s mental prowess had only led him astray. He
ought to recognize that ―the mysteries revealed in the Scriptures are immeasurably greater and
80 KGW 17:638: ―Wenn einer externa professione, und mit dem Mund / Der Wahr-Evangelischen
Religion sich beruemhet /a ber in Articulis Religionis nicht aller ding richtig ist / sondern a sana
doctrina exorbitirt / mit ungewissen zweiffelhafftigen opinionibus, und ungereimten
speculationibus, die rechte Lehr verdunckelt, sich selbst / oder auch andere neben ihme,
verwirret / nach seinem eigenen Duencken in Glaubens Sachen et Mysteriis Divinis schwermet /
an kein gewisse Form der reinen Lehr gebunden seyn will / auch der Ursachen / Formulae
Concordiae, als publico Orthodoxorum nostri temporis Ecclesiarum Symbolo, so in der heiligen
goettlichen Schrifft gegruendet / zu subscribiren / Bedenckens hat / derselben in einem oder
mehrern Artiulis widerspricht: so kan Minister Ecclesiae, welcher ein getreuen hausshalter
ueber die Geheimnuess Gottes sich werweisen will / einen solchen / ihme der Lehr hablen
bekannten Menschen / ad communionem nicht admittiren / so long und viel er seine erroneas
opiniones nicht fallen lassen / noch mit unsern Ecclesiis, in consensu doctrinae, sich vereinigen
will.‖
81 Ibid.: ―Als welcher sein Glauben und Meynung in strittigen Religions Sachen nicht auf die
Heil. Prophetische und Apostolische Schrifften sondern auf Herrn Keppleri gut Ingenium, und
daher gefasstes judicium zu gruenden gedaechte. ―
60

superior to the cleverness of Plato and Aristotle, Ptolemy and Copernicus.‖ 82
The members of
the consistory reminded Kepler of Paul‘s words in 1 Corinthians 2: ―When I came to you, I did
not come with eloquence or human wisdom as I proclaimed to you the testimony about God.‖
God‘s cause was not served, they insisted, by new subtleties and questions. If Kepler recognized
this and embraced true doctrine, he could be readmitted to the church.
In many ways, the consistory‘s words against Kepler echoed those of Luther against the
medieval scholastic theologians who had purposefully applied their reason to issues of theology.
In his ―Disputation against Scholastic Theology,‖ Luther argued that scholastic theology
represented the inappropriate use of reason; God and his work could be understood only through
faith, with the Scriptures as the only guide. ―No syllogistic form holds for divine terms,‖ Luther
wrote. 83
Faith that relied on logic was not true faith, but its opposite. True, Melanchthon had
found a place for natural philosophy within Luther‘s vision, by this was natural philosophy
expressly concerned only with the discernment of God‘s providence in the world. 84
And though
Kepler was in many ways a follower of Melanchthon, the consistory felt that his approach
smacked more of scholasticism than of a proper Lutheran concern with nature. Kepler, like his
scholastic predecessors, felt that it was possible to achieve rational knowledge about God, and to
use natural philosophical or mathematical arguments to demonstrate specific theological
claims—his Mysterium Cosmographicum made that quite clear. Luther, by contrast, denied that
82 Ibid.: ―Bedencket aber darneben dass Mysteria in scripturis revelata unvermesslich hoeher
und euerm Verstand wann ihr gleich an Scharffsinnigkeit Platoni et Aristoteli, Ptolomaeo et
Copernico weit ueberlegen waeren zu begreiffen schlecht unmueglich seyen.‖
83 Martin Luther, ―Disputatio contra scholasticam theologiam‖ 1517: ―Nulla forma syllogistica
tenet in terminis divinis.‖ (Weimer, 1883, vol. 1), 47.
84 See Sachiko Kusukawa, The Transformation of Natural Philospohy: The Case of Philip
Melachthon (Cambridge: Cambridge University Press, 1995).
61

there could be any direct path from human reason to theological truth. 85
The consistory
underscored to Kepler that as a good Lutheran, he ought to take this to heart.
Kepler was not prepared to follow the advice of the consistory and embrace doctrines
with which he so strongly disagreed. Disheartened, he replied to them that he would not bother
Hitzler further, nor would he cause further scandal in Linz. He would, however, continue to try
and obtain admission to the Communion, if not in Linz then elsewhere. And he would continue
to try and prove that he was a good Lutheran, despite his reservations about specific issues.
Kepler and Hafenreffer Revisited
In 1617, five years after Kepler had received his letter from the Stuttgart consistory,
Kepler visited Tübingen, in the hopes that his supporters there might intercede with the
consistory on his behalf and get him readmitted to the Communion. In particular, he met with
Matthias Hafenreffer. As Hafenreffer was both a dear friend of Kepler‘s and a theologian who
stood high in the ranks at Tübingen, Kepler felt that if anybody could help him, Hafenreffer
could. When Kepler left Tübingen, he seemed convinced that Hafenreffer would take up his
cause soon afterward, and was disappointed when no word from Hafenreffer arrived. One year
later, in November of 1618, he took the initiative and wrote directly to Hafenreffer, reminding
him of his situation and pleading once again for Hafenreffer‘s aid. He assumed, he wrote, that
Hafenreffer‘s silence stemmed from the fact that he had no good news, and was worried about
offending a close friend like Kepler with a letter of negative tidings. Yet Kepler implored
Hafenreffer to revisit his case, and to consider setting a new standard in its resolution by valuing
real religious devotion and true belief over an insincere subscription to the Formula of Concord.
85 Ibid. 201.
62

What many took to be arrogance on his part, Kepler insisted, was simply sincerity, ―because on
this one point I don‘t want to turn my speech away from my innermost thoughts towards your
Formula of Concord, and to profess something on the outside that is other than what I feel on the
inside.‖ 86
Kepler dearly loved and respected his fellow Lutherans, and deemed theologians like
Hafenreffer to be his ―spiritual fathers in all questions of faith‖—―but as human beings,‖ he
added pointedly. 87
Their words could not overcome the clear words of the Scriptures and the
ancient church Fathers.
Though he wouldn‘t use a fabricated confession to end his exclusion from the
Communion, Kepler wrote, he greatly lamented that exclusion, and endeavored to always act
righteously so he would not come to actually deserve it. Still more, Kepler emphasized that he
did not want to assume the mantle of theologian, deciding on true doctrine for others; ―I am
rather a layman,‖ he insisted, and the question at hand was one of ―purely personal
conscience.‖ 88
Moreover, he lamented not only his own personal dispute with the Lutheran
Church, but rather the general disputes among Christian confessions: ―My family and I,‖ he
wrote, ―say daily prayers for the unification of the thrice-divided church.‖ 89
He worried that
things had progressed so far that the wounds of the church would only heal ―if first the rotten
flesh around them are cut off by the knife of a general German religious war…and burned out
86 KGW 17:808: ―…quod in hoc unico puncto, nolo linguam a mea penitissima mente deflectere
ad vestram formulae Concordiae; aliudque, quam intus sentio, foris profiterj.‖
87 Ibid.: ―…omnia Christj membra, vosque inter caetera, et ante omnes, ut spirituales patres in
omnibus Religionis capitibus caeteris (ut homines tamen) complector.‖
88 Ibid.: ―…sic etiam me comparo, ut in hoc dissensu meo, non judex vester, quippe laicus ipse,
sed conscientiae privatae mundae custos inveniar, et ut persecutiones bona conscientia feram.‖
89 Ibid.: ―Pro Ecclesiae vero trifariam divisae adunatione ipse cum familia mea quotidiana vota
facio.‖
63

with the fire of many tribulations and suffering.‖ 90
The troubles that were already plaguing
much of the Empire might soon come even to Württemberg itself, though Kepler would hoped
that this would not occur, and prayed that if it did, the harmony of the church at large would
swiftly prevail.
From the harmony of the church, Kepler next moved in his letter to a discussion of
astronomical harmony. He had included with his letter the title page to Book V of his
Harmonice Mundi, which he hoped Hafenreffer would publicize and distribute to booksellers in
Tübingen. Like the harmony of the church, the harmony of the cosmos was an issue dear to his
heart, and he hoped that Hafenreffer would help him with both. He also emphasized to
Hafenreffer that he only claimed the mantle of expert when it came to the latter kind of harmony:
―I submit,‖ he wrote, ―to the distinction which your reverence has made between me the
mathematician and me the theologian. I do not claim the latter title at all.‖ 91
Kepler ended his
letter with good wishes for Hafenreffer, and enclosed as well a copy of his ―Unterricht von H.
Sacrament des Leibs Bluts Jesu Christ unders Erlösers,‖ a short pamphlet he had written during
the previous year summarizing his views on the Eucharist. It was intended primarily for his
children, and it was written simply and in question and answer format; Kepler hoped that through
it his family might better understand both the theological basis for Kepler‘s own views on the
body of Christ and the nature of the conflict in which he was embroiled. By including it in his
letter to Hafenreffer, Kepler hoped to provide his mentor with another clear statement of his own
theological views. At the same time, by including it alongside the title page from his Harmonice
90 Ibid.: ―…nisj quod caro putrida totum vulnus obsidens, prius recidenda est cultris generalis
alicujus bellj Germanicj super religione, quod nescio an incenderint Bohemj, et igne exurenda
tribulationum et afflictionum variarum.‖
91 Ibid.: ―…acquiesco in distinctione, quam R. T. fecit inter me Mathematicum et me Theologum,
nec hunc titulum mihi vindico.‖
64

Mundi, he emphasized the degree to which he believed that both ideas—the harmony of the
church and the harmony of God‘s creation—were so closely linked.
With this letter, Kepler endeavored to reframe the issues that had led to his
excommunication; his was not a case of heresy or of boundaries wrongly crossed, he claimed,
but simply a case of a devout believer staying true to his convictions. Kepler specifically
emphasized that as he was merely a layman, and not a theologian, he had no interest in debating
doctrinal issues with Hafenreffer and his peers, nor did he hope to sway others to his point of
view by arguing theology with them; his personal qualms would remain personal when it came
to theological details. Yet he was an expert mathematician, and if he hoped to convince others of
anything it would be in this regard: in demonstrating the harmony of the cosmos, a harmony
which could serve the church by providing a model for the church to emulate. 92
But unlike in
1597, Kepler made no mention of any more direct ways that his mathematics might reflect on
doctrinal issues like ubiquity; the implied linkage between his theological beliefs and his
mathematical ones was now far more indirect.
Hafenreffer‘s reply to Kepler, written in February of 1619, was supportive but troubled.
While Kepler had guessed that Hafenreffer hesitated to write to him after their Tübingen meeting
out of fear that he might offend a friend, Hafenreffer insisted at the start that this was not the
case: ―I have always been most certain,‖ he wrote, ―that it ought to be considered no offense, but
rather the greatest kindness, to lead a friend—even if he suffers and resists—on the path of
92 See Chapter 6 of this dissertation for a more detailed account of how Kepler felt that this
linkage between mathematics, harmony of nature, and harmony of Church might be practically
realized.
65

truth.‖ 93
If Hafenreffer had hesitated, it was because he had thus far seen all his efforts on
Kepler‘s behalf fail, due to Kepler‘s own obstinacy. But he would try yet again tried to lead
Kepler toward the truth by reminding him of the proper outlet for his inquiring mind. He wrote,
I always esteem and make much of your remarkable and celebrated thoughts, knowledge,
and work dealing not only with the sublunar world but also the entire upper world, all the
way to the outer surface of Saturn. But with regard to that ―upper‖ world which is
heavenly in a spiritual sense—here, hands off! Here all the sharpness of human intellect
necessarily becomes foolish. 94
Kepler should focus on his mathematics and astronomy alone, Hafenreffer insisted, and leave
theological mysteries to those who better understood them. If Kepler could not help but apply
his discerning mind to questions of theology, Hafenreffer urged him to focus on one phrase
alone: ―et verbum caro factum est,‖ ―and the word was made flesh.‖ Hafenreffer implored,
If you love me, if you have ever loved me, forget the passions which you affected in your
last letter and focus on this: There are three words: 1. Verbum, 2. Caro, 3. Factum. Either
I am foolish or crazy, or you will understand how foolish, crazy, and absurd we are when
we attempt to investigate the divine mysteries with our rational method of [human]
stupidity. 95
The clarity of this message from the gospels, Hafenreffer hoped, would help Kepler realize that
even his lofty intellect was could not attempt to scale the divine mysteries; human reasoning was
simply not up to the task, and could only hope to appreciate wonders like the incarnation as God
had intended—as mysteries.
93 KGW 17:829: ―Nam iste mihi semper Animus, eaque constantissima mens fuit, non
offensionem, sed longe maximum beneficium habendum esse, etiam dolentem et resitantem
Amicum, in via ducere veritatis.‖
94 Ibid.: ―Meditationes, cognitionem et labores tuos insignes et nobiles, non tantum in
sublunaribus, sed in superioribus omnibus, vsque ad supremam Saturni superficiem, semper
veneror, magnifaciamque semper: sed quae superiora, quae spiritualiter coelestia sunt, vno
verbo, quae Theologica sunt, hic manum de Tabula! Hic stultescere oportet omne humani
ingenjj acumen.‖
95 Ibid.: ―Si amas me, si amasti vnquam, obliviscere (quos in hac postrema epistola tua induisti)
affectuum tuorum et tenta rem: Tria verba sunt, 1 verbum, 2 Caro, 3 factum: aut stultus et amens
ego sum, aut Tu deprehendes, quam stulti, amentes et furentes simus in divinis mysterijs, nostra
stultitiae ratione scrutandis.‖
66

As to the second harmony Kepler had mentioned—his astronomical Harmonice Mundi—
Hafenreffer noted that he had distributed the title pages as Kepler had asked, and that he wished
the book well. Though Kepler had linked—however indirectly—his astronomical harmony to
his hopes for religious harmony, Hafenreffer took the opportunity to exhort him yet again to steer
clear of theological questions, and to remind him of ―my Christian distinction between you the
mathematician and you the theologian, a title suited only to the disciples of the heavenly [i.e.
divine] Word.‖ 96
Kepler‘s Unterricht, the pamphlet that Kepler had written on the Eucharist and
had appended to his letter to Hafenreffer, Hafenreffer took to be further proof of the problematic
overlap between reason and theology, for he felt it contradicted the clear words of Scripture on
which he urged Kepler to reflect.
In Hafenreffer‘s reply, Kepler sensed a door closing to him. If even his close friend and
mentor believed him guilty of heresy and refused to consider things from his point of view, what
hope was there for him? Unwilling to fully give up hope, Kepler replied once more to
Hafenreffer in a lengthy letter of April 1619, and attempted one last time to convince Hafenreffer
of the justice of his position. He began the letter by noting that he had debated whether or not to
write to at all after his last letter, but decided that he could not leave ―a man who had done me
the utmost good with the wrong opinion of my words and actions; for to be condemned by [you]
would truly mean my end.‖ 97
Kepler insisted that he felt no bitterness towards Hafenreffer
himself, but merely sorrow over his exclusion from the communion. Moreover, despite all that
96 Ibid.: ―Tu interim sis memor, quod per Christum et salutem tuam te oro, Christianae meae
distinctionis inter Mathematicum, et te Theologum, qui titulus in neminem, nisi verbi coelestis
discipulum, quadrare potest.‖
97 KGW 17:835: ―…si Virum benevolentissimum mihi, in sinistra de meis dictis factisque
opinione relinquerem; a quo damnarj, id vero perire est.‖
67

had been said he still retained the hope that Hafenreffer and his fellow theologians might
alleviate that bitterness, by granting him the right to rejoin the church and participate yet again.
To that end, Kepler asked Hafenreffer the following: if the theologians insisted that he
abandon his qualms, leave theological questions aside, and act as a simple layman, then could
they not at the very least treat him as a layman when it came to questions of communal
participation? Why, in other words, should he be forced to sign the Formula of Concord at all?
He lived in Linz simply as a layman—he was neither a member of the university nor an official
in a Lutheran government. The theologians, he wrote, should
give me the right which is enjoyed by the majority of simple laymen, who are not
commanded to subscribe [to the Formula of Concord]. In what way am I more at fault
than these men? It is necessary to become a fool, you say: I do this as often as I compose
myself for worship, and say goodbye to all human sharpness of intellect. Why can I not
be accepted as a simple layman? If the fact that I refuse to subscribe makes the
theologians suspicious (which a simple layman does not have to do), then the fact that the
theologians ordered me to subscribe made me suspicious first, since they would not order
a simple laymen thusly. 98
Here, Kepler tried to use Hafenreffer‘s own arguments against him, and to move the blame from
his own shoulders to those of Hafenreffer and his colleagues. Kepler was not the one who had
tried to assume the role of theologian—the consistory and the faculty at Tübingen had done that
for him. Though they claimed that they wanted him to act as a simple layman, they continued to
send him mixed messages by insisting that he needed to sign the Formula of Concord, something
not required of the simple layman. 99
98 Ibid.: ―…possunt eam ipsi mitigare, concedentes mihi beneficium illud, quo gaudent plerique
laicorum simplicium, qui non jubentur subscribere. Quid pecco prae illis? Stultescere oportet,
inquis. Facio, quoties ad sacra me compono, valedico omni acuminj humanj ingenij. Cur non ut
simplex laicus recipior? Si hoc theologis movet suspicionem, quod recuso subscribere, quod non
facit simplex laicus: Theologj mihi prius suspicionem movent, quod me jubent subscribere, cum
non jubeant laicum simplicem.‖
99 On this point, Hafenreffer noted in the margins of Kepler‘s letter ―magna differentia‖—―there
is a great difference,‖ both between what the theologians expected of Kepler and what he
68

Kepler wrote that he was perfectly willing to ―say goodbye to all sharpness of intellect‖
and act the layman, but only if he did not have to subscribe; the very requirement that he sign the
Formula made it impossible to subsume his theological concerns in favor of ―simple‖ faith.
After all, he wrote, ―a signature presupposes approval of each and every thing which is written in
the book.‖ 100
While the layman could simply overlook much of the theological details that were
subject to debate and not take a stand one way or another, one who signed the Formula of
Concord necessarily took a clear stand on everything within it—even the many things, Kepler
pointed out, that were not strictly doctrinal. He had personal reservations about the idea of
ubiquity, as he had made clear earlier; he also believed that much of what the Formula detailed
should not require universal assent at all. With these doubts, he felt that he could not subscribe,
for if he did it might seem ―that I subscribe to authority rather than to truth.‖ 101
This dispute between Kepler and Hafenffer resonates with some of the larger changes
occurring in the Lutheran Church around the turn of the seventeenth century. Luther had initially
called for the supremacy of individual belief and individual faith; in contrast to the hierarchy of
the Catholic Church and the right of exclusive interpretation granted to its leaders, Luther had
intended to place the power of interpretation directly in the hands of the individual. Those
pastors who led Lutheran congregations were supposed to possess greater education than their
followers, to be sure, but were by no means supposed to compel belief. Yet it soon became clear
expected of them, and also between Kepler and the ordinary layman. In some ways, of course,
he was right—Kepler had worked as a Lutheran teacher and official in the past, he had tried to
obtain a post at the university, and his role as Imperial Mathematician made him a far cry from
your average layman. Yet Kepler‘s claim was not without merit—had he not brought up his
objections with Pastor Hitzler, he would likely not have been expected to sign the Formula of
Concord at all in order to receive Communion at his church in Linz.
100 KGW 17:835: ―Subscriptio praesupponit comprobationem omnium et singulorum, quae sunt
in libro perscripta.‖
101 Ibid.: ―…at impedit me, ut non debeam subscribere, ut ne videar authoritatj potius
subscribere quam veritatj.‖
69

that a movement could not sustain itself with this attitude; a hierarchy and an orthodoxy soon
developed in the post-Luther Lutheran Church. 102
Kepler, in many ways, seems to hearken back
to the early days of the movement; his arguments rest on the belief that he ought to be able to
interpret Scripture as well as anyone else, and that personal conscience ought to preempt
authoritative hierarchy. When urged to avoid theology, Kepler insisted not that he wanted to be
a theologian, but quite the opposite—he wanted to be a layman, and yet still have the right to
freely interpret and believe as he saw fit. He emphasized that though he respected the
theologians at Tübingen, he did not believe that there was anything divine in their claim to
authority. Hafenreffer, by contrast, focused on the figure of the theologian as authority—as
Kepler was no theologian, he ought to avoid all questions of faith and interpretation, and leave
those questions to those experts who, ensconced in the halls of Tübingen, could answer them
best. The distinction between layman and theologian for Kepler meant that he ought not to be
compelled to sign anything; for Hafenreffer, it meant that he needed to be compelled to sign, for
he had no right to decide these issues for himself.
Moreover, when Hafenreffer urged Kepler to steer clear of theological questions, he
emphasized Kepler‘s astronomical expertise. Kepler should stick to those areas he knew well,
Hafenreffer insisted, and not to those areas in which he was only a novice. Kepler himself
agreed that he was no expert in theology, and—in reference to Hafenreffer‘s seemingly oftremarked
distinction between Kepler as mathematician and Kepler as theologian—agreed to
name himself only the former, and not the latter. Yet in this most recent letter, when Hafenreffer
had asked Kepler to remember his distinction between ―you the mathematician and you the
theologian,‖ he had seemed to imply something further—not merely that mathematics was a
102 See, for example, the selection of essays in Robert Kolb, Luther's Heirs Define His Legacy:
Studies on Lutheran Confessionalization (London: Variorum, 1996).
70

discipline Kepler knew well, and theology one he did not. He had implied that mathematics and
theology were not only different areas of expertise, but fundamentally different ways of looking
at the world, and he had warned Kepler to avoid thinking ―mathematically‖ about theological
questions. In his reply to Hafenreffer, Kepler addressed this implication directly, and noted that
Hafenreffer had praised his astronomical prowess only to turn that very praise against him. In
linking Kepler‘s astronomical expertise to his theological ideas, Hafenreffer had suggested that
Kepler‘s refusal to sign the Formula of Concord stemmed from the fact that he was ―looking for
astronomical subtleties in theology.‘‖ 103
Hafenreffer, in other words, had suggested—much as
the Stuttgart consistory had in 1612—that the kind of thinking that characterized mathematics
(and astronomy, one of its subfields) had no place in the world of theology.
Rather than address this distinction immediately, Kepler at first only insisted that
Hafenreffer‘s suggestion about his motivations was wrong. He refused to sign the Formula of
Concord, he argued, not due to any ―sharpness of intellect, but rather [due to] the esteem of
brotherly charity.‖ 104
He would not condemn anyone who based their theological beliefs on the
teachings of the ancient church, particularly as he agreed with them against the Formula of
Concord on the specific issue of the body of Christ. Just as he had argued to the Duke of
Würrtemberg years earlier, Kepler here emphasized that aside from any specific theological
qualms, his refusal to sign the Formula was linked on a fundamental level to the antagonistic
attitude that the text and its formulators took toward those of other confessions, or those with
103 KGW 17:835: ―Quare non vult subscribere? Nimirum quia astronomicas subtilitates in
Theologia quaerit.‖
104 Ibid.: ―Non subtilitas est ingenij, sed aestimatio charitatis fraternae (in qua nulli parcendum
est acuminj); quod eos qui cum Antiquitate loquuntur et argumentatntur (quid enim cum
antiquitate sentiat quisque, deus [Greek] judicet) damnare nolo, sed illos potius loquendo
imitarj, quam formulam Concordiae, sicubi diversitas est, idque in uno articulo de persona
Christj.‖
71

differing opinions. How could he put his signature on a document that seemed to only further
the divisions in the church, rather than try and heal them? Even if the Calvinist and Catholic
opponents of the Lutheran Church did not themselves seem interested in churchly harmony, it
was still incumbent on Kepler and his Lutheran compatriots to take the initiative; citing Matthew
5:44, Kepler wrote that ―we have to be good to our enemy and love those who hate us.‖ 105 The
generally hostile attitude of the Formula of Concord, combined with Kepler‘s personal
objections to specific elements of the document, were the reasons why Kepler insisted he could
not sign in good conscience. Yet he would willingly be silent about whatever beliefs of his the
Tübingen theologians found objectionable, so long as allowed him to continue privately in those
beliefs, and granted him the right, as a layman, to participate in Communion even without
signing the Formula.
Kepler then took up the challenge from Hafenreffer‘s letter and tried to explain the words
―verbum caro factum est,‖ ―the word was made flesh.‖ In the context of this passage, Kepler
explained, Word and flesh were diametrically opposed concepts—the one was so allencompassing
that the other was miniscule by comparison. From a mathematical perspective, he
continued, the former, ―is infinite beyond the circle, the latter of infinite smallness; neither is
suited to my compass‖ 106 —neither was suited, that is, to direct geometrical analysis. Yet though
Kepler could not apply his mathematical aptitude to the analysis of the passage, certain logical
conclusions could still be drawn from it, conclusions well supported by the rest of the Scriptures
and the writings of the church Fathers. In particular, Kepler argued, the omnipresent Word had
become flesh when it descended into the womb of the virgin, yet this did not make that womb
105 Ibid.: ―Scio quid adversarij vestrj contra pecaverint in charitatem, sed id nihil ad me; scio
benefaciendum hostibus, amandos obientes.‖
106 Ibid.: ―Illud infinitum est ultra circulum, hoc infinitae parvitatis, neutrum igitur circino meo
aptum.‖
72

omnipresent; Kepler implied that likewise the physical person of Christ need not have become
omnipresent simply due to the omnipresent Word.
Here Hafenreffer, displeased with this comparison, wrote in the margins of his copy of
Kepler‘s letter: ―Mathematician, you become stupid.‖ 107
Kepler, as though sensing Hafenreffer‘s
criticism and its expression—the derogatory ―mathematician‖—finally took up the distinction
Hafenreffer had insisted on earlier, between mathematical and theological ways of thinking.
And in a surprising move, Kepler readily agreed with Hafenreffer—mathematical modes of
reasoning, he conceded, had no place in the discussion of a theological mystery like the
Eucharist. Given that the infinite Word had descended into finite womb and flesh, he wrote,
something had clearly happened ―beyond my geometrical comprehension, which must be
examined by the eye of faith.‖ 108
From a geometrical perspective, Kepler explained, there were
from the start
many contradictions: [for the Word] not to give up omnipresence but nevertheless to
descend whole into the womb; to be taken whole into circumscribed flesh; for the whole
Word to dwell in us, and nevertheless to be in the heavens; and to hang on a local cross
for the salvation of men, which is beyond worldly place; and for the cross, to which all of
our sins are attached, to be located specifically in Judea. 109
Yet Kepler insisted that he still believed in these ideas despite the geometrical contradictions
they entailed, ―because the clear word of God ordered them, and they are interpreted [thusly] by
the church of God and the Fathers from all the orders, excluding neither Luther nor
107 Ibid., ―Mathem. Stultescis.‖
108 Ibid.: ―…accedit nempe hic aliquid ultra meum captum Geometricum, quod fidei oculis
intuendum est.‖
109 Ibid.: ―Si rationem geometricam intueor, videor mihi contradictoria dicere, Non deserere
ubiquepraesentiam, et tamen totum in uterum descendere, totum iniri carni circumscriptae,
totum Verbum habitare in nobis, totum verbum, etiam quod in coelo est, etiam quod in
supermundanis locis est, pendere in una localj cruce pro salute hominum, nec tamen crucem, in
qua suffixa omnium peccata, alibi nisi in Judeaea defixam.‖
73

Hafenreffer.‖ 110
Mathematics, in other words, did not guide his theological beliefs; only
revelation and tradition did. Kepler argued that his own theological perspectives were all
consistent with Scripture, the church Fathers, and even the prevailing Lutheran understanding of
Christ‘s descent from heaven. And he emphasized that these perspectives were often totally at
odds with anything he could rationally fathom or explain; he could believe that Christ, as the
human son, both descended from heaven and remained in heaven only because he, ―with eyes
closed to geometry, adhere[d] faithfully to Scripture.‖ 111
Yet he still insisted that the ubiquity
doctrine of Hafenreffer and his colleagues was false. The relevant scriptural passages did not
imply that Christ was physically omnipresent; instead, it made far more sense to understand
Christ‘s omnipresence to refer to his power and guidance. Kepler spent much of his letter
bolstering this contention with reference to Scripture and its interpreters, past and present, who
agreed with his point of view. If the theologians were to insert an interpretation like this one
into the Formula of Concord, Kepelr wrote, he would have no qualms about signing.
Kepler‘s willingness to dismiss the relevance of mathematical thinking to theological
problems and to argue that geometry was completely at odds with theological mysteries is
particularly surprising given that he had argued exactly the opposite—and on this very issue—in
1597. Then, he had emphasized that nothing could be more relevant to theology than
geometrical reasoning, for geometry mirrored the mind of God; God had, after all, created the
world with the blueprint of geometry. He had applied these ideas to the contentious issue of the
Eucharist, and had dismissed the Lutheran doctrine of ubiquity precisely on the grounds that it
was geometrically incomprehensible. He had, in other words, been guilty of precisely what
110 Ibid.: ―Haec tamen omnia credo quia praescribit clarum Dej verbum, interpretaturque Dej
Ecclesia, Patres ex ordine omnes, non excluso neque Luthero, neque Hafenreffero.‖
111 Ibid.: ―…et ecce Keplerus Geometra clausis Geometriae oculis, fide adhaeret scripturae,
loquiturque cum illis, qui sancte scripturam sunt interpretatj.‖
74

Hafenreffer had accused him—deciding his theological positions on the basis of his
mathematical expertise, and allowing mathematical modes of thinking to determine his approach
to theological mysteries. What are we to make, then, of Kepler‘s ready agreement with
Haferneffer here that geometry and theology were incompatible modes of thought?
Of course, there is always the possibility that Kepler simply told Hafenreffer what he
thought he wanted to hear. It would have done him no good to insist on the relevance of
mathematics to this theological dispute; if he had any hope of turning Hafenreffer to his point of
view, it likely lay in Scripture and tradition, rather than geometry. This may be part of the story,
yet it cannot be the full story, for Kepler was never one to shy from or alter the truth when it
came to his faith. He had argued earlier that ―it is not in me to dissimulate in matters of
conscience,‖ 112 and this is precisely what had gotten him in trouble in the first place. On the
other hand, though Kepler may not merely have wanted to placate Hafenreffer, his change of
heart may have simply stemmed from a loss of the starry-eyed idealism that characterized him in
his early days. In 1597, Kepler was a thinker deeply committed to the absolute truth of his own
ideas, the relevance of those ideas across all domains of knowledge, and the power of those ideas
to effect real change in the world around him. As is often the case, this kind of naïve idealism
may have given way, over time, to more modest goals, and more modest beliefs about the power
of his intellect and the reach of his theories.
Yet this, too, cannot be the full story. For in most cases the Kepler of 1619 did not sound
all that different from the Kepler of 1597—at least when it came to the certainty of mathematics
and the broad reach of its relevance. Kepler continued to emphasize that geometry originated in
the mind of God, that it underpinned all aspects of creation, and that God had given man the
112 KGW 17:750: ―At mihi in rebus conscientiae simulare non est integrum.‖
75

power to use it to interpret the Book of Nature. And because geometry linked God, man, and
Nature, all three, Kepler continued to emphasize, could reflect on one another—thinking
geometrically meant thinking about God as much as about his creation. He wrote in his
Harmonice Mundi, written the very same year as this letter to Hafenreffer, that
geometry, which before the origin of things was coeternal with the divine mind and is
God himself (for what could there be in God which would not be God himself?), supplied
God with patterns for the creation of the world, and passed over to Man along with the
image of God. 113
But if Kepler‘s views on geometry had not changed substantially between the publication of the
Mysterium Cosmographicum and the Harmonice Mundi, his views on religion had. By this I
mean not his views on God, but rather on the human side of theology—on the ability of man to
understand, model, and spread God‘s will and message. And central to this change was Kepler‘s
changing conception of the role of the theologian.
In 1597, having only recently left the halls of Tübingen and with little experience of the
real world, Kepler strongly believed not only in the ideas and ideals of theology as a discipline,
but also in the person of the theologian. He himself had wanted to be a theologian, he wrote in
1597; he reconciled himself to the discipline of astronomy because there, too, he could conceive
of himself as a priest, though with respect to the book of nature, rather than the book of
Scripture. And though he continued to speak of his astronomical work in these terms, he came
over time to see theologians not as a solution to the problems plaguing the church, but as a
primary source of those problems. In a letter to Maestlin of 1616, Kepler insisted that he did not
want ―to join the fury of the theologians.‖ He linked his own more forgiving behavior to his
status as a layman, and the negativity of the theologians to their official positions: ―It is better,‖
he wrote, ―if I, who am not a doctor in the church, sin in excusing [the views of others], in
113 Harmony of the World 304.
76

speaking well of them and interpreting them for the better, than in accusing, disparaging, or
perverting them.‖ 114
His insistence to Hafenreffer in the letters of 1618 and 1619 that he
considered himself a layman, and not a theologian, may thus have stemmed not only from his
concerns about signing the Formula of Concord, but also from his growing distaste for the
attitudes and behaviors of the theologians he saw around him.
Similarly, he attributed ―the beginning of all evil‖ in Styria, the province in which Linz
was located, to the behavior of the Lutheran theologians there. In the same letter to Hafenreffer
of 1619 in which he argued for his status as a layman and his right to be readmitted to the
communion, Kepler argued that the religious crisis in Styria stemmed from the harsh pulpit
sermons of two pastors, Fischer and Kelling. In particular, in arguing against the Catholic
veneration of the Virgin Mary, Fisher had ―extended his cloak at the pulpit and asked whether it
would be decent for women to crawl under it‖; it was still more indecent, he had insisted, to paint
monks under the cloak of the Virgin as was the common Catholic practice. 115
Such a speech
could only have been intended to shame and offend the Catholics in Styria, Kepler insisted, and
therefore could be blamed for much of the troubles there. He had earlier complained of just the
same thing to Georg Friedrich von Baden, noting that the Lutheran theologians of late tended to
―confuse teaching and ruling,‖ and to rely on the power of their princes to strike out at anyone
they perceived as an enemy. 116
And in yet another letter, whose recipient is unknown, he wrote
114 KGW 17:750.: ―Irâ Theologorum communicare nolo, fratres non judicabo, qui sive stent sive
cadant, dominj sunt, et fratres mej. Praestat me peccare excusando, bene loquendo, in melius
interpretando, cum non sim doctor Ecclesiae, quàm accusando detrahendo pervertendo.‖
115 KGW17:835: ―In Stiria certe omne malj initium est ortume x eo, quod Fischerus et Kellinus
exquisitis acerbitatum aculeis usi sunt in suggestu; et Fischerus quandoque pallium suum de
suggestu protendit, rogitans quam hoc decens fuerit, si mulieres sub suum repant pallium, atque
longe absurdius monachos pingj sub pallio Mariae.‖
116 KGW 16:451: ―Die Bestelte lehrer etliche confundirn das lehrampt und Regierampt wellen
Bischoeffe sein und haben einen unzeitigen Cuffer damit sie alles ibern hauffen stossen trotzen
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that the ―preachers are being too arrogant in their pulpits, and arouse much dispute; they raise
new issues through which devotion is hindered, and often accuse one another falsely …‖ 117
If
this was what it meant to be a theologian, then Kepler wanted none of it. Still more, he no longer
felt that he could trust such people to repair the divided church, particularly if such repair
required an absolutely unified opinion on such contentious issues as the Eucharist—regardless of
what geometry had to say about the matter. Even if Kepler still believed that his geometry
presented some clear solutions to those thorny theological issues that divided Christian from
Christian, he no longer still believed that he had the audience necessary to implement those
solutions.
This accounts both for some of the change in Kepler‘s articulation of the relationship
between theology and geometry between his 1597 letter to Maestlin and his 1619 letter to
Hafenreffer, and for some of the change in tone between his Mysterium Cosmographicum and
his Harmonice Mundi, particularly as each related to theology. In 1597, Kepler hoped that the
Mysterium Cosmographicum would have immediate and direct effects on the confessional
disputes of his day. Geometry would unambiguously decide the question of the Eucharist, such
that Lutherans would no longer have grounds to dispute with Calvinists. In 1619, he still argued
that the Harmonice Mundi had clear theological relevance, yet this relevance was described in
much more general terms—terms which deliberately avoided the specifics of confessional
disputes. Instead, Kepler argued, quoting Proclus‘s commentary on Euclid, that mathematics
was ―the preparation for theology‖ insofar as it ―it perfects us in moral philosophy, implanting in
auf irer fuersten schutz und gwalt, fuehren dieselbigen offtermahls auf gefehrcliche praecipitia.
Diss hat uns in Steyrmarkht von langer hand ins verderben gebracht.‖
117 KGW 17:643: ―Antwort mein disputirn in religionsachen gehet allain dahin, das die Prediger
auff der Cantzel zu hoch fahren, und nit bey der alten ainfalt pleiben, vil disputation erwecken,
neuee sachen aufbringen, damit die andacht gehindert wuert, einander vil faelschlich
bezuechtigen…‖
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our behavior order, proriety and harmony in social relations.‖ 118
He included his own book in
this category; the Harmonice Mundi was theologically instructive only as a general model for
proper personal and communal behavior, and not as a determinant of appropriate confessional
stances on specific issues. Kepler‘s agreement with Hafenreffer that geometry could not speak
to theology may best be understood on this level; Kepler had ceased to believe that geometry
could aid in specific theological disputes. And this was primarily due not to any change in his
understanding of geometry, but rather to his growing disillusionment with theology and
theologians.
Kepler closed his 1619 letter to Hafenreffer by pleading yet again for Hafenreffer to take
up his cause with the consistory in Stuttgart. ―My exclusion has now lasted for seven full years,‖
he lamented…and up to now I have never received a categorical decision from the theologians
which would give me to understand whether or not I am to be excluded forever.‖ 119
Even the
1612 letter from the consistory, in Kepler‘s view, had not fully decided the matter—perhaps
because Hafenreffer himself had not taken a definitive stand. For this reason, Kepler begged
Hafenreffer to stand by him and help resolve things in his favor; he hoped that because of their
years of close friendship, Hafenreffer would ―take this one step forward, although it is somewhat
unpleasant, so that I know that I am not lost to you.‖ 120
Though Hafenreffer was clearly unconvinced by Kepler‘s arguments, as his many
marginal notations to Kepler‘s letter make clear, he did forward Kepler‘s letter on to both the rest
118 Harmony of the World 129.
119 KGW 17:835: ―Et quia jam annj sunt septem integri, per quos durat haec suspensio; cum
semper pretendant hujus locj ministrj, se paratos esse me admittere, si a Consistorio vel
Facultate Theologica Wirtembergica hoc impetrem: nec unquam mihi categoricum responsum a
quoquam Theologorum fuerit datum, ex quo scirem, an finaliter exclusus sim, nec ne.‖
120 Ibid.: ―Vale clarissime Vir, inque amore mej vel unum hunc, licet ingratum aliquatenus,
progressum facito: ut sciam, eo me non excidere.‖
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of the theological faculty at Tübingen and the Stuttagart consistory. Perhaps he really did try to
make one final attempt on behalf of his old friend, as Kepler had asked. Yet the consistory‘s
final reply to the question of Kepler‘s fate was uncompromisingly firm. Erasmus Grüniger wrote
on behalf of the consistory that
with regard to Kepler, we have long dealt with his craziness, but unsuccessfully…[thus]
we did not want to refrain from communicating with the theologians at Tübingen what
the consistory wrote to him several years ago about this matter…for there can be no other
perspective on his foolishness. 121
The consistory stood by their initial assessment of him and his situation, and under no
circumstances would they readmit him to the Communion or the Lutheran Church. With this
final reply on the part of the Consistory, Hafenreffer wrote back to Kepler, and placed himself
fully alongside the theologians of Tübingen and Stuttgart and against his former friend and
student.
Hafenreffer also took particular issue with Kepler‘s approach to the verse he had
suggested: ―et verbum caro factum est.‖ Kepler, he claimed, had approached the verse exactly as
Hafenreffer had urged him not to—he had analyzed it, wrote Hafenreffer, not as a theologian
would, but rather as a geometrician. For ―what theologian would have thought, said, or
written‖ 122 that the womb of the virgin or the cross in Judea could possibly have become
omnipresent? Of course, Kepler had suggested those possibilities only to deny both them and the
omnipresence of Christ‘s body, but to Hafenreffer‘s mind even the analogy of the two betrayed
121 See KGW 17:843. Betreffend Kepplerum, hat man nunmehr mit selbigem Schwindelhirnlin
lang gehandlet, aber vergebenlich, und lasst er iym nit sagen. Wir haben nit underlassen
woellen, den herrn Theolgois Tubing. zu communicirn, was ihme vom Consistorio auss vor
ettlich iaren eben de hac ipsa materia zugeschriben worden, ob es den herrn belieben moechte,
iyne uff gleichen schlag absufertigen, man kan doch keiner andern meinung umb seines
letzkoefplins willen werden.‖
122 KGW 17:847: ―Quod sane verissimum et aeternum verum esset, si maxime non Damascenus,
sed Keplerus etiam, et quivis Geometra dixisset. Quis enim vnquam Theologurm sensit, scripsit,
virgineum Deiparae vterum factum esse vbique praesentem….‖
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the fundamental errors of Kepler‘s thought. Kepler had tried to attribute his ideas to Scripture
and the church Fathers, but Hafenreffer instead attributed them ―to your hallucinations that you
imagine most falsely.‖ 123
Kepler ought to understand that there was an infinite difference
between the womb or the cross and ―that ineffable mystery‖ of divine hypostasis, in which the
infinite flesh became finite; ―it is great folly (let me not say madness) to infer similarity from
things so infinitely different.‖ 124
This was exactly why Hafenreffer had told Kepler to avoid
theological questions from the start. Kepler failed to appreciate the nature of theological
―mysteries,‖ a word that Hafenreffer used frequently throughout his letter to Kepler. The phrase
―verbum caro factum‖ represented one such mystery, and it was folly to think about how it might
have occurred or what physical things might be similar to it. Kepler had imagined ―physical and
geometrical things,‖ 125 when he should have focused on the great mysteries of worship instead.
Kepler‘s mental prowess, asserted Hafenreffer once again, only confused him when it came to
the ―sacred mysteries of worship.‖ 126
For all these reasons, Hafenreffer concluded that neither he nor the members of the
consistory or the theological faculty could ―approve your absurd and blasphemous
imaginings.‖ 127
Rather, they could only offer him the following advice: ―that you abandon the
imaginings of foolish reason, cling to the heavenly truth in true faith and the divine mysteries in
123 Ibid.: ―…tuae hallucinationj tribuo, quod tu tibj falsissime imaginaris…‖
124 Ibid.: ―…quae igitur Amentia (ne dicam furor) est ex rebus infinitis modis differentibus,
similitudinem concludere!‖
125 Ibid.: ―Physica tibj imaginaris et Geometrica.‖
126 Ibid.: ―…quae res totum ingenium tuum, rerum sacrarum adorandis mysterijs non subditum,
miserandum in modum perturbat.‖
127 Ibid.: ―Eam ob causam neque Ego, neque Dominj collegae et fratres mei, absurdas et
blasphemas imaginationes tuas approbare possumus.‖
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simple faith, which all true Christians do, and worship and honor [God] in pious obedience.‖ 128
If Kepler refused to do this, ―we see no remedy for that unfortunate wound inflicted on you by
the sword of foolish human reason.‖ 129 Nor could they see how Kepler could possibly be
readmitted to Communion: ―how can he who does not cultivate or profess the same faith as the
orthodox church enjoy the sacraments with that same church, from whose faith he departs?‖ 130
Kepler needed to reject his erroneous beliefs and embrace the truth, ―or shun the community of
our church and confession. For Christ must not be ridiculed, nor does the purest bridegroom of
his church share his love with vain and blasphemous opinions.‖ 131
With a final exhortation that
reason was ―blind and foolish in matters divine,‖ 132 Hafenreffer urged him to instead embrace
the ideals of simplicity and humility. He prayed that Kepler would take his letter in the brotherly
spirit which it was intended, and recommended Kepler‘s soul ―to the omnipresent Christ, your
savior.‖ 133
The letter concluded with the signatures of not only Hafenreffer but his colleagues in
the theological faculty as well, along with a copy of the 1612 letter from the Stuttgart Consistory,
testifying that the Tübingen theologians agreed with everything it said.
Even as Kepler insisted that he no longer sought to link geometry and theology, then,
Hafenreffer insisted that this was precisely what he continued to do. Though in all his writings
128 Ibid.: ―…vt abiectis stultae rationis imaginationibus, veritatem coelestem vera fide
apprehendas, et divina mysteria simplicj fide; quod omnes verj christianj faciunt, pio obsequio
adores ac venereris.‖
129 Ibid.: ―…sin fraternis nostris admonitionibus diutius etiam refragabere, nos infelicis istius
uulneris (stultitiae humanae rationis gladio tibj inflictj) neque medicinam videmus.‖
130 Ibid.: ―Qui enim cum Ecclesia Orthodoxa non eandem Fidem et profitetur et colit, quomodo
ijsdem cum Ecclesia, a cuius Fide dissentit, Sacramentis vtatur.‖
131 Ibid.: ―…aut Consortium nostrae Ecclesiae et Confessionis vites, fraterne suadent et
exhortantur. Nam Christus non irridetur: neque idem purissimus Ecclesiae suae sponsus cum
vanis et blasphemis opinionibus amorem suum partitur.‖
132 Ibid.: ―…vt Rationj, quae in rebus divinis caeca et stulta est…‖
133 Ibid.: ―Hisce te animamque tuam preciosissimam, Christo omnipraesentissimo tuo Salvatorj,
devotissime commendo.‖
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to Hafenreffer Kepler had avoided the explicit linkage between geometry and confession that he
had emphasized in 1597, and had claimed to approach the Eucharist issue strictly theologically,
Hafenreffer still saw his primary flaw to be his mathematical thinking, his mental prowess
leading him astray. Once a geometrician, always a geometrician, to Hafenreffer—and perhaps
he was right. Kepler‘s firm conviction that God was a geometer who had used the model of
geometry in all he had created made it difficult for him to ever firmly separate the geometrical
from the theological, despite his protestations to Hafenreffer. The Book of Nature and the Book
of Scripture were too closely linked in Kepler‘s mind for him, ―with eyes closed to geometry,
[to] adhere faithfully to Scripture‖ as he had tried to argue to Hafenreffer. Even the inscription
that was placed on his tomb, at his request, betrays this. ―I measured the heavens, now I measure
the shadow of earth,‖ Kepler had written. ―My mind was from heaven; the shadow of my body
lies dead.‖ 134
The two heavens, astronomical and spiritual, were always necessarily connected to
Kepler; his disagreements with theologians and his despair at the state of his church could never
truly shake his belief that geometry, at a fundamental level, could ultimately point the way to an
omnipresent truth.
Conclusion
The story of Kepler and Hafenreffer is in many ways a story of two men at odds despite
themselves. Over the course of their dispute, they used many of the same words, yet those words
meant dramatically different things to each of them. Perhaps the biggest example of this divide
is their use of the word ―church.‖ When Hafenreffer spoke of the need to preserve the strength
and unity of the church, he meant the Lutheran Church in particular—for only the Lutheran
134 ―Mensus eram coelos, nunc terrae metior umbras./Mens coelestis erat, corporis umbra
jacet..‖
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Church, in his mind, represented the ―true‖ church. Kepler, by contrast, consistently articulated
a conception of the church that was far more expansive than many of his contemporaries. The
church that he hoped to strengthen was far broader than Hafenreffer imagined, and the union he
sought was not limited to the Lutheran confession, but rather encompassed them all. In his mind,
geometry was central to this potential union, since it represented common ground, and provided
a tool for understanding God‘s creation, and indeed, for understanding the mind of God itself.
This leads us to yet another instance in which Kepler and Hafenreffer used the same word
with very different implications—in this case, the word ―mystery.‖ In titling his first book the
Mysterium Cosmographicum, Kepler had deliberately invoked the theological overtones of the
word mysterium, a word which had never before been used with astronomical or natural
philosophical implications. 135
The sacraments, in particular, were often referred to as ―divine
mysteries,‖ which typically implied both that they conveyed some spiritual message in a physical
way, and that the means by which this was accomplished was inscrutable to man. Hafenreffer
used the word again and again in this way in his letters to Kepler; divine mysteries, he insisted,
could not possibly be explained by recourse to reason or intellect. Following Luther, Hafenreffer
emphasized that man, in his fallen state, could not possibly hope to access the full heavenly
truth. 136
Mysteries were those truths which specifically beyond the grasp of mere mortals;
simple faith was the only way with which man could access the message of salvation they
conveyed. Kepler, however, intended something entirely different in his use of the word
―mystery.‖ Mysteries were manifestations of the divine, to be sure, but his book argued that
God‘s ways were fundamentally geometrical. In using geometry to explain the workings of the
135 Howell 114.
136 James J. Bono, The Word of God and the Langauges of Man: Interpreting Nature in Early
Modern Science and Medicine (Madison: University of Wisconsin Press, 1995), 69.
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universe, then, Kepler was explaining precisely that which many believed to be inexplicable—he
was demonstrating the way God‘s mind worked. The theological connotations of the word
―mystery‖ in the title of his first book were likely intended to point to just this—to the ways that
his mathematical and astronomical text revealed the true divine mysteries for all to understand.
And it was ultimately this divergence that led Hafenreffer to confirm Kepler‘s exclusion from the
communion.
Kepler‘s arguments here place him alongside those medieval exegetes who, influenced by
the work of Plato, argued that the secrets of God might be revealed through a study of the natural
world. Though it was understood by all that the Fall had alienated man from God‘s truth, the
study of nature allowed man to reunite with the divine once again; ―to know the world,‖ as Peter
Harrison has written, ―[was] not merely to come to know God…[but] to become like God:…to
restore a likeness which had been lost.‖ 137
Men like Hugh of St. Victor argued that the study of
nature allowed man to rediscover those divine mysteries which had been lost in the Fall, and to
reunite that which the Fall had divided. The study of nature was a religious enterprise, in this
view, because it allowed man to regain the godlike Adamic view in which all of nature was open
and explicable to his gaze. By the seventeenth century, this viewpoint had begun to change.
Francis Bacon famously argued that man could never truly know the mind of God—Adam‘s very
fault in Eden, according to Bacon, was his ―approaching and intruding into God's secrets and
mysteries.‖ 138
Only if men recognized the limits of their reasoning capacities and the proper
boundaries of their inquiries, wrote Bacon, could they begin to build up a true foundation of
137 Peter Harrison, The Bible, Protestantism, and the Rise of Natural Science (Cambridge:
Cambridge University Press, 2001), 57.
138 Francis Bacon, Valerius Terminus: Of the Interpretation of Nature, in The Works of Francis
Bacon: Philosophical Works, Eds. James Spedding, Robert Leslie Ellis and Douglas Denon
Heath (New York: Hurd and Houghton, 1864), 28.
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knowledge. 139
Kepler positioned himself alongside the earlier, more optimistic approach; much
as he denied the view of Hafenreffer and Luther before him that man could never truly penetrate
the divine mysteries, he denied too the possibility that man‘s flawed intellect needed to be
reigned in. Like the medieval Platonists, Kepler continued to believe that man, a true microcosm
of the heavenly macrocosm, was capable of being like God, and that, as Hugh of St. Victor had
written, ―every nature tells of God.‖ 140
Much as Kepler and Hafenreffer differed when it came to the question of divine
―mysteries,‖ they differed as well in their understandings of the proper relationship between the
realm of geometry and the realm of theology. And this disagreement, as articulated over the
course of their correspondence, reveals a great deal about larger sixteenth- and seventeenthcentury
understandings of the relationship between science and religion. Much of the literature
analyzing this relationship in recent years has tended to emphasize the importance of early
modern disciplinary divisions. This is particularly true when it comes to the story of Copernicus
and his reception, and Galileo‘s ultimate confrontation with the Catholic Church over the
Copernican question. Robert Westman, in particular, has emphasized that Copernicus‘s ideas
were controversial not primarily because of the heliocentrism that he taught, but rather because
Copernicus overturned the disciplinary boundaries of the universities. 141
Natural philosophy was
the traditional discipline that could speak about the reality of the cosmos, while mathematics was
only supposed to offer a provisional and predictive picture of the celestial motions. In arguing
that his mathematics was written for mathematicians, Copernicus ―appeal[ed] to the autonomy
139 Bono, The Word of God, 218.
140 Harrison, The Bible, Protestantism, 56.
141 Robert Westman, ―The Copernicans and the Churches,‖ in God and Nature: Historical
Essays on the Encounter between Christianity and Science, eds. David C. Lindberg and Ronald
L. Numbers (Berekely:University of California Press, 1986): 76-113.
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and superiority of mathematical astronomy‖ 142 ; he argued both that mathematics could offer a
true picture of the cosmos, and that mathematicians were uniquely positioned to understand and
interpret the picture—and that natural philosophers and even theologians ought to give way to
the authority of mathematicians on this subject. The Galileo affair Westman paints as well as a
story of disciplinary boundaries overturned. Galileo‘s fatal flaw was not his insistence on
Copernicanism, but rather his insistence that he, a natural philosopher and mathematician, could
interpret Scripture as well as—or better than—any theologian. 143
The stories of Copernicus and
Galileo, in this view, support the notion that in the early modern period, disciplinary identities
were both deep-rooted and subjected to continual challenge; the story of science and religion in
this period is thus a story of the ways that these disciplinary identities were contested and
reformed over time.
To Amos Funkenstein, by contrast, the story of early modern science and religion is not a
story of boundaries and divisions, but rather a story of overlap and entanglement. In contrast to
the earlier separation of the two realms, Funkenstein argues, ―to many seventeenth-century
thinkers, theology and science merged into one idiom, part of a veritable secular theology such
as never existed before or after.‖ 144
In Funkenstein‘s view, it is nearly impossible in this period
to speak separately of theologians or natural philosophers or mathematicians. Men like Galileo,
Descartes, Leibniz, and Newton commonly treated theological issues in great depth; they used
natural philosophical and mathematical ideas to reflect on theology, and theological ideas to
142 Ibid. 50
143 See also Ernan McMullin, The Church and Galileo (Notre Dame: University of Notre Dame
Press, 2005) and the extensive introduction to Maurice A. Finocchiaro, The Galileo Affair: A
Documentary History (Berkeley: University of California Press, 1989).
144 Amos Funkenstein, Theology and the Scientific Imagination from the middle ages to the
seventeenth century (Princeton: Princeton University Press, 1989), ix.
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eflect back in the other direction. His story is not one of boundaries challenged and reformed
along new axes, but rather one of boundaries dissolved entirely.
These stories are not, of course, mutually exclusive; Westman focuses at length on
Galileo‘s attempt to dissolve the boundary between astronomy and scriptural interpretation,
while Funkenstein discusses the extent to which ―the separation of science from religion may
have been as often demanded as it was violated.‖ This chapter, as well, demonstrates the extent
to which early modern disciplinary identities were at once understood in fixed and specific ways,
and at the same time could be used with multivalent and changing meanings. At the start of the
story, Hafenreffer relied on accepted disciplinary boundaries between natural philosophy and
astronomy in order to protect the discipline of theology. ―Act as a mathematician alone,‖
Hafenreffer urged Kepler; in this way, his words would be understood only hypothetically, and
would pose no challenge to accepted theological beliefs. In 1619, by contrast, Hafenreffer urged
Kepler to think theologically, and not mathematically; mathematics would only set Kepler astray
when he contemplated matters divine. Hafenreffer, it appears, conceived of ―mathematician‖
both as a fixed professional identity and as a more fluid mode of thought, one way among many
to approach any issue. Kepler, likewise, approached mathematics both as a discipline and as a
way of thinking. From the perspective of disciplinary identity, Kepler fits in well with
Westman‘s story—he, too, tried to challenge and broaden the conventional role of the
mathematician, and to argue that mathematicians were capable of offering a true picture of the
physical world. From the perspective of Funkenstein‘s story, too, Kepler‘s struggle makes sense.
In contrast to Hafenreffer‘s attempt to separate ―mathematical‖ and ―theological‖ modes of
thought, Kepler sought to merge the two; thinking geometrically meant thinking in a clear and
direct way about both God and his creation.
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Kepler and Hafenreffer‘s disagreements rested not only on the question of disciplinary
identities but also on the question of the relationship between the individual and his community,
and the relationship between the layman and the theologian. Kepler emphasized the importance
of action and participation to religious life—if he participated in his churchly community, took
the mass, and spoke no public word against the community, what matter what he believed on the
inside? Personal conscience, in his view, ought not to impede public communal participation.
For Hafenreffer, by contrast, what mattered was not orthopraxy but orthodoxy—if Kepler did not
believe, he could not participate. At the same time, Kepler attempted to minimize his
disagreements with the church by emphasizing his status as a layman. He did not want to sway
public belief, he argued, nor did he want to be forced to take a public stand on complex
theological questions; he merely wanted the right to worship simply, on the sidelines, as he saw
fit. Hafenreffer, by contrast, saw Kepler as something above the common layman, and argued
that he needed to sign the Formula of Concord in order to publicly stand with the opinion of his
Lutheran brothers. Likewise, Hafenreffer emphasized that if Kepler wanted to consider
questions of Scritpure and doctrine, he needed to do so as a theologian would—and not as a
layman mathematician would. In many ways, what we see here is the reversal of the Galileo
story; Galileo was punished for acting as a theologian rather than a layman, while Kepler was
punished for acting as a layman, rather than a theologian.
In sum, Kepler‘s clash with the Lutheran Church boiled down to a disagreement about
those two central words on whose meaning he and Hafenreffer disagreed—―mystery‖ and
―church.‖ The mysteries of God—be they theological or cosmological—were not, in Kepler‘s
view, secrets to be hoarded by a select few, nor were they enigmas impervious to rational
inquiry. Rather, God had provided a blueprint by which they could be interpreted—geometry—
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and a model by which that interpretation might be judged—the model of harmony. That model
demonstrated that the church was not simply the specific confession that most closely adhered to
one narrow perspective on theological truth, but rather all the confessions, united by common
beliefs and the occasional counterpoint of disagreement.
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Chapter 2:
“Of God and His Community”: Kepler and the Catholic Church
In February of 1605, the Italian mathematician Bartolomeo Cristini had good news to
report to fellow mathematician and astronomer Giovanni Antonio Magini in Bologna. The papal
nuncio to the Imperial court in Prague, wrote Cristini, ―declares that he hopes to convert master
Kepler to the Catholic religion within the next few days.‖ 1
This imminent conversion would
fulfill a dearly held hope of many of Kepler‘s Catholic friends and colleagues, who had often,
subtly or directly, pressed him to consider the religious and professional benefits of becoming a
Catholic.
Cristini‘s news was, in point of fact, wide of the mark—Kepler had no intention of
conversion to Catholicism, and remained committed to his Lutheran faith long after 1605—and
indeed, long after his official excommunication from the Church to which he clung so
tenaciously. Yet Cristini‘s report, though false, was just one of many rumors about Kepler‘s
impending conversion that swirled around Kepler throughout his lifetime. These rumors
stemmed, in part, from Kepler‘s close personal and professional relationships with many
influential Catholics. These included Bavarian Chancellor Herwart von Hohenburg, lifelong
friend and patron of Kepler, as well as Jesuit mathematicians like Paul Guldin, Johannes Decker,
and Albert Kurz. These men not only corresponded with Kepler on questions of mathematics,
astronomy, astrology, and chronology, but also helped Kepler to circumvent some of the troubles
that plagued his fellow Lutherans living in Catholic territories in the Empire. Herwart, for
instance, likely helped Kepler to obtain the exemption that allowed him to remain temporarily in
1 KGW 15:333: ―Habui ab illustrissimo nuntio S. S. apostolicae apud Imperatorem, episcopo
vercellensi, observationes stellae novae factas a Domino Tengnagelio manu propria eius ut
existimo scriptas nigris et rubeis caracteribus, quem idem Illustrissimus nunc catholicam
religionem profiteri et sperare intra paucos dies ad eandem Dominum Keplerum convertere.‖
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Graz when all other Lutheran teachers and priests were banished by official decree. Guldin
helped Kepler with some of his publication difficulties, and arranged for a Jesuit telescope maker
to provide Kepler with his very own telescope.
The close interest which so many Jesuits took in Kepler, particularly after he rose to the
position of Imperial mathematician, bolstered the impression that they harbored hopes for the
conversion of so well-respected a figure. Indeed, in letters to Kepler his Jesuit correspondents
emphasized both their respect for his mathematical prowess and their fears for the current state
of his soul, fears to which they believed he would be receptive. As Albert Kurz wrote to Kepler,
the very fact that Kepler was willing to discuss his theological difficulties implied that he had
doubts about his faith, and those doubts would be resolved if he would only trust in the leaders
and traditions of the Catholic Church. Kurz wrote,
In other things I will admire you, in other things I will praise you but in that business of
your salvation, I ask you to rely on the blood which drips from Jesus Christ, rather than
on your mental prowess alone, as though you alone could hope to touch on the truth
without a guide or companion; rather, you ought to fear going astray amidst the light and
company of so many great stars. 2
Nearly echoing the Lutheran theologians at Tübingen who warned Kepler about the dangers of
using reason to navigate the world of faith, Kurz urged Kepler to rely on the guidance of others
skilled in the truths of theology, rather than on his own limited understanding of those truths.
The Jesuits believed that were the ones best suited to offer Kepler the guidance he needed
in order to find his way the truths of Christ and his church, and they made repeated attempts to
do so. Kepler‘s own willingness to consider Jesuit perspectives on mathematical issues, and
2 KGW 18:1053: ―…in caeteris admirabor te, in caeteris laudabo in isto autem Salutis taue
negotio, per illum ego te stillantem Jesu Christi sanguinem rogo, ne ingenio tuo tantum tribuas,
ut solum te sine duce sine comite uerum tangere posse speres; uel in ista luce et societate tot
tantorumque siderum errare metuas.‖
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even to take the Jesuit side in a chronological dispute against the Protestant one, 3 signaled to the
Jesuits that he would be receptive to their message. Still further, at a time when relations
between Catholics and Protestants were stridently antagonistic, Kepler‘s willingness to seriously
consider the Catholic position on questions of theology and his repeated declarations that he
belonged to the ―Catholic Church‖ made it seem that his eventual move to Catholicism was
already well underway.
In this chapter, I consider Kepler‘s relationship with both specific Catholics and with the
larger Catholic Church. I look first at Kepler‘s relationship with Herwart von Hohenburg,
focusing in particular on a 1607 discussion between the two about the religious significance of
the new star of 1604, and of astrology more generally. Next, I turn to Kepler‘s relationship with
Jesuit Paul Guldin, moving ahead twenty years in time and focusing on a discussion between the
two about the proper definition of the Catholic Church, and the means by which unorthodox
views could be accommodated within a traditional religious community. I conclude by
considering Kepler‘s conception of the Jesuit Order, and of Jesuit science in particular, drawing
on letters that spanned the range of his life and work. Along the way, I touch on several other
Catholics with whom Kepler corresponded, yet this chapter does not provide an exhaustive
survey of Kepler‘s relationship with Catholics, or even with Jesuits. Instead, the episodes I‘ve
selected are emblematic ones that help tell a story about Kepler‘s unique approach to religious
community and his hopes for the future of the Church, understood in very broad terms.
This story is, in many ways, similar to the one I told in Chapter 1; there, I focused on the
process by which Kepler fashioned his own identity as a Lutheran while simultaneously
3 See Anthony Grafton, ―Chronology, Controversy, and Community in the Republic of Letters:
The Case of Kepler,‖ in Worlds Made by Words: Scholarship and Community in the Modern
West (Cambridge: Harvard University Press, 2009).
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constructing a new vision of the Lutheran Church and its relationship to Christendom at large. In
this chapter, I also explore questions of religious identity and community, but I do so by focusing
not on Kepler‘s understanding of his own Church, but rather of a Church which many of his
fellow Lutherans saw as a direct embodiment of the Antichrist. In so doing, I hope to better
illuminate Kepler‘s understanding of his own religious identity and his vision of his place within
the larger religious community, a vision which centered on the idea of a harmony that Kepler
hoped to extend from the realm of the heavens to the realm of earthly society.
At the same time, I hope to further explore the multi-faceted relationship between
Kepler‘s astronomical and religious pursuits. In Chapter 1, I demonstrated some of the ways in
which Kepler‘s cosmological work figured centrally in his plans for confessional reconciliation;
At the start of his career, I argued, Kepler believed that cosmological ideals could be directly
mobilized to solve specific confessional disputes. Yet I also explored the ways that Kepler‘s
views had changed by the time of his excommunication from the Lutheran Church. While he
still believed staunchly in the idea that geometry might point the way to a universal truth—even
one that encompassed theology—he no longer trusted in the theologians of his time to identify or
implement that truth. In this chapter, I further explore Kepler‘s conception of the relationship
between cosmos and confession, by highlighting certain instances in which Kepler did not feel
that a direct linkage between the two was warranted. In the episode with Herwart, I argue that
Kepler avoided positing too close a connection between his astrological work and its religious
ramifications, and maintained that religious claims, specifically ones that related to sensitive
confessional issues, ought to be made cautiously and humbly. In the episode with Guldin I
emphasize that Kepler‘s irenical approach to religious truth—an approach which embraced the
possibility of considering religious questions from multiple perspectives, and arriving at
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potentially different answers—was, in many ways, directly opposed to his realist stance on
astronomical truth, which emphasized that the Copernican and Ptolemaic systems, though
instrumentally equivalent, were not equally valid accounts of the motions of the heavenly bodies.
In ending with a discussion of Kepler‘s approach to Jesuit science, I speculate more broadly on
Kepler‘s understanding of the appropriate relationship between the realms of natural philosophy,
mathematics, and religion, and on the ways in which Kepler‘s approach related both to that of his
fellow Protestants and to their Jesuit counterparts.
Kepler, Herwart, and the New Star of 1604
In September of 1604, observers across Europe were enthralled by a dazzling new object
in the sky, often referred to as a new star. Portentous in its own right, the new star was made
doubly significant by the place of its emergence: it appeared in close proximity to the
conjunction of Mars, Jupiter, and Saturn in the sign of Sagittarius—a conjunction which initiated
the Fiery Trigon, a period of great astrological significance. These two momentous events, and
their close proximity, resulted in a flood of pamphlets arguing for the new star‘s earthly
significance. Kepler also produced a work that focused on the implications of the new star—De
stella nova—though it was not published until two years later, and it was far more circumspect
than many of the texts that preceded it. 4
The majority of the book was devoted to the physical
significance of the new star, while only the final chapters addressed what future events it might
portend. And though Kepler willingly speculated on some possibilities for its future
significance—among them the fall of the Ottoman empire, the second coming of Christ, and the
4 For a detailed discussion of Kepler‘s approach in De Stella Nova, see Patrick Boner‘s 2006
dissertation, ―Kepler‘s Living Cosmos: Bridging the Celestial and Terrestrial Realms,‖ currently
unpublished.
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conversion of all non-believers to Christianity—he did not endorse any option as certain.
Reading detailed significances into the heavens was risky business, he argued, because God had
provided no formula by which heavenly phenomena could be easily interpreted. ―If it had
pleased God to openly indicate what he wished to men,‖ he wrote, ―he would have inscribed it in
the heavens with written words; thus men struggle in vain to conjecture about the divine will.‖ 5
Though he considered it clear that the new star, appearing precisely where and when it did, was a
sign of divine providence, Kepler hesitated to proclaim what such providence signified in the
realms of communal politics or religion. Instead, he urged his readers to use the new star as an
opportunity to examine their own lives, while maintaining a sense of humility about its global
significance. 6
Rather than focus on the arguments in De stella nova, I want to consider instead an
exchange that took place shortly after its publication, between Kepler and Herwart von
Hohenburg, Bavarian Chancellor and friend and patron of Kepler‘s. Though primarily a
statesman, Herwart also had deep scholarly interests in astronomy, chronology, mathematics and
philology, and it was Kepler‘s detailed answer to a chronological query of Herwart‘s in 1597 that
spearheaded a relationship that would span fourteen years and more than ninety letters. Over the
course of this relationship, Herwart lent Kepler books, supplied him with information about the
work of other scholars in the Republic of Letters, and pushed Kepler to refine his own scholarly
views, particularly when it came to questions of astrology. 7
Herwart had read Kepler‘s De Stella
5 KGW 1, 346.38–39: ―Ego interdum sic existimo; si Deo placuisset, aperte hominibus, quod
vellet significare: literis caelo exaratis scripturum fuisse; frustra itaque homines conjectando
divinae voluntati obniti.‖
6 See also Patrick Boner. ―Kepler v. the Epicureans: Causality, Coincidence and the Origins of
the New Star of 1604.‖ Journal for the History of Astronomy 38 (2007): 207–221.
7 See Patrick Boner. ―A Scholar and a Stateman: Hans Georg Herwart von Hohenburg as a Critic
and Patron of Johannes Kepler.‖ Forthcoming.
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Nova with some interest. There, Kepler had suggested—though only as possibilities—some
religious implications of the new star, yet he had not considered what significance the new star
might have when viewed within a specifically confessional context. In March of 1607, Kepler
received a letter from Herwart, asking him to push his ideas further and contemplate the
distinctively Catholic significances of the heavenly bodies.
Kepler‘s discussion of the new star and the birth year of Christ, Herwart wrote, had
motivated him to provide Kepler with a brief judicium he had written which considered questions
of astrology and religion, as he was aware that there were many Catholic theologians who still
attributed inclinations or significances to the stars. Herwart maintained a degree of skepticism
on the question, noting that he had yet to find a firm foundation on which to base such
suppositions; he therefore admitted that ―I would well have cause to withhold [my judicium], for
perhaps it is not worth the effort of writing or of rebuttal.‖ 8
Yet he had read in Kepler‘s
astrological writings a similar uncertainty on issues of astrological inclination or signification, he
wrote, and for that reason, he hoped that Kepler would openly communicate his thoughts on the
matter. He asked that Kepler keep Herwart‘s musings secret, since they were, after all, only
―bare speculation.‖ 9
Moreover, he emphasized that though his speculations were ―drawn out
from the tradition of our Catholic Church,‖ with which he knew Kepler was not in full
agreement, he hoped that Kepler would take them as nothing less than well intentioned. 10
8 KGW 15:412: ―…ich woll ursach hette, damitt zu hinder halten, weyll es villeicht der muehe
des schreibens, und confutierens nitt wehrd.‖
9 Ibid.: ―Unnd uberschickh dem herrn benuerwart hierueber ein speculationem, Die ich aber bitt
in vertrawen unnd gehaim, tanquam nudam quandam speculationem, zu halten.‖
10 Ibid.: ―Videntur quidem haec deprompta ex traditione Ecclesiae nostrae Catholicae, ich will
aber in kienen Zweyuell stellen, Er werde Es pro suo candore, etsi eidem non sis addictus,
dannoch anderst nitt alss woll gemaint ausnemmen, unnd mir darueber sein spetial bedenckhen
mittahilen….‖
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Despite the Catholic Church‘s formal opposition to the practice of judicial astrology,
Herwart‘s contention that many Catholic theologians still accepted its basic tenets is well
supported by the historical literature. Ugo Baldini describes the paradox of a society in which,
up until the seventeenth century, ―outright condemnations of judicial astrology coexisted with its
widespread and public practice…and with its substantial acceptance by social elites, and even by
the ecclesiastical hierarchy.‖ 11
Part of this paradox lies in the church‘s somewhat unsystematic
approach to the discipline of astrology, to the distinctions between natural and judicial astrology,
and to the enforcement of its own astrological condemnations. Though Pope Sixtus V‘s bull
―Coeli et terrae creator Deus‖ of 1586 formally condemned astrology in fairly restrictive terms,
arguing that ―God has reserved certain knowledge of future things only unto himself,‖ 12 the bull
focused specifically on the application of judicial astrology to the future lives of individuals, and
did not discuss the implications of natural astrology more broadly. And even after the Pope‘s
bull was officially accepted by the Catholic world, judicial astrology still had many supporters;
Jesuits still taught private classes in astrology, 13 Catholic courts still had official judicial
astrologers, 14 and astrological discourses were still addressed even to cardinals at the papal
11 See Ugo Baldini, ―The Roman Inquisition‘s Condemnation of Astrology: Antecedents,
Reasons, and Consequences,‖ Church, Censorship and Culture in Early Modern Italy. Ed.
Gigliola Fragnito. Trans. Adrian Belto (Cambridge: Cambridge University Press, 2001): 79–110,
at 87.
12 Ibid. 91; see also Bullarum, Diplomatum et Privilegiorum Sanctorum Romanorum Pontificum
Taurinensis Editio, VIII. Turin, 1863. 646–7.
13 See Henrique Leitão, ―Entering Dangerous Ground: Jesuits Teaching Astrology and
Chiromancy in Lisbon,‖ The Jesuits II: Cultures, Sciences, and the Arts, 1540–1773. Eds. John
W. O‘Malley, et al. (Toronto: University of Toronto Press, 2006): 371–404.
14 Giovanni Antonio Magini, for instance, served as judicial astrologer in the court of Mantua
beginning in 1599.
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court. 15 Though officially on doctrinally shaky ground, then, Herwart‘s astrological speculation
was in good company, as he indicated. In the ―judicium‖ that he appended to his letter to Kepler,
Herwart began his speculation by equating the three divisions of the heavens with the three
aspects of God—the supreme and invisible heaven, according to Herwart, signified the Father;
the intermediate heaven, or the fixed stars, signified the Son; and the lower heaven, or the seven
plants, signified the Holy Spirit. This kind of association, he would have known both from
Kepler‘s letters and books, was very familiar to Kepler, who himself had identified the Trinity in
the configuration of the heavens. Kepler‘s argument for the Trinity was slightly different, of
course. He first analogized the sphere to the Trinity, with the center symbolizing God the
Father, the surface symbolizing the Son, and the intermediate space symbolizing the Holy Spirit.
He then extended this analogy to encompass the entire cosmos, with the sun in the center of the
universe representing the Father, the fixed stars at the surface representing the Son, and the
intermediate ether representing the Holy Spirit. But despite these differences, the Trinity was
essential to Kepler‘s own cosmological perspective, and he would have been sympathetic to
Herwart‘s invocation of it in this context.
Herwart then moved on to the more exclusively Catholic portion of his judicium. Since
the seven planets, in his view, represented the Holy Spirit, they represented more specifically the
gifts of the Holy Spirit, or the seven Sacraments. The moon, because of its connection with
water, represented baptism. Mercury, wrote a cynical Herwart, represented the sacrament of
marriage, as it was ―somewhat obscure, wandering, constantly beneath the sun or needing
15 In The History of Magic and Experimental Science (New York: Columbia University Press,
1953), 6:171, Lynn Thorndike notes the publication of an astrological discourse by Gioanni
Bartolini addressed to a cardinal at the papal court in 1618.
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penance.‖ 16
By extension, Venus, ―clear, lucid, shining, most beautiful of all,‖ represented the
sacrament of Holy Orders. 17
The sun represented penance, as it was the source of all the other
planets, which all inclined themselves toward it and depended on its motion, just as all the other
sacraments depended on penance. Mars, which recurred every two years, corresponded to
childhood, and hence to confirmation. Jupiter, recurring every twelve years, corresponded to
puberty, and hence to the Eucharist. Finally, Saturn‘s thirty year cycle corresponded to the
sacrament of extreme unction, as Herwart noted that thirty years ―concludes the age of the
perfect man‖ 18 —likely an allusion to Jesus, who began to preach at the age of thirty, according
to Luke.
In his reply to Herwart, Kepler first addressed Herwart‘s contention that he hadn‘t clearly
articulated his own astrological position, and he took pains to emphasize that he generally
considered himself an opponent of the kind of astrology practiced by the majority of its
adherents. ―What else is the entire little book,‖ he wrote of De stella nova, ―but a near
crucifixion of all judicial astrology, with the aspects alone enduring as parts of the natural
order?‖ 19
But he willingly engaged with the linkages that Herwart had posited between the
heavens and the seven sacraments, and included a ―judicium de speculatione‖ of his own at the
end of his letter. He first addressed the premise that the heavens represented the church overall,
and deemed this premise ―probable.‖ 20
―Because it is a general belief,‖ he explained, ―that God
sends us signs with reference to our earthly circumstances, and sends these signs from the
16 KGW 15:412: ―Mercurius est stella Sacramenti Matrimonii, subobscura, vaga, subinde sub
Sole, seu paenitentiâ indigens.‖
17 Ibid.: ―Venus est stella sacri ordinis, clara lucida fulgens omnium pulcherrima….‖
18 Ibid.: ―Saturnus denique trigesimo anno demum, qui aetatem perfecti hominis claudit,
recurrens…refert nobis Sacramentum extremae unctionis.‖
19 KGW 15:424: ―Et quid aliud est totus libellus, quam solennis άποτσμπάνισις totius fere
Astrologiae judiciariae, solis Aspectibus in naturae partes traductis.‖
20 Ibid.: ―Comparatur hic caelum cum Ecclesia. Probabile.‖
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heavens...[and] the most important of our circumstances are those related to the Church.‖ 21
Therefore, he concluded, it was sensible to assume that heavenly signs referred to churchly
matters.
Kepler then went one step further, and conceded it likely that heavenly signs referred not
merely to churchly matters, but to matters specifically relevant to the Catholic Church. His
argument for this assumption was based primarily on practicality. He wrote,
If I conceded it plausible that it is not absurd that God speaks with astrologers, who are
few in number, and forms his words from the particular principles of astrology, although
little certain, it will be much less absurd [to believe] that God says something through
celestial signs to those who extend the name of Rome through the whole breadth of the
Catholic Church—for they are today the most numerous and most powerful part of the
world—and that he speaks to them in their principles, and according to their
understanding. 22
God wants to speak to his people, Kepler explained, and to do so he will employ whatever means
necessary for them to understand him. In his interpretation of Scripture, Kepler had employed
the traditional principle of biblical accommodation, which asserted that scriptura humane
loquitur—Scripture speaks in the language of man. 23
When the Bible spoke of Joshua stopping
21 Ibid.: ―Nam Deus populariter creditur nobis de rebus nostris in Terris signa mittere…Ex rebus
nostris potissimae Ecclesiasticae…‖
22 Ibid.: ―Etenim si hoc prababiliter concessi, non esse absurdum, ut loquatur Deus cum gente
Astrologorum, minime numerosâ, et formare sua verba ex principijs Astrologiae proprijs, licet
parum certis, multo minus erit absurdum, loqui Deum aliquid per signa caelestia, cum eorum
gente, qui Romae vocabulum per omnem Ecclesiae Catholicae amplitudinem extendunt, est enim
hodie numerosissima, adeoque potissima pars orbis Terrarum: et loqui quidem ad eorum captum
ex suis principijs.‖
23 On the idea of accommodation, see Amos Funkenstein, Theology and the Scientific
Imagination from the Middle Ages to the Seventeenth Century (Princeton: Princeton University
Press, 1989): 213–221. See also Ernan McMullin, ―Galileo on Science and Scripture,‖ in The
Cambridge Companion to Galileo, ed. Peter K. Machamer (Cambridge: Cambridge University
Press, 1998): 271–34. Kepler employed this argument in the introduction to the Astronomia
nova, noting that ―…the Holy Scriptures…speak with humans in the human manner, in order to
be understood by them […]. No wonder, then, if Scripture also speaks in accordance with human
perception when the truth of things is at odds with the senses, whether or not humans are aware
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the sun, for instance, it portrayed the event as men would perceive it, not as it had actually
occurred. Along similar lines, Kepler here implied that even if the sacraments of the Catholic
Church carried no great weight from a divine perspective, God might employ them as a means to
transmit his messages, given their significance for so many people on earth.
Kepler had made a similar argument linking astrology to the principle of accommodation
in the De Stella Nova itself, when he discussed the possible effects of the new star. He expressed
his hopes that the new star might signal the rise of a leader who would quell some of the warfare
plaguing Europe, and he noted that such might have been God‘s purpose in making the star
appear where and when he did. To clarify what he meant, he provided an example from an
entirely different realm: Jose de Acosta‘s descriptions of his encounters with the native peoples
of the New World in his Natural and Moral History of the Indies. Kepler focused on Acosta‘s
descriptions of Indian idolatry and the remedies for it, and quoted directly Acosta‘s account of
the ways in which idolatry was an inseparable part of daily life for the Indians. He highlighted in
particular Acosta‘s suggestion for the extirpation of idolatry. Kepler cited directly Acosta‘s
claim that
It is much to be desired that salutary rites be introduced in place of noxious ones, and
ceremonies be replaced by ceremonies. Therefore, priests should persuade themselves
how opportune are the uses of holy water and statues, and rosaries and beads, and candles
and palms, and all other things which are approved by the holy Church and bring
neophytes around. Moreover, they ought to praise these things highly in popular
sermons, so that the old superstitions may be supplanted by new and religious signs.… 24
Kepler focused on Acosta‘s argument that, rather than trying to remove all shades of idolatry
entirely, priests should consider the function that idolatrous practices served. Idolatry was
of this.‖ See New Astronomy, trans. William H. Donahue (Cambridge: Cambridge University
Press, 1993), 60.
24 Quoted in M.W. Burke Gaffney, Kepler and the Jesuits (Milwaukee: The Bruce Publishing
Company, 1944), 31.
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essentially about religious ceremony, in his view, and hence the best way to remove idolatry
would be to substitute religiously appropriate ceremonies for the idolatrous ceremonies to which
the Indians were accustomed. In other words, priests might accommodate the Indians habits,
desires, and ways of thinking by channeling them to an appropriate religious end. Still more, the
idolatrous practices of the Indians, instead of being a stumbling block, could be used as a means
by which to bring them to the Church, by showing the Indians the ways that Christian practices
could serve similar purposes.
Kepler implied in De Stella Nova, through quoting this passage, that God‘s use of the
new star might be conceived of in similar terms to the priestly use of religious ceremony in the
new world. Many of the astrological beliefs of the common man might well be baseless
superstition, that is, yet that very superstition might serve a purpose. Like the priests who might
latch on to the desire for religious ceremony inherent in the practice of idolatry, God might use
the astrological beliefs of his people, though faulty, as a means to turn their attention in
appropriate directions and effect positive change.
Kepler made this kind of argument once again in his 1609 Antwort auff Röslini Discurs, a
reply to a work by Helisaeus Röslin which supported the entire discipline of astrology against
some of Kepler's attempts to limit it in De Stella Nova. There, Kepler insisted that his arguments
against the natural foundations of certain astrological principles like the zodiacal signs, or even
his argument that the nova of 1604 signified nothing ―by nature,‖ need not imply that therefore
they contained no messages for mankind. God might, he averred, employ mistaken but
commonly-held astrological beliefs in order to start a conversation with men and signify
something of future importance. God might, that is, employ the very prejudices of his followers
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in order to lead them to truth. 25
Kepler‘s answer to Herwart‘s judicium was based on a very
similar premise. The astrological linkage that Herwart had posited between the sacraments and
the planets was warranted, Kepler argued, since it was yet another example of divine
accommodation. Since sacramental language was the language of a large majority of his
followers—though not, it should be emphasized, of Kepler himself—Kepler believed that it was
sensible that God would embrace that language as a means to reach them.
One might suppose that Kepler conceded so much to Herwart because of the value of his
patronage, not because of genuine agreement on Kepler‘s part—Herwart was a courtier with
important connections, and Kepler certainly had no wish to alienate him. Yet Kepler, as a
Lutheran, clearly and openly disagreed with his Catholic patron on many questions of religion.
Here, however, he exhibited no such dissent. ―This all seems to me entirely believable,‖ he
concluded, so much so that he would be willing to deny that it was possible to produce a better
comparison of heavenly bodies with churchly things. 26
Given this acknowledgment, Kepler
readily concurred with Herwart‘s particular designations of each planet with each respective
sacrament, and ventured still further to contemplate the meaning of the new star in this context.
The new star, he speculated, signified a great new bishop, and its coincidence with the Fiery
Trigon signified a new doctrine or heresy connected with the sacraments of extreme unction, the
Eucharist, or confirmation. He speculated still further that because the new star appeared along
the ecliptic, it signified that the new bishop would assume power in the usual way, through
apostolic succession. And as the new star was beautiful, the new bishop would entice people
25 See Miguel A.Granada, ―After the Nova of 1604: Roeslin and Kepler's Discussion on the
Significance of the Celestial Novelties (1607-1613),‖ Journal for the History of Astronomy 42.3
(2011): 353-390.
26 KGW 15:424: ―Itaque his datis quae mihi plane sunt verisimilia….‖
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with his words, but would fall from power quickly, as the new star had disappeared in February
or March of 1606.
At this point Kepler rather abruptly backed away, and ceased elaborating further on the
star‘s significance. Because his speculation had led him to the realm of prophecy, he wrote, he
would end his ruminations and be content with this short ―prelude,‖ as he called it. He likened
this to his attitude in De stella nova, in which he had briefly speculated on the new star‘s future
significance only at the end of the book, where, as he wrote, ―I wanted to add an ending
appropriate to the fabula.‖ 27
―For truly,‖ he explained, ―there is no other method in my
predictions than the one that my speculation has used here.‖ 28
His astrological predictions, that
is, like the speculation he sent to Herwart, were based not on certain truths, but rather on
assumptions that needed to be accepted in order for the conclusions to seem valid.
This is not the only place where Kepler highlighted the uncertainty that lay at the heart of
astrological speculation. He emphasized precisely this point in De stella nova, when he left the
significance of the new star undecided. There and elsewhere, Kepler compared the practice of
astrology to the practice of medicine—both were imprecise arts, based on a posteriori
observations and experiences, in striking contrast to the certain demonstrability of
mathematics. 29
Kepler also emphasized the degree to which the practice of astrology was tied up
with cultural assumptions—he included here the signs of the zodiac and their associations with
27 Ibid.: ―Itaque quia speculatio coepit vaticinari, quod desijt in ipso exordio, contenta hoc
praeludio. Ego fabulae convenientem subjungere volui epilogum.‖
28 Ibid.: ―Nam profecto non est alia mearum praedictionum methodus quam haec ipsa, qua usa
est speculatio.‖
29 See Boner, Kepler‘s Living Cosmos, 21.
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the earthly elements. 30
Should any of those assumptions be false, predictions based on them
would also be false. Finally, Kepler emphasized the inscrutability of God‘s intentions;
professing certainty about the meanings of obscure divine mysteries could only be a sign of
hubris. 31 Kepler‘s speculative play with Herwart, then, is revelatory on two levels, both of which
pertain to his understanding of religious community and confessional identity. First, it illustrates
Kepler‘s very broad conception of God‘s relationship with his people, be they Lutherans,
Calvinists, or Catholics. Kepler himself had a complicated view of his own confessional
identity; as noted in the previous chapter, he disagreed with some of the central tenets of
Lutheran orthodoxy, and aligned himself more closely with the Calvinists when it came to the
presence of Christ in the Eucharist. Yet Kepler‘s consideration of Herwart‘s Catholic astrology
is not indicative, as some have argued, of any close affinities with Catholic sacramental
thought. 32
Instead, it reveals Kepler‘s very practical understanding of God‘s communications
with His people, as well as his expansive sense of who God‘s people were. Kepler extended the
principle of accommodation—the belief that God speaks in the languages of man—from the
realm of the scriptural/physical to the realm of the physical/theological. Just as God could use
language to refer to faulty physical theories or perspectives of men in order to convey some
30 Ibid. 25. On Kepler‘s criticism of astrology more generally, see Sheila J. Rabin, ―Kepler‘s
Attitude Toward Pico and the Anti-Astrology Polemic,‖ Renaissance Quarterly 50.3 (1997):
750-770.
31 See, for example, KGW 1, 292.1–6: ―…Ipse enim est, cujus similis nemo; qui solus vocat, et
quae futura sunt, annunciat: Irrita faciens signa divinorum, et ariolos in furorem vertens:
Convertens sapientes retrorsum, et scientiam eorum stultam faciens.‖
32 Jürgen Hübner, for example, cites this interchange with Herwart as an example of the fact that
Kepler embraced certain Catholic teachings openly and actively (―…er die katholische Lehre
nicht nur mit seinem Willen, sondern auch durch sein Urteil anerkenne‖). See Die Theologie
Johannes Keplers zwischen Orthodoxie und Naturwissenschaft (Tübingen: Mohr, 1975), 155.
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greater message, Kepler maintained, so too could God utilize the bodies of the heavens to refer to
faulty theological doctrines of men, in order to achieve the same purpose.
Though Kepler himself had specific opinions about which positions were theologically
valid and which were not (his was neither a plea for deism nor for theological skepticism) this
did not mean that God was only interested in addressing the privileged few who had succeeded
in divining this religious truth. Unlike many of his time, that is, for whom God‘s people
represented very narrowly their own confessional allies—and for whom members of competing
confessions were not merely misguided, but sinful heretics—Kepler understood God‘s people in
a very broad sense. God‘s people were all Christians, regardless of confession. Though
Catholics had certainly erred in adopting specific theological positions, like the belief in the
seven sacraments, this did not mean that they had forfeited the right to their place in the larger
brotherhood of Christendom. And as God undoubtedly intended to communicate with all his
people—among whom Catholics still encompassed the majority by far—considerations of the
manner in which he might do so, and the specific religious language that he might employ, were
surely warranted. Indeed, the very fact that Kepler cited Acosta—a Jesuit whom most
Protestants would have been loathe to embrace—illustrates his own embrace of this very broad
notion of where truth might be found.
The other noteworthy aspect of Kepler‘s discussion with Herwart lies in the reason why
he hesitated to speculate too closely on any concrete confessional implications of the planets. In
marked contrast to Kepler‘s earlier insistence that the claims of the Mysterium cosmographicum
were demonstrable via reason alone, and therefore indisputable 33 —as were any religious
33 On Kepler‘s belief in the a priori nature, and thus the certainty, of cosmology, see Rhonda
Martens, Kepler‘s Philosophy and the New Astronomy (Princeton: Princeton University Press,
2000), 48–56. It is noteworthy, however, that by 1607, Kepler already recognized that the
107

conclusions drawn from them—Kepler argued here that his astrological speculations lacked
method and certainty, as astrology was a discipline characterized by a posteriori observations
and experiences collected over time. It would therefore be impractical, he claimed, to draw any
strong religious conclusions based on them. Yet given the focus on religious implications, it is
likely that Kepler recognized not merely the impracticality of such speculations, but also the
danger inherent in them. After all, the problems of confessional divide were tearing Europe
apart in direct and deadly ways, ways with which Kepler was already all too familiar. 34
To
attempt to speak about the future of an individual was uncertain business, to be sure—but to
attempt to do so about religious groups, and in weighted, confessional terms, was a far more
dangerous game to play. Kepler was fully aware that his speculations could easily be mobilized
by opposing groups to suit their own agendas, and could be used to fan the flames of a fire
already perilously out of control. 35
Moreover, much as he knew that astrological predictions were based on cultural
assumptions, he knew too that religious conflicts were based on assumptions of their own.
Kepler had argued in De stella nova that David Fabricius, a Lutheran theologian and astronomer
who had also observed and interpreted the new star, had allowed his own biases to color his
interpretations. Fabricius‘s predictions, he wrote, were ―nothing other than complaints about his
neighbors, his opinion concerning the condition of the empire, and his desire for vengeance and
polyhedral hypothesis he had outlined in the Mysterium Cosmographicum did not account for the
phenomena as fully as he had once believed.
34 Kepler was expelled from Graz permanently in 1600, and dealt with the ravages of expulsion
and war throughout his life.
35 On the astrologer as a political figure—and the consequent dangers of such a role—see
Anthony Grafton, ―The Astrologer as Political Counselor,‖ in Cardano‘s Cosmos: The Worlds
and Works of a Renaissance Astrologer (Cambridge: Harvard University Press, 1999): 109–126.
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improvement.‖ 36
Worried that any predictions he might make would either be interpreted
similarly, or still worse, used to further the grievances of others, Kepler steered clear of making
claims with obvious confessional implications when they were based on so uncertain a
foundation to begin with. In other words, if his work was more likely to aggravate disputes
between the confessions, rather than settle them, Kepler sought to deemphasize its linkage with
religion. He highlighted what he perceived to be the essential continuity between cosmos and
confession only when he felt that such continuity would help to heal the church, rather than add
to its troubles.
Kepler, Guldin, and Religious Community
By 1627, Jesuit mathematician Paul Guldin had already sustained a friendly
correspondence with Kepler for many years. The two had discussed innovations in mathematics
and the hardships of daily life, and Guldin had even arranged for Nicholas Zucchi, Jesuit
mathematician and telescope maker, to gift Kepler with one of his reflecting telescopes. In
thanks, Kepler sent Guldin copies of his Harmonice Mundi and the second edition of the
Mysterium Cosmographicum, and he had appended his Somnium with a grateful letter to Guldin.
There, he asserted that ―there is hardly anybody with whom at this time I should prefer to talk
about astronomical studies face to face than with you,‖ 37 and emphasized that he delighted in
both Guldin‘s friendship and his scholarship.
36 KGW 1, 354.25–28: ―…quod et FABRICIO, cujus scriptum de significationibus hujus stellae
nihil aliud continent, quam querelas de suis vicinis, opinionem de statu Imperij, et desiderium
vindicate atque emendationis.‖
37 Kepler‘s Somnium: The Dream, or Posthumous Work on Lunar Astronomy, ed. Edward Rosen
(Madison: University of Wisconsin Press, 1967), 149.
109

When in 1627 Guldin finally broached the topic of religion by asking Kepler whether he
would consider conversion to the Catholic Church, Kepler‘s answer was likely not what Guldin
expected. ―My piety toward God must be considered very poor indeed if I began to be a
Catholic only now,‖ Kepler wrote. ―[After all,] I was baptized into the Catholic Church by my
parents immediately when I first crossed the threshold into life…nor did I ever leave the church
from that time, nor did I act otherwise than according to the church‘s particular doctrines….‖ 38
Rather than respond positively or negatively to Guldin‘s question, that is, Kepler insisted that it
was beside the point—why should he convert to Catholicism when he already considered himself
a true and life-long member of the Catholic Church?
Of course, what Kepler had really done was redefine the question, by redefining the
meaning of the ―Catholic Church.‖ Indeed, he proceeded to explain to Guldin exactly what the
concept entailed to him—and what it did not. He wrote,
If you say that the church is a congregation of men beneath one leader, [directed toward]
the propagation of abuses rejected by the followers of the Augsburg Confession and
[toward] the ruling of consciences, then truly you describe a church distinguished by
exactly the thing which I could never accept, if it were characterized by this alone. 39
In other words, Kepler argued that ―the church‖ could not be defined solely in terms of the
official hierarchy of the Catholic Church as it was constituted at the time. Rather, Kepler went
on to clarify—very much in line with the teachings of Luther—that any hierarchy which saw
itself as the promulgator of true doctrine was fundamentally unnecessary. He explained,
38 KGW 18:1072: ―Male vero cum pietate mea in Deum hactenus fuerit actum: si nunc demum
incipere debeam fierj Catholicus qui primo statim in vitae limine a parentibus in Ecclesiam
catholicam illatus, sacro lavacro aspersus, et in eo spiritu adoptionis filiorum Dej donatus sum:
nec ab eo tempore unquam ex Ecclesia exivj, nec aliter nisi in doctrina Ecclesiae propriA
institutus fui: quam Augustanj conventus gloriationem nemo est qui refutaverit unquam.‖
39 Ibid.: ―Si vero tu hoc dicis Ecclesiam, coetum hominum sub uno capite congregatorum ad
propagandos imperandosque conscientijs abusus, ab Augustanis recusatos: nae tu Ecclesiam
mihi a nota talj describis, a qua Ecclesiam ego, si solam eam haberet, nequaquam agnoscerem.‖
110

If the church teaches me something, then I will willingly obey whatever does not
contradict its instruction, which it itself shows me, and I will honor the messenger it
sends. But it is absurd that I should trust the interpretation of its instruction [given] by
the messenger alone…[for] the same spirit that wrote this instruction for him gave it to
me in baptism. 40
The doctrines of the true Church, Kepler believed, were available directly to all individuals
through the grace of the Holy Spirit, conferred via baptism.
Kepler went on to explain that the arrogance and ostentation that characterized most of
the leaders and institutions of the Roman Catholic Church made it clear that they had strayed
from the true teachings of the Holy Spirit. That Spirit also made clear that certain other churchly
practices were in error. Kepler listed variants on the idea of idolatry which he saw in the
Catholic Church of his time: the worship of the image of the crucifix, the worship of saints, and
the worship of Christ in the Eucharist, which Kepler thought characterized the idea of
transubstantiation. He argued that the laity should be allowed to take part in the Mass under both
kinds, the bread and the wine, and that their exclusion from it was a modern invention. ―These
are only a few [of the reasons],‖ he continued, ―which inspire me to hold back from fully
obeying the church of the Western Metropolitan and Patriarchs: which I reject not out of pride,
but because I think that Christ, its head, must be obeyed more.‖ 41
Moreover, Kepler argued that
his firm commitment to the true Catholic Church was so strong, that
on behalf of the refusal of those things which I do not recognize as apostolic, and thus
which are not Catholic, I am prepared not only to abandon the rewards which are now
held out to me, and in which his holy majesty [the emperor] most magnificently and
40 Ibid.: ―Ecclesia si quid mihi praecipit, quod non pugnet cum Instructione sua, quam ipsa
ostentat, obediam illi lubens, honorabo legantem in legato. Absurdum est ut Legato, naevos
suorum manjorum palliantj, soli credam interpretatinem Instructionis suae. Spiritus idem est,
qui et hanc illi conscripsit Instructionem, et jam mihi datus est in Baptismo.‖
41 Ibid.: ―Haec paucula sunt, quae mihi remoram injiciunt, quo minus Ecclesiae nostri
Occidentis Metropolitanae et Patriarchali, plenarie possim obedire; quod recuso non ex
superbia, sed quia Christo ejus Capiti plus obediendum esse censeo.‖
111

liberally shares, but also the Austrian lands, the whole empire, and even something more
serious than all those things, astronomy itself. 42
This was no mere boast—Kepler had already suffered much on behalf of his religious principles,
and his frequent moves made it increasingly difficult for him to devote himself fully to his
astronomical pursuits.
Up to this point, Kepler‘s answer to Guldin was fairly typical of Protestant attempts to
redefine the idea of the church in the wake of the Reformation. From the start of the
Reformation, Reformers had based their movement on the idea that the Roman Catholic Church
was not the ―true‖ church. At some point in the past, they argued, the Catholic Church had
strayed from the truth; rather than creating something new, reformers were simply restoring the
true doctrines and practices of the ancient apostolic church that had been lost over time. Though
Catholics and Protestants alike agreed that some notion of ―the church‖ needed to be continuous
over time—after all, Christ had promised that the Holy Spirit would always be with his
followers—Reformers came to identify the true Church not with the institutions of the official
church hierarchy or even with the succession of individuals who made it up. Rather, they
identified the true church with true doctrine, and the small continuous body of faithful people
who adhered to it while the majority strayed. 43
Kepler‘s answer, at least to this point, adhered fairly closely to this idea. In claiming to
be a Catholic, he essentially redefined ―Catholic Church‖ to mean ―true church,‖ and the ideas
42 Ibid.: ―Itaque hoc de me habeto amicorum optime, me sic manere in Ecclesia Actholica, ut pro
recusatione talium, quae non agnosco pro apostolicis, eoque non pro Catholicis, paratus sim
non tantum praemia, quae mihi nunc ostentantur, et in quibus S. C. M.tas magnificentissime et
liberalissime consensit, sed etiam ditiones Austriacas, totum imperium, et quod omnibus gravius
est, astronomiam ipsam dimittere.‖
43 See Euan Cameron, ―Church Historians‘ Response to Change and Diversity,‖ Interpreting
Christian History: The Challenge of the Churches‘ Past (Oxford: Blackwell, 2005): 103-166.
112

which he associated with it were for the most part Lutheran ones. 44
In beginning to answer
Guldin, Kepler essentially responded by saying ―If by Catholic you mean true believer, than I am
a Catholic,‖ while implying that the Lutheran Church had established itself as the church which
most closely aligned with true belief and practice. Yet in the remainder of his letter, Kepler
departed from the typical Lutheran approach, which both asserted itself as the true church and
also positioned the Catholic Church as not only false with respect to particular practices and
doctrines, but as false through and through. In this view, the Catholic Church was a community
brought to its current state not by weakness or human error, but by the workings of Satan and the
Antichrist. The true church was distinguished both by its own adherence to truth and by its
active resistance and opposition to Rome.
Kepler, by contrast, continued his letter to Guldin by clearly distinguishing between the
doctrines and practices of the Catholic Church with which he disagreed and the larger communal
structures of the church. Though the Catholic Church clearly suffered from problems within, it
was still a community of God, and it ought to be recognized as such even by those who disagreed
with it or identified with one of the other confessions. Still further, he explained that
I remain firmly in the Catholic Church, and I join in the full affection of God and his
community, even when it rages and strikes out, as much as any human who suffers
weakness. And if indeed I am tolerated, with those few reservations, I am prepared in
silence and patience to practice and acquit my art among the common men of the
predominant party, while abstaining from all insults, sneers, improper interpretations,
hyperbolic exaggerations, accusations, and perversions of all those having good sense.
From the sermons I will cull only as much at any time as seems filled with divine grace.
I will avoid processions and similar acts lest I cause anyone offense. 45
44 Of course, as we saw in Chapter 1, his emphasis on personal authority and the absence of
hierarchy was more characteristic of the early days of Lutheranism than of the Lutheranism in
seventeenth-century Würrtemberg.
45 KGW 18:1072.: ―Interim ego Ecclesiam Catholicam teneo firmiter, ejusque communionj pleno
charitatis affectu, etiam cum saevit et ferit, quantum humana patitur infirmitas, consocior: et si
quidem toleror, illa paucula recusans, paratus sum in silentio et patientia artem meam inter
medios factionis praedominantis homines excolere et absolvere, abstinens ab omnibus
113

He argued, in other words, that the doctrinal errors of the Catholic Church would not necessarily
prevent him aligning himself to it and participating in communal activities, with his theological
reservations duly noted. If he did so, he would act respectfully even towards those activities with
which he disagreed, as befitted any member of a religious community.
Thus far, Kepler described a rather passive participation in a Catholic community—he
would remain a silent observer, taking what he could and attempting to cause as little offense as
possible. Kepler continued, however, to argue for a more active religious participation in
Catholic communal activities. As he explained,
In fact still more, there is a condition by which both I can take part in the Mass and join
my prayers to the prayers of the available church (although it errs about the claim that
there is a sacrifice): if it clearly accepts my protestation and that of all of my [family] that
we do not agree to those things which we are persuaded to be in error, but only to the
general and ultimate holy and catholic intention of the mass. 46
If the leaders of his local Catholic community acknowledged his right to believe that the Mass
was merely a visible commemoration of the death and sacrifice of Christ, Kepler argued, then
there was no reason why he could not participate in the Mass in a Catholic Church. His points of
disagreement with Catholic doctrine, in other words, were merely matters of personal
conscience, matters that should not necessarily rule out participation in the Church‘s communal
contumelijs, subsannantionibus, sinistris interpretatinibus, hyperbolicis exaggerationibus,
calumnjijs, depravationibus bonum sensum habentium; ex sacris concionibus tantum quovis
tempore decerpturus quantum affulserit gratiae divinae: processiones vero et similes actus
vitabo ne cui sim scandalo: non quod damnem eos, qui intersunt, sed quia duo cum faciunt idem,
non est idem.‖
46 Ibid.: ―Quin imo, est aliqua conditio, sub qua et interesse Missae et preces meas precibus
Ecclesiae reliquae (licet erranti circa praetensum sacrificium) jungere possum: si nimirum
recipiatur mea meorumque omnium protestatio, quod non consentiamus in id quod errorem esse
persuasi sumus, sed in illud tantum generale et ultimum intentum missae sanctum et catholicum,
offerendi Deo preces nostras et sacrificum laudis et bonorum oeprum in nomine sacrificij illius
unici in ara crucis peractj, illudque verA fide nobis applicandj, et Ecclesiam per actus illos
visibiles instruendj de hac applicatione deque commemoratione Mortis Dominj.‖
114

eligious activities. Kepler argued still further that this was a position with which Guldin ought
to agree, because it was one which was rooted in the Bible itself. ―If you love me, I think that
even you ought to support my candor,‖ he insisted, ―because you know the rule: he who has
doubts is condemned if he eats, because it is not from faith: however, nothing is unclean through
itself, unless there is someone who thinks it unclean.‖ 47
Here, Kepler referred to Paul‘s discussion in Romans 14 about eating meat deemed
―unclean‖ by the laws in Leviticus. Those who are strong in faith, Paul had argued, would
recognize that ―nothing is unclean in itself,‖ and therefore that no food could automatically make
a person impure; those weaker in faith would continue to avoid eating ―unclean‖ meat because
they believed it would affect their own purity. Yet Paul insisted that two things ought to take
precedence for both the weak and the strong in deciding whether or not to eat ―unclean‖ meat—
one‘s personal convictions along with the larger cohesion of the community. If the weak
believed the meat to be unclean, Paul wrote, they should not eat it—they should be ruled by their
own personal faith and conscience. Yet the strong likewise should not distress the weak by
eating unclean meat in their presence, for, as Paul explained, ―the kingdom of God is not a matter
of eating and drinking, but of righteousness, peace and joy in the Holy Spirit.‖
With this discussion, Paul emphasized that even in issues where one approach was
theologically more justified than another, the harmony and peace of the community was more
important than unity in religious practice. This approach was often applied in attempts to resolve
confessional differences in the post-Reformation era, yet it typically centered on adiaphora—
47 Ibid.: ―Equidem decere te puto, siqudem me amas, favere meae ingenuitati, cum scias
regulam. Qui dijudicat, si ederit, condemnatus est, quoniam non ex fide: etiamsi per se nihil sit
commune, nisi ej qui id commune existimat.‖
115

matters not considered essential to faith. 48
Kepler here took the controversial step of applying it
to the central and highly contentious issue of the Mass. Yet rather than argue that the Mass was
not essential to the faith, Kepler argued that the question of faith could be accommodated by a
personal objection—in other words, he claimed that the issue of communal participation should
be considered separately from questions of personal belief. So long as he did not violate his own
beliefs, as Paul had argued with regard to the unclean meat, Kepler insisted that there was no
problem with him, as a Lutheran, participating in the Catholic Mass. To be sure, this emphasis
on personal conscience over doctrinal consensus did not serve him well with his own Lutheran
Church, and Kepler likely did not expect Guldin to take his suggestion seriously. Instead, he
hoped to give Guldin some insight into his own religious sensibilities; Guldin‘s binary
opposition between Catholic and Lutheran was simply not the way Kepler saw the world.
Kepler ended his letter by emphasizing that though he had taken the opportunity to air
some of his innermost thoughts, Guldin need not respond; it would be better, in fact, for them to
return to the less troubling questions of astronomy. Yet Guldin seems to have been caught offstride
by Kepler‘s lengthy and unusual response to his suggestion of conversion. Though he
decided not to respond personally, he felt that some response was warranted, and asked a fellow
Jesuit to respond on his behalf, perhaps hoping that colleague would answer more persuasively,
or that a response from someone without as personal a relationship with Kepler would be more
effective. Guldin then sent this reply on to Kepler. This Jesuit, whose name is never mentioned,
undertook his task with the assumption that Kepler‘s letter showed clear signs that he wavered in
48 See, for example, Bernhard J. Verkamp, ―The Limits upon Adiaphoristic Freedom: Luther and
Melanchthon,‖ Theological Studies 36.1 (1975): 52-76; James L. Jaquette, Discerning what
counts: The Function of the Adiaphora Topos in Paul's Letters (Atlanta: Scholars Press, 1995);
and Claude L. Manschreck, ―The Role of Melanchton in the Adiaphora Controversy,‖ Archive
for Reformation History 48 (1958): 165-87.
116

his Lutheran faith. To refute Kepler‘s arguments would thus be not merely to prove him wrong
on specific points, but to potentially win him fully over to the Catholic side. He began his
response by casting aside as foolish the claim that Kepler had somehow always been connected
to the Catholic Church, ―as if there were a necessary connection between baptism in Christ and
Catholic opinions.‖ 49
Indeed, he continued, if someone were baptized at infancy but seized on to
heretical opinions as he reached the age of maturity, and continued to believe in those errors
throughout his life, that person could hardly be called a true Catholic.
He likewise rejected Kepler‘s claim that the practices of the Catholic Church were
riddled with errors and novelties, and argued that by contrast, the essential elements of the
church had remained constant from its origins until the present day. ―Thus to condemn all these
things,‖ he wrote, ―to reject them as errors and to accuse them of abuses, is not to be filled with
the divine spirit, but with a malignant and poisonous hatred of the church.‖ 50
He emphasized
that Kepler‘s belief that the Holy Spirit alone would allow him to distinguish between truth and
falsehood was belied by the short history of the Protestant Church, a history in which Luther‘s
initial error led to the multiplicity of further errors and sects. He elaborated,
This is what makes the Calvinists Monstrants, Remonstrants, Arminians, and
Gomorists—or rather let me say Gomorreans. This is how the Anabaptists bring forth
thirty kinds of heresies. This is how Lutherans themselves nurture those who are strict,
those who are lenient, Majorists, Melanchtonists, Ubiquitarians, and I don't know how
many dissenting sects. 51
49 KGW 18:1080: ―Quasi uero Catholicae opiniones necessariam habeant connexionem cum
Baptismo Christano.‖
50 Ibid.: ―Haec inquam uniuersa damnare, reijcere, erroris et abusuum accusare, non sunt quae
spiritum diuinum redoleant, sed malignam et pestilentem Cacocleriam.‖
51 Ibid.: ―Haec est quae in Caluinianis genuit Monstrantes et Remonstrantes, Arminianos et
Gomorristas, ne dicam Gomorhaeos. Haec est quae in Anabaptistis 30. genera peperit
haeresiarcharum. Haec eadem quae in Lutherana schola enutrijt Rigidos, Molles, Maioristas,
Melanthonicos, Vbiquitarios et nescio quasnam dissectas sectas.‖
117

He argued that as a reliance on one‘s personal interpretation clearly led the arbitrary
multiplication of beliefs, a reliance on the long history and traditions of the Catholic Church, and
on its leaders throughout the ages, was clearly to be preferred. Finally, he responded to some of
the specifics of Kepler‘s complaints; he argued, for instance, that pointing out the moral failings
of specific Church leaders did not necessarily imply that Church doctrine was in error; after all,
morality and faith were separate issues entirely. He also focused on the small number of
Protestants compared to Catholics, and on the size and power of the Catholic Church, as well as
the might of the Catholic emperor and the Austrian Empire. The successes of the Church proved
that God must approve of it, for he would not have allowed it to thrive for so long had it been in
error.
As Kepler explained in his letter of reply to Guldin, he was much troubled by this letter
of rebuttal, and thought long and hard before deciding how to respond. He had anticipated, he
explained, ―that I had mixed an aggravating business into our pleasant conversations: and
therefore I attested in the end that there was no need for a response to it. As I see, respect for the
[Jesuit] Order, and concern for its reputation triumphed [over this request].‖ 52
Upon receiving
the unknown writer‘s letter, he explained, he had first started to respond point by point, until his
reply had filled five pages. Yet he eventually stopped, and decided not to send these pages. As
he joked,
Starting from two lines of yours I replied with a whole sheet. Your answer took four
sheets; my reply would be ten. Should I demand that you squander so many words with
52 KGW 18:1083: ―Praevideram Ego, importunum a me misceri negocium collationibus
suavisssimis: eoque contestatus sum in fine, non opus esse responso ad illud. 355 Vicit ut video,
Ordinis respectus, et existimationis cura…‖
118

impunity? And should I really have to endure your man fatally wounding me with
another fifty pages? Where would the end of the matter be? 53
But despite his jocular tone, Kepler‘s decision to respond briefly was based, as he made clear, in
part on his displeasure that Guldin had shared what he had viewed as a personal letter between
friends. He was not worried about airing his private thoughts to Guldin, but he did not know
what use would be made of the things he wrote by the Jesuit Order.
More significantly, Kepler was troubled both by the tone of the letter he had received and
by the way it appeared to misunderstand his central claims. The writer had done as many ―clever
men of our time‖ 54 tended to do, wrote Kepler; in order to defend himself, he had attacked the
words of another and taken them completely out of context. This was true on a general level
throughout the letter, according to Kepler, for ―while I said what I did for the sake of explaining
my innermost spirit, it was attacked as if it were intended as a public offense against the Roman
religion.‖ 55
This kind of debate was no true conversation, Kepler argued, for if he chose to
respond still further, at each step along the way his words would be twisted far beyond their
original intent. As an example, Kepler offered the following: Guldin‘s colleague had argued
that the Church‘s and emperor‘s successes proved that they were correct in their faith, for
otherwise God would not have permitted them to succeed. Kepler argued,
If I were to insist that the first emperors were clearly infidels and yet they seized the rule
of all the lands, the enraged and hostile debater would then interject: so you compare the
53 Ibid.: ―Duabus a lineis tuis initio facto, reposuj ego plenum folium; duplica tua quatuor dedit,
quadruplica mea jam daret decem. Egone hoc abs te petam, ut tot verba impune profuderim?
neque patiar, ut tuus ille quinquaginta alijs me confodiat? Et quis tandem finis erit?‖
54 Ibid.: ―Est aliqua, faeor, instantior causa, mos ingeniosorum hujus temporis pessimus, dicta
juris sui tuendi causa, rapere in crimen laesj juris alienj.‖
55 Ibid.: ―…dum quae ego dixi explicandi causa mej animj penetralia, arripiuntur quasi crimen
intentatum publice Religionj Romanae.‖
119

emperor to an infidel? I would have been ready to reply, but it does not follow: but
hatred departs from closed up ears…. 56
Accordingly, Kepler argued that he could respond to the entirety of the letter by Guldin‘s
colleague simply by asserting that ―my refuter has deviated from my viewpoint.‖ 57
Rather than simply end here, however, Kepler proceeded to enumerate very briefly some
of the specifics where his refuter had misunderstood him. More broadly, he emphasized that he
had not intended to attack the beliefs of his friend, for he conceived of the church in terms that
transcended both the time-bound Catholic and Lutheran perspectives. ―I acknowledge that the
church is one and the same at all times,‖ he wrote, ―but its members are mortal. The church was
[around] before Rome, still more before Wittenberg. Just as quarrels appear among the citizens
or factions of a Republic, so also among members of the church, separated by time and place,
errors appear out of human weakness.‖ 58
He insisted that Guldin and his fellow Jesuits need not
argue with him—rather, he wrote, ―dispute with someone who plainly cuts Rome from the
church, and who does not know how to distinguish between the temple of God and the one
sitting in it, and thus concludes that the whole church is the Lutheran Church.‖ 59
Kepler here clearly distinguished his own views about the definition of the ―church‖ from
those of many of his fellow Lutherans. While central to the Protestant understanding of the
church was the idea that the church had turned down the wrong path at some point in the past,
56 Ibid.: ―Si ego instem (etsi aliter in scripto) primos Imperatores fuisse plane infideles et
possedisse omnia regna terrarum. Ergo inferet disputator infensus et infestus, Caesarem tu cum
infidelibus cmoparas? Promptum mihi esset respondere, non sequi: at invidia obturatis auribus
abit…‖
57 Ibid.: ―Est igitur haec summa Responsionis meae: Confutatorem aberrasse a scopo meo.‖
58 Ibid.: ―Ego Ecclesiam unam et eandem omnibus temporibus anosco, ejus membra mortalia.
Erat Ecclesia cum Roma ejus pars non esset, nedum Witeberga. Quomodo inter ejusdem Reip:
cives vel factiones, existunt lites, sic inter ejusdem Ecclesiae membra, locis vel temporibus
differentia, existunt ex humana infirmitate errores.‖
59 Ibid.: ―Disputate cum illo, qui Romam plane rescindit ab Ecclesia, qui nescit distinguere inter
templum dej et sedentem in illo, qui Ecclesiam omnem Augustam concludit.‖
120

this was directed very pointedly at Catholics and Catholic history. The idea that the church was
subject to error and decay was true, many Protestants argued, not for ―our‖ church but for ―their‖
church, the Catholic Church—―their‖ ancestors had erred, not ―ours.‖ Moreover, error was
typically attributed not to human weakness or error, but rather to the work of the Antichrist—to
evil within the part of the church that had gone wrong. Kepler, by contrast, argued that the
church, like any human institution, was fallible on all fronts, and in all its variants. Just as in a
political community, Kepler argued that in a religious community the passage of time necessarily
led to the accumulation of mistakes and wrong turns, ones to which Protestants were as
susceptible as Catholics. Indeed, as we saw earlier, Kepler found fault with many of the
Lutheran theologians of his day, and emphasized the humanity of even those theologians, like
Hafenreffer, who he greatly admired. And though he continued to self-identify as a Lutheran, he
defined the ―true‖ church not as the Lutheran Church, inscribed backwards in time, but rather as
something that transcended the particularities of confession. The true church existed before
Rome, as it did before Wittenberg; it was not bounded by the beliefs and structures of the
Lutheran Church, nor did it exclude the Roman Catholic Church, though it did not correspond
exactly to it either.
As a result, Kepler argued that it was necessary ―to distinguish between the temple of
God and the one sitting in it‖—between the broader idea of religious community and the
particular leaders or doctrines that happened to hold sway in any given time or place. Much as in
his earlier discussion with Herwart, Kepler emphasized that while particular confessional
communities were limited, God‘s community included all of Christendom, Catholics and
Protestants alike. And he implied that as no one religious community could have a monopoly on
the truth, confessional disputes and partisan exclusivity were typically only destructive forces.
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Where no one principle could be agreed upon by all the confessions, personal conscience ought
to decide the particularities of faith, while the general outlines could be shared by those who
might continue to differ on the particulars. Religious community more generally, Kepler
insisted, ought to be characterized by harmony and freedom rather than unanimity of practice
and belief.
Kepler‘s position, though certainly unorthodox in its specifics, likely derived in part from
the religious and political environment of the Holy Roman Empire at the time. The idea of
freedom of conscience was not itself unusual; in the face of papal pressure against Luther and his
followers, Luther himself had argued for freedom of conscience and against the idea that any
kind of outward force might direct personal faith. Alongside this, with the spread of
Lutheranism throughout the Empire, jurists began to develop guidelines in order to deal with the
problem of two different religious confessions living side by side under the same rule, sometimes
even in a single city. These jurists—and the Lutheran minority, in particular—argued for the
importance of freedom of conscience and the need to allow someone from one confession to
practice according to his own beliefs while living within the jurisdiction of another confession.
The religious compromises thereby created were seen as a way to protect religious practices and
beliefs from encroachment by the civil authorities, and as a necessary and practical adjustment to
the confessional situation in the Empire. 60
While Kepler‘s answer to Guldin may have been influenced by his immersion in these
kinds of Imperial confessional debates, it differed from them in a key respect. By and large,
none of the arguments for freedom of conscience presented by either Lutheran or Catholics in the
Empire were based on the belief that individuals ought to be free to decide on their own religious
60 See Robert Von Friedeburg, ―The Juridification of Natural Law: Christoph Besold‘s Claim for
a Natural Right to Believe What One Wants,‖ The Historical Journal 53 (2010): 1-19.
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eliefs and practices, or that confessional diversity was the optimal state of affairs. Rather, each
confession was trying to protect itself as it deemed necessary given the current political and
religious configuration of the Empire—all the while hoping for the eventual reunification of the
Empire under the one true confession, whichever one it might be. And while those who made
this argument—Catholic and Lutheran alike—emphasized that civil authorities could not dictate
religious belief, they still, by and large, adhered to the belief that the clergy could and should
dictate that belief for all the laity who identified as members of the confession. Kepler‘s claims
that personal conscience was always to be preferred over simple adherence to authority and that
no one confession held the monopoly on truth were relatively unique, even in the climate of the
Empire. 61
Kepler‘s position here—his willingness to align himself with the Catholic Church and its
religious practices—is also noteworthy when compared to his own approach in two other
instances. One is his earlier approach to the Catholic Church, as articulated in a letter Kepler
wrote to Johannes Pistorius, Father Confessor and advisor to Rudolf at Prague. Pistorius had
been raised as a Lutheran, and had studied theology, law, and medicine at the universities of
Marburg and Wittenberg, eventually earning the degree of Doctor of Medicine. Dissatisfied with
Lutheranism, he later converted to Calvinism, and eventually to Catholicism, in which he studied
for the priesthood and rose through the ranks to become Imperial confessor. Kepler and Pistorius
generally respected each other‘s learning; as Imperial mathematician, Kepler was asked to report
his findings to Pistorius periodically, and the two carried on a lively and wide-ranging
61 Von Friedeburg, supra, considers Christoph Besold (1577-1638) as one of the first to argue for
personal conscience not merely as a practical compromise but as an ideal, and even a natural
right. Besold and Kepler were friends and correspondents, and their outlooks on confession were
in many ways quite similar—though unlike Kepler, Besold ultimately did convert to
Catholicism.
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conversation during their years together in Prague. In 1610, two years after Pistorius‘s death,
Kepler referred back to those conversations, hailing Pistorius as ―that master of all sciences.‖ 62
Yet in 1607, Kepler had harsher words for his colleague. Pistorius, suffering from serious
illness, had written to Kepler that he was certain the end was near. He added that this knowledge
did not trouble him, for he rejoiced in the possibility of going to heaven and leaving behind the
―inanities‖ of the world.
In response, Kepler expressed his strong sympathies for Pistorius, and noted that though
the thought of Pistorius‘s death filled him with sadness, he was ―comforted by your upright
courage and your unwavering desire for the eternal life of which your letter bears witness.‖ 63
But he also took the opportunity—and in particular, Pistorius‘s use of the word ―inanities‖—to
reflect on what he considered to be one of the primary causes of the world‘s inanities—the
practices of the Catholic Church with which Pistorius affiliated. He wrote,
Of the inanities of the world…I think a great part stems from the fiery zeal of the
factions, who believe that they have a special right to blessedness, decide that the only
gates to heaven are at Rome, and [are filled] with complete contempt for those who
embraced their liberty…. 64
Kepler added that when Pistorius made his way to heaven, ―you will bear me witness, on that
great day, that I never had any personal hatred against the Pope, bishops, and the priests, but only
zeal for God.‖ 65
That zeal had forced him to recognize that the Roman Catholic Church had
62 Kepler‘s Conversation with Galileo‘s Sidereal Messenger, ed. Edward Rosen (New York:
Johnson Reprint Corp., 1965), 21.
63 KGW 15:431: ―…tamen me consolatur erectus ille Mag: T: animus, et imperturbatum illud
immortalitatis desiderium, quo de in literis testaris.‖
64 Ibid.: ―…inanitatum hujus mundi (quarum ego magnam partem esse puto, studium partium
fervidum, privilegia beatitudinis somniantium, Romae coeli portas unicas statuentium, indeque
natum in Reges indirectos Regum, merum obsequium, merum contemptum eorum, qui libertatem
amplexi sunt…‖
65 Ibid.: ―…mihique in illo magno die, ad Tribunal Christi comparentj testis eris, me nullo
privato odio in Pontificem, Episcopos, Sacerdotes, sed mero zelo Dej…‖
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completely skewed the teachings of the apostles, leading to ―a Roman monarchy or church
tyranny.‖ 66
In this face of this tyranny, Kepler insisted that he remained
in that freedom in which I was born with God's approval, and which insists that I not
voluntarily bend myself to the Roman yoke of those who not only force Christians into
following indifferent ceremonies [i.e. adiaphora] (similar to those from which Paul
explained that the Galatians were free) but who also interpret the words and commands of
Christ and the apostles in a most dangerous way, and claim the right of interpretation
only for themselves, and [thus] put human understanding in chains, so that one cannot
judge otherwise but the interpretation here. 67
Kepler claimed that ―if one admits to this strict interpretation, then in the end the Antichrist will
lack nothing…in order to erect his empire in the church and overthrow the dominion of Christ.‖ 68
This letter is nearly always cited by historians who have considered Kepler‘s approach to
the Catholic Church. Some have viewed it as paradigmatic; for this reason, Burke-Gaffney labels
Kepler generally as ―anti-Catholic‖ and notes that his ―anti-Catholic views were exposed plain
and unvarnished‖ in his letter to Pistorius. 69
Others have simply found the letter puzzling.
Caspar writes that ―Kepler, otherwise so peace-loving in religious matters,‖ in his letter to
Pistorius leveled ―such a sharp attack on the Catholic Church, as scarcely seems possible from
him and of a kind which he makes nowhere else.‖ 70
Caspar speculates that ―memories of
specific earlier conflicts‖ played a part in the harshness of Kepler‘s response—perhaps his
66 Ibid.: ―…quae proclivitate summa mediocrium ingeniorum in Romanam illam Monarchiam vel
Tyrannidem Ecclesiasticam trahuntur.‖
67 Ibid.: ―…his inquam de causis in illa libertate stetisse, in qua Dei permissu natus sum, neque
jugo Romano mancipari ultro voluisse, eorum qui non tantum ceremonijs indifferentibus, quae
persimiles sunt illis a quibus D. Paulus Galatas asserit, Christianos onerant, sed etiam verba et
mandata Christi et Apostolorum periculosissime interpretantur, 490 jus hoc interpretandj suum
unice facientes, sensusque humanos, quibuscum Deus per suos ministros agere solitus est,
simpliciter captivantes, ut aliter ij judicare non possint, quam interpretamenta verbis alicubj e
diametro esse contraria.‖
68 Ibid.: ―Quo interpretandj stricto jure concesso, nihil porro defuerit, ne ipsissimo quidem
Antichristo (quem in templo Dei et ipsum sedere dicit scriptura) quo regnum suum in Ecclesia
stabiliat, Christi evertat.‖
69 Burke Gaffney, Kepler and the Jesuits, 38.
70 Max Caspar, Kepler, Trans. and Ed. C. Doris Hellman (New York: Dover, 1993), 163.
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expulsion from Graz. He also emphasizes that the harsh attitude in Kepler‘s letter to Pistorius
was likely tempered over time by Kepler‘s experiences with the Lutheran Church, experiences
which made him realize, over time, ―the Württemberg consistory was more popish than the Pope,
and did not possess that tolerance with which Kepler was treated by the Catholics in Prague and
also later in the Hapsburg lands.‖ 71
It is certainly true that Kepler‘s approach in the letter to Guldin was motivated in part by
the personal circumstances in which he found himself in 1628. When Kepler replied to Guldin,
it had already been nine years since he had received the final word about his excommunication
from the Lutheran consistory in Stuttgart. Adrift, no longer fully part of any religious
community, and his faith in the principles of his own Church shaken, Kepler was highly
motivated to find a way to participate in religious communal life in any way he could, while still
preserving his own particular religious beliefs. His views on the Catholic Church thus likely did
become somewhat milder over time, as his personal motivation for tolerance increased.
Yet I think it is a mistake to view the letter to Pistorius as indicative of his larger attitude
to the Catholic Church in 1607. Instead, the letter to Guldin, personal motivation
notwithstanding, should be taken as more paradigmatic of Kepler‘s attitude throughout his life.
After all, his letter to Herwart also written in 1607 evidenced a very broad conception of
religious community, one which included Catholics and took seriously their theological
perspectives. To be sure, twenty years separated the letters to Herwart and to Guldin, and in the
former Kepler‘s openness to the Catholic faith was largely theoretical; he did not evidence a
willingness to personally align himself with a Catholic community, but rather a belief that God
included all confessions in his larger communal embrace. As Kepler was forced from his own
71 Ibid.164.
126

Lutheran community, his openness to Catholicism moved from the realm of the theoretical to the
realm of the personal and practical. Yet throughout that time span, he sustained friendly
conversations with Catholics other than Herwart, and with Jesuits other than Guldin, some of
which also openly touched on questions of religion. Likewise, on issues of mathematics or
natural philosophy he never aligned himself only with the Protestant position—he supported
Jesuits on chronological issues throughout his career, even when the opposing position was held
by a prominent Protestant like Scaliger.
Hence instead of arguing for the letter to Pistorius as representative of an earlier, ―anti-
Catholic‖ Kepler, and the letter to Guldin as representative of a later, more tolerant Kepler, I
believe the letter to Pistorius should be viewed as a very specific letter directed toward a very
specific person in very specific circumstances. Pistorius was, after all, a master polemicist, and
his polemical writings were notably strident and abrasive. His famous Anatomia Lutheri, for
instance, was a personal attack on the reformer, which argued that Luther was filled with the
seven evil spirits and was an abomination. Moreover, Kepler knew well that Pistorius had
moved through the different confessions, and that he had argued strongly, at different times of
his life, for all of them. Kepler clearly respected Pistorius, yet he debated with him as someone
who knew the details of Lutheranism intimately, and had chosen not only to convert to
Catholicism but to become one of its most prominent and belligerent spokesmen. It is likely that
their conversations on topics of religion, despite their friendly personal relationship, were always
somewhat aggressive; indeed, Kepler ended his letter to Pistorius by adding that ―I hope you
receive these thoughts from my writing as you customarily do when we speak and debate about
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the same subject.‖ 72
For his part, Pistorius responded dismissively in his next letter with only
one sentence devoted to religion: ―I wish you would avoid theology; clearly you understand
nothing about it.‖ 73 The tenor of their debates, in other words, likely lent itself to the tone of
Kepler‘s letter because of who Pistorius was, not because of who Kepler was.
Kepler‘s position vis-à-vis religious conflict and religious truth, as articulated in his letter
to Guldin, is also noteworthy in the ways that it differed from his own position with regards to
another realm—that of cosmological conflict, and cosmological truth. In his letter to Guldin,
Kepler maintained that religious conflict need not always be settled in favor of one specific
position—he held that a variety of approaches could flourish side by side in the larger religious
community. Yet when it came to cosmological conflict—specifically, the conflict between the
Ptolemaic universe and the Copernican—Kepler insisted, in the face of strong opposition from
most of the astronomers of the time, that only the Copernican approach represented the truth.
Indeed, he insisted that the astronomical counterpart to his religious irenicism—the idea that the
Ptolemaic and Copernican theories were equally valid tools for considerations of planetary
positions and motions—was unsatisfactory. Astronomical theories ought to represent the
physical truth of the universe, Kepler argued, and there was only one such truth—
Copernicanism. 74
He devoted much of his life‘s work to proving the truth and superiority of
Copernicanism, and converting as many as possible to his way of thinking. Why was Kepler so
insistent on the establishment of an astronomical community that adopted one astronomical
72 KGW 15:431: ―Spero, haec ita excipies a scribente, utj solitus es excipere loquentem et
disputantem de eadem materia.‖
73 KGW 15:433: ―Theologiam uellem missam faceres: cuius certe nihil intelligis.‖
74 On Kepler‘s astronomical realism, see Nicholas Jardine, The Birth of History and Philosophy
of Science: Kepler‘s A Defence of Tycho against Ursus, with Essays on Its Provenance and
Significance (Cambridge: Cambridge University Press, 1984), and Nicholas Jardine, ―The
Forging of Modern Realism: Clavius and Kepler against the Sceptics,‖ Studies in History and
Philosophy of Science 10 (1979): 141–173.
128

world-view, yet so willing to embrace a religious community characterized by multiple
theological perspectives and practices?
One answer to this question comes through in both Kepler‘s arguments for the religious
role of his astronomical work, as articulated both in Chapter 1 and in his discussion with Herwart
at the start of this chapter. Kepler believed that certain kinds of mathematical and cosmological
claims could be demonstrated a priori, via reason alone, in ways that were certain and could
brook no dissent. In such instances, Kepler felt comfortable emphasizing the certain truth of a
particular cosmological theory, like Copernicanism. He even felt that such certainty justified
taking a clear position on particular religious doctrines like the Eucharist, when such a position
was the inevitable result of his cosmological claims. When it came to astrology, by contrast,
Kepler steered clear of similar proclamations of certainty, and consequently did not make any
religious truth-claims that hinged on astrological arguments. By extension, it seems that Kepler
believed more broadly that while mathematics and cosmology were realms where certainty (and
hence unanimity) were theoretically possible, theology was a realm where certainty could only
be achieved on specific individual questions, but not on a larger communal basis. And even
when it came to those specific questions like the Eucharist, as we saw in Chapter 1, Kepler came
increasingly to believe that the theologians around him were unable to take his lessons of
certainty to heart.
This conclusion was one Kepler drew both from his own investigations and experiences
and from the very different consequences apparent from the history of astronomy and the history
of the Church. As Nicholas Jardine has noted, one of the supports for the astronomical
skepticism common to the sixteenth and seventeenth centuries was historical—men like Ursus,
for instance, argued that the abundance and absurdity of competing past astronomical hypotheses
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proved that astronomers were unlikely to ever arrive at one true hypothesis. 75
Kepler, by
contrast, relied on the history of astronomy to argue exactly the opposite. Most famously in his
Apologia for Tycho against Ursus, Kepler recounted a history of astronomy which proved that
though there were still unanswered questions in the field, many of the old astronomical questions
were now settled beyond any doubt. He argued that clear astronomical progress had been
achieved over time, via improved theories, improved technical procedures, and improved
instruments. And he used this history of progress as the basis for his realist approach to
astronomy—his belief that astronomy could and would discern the truth of the cosmos. Though
astronomy was beset by conflict, in other words, and though it was a human and fallible
enterprise, Kepler argued that the clear history of astronomical progress over time indicated that
the discipline moved slowly toward a true and complete picture of the world. 76
The history of the Church, by contrast, revealed something else entirely. As confessional
disputes grew only more violent and entrenched, history itself became a weapon in the
confessional battle, with historical arguments used on all sides to show that one confession or the
other had unique access to the truth. Yet even as confessional propagandists used church history
to further their own orthodox dogmas, by projecting their own views back onto their vision of the
original, apostolic church, that same history, when viewed in its totality, made it increasingly
difficult to argue for the possibility of a world united by one religious truth. Doctrinal
disagreements between the three main confessions, as Schmidt-Biggemann has argued, resulted
over time in the ―paralysis of theology‘s claim to truth… The polemical debate which dragged
on for generations […] discredited not only the respective opponents but also the entire area of
75 See Jardine, Birth of History and Philosophy of Science, Chapter 6: ―Against the sceptics,‖
211-224.
76 See Ibid., Chapter 8, ―Historiography and validation,‖ 258-286.
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confessional theology.‖ 77
As Kepler saw it, the history of the Church revealed it to be not a
timeless and unchanging institution, but rather a human one, susceptible to error and decline. He
sympathized with its travails, he wrote, ―as much as any human who suffers weakness‖; he
likened confessional disputes to ―quarrels [that] appear among the citizens or factions of a
Republic,‖ and linked both to the ―errors [that] appear out of human weakness‖ over the passage
of time. And unlike in the case of astronomy, he was highly skeptical that those errors could
ever be universally resolved in favor of one agreed upon religious truth. Thus in arguing for
churchly unity, Kepler emphasized peace and harmony rather than complete agreement, and
outlined ways in which disagreements could be accommodated in a united religious community.
Kepler did not privilege cosmological truth over religious truth; rather, he saw the former as
universally attainable on a communal level, and believed that the latter was in many cases
attainable only at the level of the individual. In portraying himself as an astronomer-priest—a
priest of God with respect to the book of Nature—he aligned himself with a theology
independent of the confessions, a way to reveal God‘s hand in the world that had some hope of
offering universal truth claims to which anyone could assent. 78
Kepler, the Jesuits, and Jesuit Science
Protestant attitudes toward Catholics in the late sixteenth and early seventeenth centuries,
harsh as they typically were, paled in comparison to the vitriol leveled at the Jesuit Order in
77 See Wilhelm Schmidt-Biggemann, ―New Structures of Knowledge,‖in A History of the
University in Europe, Vol. II: Universities in Early Modern Europe. Ed. Hilde De Ridder-
Symoens (Cambridge: Cambridge University Press, 1996): 489-530, at 507.
78 See also Charlotte Methuen, Science and Theology in the Reformation: Studies in
Interpretation of Astronomical Observation in Sixteenth Century Germany (London and New
York: T&T Clark International, 2008), especially Chapter 6: ―From sola scriptura to astronomia
nova: novelty, authority, and the reform of astronomy in the work of Johannes Kepler.‖
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particular. Martin Chemnitz, the famed Lutheran theologian and follower of Melanchthon, was
not more strident than many of his fellow Lutherans when he wrote in his 1572 pamphlet
―Concerning the New Order of the Jesuits‖ that the Jesuits were ―no other than perjured,
treacherous, oath-breaking, dishonorable, desperate villains, against whom the German land
ought to be well on its guard.‖ 79
The widespread consensus among Protestants was that the
Jesuits were by nature deceitful and hypocritical; according to one common refrain, they were
wolves dressed in sheep‘s clothing. 80
In this view, their missionary work and their focus on
education were merely ways for them to insinuate themselves in the minds and hearts of unwary
Protestants and lure them toward the Antichrist in Rome, or toward whichever Catholic ruler
they decided to support; as everything they did was guided by this motivation, their public words
and image could never be trusted. As Antoine Arnauld, lawyer and councilor to Henry IV,
wrote of the Jesuits in 1594, ―all their thoughts, all their designs, all their actions, all their
sermons, all their confessions have no other aim than to subjugate the whole of Europe to the
domination of Spain.‖ 81
This kind of invective was by and large an extension of the general confessional dispute
between Catholics and Protestants—Jesuits were, after all, among the most visible and successful
arms of the Catholic Church, and hence an easy target for Protestant attacks. Yet it quickly
spilled over from the realms of theology and politics to the realm of scholarship. If the Jesuits
simply could not be trusted, many believed, their scholarship too must be suspect. Joseph Justus
Scaliger and Isaac Casaubon generously shared their scholarly vituperation with many, to be
79 Quoted in Johannes Janssen, History of the German People at the close of the Middle Ages
(London: K. Paul, Trench, Trübner & Co., 1905), 238-9.
80 See Eric Nelson, ―The Jesuit Legend: superstition and myth-making,‖ in Religion and
Superstition in Reformation Europe, Eds. Helen L. Parish and William G. Naphy (Manchester:
Manchester University Press, 2002), 97.
81 Quoted in ibid. 100.
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sure, but they leveled their highest scorn at Jesuit scholars, in particular. The Jesuit
mathematician Cristoph Clavius was ―smug and shameless,‖ and even ―rustic and illiterate,‖
wrote Scaliger; his books were ―foul and pedantic,‖ or ―mangy and feverish.‖ 82
Jesuit Martin
Del Rio was the ―stercus diaboli,‖ the filth of the Devil. 83
Casaubon wrote that Cardinal
Bellarmine and his Jesuit colleagues were ―ignorant...untrained and laughable‖ 84 and that Jesuit
Andreas Eudaemon Johannes was one of ―my enemies, wretched heretics, teachings of
assassination, Cretan Greeklings, and fuzzy thinkers...most assuredly a servant of Satan.‖ 85
Most Protestant members of the Republic of Letters never descended to this level of
vituperation. The Republic of Letters was, after all, a community in which religious beliefs were
supposed to be sidelined in favor of the interests of scholarship, and where religious affiliation
was supposedly irrelevant. 86
Yet despite this supposed religious neutrality of the Republic, most
Protestant scholars in the late sixteenth and seventeenth centuries continued to view the scientific
activities of the Jesuit Order with suspicion, and even disdain. This was due in part to the
perceived backwardness of certain aspects of the Jesuit approach—their commitment to
Aristotelian natural philosophy, and their condemnation of Copernican theory and subsequent
treatment of Galileo. Yet it stemmed even more from the belief that Jesuit science was itself
polluted by its linkages to the religious goals of the Order. While affirming their own ability to
separate their religious and scholarly interests, many Protestants thus insisted that the Jesuits
were uninterested in, and indeed incapable of, a similar separation; they were filled, writes Ann
82 Quoted in Thomas Conley, ―Vituperation in Early Seventeenth Century Historical Studies,‖
Rhetorica: A Journal of the History of Rhetoric 22.2 (2004):169-182, at 171-172.
83 See Mordechai Feingold, ―Jesuits: Savants,‖ in Jesuit Science and the Republic of Letters, ed.
Mordechai Feingold (MIT Press, 2003), 17.
84 Conley, ―Vituperation,‖ 172.
85 Conley, ―Vituperation,‖ 173.
86 See Ann Goldgar, Impolite Learning: Conduct and Community in the Republic of Letters,
1680-1750 (Yale University Press, 1995).
133

Goldgar, with ―the prejudice…that the Jesuits were unwilling to abandon their own
prejudices.‖ 87
Jean Cornand de la Crose merely summed up a belief that had been popular for
many years when he wrote, in 1691, that ―the Character of a Jesuit...doth not well agree with that
of a sincere Writer.‖ 88
Samuel Hartlib likewise noted in his 1648 Ephemerides that ―Kircherus, Scheinerus, etc.
apply Mathematics to experiments and Mechanicks etc. They are right Ieusuits to make a great
blaze of all things etc so as to attract more admirers and contributors to their Order.‖ 89
He
emphasized that the Jesuits had no interest in pursuing mathematics or experimental science for
their own sake; rather, they did so only in order to lure people into their religious snares.
Thomas Sprat in 1667 further argued that ―it is likely that [the Jesuits] have cherish'd some
experiments, not out of zeal to the continuance of such studies, but that the Protestants might not
carry away all the glory, and thence withal get new strength to oppose them.‖ 90
The perceived
theological motivation behind the Jesuit pursuit of science—and of scholarship more generally—
indicated to men like Sprat that the results of Jesuit scholarship and science were not to be
trusted. John Beale emphasized this in a letter to Henry Oldenburg, where he noted that the
Jesuits ―are to be suspected in point of candor and severe truth.‖ 91
Oldenburg agreed, adding that
though the global Jesuit network made the Jesuits seemingly ideal candidates for scientific
correspondence and specimen collection, their reports could not be trusted, ―considering the
87 Ibid. 197.
88 Ibid.
89 See Michael John Gorman, ―From ‗The Eyes of All‘ to ‗Usefull Quarries in philosophy and
good literature‘: Consuming Jesuit Science, 1600-1665,‖ in The Jesuits: Cultures, Sciences, and
the Arts, 1540-1773, Vol. 1, Ed. John. W. O‘Malley et al. (Toronto: University of Toronto Press,
1999), 174.
90 See Martha Baldwin, ―Pious Ambition: Natural Philosophy and the Jesuit Quest for the
Patronage of Printed Books in the Seventeenth Century,‖ in Feingold, Jesuit Science, 304.
91 See Mordechai Feingold, ―Jesuits: Savants,‖ in Feingold, Jesuit Science, 3.
134

principal end of such men‘s voyages, which is, to propagate their faith, and to greaten and enrich
themselves by their craft.‖ 92
The new forms of scientific association that arose over the course of the seventeenth
century—and the stated purposes of those associations—accentuated this suspicion of the close
linkages between Jesuit scientific and religious pursuits. Like the supposedly nonsectarian
Republic of Letters before them, many of the new academies and societies of the seventeenth
century were established in order to deliberately segregate the realm of natural philosophy from
the realms of politics and religion—and least in theory. These spaces would provide, it was
hoped, an impartial, apolitical forum where religious disputes could be sidelined and in which
―reasonable men from a wide range of ideological positions…could collaborate in gathering
information which they hoped that all would be able to accept as undeniably true.‖ 93
Rhetoric
and reality often parted ways, of course, and much like the Republic of Letters, the academies
and societies of the seventeenth century were never truly free of political or religious overtones.
Still further, this same disjunction between official rhetoric and reality characterized the Jesuit
pursuit of science as well. Though Ignatius of Loyola had maintained that the official aim of all
the activities of his Order was ―to aid our fellowmen to the knowledge and love of God and to
the salvation of their souls,‖ 94 many Jesuits were drawn to the Order specifically because it
allowed them to pursue their own natural philosophical and mathematical interests, without
thought to any religious applications of such pursuits. Moreover, Mordechai Feingold has
emphasized in his study of Jesuit science that ―while scholarship often served partisan goals in
92 Baldwin, in Feingold, Jesuit Science, 320.
93 Michael Hunter, Establishing the New Science: The Experience of the Early Royal Society
(Woodbridge: Boydell Press, 1995), 10.
94 See Ignatius of Loyola, ―Constitutions of the Society of Jesus,‖ Chapter 12 in Ignatius of
Loyola: The Spiritual Exercises and Selected Works, ed. George E. Ganss (New York: Paulist
Press, 1991), 297.
135

the charged religious atmosphere of the early modern period, Jesuit scientific practitioners as a
group seem to have resisted the temptation to yoke science to other ends as well as did
practitioners of any other religious denomination.‖ 95
In practice, that is, the members
seventeenth-century scientific academies and societies were often as likely to invoke political or
religious concerns as the Jesuits were to avoid them. Yet the official positions of these different
groups highlight why many members of both the Republic of Letters and the new scientific
societies, so invested in the formal separation of scholarship from partisan interests, would view
the Jesuit linkage of science and religion with suspicion and concern.
Given the common Protestant perspective on Jesuit science, Kepler‘s own views make
him something of an outlier. As noted earlier, he had some close relationships with his Jesuit
correspondents, whose scientific prowess he clearly respected. This, of course, was also true of
other members of the Republic of Letters; despite the institutional constraints faced by Jesuits
and the reservations of many Protestants about Jesuit ―prejudices,‖ many Jesuits both desired and
attained respected places in that community of scholars. Yet in addition to his personal
relationships with specific Jesuits, Kepler differed from many of his fellow Protestants in his
vocal opposition to all those who spoke dismissively of Jesuit science, and who rejected any
particular scientific endeavor simply because it originated with the Jesuits. He supported the
chronological work of some of his Jesuit correspondents against the work of Scaliger, a fellow
Protestant, and bemoaned the fact that both sides—and he excoriated the Protestants, in
particular—allowed their religious affiliation to color their evaluation of each other‘s work.
―Everyone is preoccupied with prejudices and hatred,‖ he wrote. ―If a Jesuit writes, it is
95 Feingold, Jesuit Science, 2.
136

considered as though not written by those among whom [Scaliger] reigns.‖ 96
When Thomas
Lydiat scornfully attacked Kepler‘s chronology as ―that of the Jesuits,‖ Kepler criticized the
basis of Lydiat‘s attack. ―Judging by the way Jesuits are treated in England,‖ he wrote, ―it must
be a great crime to hold Jesuit doctrine; but if Lydiat has no more serious charge against the
Jesuits than that they approve the Keplerian chronology, by that very charge the conduct of his
country stands condemned.‖ 97
Why was Kepler so open willing to openly and favorably consider the work of the
Jesuits, at times even supporting them against his fellow Protestants? The answer relates in part
to Kepler‘s irenical stance more generally—his refusal to limit the larger community of
Christians to merely one confession, and his lifelong pursuit of churchly unity and harmony. Yet
in this case, I believe that something still more underpinned Kepler‘s attitude. Kepler‘s fellow
Protestants were troubled not merely by the religious beliefs and goals of the Jesuits, but more
broadly by the close alliance between their scientific and religious pursuits. Though surely
influenced by religious agendas of their own, many Protestant natural philosophers of the early
modern period increasingly tended to argue that natural philosophy or experimental science
ought to occupy a realm separate from all partisan interests—and here they included both politics
and confessional theology. This was in marked contrast to the explicit structuring of knowledge
96 KGW 15:398: ―Omnia parejudicijs, omnia odijs praeoccupata vides. Si Jesuita scribat: apud
illos penes quos regnat, pro non scripto habetur.‖
97 Cited in Burke-Gaffney, Kepler and the Jesuits, 38; see KGW 15:398: ―Lidiati Angli libellum
de Annorum formis inter primos emi…Itaque in tanta praesertim Astronomiae ignorantia, tanta
praeterea trabis magnitudine in oculo proprio jure modestiam hominis desidero in eruenda
festuca ex oculo Scaligeri. Quicunque hanc provinciam, iis conditionibus, quas dixi, suscipit.‖
Lydiat was chronologer and cosmographer to Henry, Prince of Wales, a close friend and
colleague of James Ussher, and eventual rector at Alkerton. Though he opposed the Jesuit
chronologers, he was also a strong opponent of Scaliger‘s work. Scaliger referred to him as ―the
greatest monster that ever England produced‖ and ―the veryest fool in the whole world.‖ See
Peter Sherlock, ―Lydiat, Thomas (1572-1646)‖ in Oxford Dictionary of National Biography
(Oxford: Oxford University Press, 2004).
137

in the medieval university, in which natural philosophy, along with the other branches of
university learning, was considered instrumental to the study of theology in all its particulars.
Natural philosophy was understood to be knowledge of God‘s creation, and its arguments were
often directly marshaled in discussions about God and his Church, discussions which considered
topics as varied as the physical implications of transubstantiation and the possibilities of
―measuring‖ the relationship between God and his creation. 98
This was a view that continued, as
Sachiko Kusukawa has argued, down through to Melanchthon, for whom natural philosophy was
significant because it offered confirmation of God‘s providential design. 99
Yet over the course
of the seventeenth century, as religious tensions escalated and confessional disagreements grew
more heated, this linkage—not between natural philosophy and a more general understanding of
―providence,‖ but between natural philosophy and the specifics of confessional theology—was
increasingly dissolved, as scholars argued that it stood in tension with the need for civility and
community that the new science demanded. Jesuits, who upheld the old linkage, were therefore
viewed with an increasing degree of distrust.
Yet as many began to argue that the new science ought to be theologically neutral, Kepler
continued to openly proclaim, in both his letters and his published books, that he viewed his
astronomy as a means to bring people closer to God. Like his medieval predecessors, he
intended this to apply not simply to the broader outlines of a religious worldview which any
Christian would necessarily accept, but more specifically to the linkages between his
cosmological theories and the very religious issues that were being hotly debated by the
competing confessions. At the very start of his career, he emphasized that his astronomy served
98 See Sachiko Kusukawa, The Transformation of Natural Philosophy: the case of Philip
Melanchton (Cambridge University Press, 1995), 9.
99 Ibid.
138

a theological purpose and that he saw himself as an interpreter of the messages that God had
built into his Creation. ―I wanted to be a theologian,‖ he emphasized then. ―For a long time I
was distressed: behold God is celebrated now too in my astronomical work.‖ 100
He continued to
emphasize throughout this career that he saw himself as a ―priest of God with respect to the
Book of Nature,‖ 101 and that he linked his scientific and religious pursuits in very direct ways.
In many ways, that is, Kepler conceived of his own scholarly pursuits along similar lines
to his Jesuit counterparts—though of course their religious beliefs differed dramatically. Indeed,
he explicitly connected his own attitude with that of the Jesuits, in an analogy which at first
seems merely a rhetorical flourish, but betrays something deeper. In a letter to Maestlin, in
which he discussed his goal of reforming astrology, Kepler argued:
Do I not act rightly if I dedicate this work to persuading learned men and philosophers
about the distinct operation of the heavens? And thus I act as the Jesuits do: who
improve many things in order to make men Catholics. Or on the contrary, I do not act [as
the Jesuits do]: for those who defend all the nonsense are like the Jesuits. I am a
Lutheran astrologer, who rejects the chaff and retains the kernel. 102
On a simple level, Kepler invoked the Jesuits because of their skill at persuasion; much as they
used their learning to persuade men to become Catholics, Kepler argued, he used his learning to
persuade men about the true workings of the heavenly bodies. Still further, he invoked the
Jesuits as a trope to represent the old, traditional approach, while his description of himself as a
―Lutheran‖ astrologer alluded to his new, reformed approach to the discipline of astrology. This
accounts for Kepler‘s association of Jesuit learning and ―nonsense,‖ a linkage which he surely
100 KGW 13:23: ―Theologus esse volebam: diu angebar: Deus ecce mea opera etiam in
astronomia celebratur.‖
101 KGW 13:91: ―Ego vero sic censeo, cum Astronomj, sacerdotes dej altissimj ex parte librj
Naturae simus.‖
102 KGW 13:89: ―Optime praeceptor, an non recte ago, si operam do, ut doctis et philosophis
etiam operationem caelj persuadeam distinctam? Ago itaque ut Jesuitae: qui multa emendant ut
hominess catholicos faciant. Imo non ita ago, nam qui omnes nugas defendunt sunt Jesuitis
similes, Ego sum Lutheranus astrologus, qui nugis abjectis retineo nucleum.‖
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did not believe when applied beyond this analogy. Yet the choice of this analogy—and Kepler‘s
claim that ―I act as the Jesuits do‖—was not merely happenstance. Kepler implied, through this
comparison, that his work was in many ways as closely tied to a religious agenda as that of the
Jesuits. He was a Lutheran astrologer, both in the sense that he hoped to reform astrology as
well as in the ways that his astrology—and his cosmological work more broadly—served a
religious, and at times a specifically confessional, purpose. Though his work, he elucidated the
patterns of Creation, brought people closer to God, helped resolve some of the issues dividing
the confessions, and pointed the way to a reunified Church.
Though at first it may seem paradoxical, Kepler‘s willingness to openly link his own
religious and astronomical pursuits made him far more willing to consider the religious and
scientific claims of his Jesuit colleagues apart from one another. When men like Oldenberg
argued that natural philosophy or experimental science occupied a realm separate from religion
or politics, and consequently condemned any explicit linkages between them, they automatically
found any science which was tinged with religious overtones to be suspect, especially if the
religious source it came from was suspect. In other words, in the instance of Jesuit science, they
furthered the very linkage they sought to avoid, by condemning the science on religious grounds.
By contrast, because Kepler argued for no such separation, and believed that religious motivation
did not automatically invalidate scientific pursuits, he was willing to consider the two—the
specifics of the religious motivation, and the specifics of the science in question—apart from one
another. He knew that his own religious beliefs should not invalidate his astronomical claims; on
the contrary, he tried to be more rigorous in his demands for accuracy and precision than many
of his contemporaries.
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Kepler‘s own religiously inflected science, in other words, seems to have resulted in his
greater ability to separately evaluate the religious and scientific claims of others than those who
openly argued for the necessity of such a separation. Thus he emphasized that calling something
―Jesuit science‖ should not necessarily invalidate the science in question. Similarly, he
counseled one of his Jesuit correspondents not to dismiss the work of Scaliger simply because
Scaliger was a Protestant. ―Perhaps he is a heretic, an innovator, a disparager of the Holy
Fathers; perhaps he even falsified his lineage. What do all these things have to do with the
present question? Why can‘t it be handled without disparaging him?‖ 103
In questions of
scholarship, as in questions of theology and religious community, Kepler struggled against the
divisiveness he saw around him, and argued for an approach characterized instead by
inclusiveness and harmony.
Conclusion
In many ways this chapter, like the previous one, focuses on the importance of harmony
to all of Kepler‘s endeavors. Yet in closing I want to focus on a related theme that was, for
Kepler, also quite central to every aspect of his life: the theme of accommodation. Kepler, like
many of his fellow Protestants, relied on the hermeneutical principle of accommodation to
emphasize that Scripture was primarily concerned with the question of salvation; accordingly, he
argued that God had no intention of using the Bible to demonstrate principles of astronomy or
physics. Moreover, Kepler used the principle of accommodation to argue—following a long
tradition reaching back to the Church Fathers—that God generally accommodated his words in
103 Kepler to Johannes Deckers, in Eclogae Chronicae, V:XVII: ―Esto sit haereticus, sit novator,
sit SS. Patrum obtrectator, esto etiam, ut stirpem sit ementitus; quid haec quaeso omnia ad
praesentem quaestionem, ut tractari non possit nisi per obtrectationem ejus?‖
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the Bible to the limited understanding of human beings. Kenneth Howell has aptly demonstrated
the ways that the principle of accommodation extended, for Kepler, beyond the simple language
of the Bible to the broad operations of God in the creation of the universe. 104
God had
deliberately constructed the universe so that the number, distances, and motions of the planetary
bodies were ―accommodated‖ to one another, and to man‘s perceptions, Kepler argued in the
Mysterium Cosmographicum. Likewise, in the Harmonice Mundi, Kepler emphasized that God
had ―accommodated‖ each planet‘s speed to the harmonic proportions. Howell has emphasized
that for Kepler these two kinds of accommodation—scriptural and physical/cosmological—were
closely linked: ―in both cases, God has adapted his creative acts (or words) to the capacities of
human minds.‖ 105
In this chapter, we have seen numerous other instances in which accommodation featured
centrally in Kepler‘s worldview. On the one hand, Kepler argued for astrology itself as a kind of
divine accommodation—yet another means by which God might reach out and speak to his
people in ways they could understand. This went hand in hand with a kind of theological
accommodation on God‘s part as well; though the Catholic sacraments might not have any real
significance, Kepler argued, God might use astrological signs to denote them, accommodating
his message to his people by using the theological ideas that most of his worshippers embraced.
In support of this position, Kepler referenced Acosta‘s theory of priestly accommodation when it
came to the idolatrous practices of the New World. Much as priests might rely on the ideas of
the native peoples about their own gods in order spread the word of the one God, God himself
might rely on Catholic ideas in order to spread his true message. This linkage—between idolatry
and issues of confession—was in fact invoked quite often during the sixteenth and seventeenth
104 Howell, God‘s Two Books, 131.
105 Ibid.
142

centuries, usually to the opposite effect. 106
Idolatry was often invoked as a synonym for false
belief, or heresy, and concerns about idolatry in the New World were often linked to the
polemics of confessional disputes in Europe itself. All those who believed differently than one‘s
own confession, in this view, were idolaters worthy of punishment. Kepler took the opposite
approach, and relied upon the idea of idolatry in order to urge more inclusiveness, rather than
more intolerance.
Kepler not only pointed to God‘s own theological accommodation of his people, but
sought as well to achieve a related communal or social accommodation for himself and his own
theological perspectives. In arguing that he be allowed to participate in the Mass in a Catholic
Church, with his particular theological objections duly noted—much as he had argued for his
participation in a Lutheran Church to Pastor Hitzler years earlier—Kepler argued that God‘s
accommodation ought to be imitated in very practical ways by those congregations that sought to
serve him. This meant reaching out not to the limited audience of those who agreed with one
another on every particular, but to the broad audience of all those who called themselves
Christians. The fabric of the religious community, Kepler argued, ought to accommodate itself
to multiple perspectives and beliefs for the good of the whole. Though some positions were truer
than others, division did not serve the community nearly as well as concord. If such concord
could not be achieved by a unified position on all the doctrinal particulars, then accommodation
of difference was the only way to reach any kind of harmony.
Finally, there is one other way that Kepler embraced an ideal of accommodation—and
this represents one final linkage between his ideas and those of the Jesuits of his time. Jesuits
106 See Carina L. Johnson, ―Stone Gods and Counter-Reformation Knowledges,‖ in Making
Knowledge in Early Modern Europe : Practices, Objects, and Texts, 1400-1800, eds. Pamela
Smith and Benjamin Schmidt (Chicago: University of Chicago Press, 2007).
143

were often distrusted in the sixteenth and seventeenth centuries because of the ways that their
religious agenda colored their other activities, and by extension, as we saw earlier, because it was
believed that they would willingly distort the truth in the service of that agenda. And there was
some legitimacy to this belief; many Jesuits argued that the Bible itself justified a degree of
dissimulation when it served a religious purpose. After all, they noted that in 1 Corinthians 9:22,
Paul had described the ways that he became ―all things to all men, that I might by all means save
some,‖ and that God had openly accommodated himself in language to the faulty understanding
of his people in the Bible. The Jesuits, much like Kepler, adopted a broad understanding of the
theory of accommodation, in this case one that applied both to God and language as well as to
their own behavior. They emphasized that missionaries might accommodate their speech and
behavior to the false beliefs of others in order to ultimately lead people to the truth of the
gospel—much as Acosta had argued about the New World. Some, in particular, argued that this
meant that missionaries were justified in dissimulating to those they hoped to convert, for in
doing so they ultimately won their audience over to the truth of Christ. 107
Kepler, wary of the ways that religion was being increasingly exploited to justify further
violence and discord, and unsure that unanimity on religious issues could ever be achieved in his
time, would have frowned on such religious dissimulation. Indeed, he emphasized that ―I have
not learned to dissimulate: I deal seriously with religions matters.‖ 108
Yet Kepler‘s belief that his
astronomical work did supply certain and incontrovertible truth, truth that revealed both the
evidence of heavenly harmony and a model for harmony on earth, convinced him that
107 See, for example, Adriano Prosperi, ―The missionary,‖ in Rosario Villari (ed.), Baroque
personae (Chicago: University of Chicago Press, 1995), 160–94. See also O‘Malley, The Jesuits,
in particular ―Part Four: Encounters with the other: Between assimilation and domination‖, and
―Part Five: Tradition, innovation, and accommodation‖.
108 KGW 13:107: ―…simulare non didicj, seria in religionibus tracto.‖
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dissimulation was warranted if it could be used to bring people closer to that truth—to the truth
of cosmology, and in particular of Copernicus. His Copernican campaign, in other words,
exhibited some close parallels to the religious campaign of the Jesuits. It is to this Copernican
campaign that I turn in Chapter 3.
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Chapter 3:
“An Ally in the Search for Truth”: Kepler and Galileo
―O telescope, much-knowing and more precious than any scepter whatsoever!‖ wrote
Kepler in his Dioptrics of 1611. ―Is not he who holds you in his right hand made king and lord
of the works of God?‖ 1
Kepler rejoiced in the telescope of Galileo, not only because it revealed
the wondrous secrets of the heavens for all to see, but also because it further supported the
Copernican cause to which Kepler was so devoted. Even before Galileo‘s remarkable telescopic
feats, Kepler had learned of Galileo‘s Copernicanism and had eagerly welcomed Galileo into the
Copernican community that he struggled to create. This chapter seeks to consider Kepler‘s
conception and construction of that community, through a focus on the relationship of Kepler
and Galileo from their initial correspondence of 1597 to the aftermath of Galileo‘s telescopic
discoveries of 1610.
The idea of a community of Copernicans was so important to Kepler not simply because
he felt that the Copernican system most closely mirrored God‘s harmonically constructed
universe. It was also the only community to which Kepler could fully and wholeheartedly
belong. As we saw in the previous two chapters, Kepler‘s hopes for a harmonious religious
community were repeatedly dashed; the Lutherans were unwilling to accept his unorthodox
views on the Eucharist, while the Catholics would also not allow him to participate in their own
communal activities without his full doctrinal agreement. With few religious allies, Kepler‘s
allies in the enterprise of understanding the Book of Nature were all the more important to him.
Upon hearing from Galileo, Kepler therefore immediately sought to support him and gain his
assistance in bolstering the larger community of Copernicans. Galileo, as it turned out, was not
1 Kepler, Dioptrice (1611), 14: ―O multiscium & quovis sceptro preciosius Perspicillium: an, qui
te dextra tenet, ille non Rex, non Dominus constituatur operum Dei?‖
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the ideal ally Kepler had in mind, and Kepler‘s Copernican campaign not as fool-proof as he
hoped. Yet over the course of the interactions between these two men, we see Kepler struggle
once again with questions of community; this time not the struggle of adhering to the norms of
an established community, but rather the struggle to create a viable new community that adhered
to his own standards.
Throughout the chapter, I focus on Kepler‘s emphasis on rhetoric as a means by which
this community might be constructed. I highlight the particular rhetorical techniques that Kepler
marshaled, among them the idea of ethos and authoritative agreement and the idea of fides, or the
power of legal testimony. In so doing, I have built on the work of recent authors on forms of
proof and persuasion, on the importance of testimony and credibility in early modern science,
and on the construction of categories like authority and expertise. Richard Serjeantson, in
particular, highlights the early modern process by which rhetoric was increasingly emphasized
not only in the human and moral disciplines, but also in the natural sciences, where certain proof
came to be seen as an elusive possibility and credible testimony a more accessible tool for the
discovery of natural truths. 2
Along similar lines, Barbara Shapiro notes that natural philosophers
of early modern England adopted the ideas of credibility, evidence, and testimony from the legal
arena, with men like Robert Boyle emphasizing moral certainty as the only standard truly
attainable when it came to the physical world. 3
Mario Biagioli focuses as well on credit and
trust, but also on the early modern construction of authority; in describing the ways that Galileo
2 See Richard W. Serjeantson, ―Proof and Persuasion,‖ Eds. Katherine Park and Lorraine Daston,
The Cambridge History of Science, iii: Early Modern Science (Cambridge: Cambridge
University Press, 2006): 132–75.
3 Barbara J. Shapiro, A Culture of Fact: England, 1550–1720 (Ithaca: Cornell University Press,
2000). See also Steven Shapin, A Social History of Truth: Civility and Science in Seventeenth-
Century England (Chicago: University of Chicago Press, 1994).
147

deployed ―techniques for constructing an authoritative persona,‖ 4 he emphasizes that Galileo‘s
authority was a resource for the production and dissemination of his work, rather than an a
posteriori result of that work.
Following the lead of these scholars, I argue not only that rhetoric was an important tool
in Kepler‘s arsenal, but also that the rhetorical techniques on which Kepler drew varied greatly
depending on his audience and purpose. 5
I do not claim that Kepler negated the possibility of
certain knowledge or that he emphasized credibility and moral certainty at the expense of logic
and demonstration. Rather, I underscore the fact that the early modern scholar had a broad range
of techniques of rhetorical persuasion at his disposal; in reading Kepler‘s correspondence with
Galileo, I argue, we see Kepler suggest and then deploy these techniques, with the ultimate goal
of supporting and promulgating Copernican theory. The theories of Copernicus, Kepler‘s own
discoveries about the nature of the planetary motions, and Galileo‘s telescopic discoveries were
all proof, in Kepler‘s mind, that the world was slowly advancing toward a complete
understanding of the mysteries of God‘s creation. ―Does God the creator,‖ he wondered in his
Dissertatio with Galileo‘s Sidereus Nuncius, ―lead mankind, like some growing youngster
gradually approaching maturity, step by step from one stage of knowledge to another?...How far
has the knowledge of nature progressed, how much is left, and what may the men of the future
4 Mario Biagioli, Galileo‘s Instruments of Credit: Telescopes, Images, Secrecy (Chicago:
University of Chicago Press, 2006), 1.
5 For other analyses of Kepler‘s use of rhetorical techniques, see the discussion of the form of
Kepler‘s Apologia in Nicholas Jardine, The Birth of History and Philosophy of Science
(Cambridge: Cambridge University Press, 1984); see also the analysis of the rhetorical nature of
the Astronomia nova in James R. Voelkel, The Composition of Kepler‘s Astronomia Nova
(Princeton: Princeton University Press, 2001); finally, see the investigation of Kepler as
humanist in Anthony Grafton, ―Humanism and Science in Rudolfine Prague: Kepler in Context‖,
in Defenders of the Text: The Traditions of Scholarship in an age of Science, 1450–1800
(Cambridge: Harvard University Press, 1991): 178–203.
148

expect?‖ 6
Kepler believed that only the mutual efforts of a community of Copernicans might
bring the world to truly understand the Book of Nature that God had written for them. And in
order to reach that point, he and Galileo would have to be at once allies working toward that
truth, and missionaries, striving to bring that truth to as broad an audience as possible.
Kepler and Galileo: First Contacts
After completing his first book, the Mysterium Cosmographicum of 1596, Kepler eagerly
sought to publish it as quickly as possible. 7
He sought an audience for the text among both his
own friends and patrons and the broader community of scholars throughout Europe with an
interest in astronomy—among the ―mathematical Republic of Letters,‖ 8 as his professor Michael
Maestlin described it. He strongly believed that the book offered a more powerful defense of the
Copernican system than any that had been offered previously—more powerful, indeed, than
Copernicus‘s own, as Kepler had constructed an a priori argument from geometry, rather than an
a posteriori argument from the observations alone. 9
By constructing an archetypal explanation
of the structure of the heavens, one that was both mathematical and aesthetic and that had
resonances in both astrology and music, Kepler felt that he might truly persuade those who
hesitated to abandon the idea of a geocentric universe. Indeed, he felt his ideas to be so
obviously true that the effort he had expended to uncover might be easily overlooked; he likened
6 Kepler‘s Conversation with Galileo‘s Sidereal Messenger, ed. Edward Rosen (New York:
Johnson Reprint Corp., 1965), 39.
7 KGW 13:40: ―…semper in occasiones ejus publicandj intentus fui.‖
8 KGW 13:58: ―Nam crede mihi, hoc modo Literariae Mathematicae Reip. melius consulitur.‖
9 See Rhonda Martens, Kepler‘s Philosophy and the New Astronomy (Princeton University Press,
2000).
149

his discovery in the Mysterium Cosmographicum to the ―egg of Christopher Columbus,‖ 10
a
story which proved that something that seemed so obvious in retrospect might seem impossible
at the start. It had taken ―the aid of divine inspiration‖ 11 for Kepler to arrive at the ideas of his
Mysterium Cosmographicum, and was eager to swiftly share those ideas with others who might
benefit from them.
Kepler arranged with his printer to send copies of his book along to the Frankfurt Book
Fair, while he himself distributed copies to friends and acquaintances. In particular, he sent two
copies of the book to Italy with friends traveling in that direction. One of these copies came into
the hands of Galileo in Padua, though Kepler had not sent it to him specifically; indeed, it is
likely that Kepler had not heard of Galileo until this point. 12
Upon receiving the text, Galileo
10 KGW 13:64: ―Recordor illius tuij ovj Christophoro columbanij.‖ In the probably apocryphal
story, as narrated by Girolamo Benzoni in his 1565 History of the New World, when Columbus
was told that the discovery of the New World was too obvious and inevitable to be a true
achievement, he responded by asking those with him to make an egg stand on its end without any
external support. Flummoxed, they returned the egg to Columbus, who simply flattened the
bottom by tapping it on the table, allowing it to stand upright. This is not the only time that
Kepler likened his discovery of the Mysterium Cosmographicum to the discovery of the new
world. In the second edition of the book, published in 1621, Kepler described the relationship
between the Mysterium Cosmographicum and his later books as follows: ―the forerunner was
like the first voyage of Amerigo Vespucci; the successors are like today's annual voyages to
America.‖ (―Talis fuit Prodromus, navigatio prima Americi Vespucij, tales Epidromi
navigationes hodiernae annuae in Americam.‖ See Mysterium Cosmographicum, 51)
11 KGW 13:40: ―Cum superiorj Julio, Divina aspirante gratiâ, Astronomicum sive
Cosmographicum quoddam ζήτημα invenissem; quod non tantum ad Dej ex Natura cognitionem
plurimum facit, sed etiam Professionem meam ornat.‖
12 Although Edward Rosen argues that ―Kepler sent Galileo a book because he had heard about
him‖ (see―Galileo and Kepler: Their First Two Contacts‖, Isis 57 (1966): 262–4, at 264),
Stillman Drake‘s assertion that ―that up to this time, Kepler had no more heard of Galileo than
Galileo of Kepler‖ fits better with the textual evidence (see ―Galileo, Kepler, and their
Intermediaries‖, in Galileo Studies: Personality, Tradition, and Revolution (Ann Arbor:
University of Michigan Press, 1970), 123)—in particular, with Kepler‘s description of Galileo‘s
letter to Maestlin, in which he described ―a Paduan mathematician, by the name of Galileo
Galilei‖ (13:75). Although Rosen argues that Kepler was merely struck by the repetition of
Galileo‘s full name in its Latin form (Galileus Galileus), it seems more likely that Kepler had
simply not heard of Galileo before receiving his letter. Moreover, as Drake points out, Kepler‘s
150

immediately wrote a quick letter to Kepler, praising him for his achievement. ―I received your
book, most learned man, sent to me by Paul Homberger not days but mere hours ago,‖ he
wrote. 13
Since Homberger was set to return to Germany immediately, Galileo had decided to
write to Kepler on the spot, having only read the preface of the book. From the preface alone, he
wrote, he could discern the general argument of the book, and he thanked Kepler for that
argument: ―I am extremely grateful,‖ he wrote, ―that I have an ally in the search for truth, and
indeed a friend of that same truth.‖ 14
He greatly lamented that ―those who are devoted to truth
are rare, and that those who are not pursue a perverse method of philosophizing.‖ 15
Galileo went
on to clarify that the specific truth to which he referred was the truth of Copernicanism, a truth
which much of his generation was still unwilling to accept. He himself, he explained, ―came to
the Copernican belief many years ago, and on the basis of this set of propositions I discovered
the causes of many natural effects, which certainly could not be explained through the common
hypotheses.‖ 16
comment that he sent his books ―in Italiam‖ seems to indicate that he sent them generally to Italy
rather than to a specific location (Padua) or person (Galileo).
13 KGW 13:73: ―Librum tuum doctissime uir Paulo Ambergero ad me missum accepi, non
quidem diebus, sed paucis abhinc horis.‖
14 Ibid.: ―…summopere gratulor tantum me in indaganda ueritate socium habere, adeoque ipsius
ueritatis amicum.‖ Galileo here refers to the old saying, ―amicus Plato, magis amica veritas,‖
implying that the scholars who do not agree with him prefer to follow the old authorities rather
than the truth.
15 Ibid.: ―…miserabile enim est adeo raros esse ueritatis studiosos, et qui non peruersam
Phylosophandi rationem prosequantur.‖
16 Ibid.: ―… id autem eo libentius faciam quod in Copernici sententiam multis abhinc annis
uenerim, ac ex tali positione multorum etiam naturalium effectuum causae sint a me adinuentae,
quae dubio procul per commune hypothesin inexplicabiles sunt.‖ Although Galileo did not
specify the particular natural effects whose causes he had used Copernican theory to determine,
Kepler guessed that he referred to the theory of the tides — and noted in a letter to Herwart von
Hohenburg that if this was the case, he believed that Galileo was wrong: ―… cum nuper
Galilaeus Patavinus Mathematicus in literis ad me scriptis testatus esset, se plurimarum rerum
naturalium causas ex hypothesibus Copernici rectissime deduxisse, quas alii reddere ex usitatis
non possint, neque tamen in specie quicquam commemoraret, ego hoc de maris fluxu suspicatus
151

Galileo added that though he had assembled many proofs for Copernicanism and
refutations of its detractors, ―thus far I have not dared to bring them to light, having been
frightened because of the fate of Copernicus, our teacher, who was given immortal fame among
some, but was nevertheless ridiculed and rejected by an infinite many others (for such is the
number of fools).‖ 17 If he truly believed that there were others of the same opinion as he and
Kepler, he continued, he might disclose his true beliefs, but ―since there are not, I will refrain
from business of this kind.‖ 18
Kepler was thrilled to receive Galileo‘s letter; both ―on account of the friendship begun
with you, an Italian, [and also] on account of our consensus in the Copernican cosmography.‖ 19
He hoped that Galileo might have since had the time to finish reading his book, for he eagerly
awaited Galileo‘s opinion. ―I prefer the censure of one judicious man, however harsh,‖ he wrote,
―to the thoughtless applause of all the masses.‖ 20
Still further, in response to Galileo‘s more
subdued initial letter of support, Kepler argued impassionedly for the vocal defense of
Copernicanism by its adherents, claiming that only if all Copernicans banded together could the
rest of the world be swayed. He acknowledged that Galileo had the noble precedents of Plato and
Pythagoras behind his belief that ―we must yield to universal ignorance, nor must we rashly
sum. Sed tamen ubi rem diligentius perpendo, non videmur a Luna discedere debere, quoad
rationes fluxuum ex illa deducere quimus: quod quidem fieri posse existimo …‖ (KGW 13:91).
17 Ibid.: ―… multas conscripsi rationes et argumentorum in contrarium euersiones, quas tamen
in lucem hucusque proferre non sum ausus fortuna ipsius Copernici praeceptoris nostri
perterritus, qui licet sibi apud aliquos immortalem famam parauerit apud infinitos tamen (tantus
enim est stultorum numerus) ridendus et explodendus
prodijt.‖
18 Ibid.: ―…auderem profecto meas cogitationes promere si plures, qualis tu es, extarent: at cum
non sint, huiusmodi negocio supersedebo.‖
19 KGW 13:76: ―Literas tuas, vir humanissime, 4 Augusti scriptas, 1 Septembris accepi, quae
quidem gemino me affecere gaudio: primum, propter amicitiam tecum Italo initam; post, propter
consensum nostrum in cosmographia Copernicana. ―
20 Ibid.: ―mihi credas velim, malo unius cordati censuram, quamvis acrem, quam totius vulgi
inconsideratos applausus.‖
152

throw ourselves before or oppose the rages of the learned masses.‖ 21
Indeed, Galileo was not
alone in this approach—many early modern scholars emphasized the importance of secrecy as a
means to safeguard the ideas of the wise from foolish attacks. 22
Yet Kepler insisted that the
opposition that Galileo feared was no longer universal, and that theirs would not be the first
voices to argue for a new way of conceptualizing the cosmos. With Copernicus and several
others having already paved the way, wrote Kepler, ―moving the Earth should not be a new thing
anymore.‖ 23 Kepler argued still further that since the ideas of Copernicus were not well
understood, learned Copernicans like Galileo and Kepler needed to guide the world to the correct
views cautiously and deliberately, rather than letting the opponents of Copernicanism gain the
upper hand and watching from the sidelines as things spiraled out of control. 24
Kepler then outlined an ambitious plan with which he and Galileo, and with them other
Copernicans, could set about actively changing the minds of the public, bringing the world
slowly around to the Copernican cause. His picture of the gradual dissemination of
Copernicanism involved a strong emphasis on authority and the use of small deceptions,
justifiable because they led the public to the ultimate larger truth of Copernicanism. The
vulgus—the ignorant masses—reasoned poorly and needed guidance, Kepler argued, and it was
incapable of judging arguments on their merits. The only way for Kepler and Galileo to convince
the public of the truth of Copernicanism, then, was to rely on the idea of authority, overpowering
21 Ibid.: ―sapienter tu et occulte, proposito exemplari tuae personae, mones cedendum universali
ignorantiae, nec sese temere ingerendum vel opponendum vulgi doctorum furoribus, qua in re
Platonem et Pythagoram, nostros genuinos magistors, sequeris.‖
22 See, for example, James Hankins, Plato in the Italian Renaissance (Leiden: Brill, 1990).
23 KGW 13:76: ―… cum hoc saeculo, primum a Copernico, deinde a compluribus, et doctissimo
quoque mathematicorum, immanis operis initium sit factum, neque hoc iam porro novum sit,
terram movere.‖
24 Ibid.: ―… praestiterit fortasse, communibus suffragiis semel impulsum hunc currum
continenter ad metam rapere.‖
153

the public with the supposed number of experts who came down on the side of the Copernican
system. ―Let us begin to overwhelm the public more and more with authority,‖ he wrote, ―if,
perhaps, we can guide it to the same knowledge of truth through deception.‖ 25
This would serve
two purposes. On the one hand, those who already believed in the ideas of Copernicus but, like
Galileo, were frightened to publicly state their opinions would receive comfort in hearing of
others who shared their views. Coming forward, Kepler urged, ―would help all allies laboring
against unfair judgments, long enough for them to either take solace from your agreement, or
protection from your authority.‖ 26
Indeed, though he still insisted that the Copernican question
had already been broached by others before, he acknowledged that ―it is not only you Italians
who are not able to believe that they move unless they feel it, but also we here in Germany do
not find ourselves in the best favor with our enemies because of this dogma.‖ 27
While the vocal support of committed Copernicans would help all those who already
believed in the ideas of heliocentrism, that support was also important, Kepler argued, in order to
counter the cries of the ignorant masses who opposed it. Those disagreed with the ideas of
Copernicus would be far less likely to voice that opposition when overwhelmed by the presence
of experts who supported those ideas with the voice of authority. The vulgus would be forced to
concede to the authoritative voices of Kepler, Galileo, and all those who stood with them, or
would be too overwhelmed to say anything to the contrary. Yet Kepler hoped to convince not
merely an unskilled and ignorant vulgus; in fact, on many occasions he seemed ready to discount
the vulgus entirely. Rather, he hoped to focus most of his energies on the docti mediocriter,
25 Ibid.: ―… quia rationum pondera vulgus minus librat, authoritatibus illud magis magisque
obruere incipiamus, si forte per fraudem ipsum in cognitionem veritatis perducere queamus.‖
26 Ibid.: ―…qua ratione simul laborantes tot iniquis iudiciis socios adiutares, dum illi vel
solatium caperent ex tuo consensu, vel praesidium ab authoritate.‖
27 Ibid.: ―Non enim tui solum Itali sunt, qui se moveri, nisi sentiant, credere non possunt; sed
etiam nos hic in Germania non optimam dogmate isto gratiam inimus.‖
154

those moderately learned men who dabbled in the scholarly debates of many fields—erudite
patrons, perhaps, or scholars not well acquainted with the rudiments of mathematical
astronomy. 28 To convince such men of the truth of Copernicanism, Kepler argued for a rhetorical
campaign of persuasion, anchored in the idea of scholarly expertise and dependent upon the
structures of the Republic of Letters itself.
Kepler himself was well attuned to rhetorical traditions and techniques, having studied
rhetoric at Tübingen with Martin Crusius and then having taught rhetoric himself in Graz. He
knew well that rhetoric, a central feature of the classical curriculum, was at its core a legal tool
that focused on the art of persuasion. Ancient rhetoricians like Aristotle, Quintilian, and Cicero
had noted that while legal arguments based on logic were preferable, it was necessary always to
try and sway the opinions of the judicial audience through other means, particularly when the
audience could not be trusted to judge the case on its merits. One such means was a focus on
ethos—on the person conveying the message (whose authority and character were emphasized)
rather than on the message itself. The advocate needed to convince the audience that he
himself—or his client—was trustworthy and possessed a character that couldn‘t be doubted.
And it was less important to theorists like Aristotle and his successors that he actually possess
these characteristics than that he project them. 29 Ethos was not necessarily an inherent
characteristic, but an aura acquired deliberately through skilled manipulation. To project this
ethos the advocate might need to disguise his true intentions or rely on some deliberate
28 Ibid.: ―… qui mihi sunt proximi, vulgus hominum est, qui cum haec abstruse, ut aiunt, non
capiant, mirantur tamen, nec, credere velint an non, unquam secum ipsi cogitant. Docti
mediocriter, quo sunt prudentiores, hoc cautious sese immiscent hisce mathematicorum
litibus….‖ These might be men like Herwart von Hohenburg, the patron with whom Kepler
discussed astrology, mathematics, and chronology, or Duke Frederick of Würrtemberg, as we
shall soon see below.
29 See, for example, Michael H. Frost, Introduction to Classical Legal Rhetoric: A Lost Heritage
(Burlington: Ashgate, 2005), 67.
155

deceptiveness, justifiable so long as such deception went undetected and led to the ultimate
success of the case. 30
Kepler drew directly on this rhetorical tradition—a tradition still flourishing in the
sixteenth century—when he outlined to Galileo the method by which they might convince their
audience of moderately learned men to judge their case favorably. By providing examples of
reliable and authoritative sources on whom their readers could rely, Kepler argued, he and
Galileo would be providing them with persuasive grounds for assent. Yet there remained a
problem: there were, in fact, few Copernicans whom Kepler and Galileo could legitimately hold
up as authoritative witnesses to support their cause. This was where the ―deception‖ to which
Kepler referred came in. Kepler and Galileo, and other Copernicans along with them, needed to
marshal their own authority in the absence of external support, and project an image of such
unquestionable expertise as to make it appear that the weight of all authority was on their side.
The moderately learned would thus be ―bewitched by the authority—I speak from experience—
of those with mathematical expertise.‖ 31
How would this be accomplished? First, Kepler emphasized the production of
astronomical tables by Copernicans. When people, he wrote, ―hear what ephemerides we already
have, constructed from the hypotheses of Copernicus, [they will hear that] all those who write
ephemerides today follow Copernicus.‖ 32 When, moreover, they are provided with mathematical
demonstrations of the phenomena from a Copernican perspective, he said, it will seem to them
30 Ibid. 70; see also Richard W. Serjeantson, ―Proof and Persuasion,‖ 145–9.
31 KGW 13:76: ――Docti mediocriter, quo sunt prudentiores, hoc cautius sese immiscent hisce
mathematicorum litibus; quinimo fascinari possunt, quod expertus loquor, authoritate matheseos
peritorum.‖ It is, perhaps, no coincidence that in his emphasis on deceptive persuasion Kepler
invoked the verb fascinare, the technical term for
the means by which witches could capture the souls of their victims.
32 Ibid.: ―… cum audiunt, quas iam habeamus ephemerides, ex Copernici hypothesibus
extructas; quicunque hodie scribant ephemerides, Copernicum omnes sequi.‖
156

that ―the phenomena cannot be established without the motion of the Earth.‖ 33
Neither
conclusion, of course, was justified—ephemerides were often constructed based on the older,
Ptolemaic system, and mathematical demonstrations could bolster Ptolemaic as well as
Copernican theory. Yet Kepler argued that this deceptive strategy was justifiable because of the
ultimate truth of Copernicanism: ―since [the claims of Copernican theory] are true,‖ he wrote,
―why should they not be forced upon [others] as irrefutable?‖ 34
In addition, Kepler emphasized that Copernican mathematicians like himself and Galileo
should write frequently and supportively to one another. Most university mathematicians, he
noted dismissively, were lost causes, who demanded certain proofs and were hostile to the
Copernican cause. If Copernicans isolated themselves from other mathematicians, and then
wrote supportively to one another, they could then show these letters to the public, a practice that
would make people think that Copernicanism was the accepted norm in scholarly, mathematical
circles—that, as Kepler wrote, ―all professors of mathematics everywhere agree.‖ 35
The sharing
of letters, according to this strategy, would create not only a bond between like-minded
individuals, but also the illusion of universal assent. And this illusion would make the claims of
individual Copernicans much more readily accepted by an audience easily swayed by the specter
of authority. 36
After outlining this ambitious plan, Kepler ended his letter by backtracking. ―Is there
truly need of this deception?‖ he asked. ―Be confident, Galileo, and go forth. If I conjecture well,
33 Ibid.: ―… et cum ab ipsis postulatur ut concedant quod non nisi in mathesi institutis
demonstrari possit, phaenomena sine motu terrae consistere non posse.‖
34 Ibid.: ―…cumque sint vera, cur non pro irrefutabilibus obtruderentur?‖
35 Ibid.: ―qua ratione, monstratis literis (quorsum etiam mihi tuae prosunt), opinionem hanc in
animis doctorum excitare potest, quasi omnes ubique professores mathematum consentirent.‖
36 Along similar lines, Biagioli argues that Galileo relied upon distance as a crucial device by
which his authority could be constructed; he posits ―knowledge as constituted through a range of
distance-based partial perceptions‖. See Biagioli, Galileo‘s Instruments of Credit, 26.
157

few of the distinguished mathematicians of Europe will want to separate from us: such is the
force of truth.‖ 37 Having only just heard from Galileo, one of the few fellow Copernicans with
whom Kepler was familiar, Kepler could not have intended this statement as anything more than
a rhetorical flourish. Or perhaps that was precisely the point—in ending with a forceful statement
about the power of truth to unite all learned experts, Kepler was demonstrating the way he hoped
to marshal rhetoric to achieve, with effort and skill, the very goal that he presented as artless and
inevitable.
Kepler’s Strategy Enacted with Duke Frederick of Würrtemberg
The strategy that Kepler articulated to Galileo was not simply a hypothetical suggestion.
Even before Kepler‘s Mysterium cosmographicum ever made its way to Galileo, Kepler had
already enacted some of his own suggestions in his attempt to solicit princely patronage for the
book, in the person of Frederick, the Duke of Würrtemberg. Kepler recognized that Frederick
would have little reason to support an unknown mathematician who advanced hypotheses that
seemed to contradict accepted scholarly wisdom. He pursued a two-pronged strategy in his
attempts to convince the duke that his discovery was worth supporting—on the one hand, he
argued that his discovery was novel and unprecedented, sure to set its readers alight with
wonder; at the same time, he argued that Copernican theory, which formed the foundation of his
text, was accepted by all those with real expertise, and hence was neither dangerous nor
controversial. Moreover, not only was Copernicanism accepted by modern astronomers, but it
had an ancient pedigree, which harked back to Plato and Pythagoras. He thus provided a context
37 KGW 13:76: ―Verum quid fraude opus est? Confide, Galilaee, et progredere. Si bene coniecto,
pauci de praecipuis Europae mathematicis a nobis secedere volent: tanta vis est veritatis.‖
158

out of which his work emerged, while highlighting the ways that it advanced beyond that context
and provided a valuable contribution.
Positing Copernicus as the theorist ―whom all the famous astronomers of our time follow,
instead of Ptolemy and Alfonso,‖ 38 Kepler briefly summarized Copernican theory, and noted that
no one had yet ascertained why things were as Copernicus had described them. He then
described his own theory, in which he had proven geometrically that the universe was structured
around the five Platonic solids. Kepler was right to stress the novelty of his own contribution, yet
his contention that Copernicanism was accepted by all experts—indeed, by ―all the famous
astronomers of our time‖—was dubious at best. Kepler had not yet received Galileo‘s letter, and
aside from himself and Michael Maestlin, his teacher of mathematics and astronomy, there were
few astronomers that he could legitimately claim for the Copernican cause.
Kepler also proposed to create a unique and tangible materialization of ideas of the
Mysterium Cosmographicum for the duke‘s kunstkammer. As he explained, he would create ―a
credenza-goblet…with a real and actual image of the world and a model of the creation, up so far
as human reason can reach, and the likes of which has previously neither been seen nor heard by
anyone.‖ 39
Here, he appealed both to Frederick‘s respect for the authority of expert astronomers
as well as to traditions of patronage and courtly culture, which placed great value on novelty and
38 KGW 13:30: ―Copernicus (welchem alle berhuembte Astronomi unserer Zeit, an Ptolemaei
und Alphonsi
statt, nachfolgen)….‖
39 KGW 13:28: ―Auch das gantze Werck und die Demonstration des fuernehmisten intenti
fueeglich und zierlich in einen Credentzbecher, dessen diameter einen werckhschuch hieltte,
moechte gebracht werden: Woelliches dan ein recht eigentlich Ebenbild der Weltt, und Muster
der Erschaffung, so weitt Menschliche Vernunfft reichen mag, und dergleichen zuvor nie von
kheinem menschen gesehen noch gehoertt worden, sein und heissen moechte.‖ For a more
detailed description of the goblet and Kepler‗s plans for it, see Adam Mosley, ―Objects of
Knowledge: Mathematics and Models in Sixteenth-Century Cosmology and Astronomy,‖ in
Transmitting Knowledge: Words, Images, and Instruments in Early Modern Europe, Eds.
Sachiko Kusukawa and Ian Maclean (Oxford: Oxford University Press, 2006).
159

collectability. According to these traditions, the prestige of a patron was demonstrated not
merely by political conquests and by the men who populated his court, but also by the value and
uniqueness of the objects he assembled to fill his cabinet of curiosities. By acquiring objects
which embodied learning and beauty, patrons confirmed themselves as erudite and cultured. 40
Kepler sought to entice the duke to support both his own career and the ideas of Copernicus by
embodying his discoveries in the credenza-goblet, something concrete and collectible.
At Kepler‘s request, Maestlin also wrote to Frederick, adding his own authoritative voice
to Kepler‘s. Like Kepler, Maestlin argued that Copernican theory had an ancient pedigree and
was the standard from which all expert astronomers operated, although he was a bit more
circumspect in his language. ―Kepler follows the new or newly revived hypotheses of
Copernicus‖, wrote Maestlin, ―which some time ago Aristarchus and other very wise
philosophers taught: that the Sun sits at the centre of the world, immobile, but the Earth moves,
etc.‖ 41 Maestlin noted that Copernican theory had not yet been perfectly formulated and was
more complicated than Ptolemaic theory; for this reason ―the common and ancient hypotheses
[here, Ptolemaic theory] are kept for the youth, and since they are easier to understand (as is only
fair), they are taught: but all practitioners remain convinced by the demonstrations of
40 See Paula Findlen, Possessing Nature : Museums, Collecting, and Scientific Culture in Early
Modern Italy (Berkeley: University of California Press, 1994). For collectors within the
Empire—particularly Emperor Rudolf II himself—see R.J.W. Evans, Rudolf II and his World: A
study in Intellectual History, 1576-1612 (Oxford: Oxford University Press, 1973) and Thomas
DaCosta Kaufmann, ―Remarks on the Collections of Rudolf II: The Kunstkammer as a Form of
Representatio,‖ Art Journal 38.1 (1978): 22-28.
41 KGW 13:31: ―M. Johann Kepler den newen oder von newem auf die ban wider gebrachten
hypothesibus Copernici, nachgeht, welcher, wie vor zeiten Aristarchus und andere
hochverstendige philosophi, lehrt, das
die Sonn sehe centrum mundi immobilis, die Erd aber bewege sich etc.‖
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Copernicus.‖ 42 Though it is possible that Maestlin referred to the technical use of Copernican
theory for the production of tables (such as the Prutenic Tables), his language was ambiguous,
and most likely conveyed to the duke the impression that Copernicanism in its entirety was
adopted by all experts.
Duke Frederick, reassured by Maestlin‘s letter and intrigued by the idea of the goblet in
the form of the cosmos, agreed to accept the goblet and patronize Kepler‘s book. In addition to
setting to work on the construction of the goblet, Kepler acknowledged Frederick‘s support by
dedicating the opening diagram of the book—a depiction of the goblet—to him. Unfortunately,
the credenza-goblet was never finished; the project was a difficult one, and Kepler ran into
trouble dealing with the artisan responsible for its construction, particularly from a distance.
Likewise, Kepler did not immediately receive any monetary gifts for his work—he had to wait
until several years later for his 250 gulden reward from the estates of Styria. Still, Kepler did
benefit from the dedication to the duke, and in ways he had not fully anticipated. As the
Tübingen theologians began to express their reservations about Kepler‘s book, they were
restrained by the power of the important patron Kepler had secured for himself. Indeed, when
Masetlin wrote to Kepler describing the complaints of the theologians, he noted that ―the book
somewhat offends our theologians, though moved by the authority of our prince (to whom the
principle diagram is dedicated), they leave it undecided.‖ 43
Likewise, Kepler himself
acknowledged that his book likely could not have been printed in the first place had he not
secured Duke Frederick‘s support. He was pleased, he wrote to Maestlin, that
42 Ibid.: ―… werden zwar in allen Schulen die communes et antiquae hypotheses bey der Jugent
behalten, und als leichter zu verstehen, wie billich, gelehert: Aber alle Artifices bleiben doch
samentlich ben des Copernici demonstrationibus.‖
43 KGW 13:80: ―Idem (quod tamen tibi hic concreditum velim) nostros Thelogos etiam nonnihil
offendit, authoritate tamen Principis nostri, cui principale Schema dedicatum est, moti, in medio
relinquunt.‖
161

…with the authority of the prince having been indirectly won over, the book was able to
be printed at Tübingen, which certainly could not have been done if the court had not
fortified me against the hidden thoughts of many people. They perhaps thought they
would have gotten in the way of the prince‘s pleasures if they had impeded my little
book. At any rate, I truly did not consider this when I first approached the prince. 44
Though he may not have turned the duke into a Copernican, in other words, Kepler realized that
the support of the duke had been crucial to the spread of his Copernican message. By impressing
on the duke that his theories were both novel and authoritative, and then by making those
theories the concrete property of the duke in the form of the credenza-goblet, Kepler had secured
himself against some of the ―rages of the masses‖ that Galileo had so worried about.
In their dealings with Duke Frederick, Kepler and Maestlin thus performed the very
rhetorical maneuvers that Kepler outlined to Galileo shortly thereafter. Kepler contended that
Copernicanism was a theory to which all experts gave their ready consent, and he provided the
Mysterium cosmographicum as an example of a great achievement made possible by the ideas of
Copernicus. He then had Maestlin send a supporting letter, emphasizing precisely these points
and reinforcing Kepler‘s contention that the weight of authority was on his side. And he
imagined an object which the duke could hold up as a material embodiment of that authority. As
Kepler would later emphasize to Galileo, the slight deceptions involved in this campaign were
justifiable, for Frederick‘s support would do wonders for the spread of Kepler‘s book, and hence
the Copernican cause more broadly. 45
44 KGW 13:85: ―Sufficit tamen mihi, negocium hoc tantum mihi profuisse, ut sub oblique
conciliata principis authoritate, liber Tubingae excudj potuerit, quod fieri procul dubio non
potuisset, nisj me aula contra multorum occultas cogitationes munivissem. Videbantur sibj forte
Principis delicias impedire, si meum libellum impedissent. Ego vero hoc certe non spectavj, cum
Principem primum adirem.‖
45 Interestingly, Galileo may not have been averse to Kepler‘s strategy of ―deceptive‖ persuasion.
Paul Feyerabend argues that in the Dialogue, ―Galileo uses propaganda. He uses psychological
tricks in addition to whatever intellectual reasons he has to offer. These tricks are very
successful: they lead him to victory. But they obscure the new attitude towards experience that is
162

Kepler’s Strategy Enacted: The Dissertatio cum Sidereo Nuncio
Despite Kepler‘s best wishes, Galileo never replied to Kepler‘s letter of encouragement.
But thirteen years later, Galileo published his famous Sidereus nuncius, which contained reports
of his telescopic observations of the moon and stars, and of his discovery of the moons of
Jupiter, which he called the ―Medicean stars‖ in honor of his Medici patrons. After publishing
the book, Galileo renewed his contacts with Kepler, writing to the Tuscan ambassador in Prague
with a request for Kepler‘s opinion of the work. Though Kepler had no telescope with which to
verify Galileo‘s claims, he responded with a long letter of support, published with few changes
under the title Dissertatio cum Nuncio Sidereo, or A conversation with Galileo‘s Sidereal
Messenger. 46
When we consider Kepler‘s Dissertatio in light of his 1597 letter to Galileo, his quick
show of support makes perfect sense. 47
Not only was Kepler excited about the telescope with
in the making…they obscure the fact that the experience on which Galileo wants to base the
Copernican view is nothing but the result of his own fertile imagination, and that it has been
invented. They obscure this fact by insinuating that the new results which emerge are known and
conceded by all, and need only be called to our attention to appear as the most obvious
expression of the truth‖. See his Against Method (London: Verso, 1993), 65. Maurice
Finocchiaro likewise examines the rhetorical and propagandistic elements of the Dialogue,
which he sees as ―an attempt by verbal means and techniques to induce or increase adherence to
Copernicanism‖. See his Galileo and the Art of Reasoning: Rhetorical Foundations of Logic and
Scientific Method (Dordrecht: Springer, 1980), 22.
46 Shortly thereafter, Kepler obtained a telescope and published his verification of Galileo‘s
results, titled Narratio de Jovis satellitibus (1611). For a translation and detailed analysis of the
two texts, see Isabelle Pantin, Discussion avec Le Messager Céleste: Rapport sur l‘observation
des satellites de Jupiter (Paris: Les Belles Lettres, 1993). For an English translation of the
Dissertatio, with detailed notes, see Edward Rosen, Kepler‘s Conversation with Galileo‘s
Sidereal Messenger, ed. Edward Rosen (New York: Johnson Reprint Corp., 1965).
47 For a different interpretation of Kepler‘s relationship with Galileo, and in particular of
Kepler‘s support of Galileo‘s Sidereus nuncius, see Biagioli, Galileo‘s Instruments of Credit. My
approach follows Biagoli‘s general depiction of Galileo by emphasizing Kepler‘s construction of
authority. My disagreement with Biagioli‘s specific interpretation of Kepler‘s response to the
Sidereus nuncius rests primarily on its emphasis on Galileo‘s prestige at the expense of Kepler‘s.
According to Biagioli, Kepler supported Galileo because by attaching himself to Galileo he
163

which Galileo made his observations in the Sidereus nuncius, but he also could not have failed to
note that in the Sidereus nuncius Galileo had, for the first time, publicly supported the
Copernican system, when he remarked, almost as an aside, that the four Medicean stars
―execut[e] with one harmonious accord mighty revolutions every dozen years about the centre of
the universe; that is, the Sun.‖ 48
When Kepler received the request to evaluate Galileo‘s
telescopic work, he saw it as a prime opportunity to support a fellow Copernican. Indeed, when
asked for his opinion of Galileo by Giovanni Magini, he responded at the outset that ―we are
both Copernicans,‖ and noted, echoing Erasmus, that ―like rejoices with like.‖ 49
Moreover, the strategy that Kepler marshalled within his Dissertatio has much in
common with the outline for the dissemination of Copernicanism that he had first laid out in the
letter of 1597—both in the emphasis on expertise and authority as grounds for assent, and in the
idea of communication as a means to convey the impression of a community of believers. First,
Kepler wrote of his support in a quick letter to Galileo, which he published thereafter as the text
of the Dissertatio, with very few changes. He emphasized at the opening of the text that the
Dissertatio represented a private conversation between two like-minded experts, one which he
was sharing only to make clear to everyone his agreement with Galileo. In his dedication to
Giuliano de Medici he described the book as a text which had been ―private and particular to
would advance his own credit and prestige. Yet as Imperial Mathematician, Kepler‘s prestige
was at this point far greater than that of Galileo. Moreover, Kepler viewed Italian science, and in
particular Italian astronomy, as less advanced than the astronomy of Germany; he noted to
Galileo, for instance, that he should not be surprised at opposition in Italy, a place ―in qua rei
tritissimae et apud omnes Astronomos contestatissimae, Parallaxium scilicet, extant
oppugnatores loco eminentissimi, eruditionis fama celeberrimi‖ (KGW 16:584).
48 Stillman Drake (ed.), Discoveries and opinions of Galileo (Garden City: Anchor Books, 1957),
23.
49 KGW 16:573: ―Copernicani sumus uterque; similis simili gaudet.‖
164

Galileo‖ and was only now being made public in printed form, 50 and he remarked in his notice to
the reader that in creating the Dissertatio he had simply adopted ―this short cut: I have had
printed the letter that I sent to Galileo (which was composed with great speed, within the
prescribed time, among other urgent occupations).‖ 51
The publication of the Dissertatio, literally
―conversation,‖ was, for Kepler, equivalent to the supportive sharing of letters which he outlined
so many years earlier.
Within the Dissertatio, Kepler emphasized Galileo‘s expertise—and the expertise of
those who transmitted his message—as a reason why his claims must be accepted, also a theme
of the 1597 letter. Kepler noted that Wackher, who had first brought him the news of Galileo‘s
discovery, had told him that ―very illustrious men, exalted by their education, dignity, and
constancy far above the foolishness of common people, report these things about Galileo.‖ 52
The
authority of these reports influenced Kepler, he wrote, as did ―the authority of Galileo …
acquired by the rectitude of his judgement and by his skilled nature.‖ 53 In explaining his
immediate concurrence with Galileo‘s writings, he wrote, ―perhaps I shall seem reckless, since I
trust your assertions so willingly, bolstered by no personal experience. But why should I not trust
50 KGW 4:285.26–27: ―Accipe igitur ex privata et Galilaei propria, publicam descriptione
factam,
publica dicatione iam Tuam.‖
51 Ibid., 286.2–4: ―Cum multi sententiam meam super Galilaei nuncio siderio expeterent;
satisfacere placuit omnibus hoc operae compendio; ut Epistolam ad Galilaeum missam
(magnam quidem festinatione inter occupations necessarias, intra praescriptum diem fusam)
publicis typis excriberem.‖
52 Ibid., 286.28–30: ―… viros esse clarissimos, doctrina, gravitate, Constantia, supra popularem
vanitatem
longissime evectos, qui haec de Galilaeo perscribant.‖
53 Ibid., 286.32–33: ―Me … Galilaei potissimum movit authoritas, iudicii rectitudine, ingeniique
solertia parta.‖
165

a most learned mathematician…?‖ 54
He emphasized Galileo‘s expertise as a user of the
telescope in contrast to his own inexperience: ―Should I, dim-sighted, disparage someone with
keen sight? Or someone equipped with optical instruments, while I myself, bare, lack this
equipment?‖ 55 Kepler presented Galileo‘s expertise as incontrovertible, and implied that his
claims were similarly unassailable.
Kepler also noted external factors that bolstered the credibility of Galileo‘s testimony.
Galileo had publicly made his views available, so that they could be verified by others. He was,
moreover, a ―Florentine noble,‖ 56 one who was backed by one of the most respected families in
Tuscany, the Medici. ―Would it have been a small thing‖, wrote Kepler, ―for him to trifle with
the family of the Grand Dukes of Tuscany, and to affix the Medicean name to his own
inventions, while on the other hand promising planets?‖ 57
Kepler also pointed out that if Galileo
had wanted to perpetrate a fraud, he would have done so in a way that was more logical and
intuitive, one that would more easily gain the assent of his victims. Why, asked Kepler, would
Galileo have invented planets only around Jupiter and not around any of the other planets? And
why would he have chosen four planets specifically, a number not paralleled elsewhere in
nature? With this line of reasoning, Kepler argued that Galileo‘s claims were credible precisely
54 Ibid., 290.13–15: ―Temerarius forte videri possim, qui tuis assertionibus, nulla propria
experientia
suffultus tam facile credam: At qui non credam Mathematico doctissimo….‖
55 Ibid., 290.20–22: ―Egone ut Patricio Florentino fidem derogem de iis quae vidit? perspicaci
lusciosus?
instrumentis ocularibus instructo, ipse nudus et ab hac supellectili inops?‖ Kepler here
referenced
not only Galileo‘s telescope but also his own myopia.
56 Ibid., 290.20–22.
57 Ibid., 290.25–27: ―An parum hoc fuerit, Magnorum Hetruriae Ducum familiam ludificari,
Mediceumque
nomen figmentis suis praefigere, planetas interim verso pollicentem?‖
166

ecause they were unusual, and even illogical, of the sort that no one would deliberately
fabricate.
Finally, a key element of Kepler‘s strategy of persuasion, as outlined in his 1597 letter,
involved his conveying the illusion of wide-ranging assent. To this end, Kepler devoted much of
the Dissertatio to an illustration of the many people who anticipated Galileo, or whose ideas and
discoveries coincided with those of Galileo. 58
Kepler first noted that although the idea of so
powerful a telescope may have seemed unbelievable, ―it is by no means impossible or new.‖ 59
In
fact, not only had it been produced recently by the Dutch, but it had been discussed even earlier,
when ―already many years ago it was revealed by Io. Baptista Porta in his book of natural
magic.‖ 60 Likewise, Kepler himself had anticipated the telescope in his Optical part of
astronomy. 61
58 Kepler likely also had personal reasons for emphasizing Galileo‘s scholarly precedents. He
was not pleased that Galileo had neglected to mention any of his own achievements that had
contributed to Galileo‘s work, and wrote to Magini that though he approved of Galileo‘s book
and rejoiced in its claims, ―puto tamen (si legas attente) me satis mihi cavisse; et ubi potui ad
sua ipsum principia revocasse‖ (KGW 16:573). Likewise, Martin Hasdale noted that while
Kepler endorsed Galileo‘s book, ―se medesimo, professando di havere accennato simili cose …
et haveva portato seco il suo libro, per mostrar allo Ambasciatore Sassone il luogo‖ (KGW
16:564). Finally, Kepler always felt it to be his duty, like any good humanist, to document his
sources fully and precisely, and Galileo‘s failure to give credit where credit was due would have
been seen as an omission on his part. Thus Isabelle Pantin notes that Kepler‘s citation of
Galileo‘s sources was intended to add back to the work the crucial element of dialogue with a
textual tradition [Pantin, Discussion avec Le Messager Céleste, cv]. Yet whatever critique Kepler
hoped to convey in his citation of Galileo‘s sources, he meant it to be mild, and subsumed to his
larger goal of supporting Galileo‘s work and the Copernicanism that underpinned it. This is
evident in his distress when his book was misunderstood, as we shall see below, and in the
lengths he took to correct the misunderstanding.
59 KGW 4:291.36–37: ―Incredibile multis videtur epichirema tam efficacis perspicilli, at
impossibile
aut novum nequaquam est.‖
60 Ibid., 291.37–38: ―…nec nuper a Belgis prodiit, sed tot iam annis antea proditum a Io.
Baptista Porta, Magiae naturalis libro.‖
61 Ibid., 292.28–35.
167

Kepler also cited authoritative predecessors who agreed with Galileo‘s claims about the
nature of the Moon‘s surface, the possibility of additional planets, and the mass of stars in the
Milky Way—predecessors who included Pythagoras, Plutarch, Bruno, Maestlin, and of course,
Kepler himself. ―You confirm those who previously asserted the very same thing as you‖, Kepler
wrote. 62
Galileo, in Kepler‘s telling, followed in the tradition of many innovators who
progressed by walking in the footsteps of illustrious predecessors: ―that which you say you
recently discovered with your own eyes, they had predicted long before you, as is required.‖ 63
In
citing the members of a preexisting community of believers, Kepler hoped to bolster Galileo‘s
claims, if not to present them as foregone conclusions, then at the very least depicting them as
commonly held beliefs, rather than novelties. 64
The weight of authority, he hoped to show, was
on Galileo‘s side.
Kepler’s Strategy Backfires: The Dangers of an Ethos-based Campaign
Before Kepler published his Dissertatio, a number of interested friends and fellow
scholars wrote to him requesting his opinion of Galileo‘s new discoveries. Martin Horky, a
young Bohemian living in Bologna, was one such friend. ―It is a wondrous thing, and an
astounding thing,‖ wrote Horky to Kepler of Galileo‘s story of the moons of Jupiter in late
March, 1610. ―Whether it is true or false I do not know.‖ 65
He wrote two more letters in the
62 Ibid., 303.34–35: ―… confirmatis iis, qui pridem hoc idem tecum asseverabant….‖
63 Ibid., 305.6–7: ―… quod nuperrime tuis oculus deprehendisse ais, sic esse oportere tibi tanto
ante praedixerant.‖
64 As Elizabeth Spiller notes, ―Kepler‘s emphasis on established textual evidence clearly works
to create a more recognizable scholarly context for Galileo‘s remarkable claims. If Galileo is
anticipated by Pythagoras or supported by Maestlin, he is less likely to be wrong‖. See her
Science, Reading, and Renaissance Literature: The Art of Making knowledge, 1580–1670
(Cambridge: Cambridge University Press, 2004), 119.
65 KGW 16:562: ―Est res miranda: est res stupenda. Vera an falsa, ignoro.‖
168

next two weeks again asking for Kepler‘s opinion of the Galilean discoveries, though by last he
was starting to doubt Galileo, and wondered whether they might be simply a fabula, a tall tale. 66
Finally, by April 27, he had decided that Galileo was simply not to be trusted. Indeed, he wrote
to Kepler, Galileo had visited him and his mentor, the mathematician and astronomer Giovanni
Antonio Magini, in Bologna only recently, and had brought his telescope with him in order to
show them ―those made-up planets.‖ 67
At night, they had tested the telescope out, with very
disappointing results. ―On earth it works miracles,‖ he wrote, but ―in the heavens it deceives.‖ 68
In particular, he noted that while he was able to see four very small stars around Jupiter, as
Galileo had claimed, as had those with him, ―all acknowledged that the instrument deceived.‖ 69
According to Horky,
Galileo became silent, and on the twenty-sixth, a Monday, he sorrowfully departed from
from our most illustrious master Magini very early in the morning. And he gave no
thanks for infinite kindnesses and reflections [he had received], because he sold a tall
tale. 70
Horky added, in a German post-script at the very bottom of the otherwise Latin letter, that he had
surreptitiously ―made an impression of the spyglass in wax,‖ 71 so that he might construct one
better than Galileo‘s upon his return home. Rather than immediately replying to Horky, Kepler
wrote his Dissertatio to Galileo as an open letter for all to see. He hoped that Horky and others
might read his letter and see in it his clear support of Galileo, and alter their own views
66 KGW 16:565: ―Ephemerides quas T.E. cum Magino secundum fundamenta Tychonica edere
vult, opus est ut 11 Planetas habeant, si datur fabula illa Galilei esse vera.‖
67 KGW 16:570: ―Galileus Galileus Mathematicus Patauiensis venit ad nos Bononiam et
perspicillum illud per quod 4 fictos Planetas vidit attulit.‖
68 Ibid.: ―In inferioribus facit mirabilia, in coelo fallit.‖
69 Ibid.: ―Sed omnes instrumentum fallere sunt confessi.‖
70 Ibid.: ―At Galileus obmutuit et 26 die lunae tristis ab Illustrissimo Domino Magino discessit
summo mane et pro beneficiis cogitationibus infinitis quia fabulam vendidit repletus gratias non
egit.‖
71 Ibid.: ―Ich hab das Perspicillum als in Wachs abgestochen das niemandt weiss.‖
169

accordingly. In June of 1610, after publishing the Dissertatio, he finally wrote back to Horky
and held up the Dissertatio as both his response to Horky and his true opinion of Galileo. ―You
are still caught up in your original doubts about the stars of Galileo,‖ he wrote to Horky. ―I do
not marvel, nor do I blame you: it is proper for the opinions of philosophers to be free.‖ 72
Yet
Kepler hoped that if Horky truly respected his opinion, as he had claimed, he might read
Kepler‘s Dissertatio with an open mind, and his doubts might be resolved. Horky had
mentioned to Kepler that he hoped to write a book attacking Galileo, and Kepler hoped that he
had not yet done so; if he had, Kepler asked, ―please, to gratify me, who loves both you and
truth: free me from concern, and wrote to Galileo that, having read my Dissertatio, you began to
believe that which previously seemed untrue to you.‖ 73
While Horky had managed to read Kepler‘s Dissertatio, he unfortunately did not receive
Kepler‘s June letter before going ahead and publishing his own book, the Brevissima
peregrinatio contra Nuncium Sidereum (―Brief Foray Against the Sidereal Messenger‖). And
while Kepler had hoped that Horky might read his Dissertatio and decide to judge Galileo more
favorable, Horky learned exactly the opposite lesson from Kepler‘s published letter. He believed
that Kepler had intended his Dissertatio as a critique—not an endorsement—of Galileo‘s text.
Kepler‘s Dissertatio, to Horky‘s mind, had only bolstered his initial impressions of Galileo‘s
deceit. Indeed, Horky specifically cited the Dissertatio of Kepler in his Peregrinatio as
supporting evidence for his claims of Galileo‘s trickery. So convinced was Horky that he had
read Kepler correctly that in May of 1610 he sent Kepler a copy of his own book
72 KGW 16:580: ―Haeres tu quidem adhuc in pristina dubitatione super Galilei syderibus: non
miror nec culpo: philosophantium sententias oportet esse liberas.‖
73 Ibid.: ―…age, mihi gratificare, qui veritatem, qui te, amo; sollicitudine me libera, et ad
Galileum perscribe, quid, lecta mea Dissertatione, credere incipias, quod antea tibi veri
dissonum videbatur.‖
170

in which he wrote that he owed Kepler a great debt, for ―I know where the deception comes
from, as you most learnedly discovered in your Dissertatio.‖ 74
(This letter evidently took some
time to reach Kepler, for Kepler‘s June letter to Horky, asking him to read the Dissertatio and
write positively to Galileo, betrays no knowledge of Horky‘s use of the Dissertatio in his
Peregrinatio.)
While Horky may have simply been a poor reader, he was not the only one to understand
Kepler‘s Dissertatio as a critique of Galileo, rather than an endorsement. Michael Maestlin—
himself already a Copernican, and not someone who would rashly and unthinkingly oppose
Galileo‘s new discoveries—also praised Kepler for taking Galileo down a notch: ―You have
deplumed Galileo,‖ 75 he wrote, alluding to Aesop‘s story of the jackdaw that dressed itself in the
borrowed feathers of other birds. Georg Fugger, the Imperial ambassador in Venice, used this
reference yet again. He praised Kepler for his trenchant critique of Galileo, and wrote that
Galileo was ―accustomed to collecting … the feathers of others, in order to decorate himself as
Aesop‘s crow.‖ 76
Why was Kepler‘s Dissertatio so drastically misunderstood? 77 It seems that while Kepler
had noted all those who had anticipated Galileo‘s claims in order to highlight them as supporting
74 KGW 16:575: ―Scio deceptio unde veniat, hanc tu vir doctissime in dissertatione … invenisti.‖
75 KGW 16:592: ―Galileum deplumasti.‖
76 KGW 16:566: ―Nouit et solet homo ille aliorum pennis hinc inde collectis, uti coruus apud
Aesopum se decorare.‖
77 As noted earlier, the misunderstanding may have had some basis in fact, as Kepler was
certainly frustrated by Galileo‘s failure to cite his sources. Yet he expressed all his allusions to
Galileo‘s predecessors in ways that he hoped would serve to bolster Galileo‘s credibility, rather
than the reverse. Galileo certainly understood Kepler‘s text as praise, rather than reproach. He
wrote to Vinta, the Tuscan minister, that Kepler had ―scritto in approbazione di tutte le particole
contenute nel mio libro, senza pur contradire o dubitare in una sola minima cosa‖ (KGW
16:572). Modern scholars have also overwhelmingly read Kepler‘s Dissertatio as a favourable
document of support for Galileo. See, for instance, Rosen, ―Galileo and Kepler,‖ 264; Judith V.
Field, ―Cosmology in the Work of Kepler and Galileo‖, in Ed. Paolo Galluzzi, Novità Celesti e
171

authorities and to create the impression of a community of experts all in agreement, others
interpreted Kepler‘s work as a negative statement about Galileo‘s character. Kepler had intended
to convince people to believe him and his fellow Copernicans through a rhetorical campaign
based on the idea of ethos, focusing on their perceived characters alone; and, in a way he had not
foreseen, he did just that. In highlighting the many thinkers who had anticipated Galileo, Kepler
unwittingly created the impression that Galileo had claimed credit for the discoveries of others—
hence the two references to Galileo as Aesop‘s crow. And if Galileo could not be trusted to
name those individuals whose ideas had led to his own, perhaps his new claims should be
distrusted as well.
Maestlin clearly articulated this sentiment. ―You have deplumed Galileo‖, he wrote, ―by
showing that he was not the first author of this new telescope, nor the first to notice that the
Moon has a rough surface, nor the first in the world to show more stars in the heavens than we
have up to now found listed in the writings of the ancients.‖ 78
And on this basis, Maestlin
argued, should not Kepler be pleased that Martin Horky had taken the final, logical step, showing
that not only was Galileo not credible as a person, but also that his claims themselves—
Crisi del Sapere: Atti del Convegno Internationale di Studi Galileiani (Florence: Giunti Barb ra,
1984): 207–15, at 207; and, in the same collection, Catherine Chevalley, ―Kepler et Galilee dans
la Bataille du ‗Sidereus Nuncius‘‖, 167–75, p. 167, who writes that ―it seems certain‖ that Kepler
immediately and whole-heartedly agreed with Galileo‘s claims, and argues that interpreting the
Dissertatio in any other way merely gives credence to the claims of Horky and Magini. Michele
Camerota, by contrast, notes the many conflicting threads in Kepler‘s Dissertatio, among them
the desire to write a ―philosophical history‖ of the Nuncius, to link it to past work, and to defend
Kepler‘s own work—and concludes that Kepler‘s true motivations and intentions in the
Dissertatio are difficult to discern. See his Galileo Galilei e la Cultura Scientifica nell‘età della
Controriforma (Rome: Salerno, 2004), 177–8.
78 KGW 16:592: ―Egregie sane Tu in tuo scripto (cuius Exemplar a te mihi missum lectu
iucundissimum est, pro quo etiam ingentes tibi ago gratias) Galileum deplumasti, videlicet quod
non ipse novi huius Perspicilli primus fuerit Autor: quod ipse non primus in Luna animadverterit
impolitam superficiem: quod non primus Mundo ostendat, plures in coelo stellas, quam quas
hactenus in veterum scriptis annotatas habemus: et quae caetera sunt.‖
172

specifically, the satellites of Jupiter—were false? Horky, according to Maestlin, had completed
Kepler‘s work, when he had ―noticed the deception … in the telescope of Galileo himself, and
thus slain [Galileo] with his own sword.‖ 79
Kepler was far from pleased—he was furious with Horky‘s public misuse of his text. On
the same day, he quickly wrote to both Horky and Galileo, struggling to undo the damage. In
his letter to Galileo, Kepler tried both to distance himself from Horky, and to show that unlike
both himself and Galileo, Horky had incorrectly assumed the mantle of expert. He had only
recently received the work of Horky, Kepler wrote, and he marveled ―at the temerity of this
youth—with the native scholars only murmuring, he, foreign and ignorant, [alone] contradicts,
with the matter not yet proven.‖ 80
Perhaps, Kepler guessed, it was his very youth, foreignness,
and inexperience that made him speak so boldly—they served, Kepler wrote, ―like the mask of
an actor,‖ 81 allowing him to avoid true responsibility for his words. Though Kepler believed that
Horky‘s words were so worthless as to be a waste of Galileo‘s worry or time, he decided to write
to Galileo immediately in order to explain the specific ways that Horky had ―abused‖ his letter. 82
As soon as he had learned, Kepler explained, that Horky was one of Galileo‘s critics and
that he ―followed the passion of the vulgus,‖ he decided to take action immediately—not merely
because Kepler himself was a supporter of Galileo personally, but because ―I knew how [these
79 Ibid: ―Verum hic Martinus Horky nos hac solicitudine liberat. Qui deceptionem visus
animadvertit, non in alio simili, sed in ipsius Galilei perspicillo, ipsumque Autorem suo proprio
gladio sic iugulavit.‖
80 KGW 16:584: ―Miram adolescentis temeritatem; qui mussantibus omnibus indigenis doctis,
ipse peregrinus et imperitus, solus obloquitur, re nondum comperta. ―
81 Ibid.: ―Credo ut histrionibus Persona, sic ei novitas et obscuritas Nominis audaciam addidit. ―
82 Ibid.: ―Indignae paginae in quibus tempus teras: sed tamen, quia mea epistola abutitur, statui
rationem tibi quodammodo reddere facti alieni.‖
173

sorts of people] oppose all new discoveries, [and hoped] to forestall it on this occasion.‖ 83
In
other words, Kepler had interpreted Horky‘s dismissal of Galileo‘s claims as a dismissal of
novelty in astronomy more generally—and of Copernicanism in particular. He had hastened to
convince Horky to change his mind, in keeping with his plans from years before to remain a
vocal and committed supporter of Copernicus and his adherents. For that reason, he had sent
Horky a copy of his own Dissertatio so that Horky might learn from it either to think more
wisely, or at the very least to restrain his overly hasty attack. Much to Kepler‘s chagrin, Horky
had learned neither lesson—instead, he had ―strangled my friendship most slanderously.‖ 84
Though Kepler had claimed earlier that expert arguments would easily sway an
inexperienced public, he conceded now that the idea of expertise was itself problematic, as the
public was incapable of judging accurately who was an expert and who was not, so long as one
invoked the general idioms of science. Horky had taken advantage of the ignorance of the
vulgus, which ―unskilled in optical methods, listens freely to critics speaking of optical things. It
cannot distinguish between a blind man and a seeing one, and rejoices in any spokesperson of its
ignorance whatsoever.‖ 85
To remedy this, Kepler suggested that actual experts in optics address
the questions behind the telescope, so that Horky could be revealed as a fraud. Of course, one
could suggest to the vulgus that they study optical writings themselves, in order to rebut Horky‘s
83 Ibid.: ―Ut primum intellexi ex eius literis, esse tibi Obtrectatores, ipsum vero sequi studia
vulgi: gnarus, quam ea novis obstent inventis, properavi ad te scribere: si forte praeriperem
occasiones.‖
84 Ibid.: ―Quid vero is ea fecerit, vides. Amicitiam hanc, inquam, vix dum spirare visam
obscurissime, nece famosissima jugulavit.‖
85 Ibid.: ―Vulgus enim opticarum rationum imperitum, aures libenter accommodat obtrectatori,
ex Opticis loquenti: quia inter coecum et videntem nescit distinguere, gaudetque qualibuscunque
imperitiae suae tribunis.‖
174

―thoroughly stupid little book‖ on their own, yet this was not their way. 86
―They prefer to follow
this author when he says that a curved line is straight, in order to be able to run riot against
philosophy, rather than to take up the work themselves.‖ 87
Would they perhaps, he wondered, be
swayed from their ignorance if ―a scholar knowledgeable in this science could take up pen to
paper in order to contradict such nonsense?‖ 88
He hoped that this might be the case, and when
neither Galileo nor any other such scholar was forthcoming, Kepler did just this himself in
1611—his Dioptrics addressed the optics behind the telescope specifically in order to explain
and bolster Galileo‘s claims. Simple statements of support and general allusions to expertise
would not be enough, it seemed, to draw an impressionable public to the side of truth.
Kepler then paused to ponder why it was that so many people denied the actual objects
that the telescope revealed, even those, like Horky, who had actually had the chance to use a
telescope. He attributed this to the fact that vision in general could be deceptive and could vary
person to person; ―I see it is not impossible,‖ he wrote, ―that one person sees what thousands of
others do not.‖ 89
Kepler himself had found, he wrote, that sometimes the telescopes he used
were problematic for others, while the ones praised by others were blurry for him. Yet certainly,
he insisted, there were others who could bolster Galileo‘s account of what he had seen. Kepler‘s
attempt to cite as witnesses those who had anticipated Galileo had backfired in dramatic fashion,
so he asked instead for witnesses who could verify Galileo‘s claims using the telescope itself.
―Though I no longer have any doubts‖, wrote Kepler, ―nevertheless it has pained me that all this
86 Ibid.: ―Quos si jubeas adire scriptores optics, in rem praesentem venire, libellum stultissimum
ex seipso refellere…‖
87 Ibid.: ―…experieris eos malle hoc authore curvum dicere rectum, ut lascivire contra
philosophiam possint; quam ut id laboris sibi sumant.‖
88 Ibid.: ―Et imperabit sibi doctus aliquis, huius scientiae gnarus, ut papyrum perdat in
refutandis his nugis?‖
89 Ibid.: ―…video, non esse impossibile, ut unus videat, quod non vident mille alii.‖
175

time I have lacked other witnesses who would confirm the belief of others.‖ 90
Since Galileo had
written that he had witnesses who could testify on his behalf, Kepler asked him to name them; at
present, wrote Kepler, ―I can produce no one other than you … by which I may defend the
reputation of my letter: in you alone rests all the authority of the observation.‖ 91
His own
reputation was now entangled with the reputation of Galileo, and it would take credible
witnesses beyond the two of them to repair the misreading of their texts and convince their
readers to judge them—and more importantly, their claims—favorably.
Kepler‘s request for additional witnesses, and his post-Dissertatio letter to Galileo more
generally, are evidence of a shift in the focus of Kepler‘s rhetorical techniques—a shift that can
be implicitly detected, at times, in the Dissertatio itself, and which Kepler made explicit only
afterwards, in light of the Dissertatio‘s misreading. Kepler had focused his Dissertatio—much as
he had planned in the 1597 letter to Galileo—on the ideas of authority, expertise, and a scholarly
community all in agreement. He had cited all those who had anticipated Galileo in order to
overwhelm his readers with the weight of authority, blinding them with the image of a group of
mathematical experts who all held to the same irrefutable views. At the same time, however, he
emphasized that his audience should accept Galileo‘s discoveries based on the credibility of
Galileo as a person, rather than simply the credibility of his claims. To this end, for example, he
highlighted Galileo‘s status as a gentleman with princely patrons. This latter, more legal
standard, which focused on credible testimony and trustworthiness, was one that Kepler adopted
more unambiguously when his initial Dissertatio failed to achieve its purpose.
90 Ibid.: ―Igitur etsi mecum nondum, quicquam dubito: dolet tamen me tamdiu destitui testimoniis
aliorum, ad fidem caeteris faciendam.‖
91 Ibid.: ―…sed neminem praeter te hoc jactantem producere possum, quo famam Epistolae meae
defendam: In te uno recumbit tota observationis authoritas.‖
176

In explaining the ways in which his Dissertatio had been misunderstood, Kepler
emphasized in his later letter to Galileo that his goal in citing the work of others had been not to
criticize Galileo, but the opposite—to support him. ―I did not enumerate that earlier similar
things had been observed in order that he might disparage you, but rather so that others might
believe the testimony of many.‖ 92
The mere fact that others had said things similar to Galileo in
the past should in no way imply that Galileo had copied from them, as Horky and others had
suggested; indeed, Kepler insisted, ―often people come together to the same target in different
ways.‖ 93
Moreover, if he had wanted to make that kind of accusation, he would have said so
clearly and direct, rather than insult a fellow scholar in an underhanded way. Horky should not
―think that I am so sleepy that I do not know how to speak openly. He should let me [speak for]
myself.‖ 94
In bringing the testimony of additional witnesses to support the claims of Galileo, then,
Kepler had never intended to accuse Galileo of deception or of borrowing the ideas of others;
instead, he had hoped to ―add to the fides of the Nuncius.‖ 95
Fides, alternatively translated as
credit, faith, or belief, was the method by which ancient rhetoricians evaluated the credibility of
witnesses and their testimony. 96
It was also a standard applied in a number of early modern
92 Ibid.: ―At non ideo recensui, quid simile antea fuerit observatum, ut ipse obtrectaret, sed ut
caeteri crederent plurium testimonio.‖
93 Ibid.: ―…saepe diversis ad eundem scopum convenitur viis.‖
94 Ibid.: ―Si me credit obiter aliquid innuere voluisse, ne quaeso oscitasse putet, qui neglexerim
id aperte dicere. Me mihi relinquat.‖
95 Ibid.: ―Ego fidem Nuncio astruo.‖ Galileo appeared to see Kepler‘s efforts in this light as well.
In his response to Kepler‘s letter, he noted that Kepler was ―primus, ac fere solus, re minime
inspecta, quae tua est ingenuitas, atque ingenii sublimitas, meis assertionibus integram fidem
praebueris‖ (KGW 16:587).
96 See Serjeantson, ―Proof and Persuasion,‖ 147–8.
177

disciplines, among them the artes historicae, 97 but also the discipline of law. Kepler relied on
this latter linkage, and in the face of opposition to Galileo‘s discoveries, and of the misreading of
his own text, he explicitly reframed the entire debate as a legal one. ―Truly‖, he wrote, ―this is
not a philosophical problem, but a juridical question of fact: whether Galileo deliberately
deceived the world.‖ 98
He emphasized here that despite their philosophical implications,
Galileo‘s claims were not themselves philosophical, and could not be refuted using philosophical
reasoning. Rather, they had the status of legal questions of fact—a phrase that anticipates the
―matter of fact‖ that underpinned the program of the Royal Society years later.
Kepler named himself as witness, testifying to the character and credibility of Galileo as
author. ―This is a contest between virtue and vice‖, he wrote. ―I, as an honest person considering
Galileo‘s claims, judge that such evil does not lie within him.‖ 99
At the same time, he sought to
discredit Horky, by alluding to his general dishonesty: Horky was someone ―who has no sense of
honesty, and since he therefore does not deem it important, he probably judged others according
to his own character.‖ 100
Kepler acknowledged the possibility that he was wrong in his positive
assessment of Galileo. In this case, Kepler would be pitiable but still honest, while Horky, who
would have been right only coincidentally, would still be a scoundrel who had twisted the facts
of the matter. Moreover, Kepler insisted that there was no way to avoid the possibility of his
being wrong in his support of Galileo, ―for this is the way of the law, that anyone is presumed to
97 See Anthony Grafton, What Was History? The Art of History in Early Modern Europe
(Cambridge: Harvard University Press, 2007), 96–122.
98 KGW 16:584: ―Et vero, non problema philosophicum, sed quaestio juridica facti est, an studio
Galilaeus orbem deluserit.‖
99 Ibid.: ―Certamen hoc virtutis est cum vitio: ego ut bonus vir, de Galilaei affirmatis judico, non
cadere in illum tantam nequitiam.‖
100 Ibid.: ―… ille nullo adhuc gustu honestatis, eoque illam susque deque habens, cadere
affirmat, ex suo forte ingenio caeteros aestimans.‖
178

e good until the contrary is proven—how much more so if the circumstances have created
fides?‖ 101
Kepler concluded by noting that he hoped that this letter, unlike his earlier Dissertatio,
might speak clearly for itself, and clearly convey his opinions about the status of Galileo‘s
claims. He was pained, he wrote, only by the way his own words had been twisted, not by the
general scorn of the vulgus. He emphasized that ―I am not so stupid that I am swayed by the
negative attitude of the crowd, or by their listlessness and inability to argue against the
experience and skill of an astronomer.‖ 102
Though he had earlier urged Galileo to set aside the
Pythagorean model of scholarly silence, he now acknowledged that such an approach clearly had
its merits. Yet he was still very pleased that Galileo had seen fit to ―cast the die…[and] open the
sanctuary of heaven.‖ 103
All those who refused to look at the wonders Galileo had revealed
could only be pitied; the vulgus ―is punished for its contempt for philosophy with everlasting
ignorance.‖ 104
Kepler added finally that this letter, like his Dissertatio earlier, was written
directly to Galileo but intended for public consumption. Galileo should feel free to share it
widely—not, as he had indicated earlier, to convey the sense of a shared community of believers,
but rather to establish it as an epistola publici juris. 105
Although this phrase could simply imply
publication, Kepler likely intended it to bear some legal overtones as well, following the focus
on law throughout his letter.
101 Ibid.: ―Quia haec via juris est; ut quilibet praesumatur bonus, dum contrarium non probetur:
quanto magis si circumstantiae fidem fecerint?‖
102 Ibid.: ―Nec sum adeo stupidus, ut movear authoritate vulgi negativa; aut a vulgi oscitantia et
ineptitudine contra astronomi experientiam et dexteritatem ratiociner.‖
103 Ibid.: ―Nunc quia jecisti aleam Galilaee, vulgoque propalasti haec coelorum adyta…‖
104 Ibid.: ―Quippe vulgus contemptum Philosophiae in seipso ulciscitur perpetua ignnorantia.‖
105 Ibid.: ―Licebit tibi tamen hanc epistolam publici juris facere, si tua interesse putaveris.‖
179

Kepler and Horky revisited
On the same day that Kepler sent his letter off to Galileo, Kepler drafted a second letter
and sent it to Horky. Here, Kepler made clear that he was greatly displeased with Horky‘s
misuse of his Dissertatio. While he knew, he wrote, that his harsh words might well cause
Horky to end their friendship, he hoped at the very least not to make an enemy of Horky, largely
out of respect for Horky‘s father, a diplomat at the court in Prague and a friend of Kepler‘s. He
thus warned Horky that he had written a letter to Galileo (―a letter of the sort you can imagine,‖
he added), and that he had granted Galileo the authority to print it at his own discretion. 106
He
also that Horky‘s father worried about him, and would be still more worried ―if he knew about
your Peregrinatio and my foray against you.‖ 107
Kepler advised Horky to avoid the public stage
and leave Italy soon, if possible.
As it happened, Horky did leave Italy—but he did so before Kepler‘s letters to him
arrived. Consequently, he left with no idea that Kepler opposed his criticism of Galileo and his
reliance on the Dissertatio. In fact, on his journey home he specifically stopped at the home of
Kepler, in order to further discuss their supposed mutual disapproval of Galileo‘s ―deceptions.‖
Kepler, at the same time, had no idea that Horky had not received his letter, and thus assumed
that Horky knew of his disapproval. As Kepler related to Galileo afterward,
It was a strange and remarkable meeting, when he with an exultant expression and as if
triumphant over Galileo spoke to me as though I agreed, while I responded as I had done
in my letter, in which I had renounced my friendship with him. It threw each of us into a
great confusion, because he did not know about my renunciation (since my letter was
106 KGW 16:585: ―Primust est, quod epistolam ad Galilaeum scripsi, qualem te meruisse
aestimare potes: eique postestatem feci, si velit, publice imprimendi.‖
107 Ibid.: ―Pater non minus quam ego, imo multo maxime pro te est sollicitus. Quanto magis si
sciret de tua Peregrinatione, et mea invectiva?‖
180

delivered after his departure from Bologna), nor did I think otherwise than that he had
read the letter in which I had explained myself. 108
After a great deal of awkwardness and confusion, the two finally realized their mistake, and
Horky immediately endeavored to regain the favor of Kepler, whom he greatly respected. He
clarified to Kepler the reasons for his suspicion of Galileo, while Kepler relayed to him his own
observations, ones which refuted Horky‘s claims. ―It hurt him badly,‖ Kepler wrote to Galileo,
―when I recounted to him what I had written to you.‖ 109
Horky was particularly distraught that
Kepler had accused him of treachery; even if he had misrepresented Kepler‘s views, he insisted,
he had done so with only the best intentions, fully convinced that he had accurately represented
Kepler‘s own point of view.
Horky not only tried to prove his good intentions to Kepler, but to make clear to Kepler
why he still opposed Galileo‘s discovery of the moons of Jupiter, even as Kepler held up his own
observations, as reported in his Narratio, as proof. To bolster his own position, Horky argued
that ―he had followed the public opinion of many of the most learned professors at the University
of Bologna and others throughout Italy.‖ 110
He argued that the absence of any rebuttal by
Galileo to the claims of these university professors proved that his conjectures were unsound, for
if he had real proof of his claims, would he not, as a man of honor, have immediately taken it
upon himself to supply it? Indeed, Horky added, many scholars in Italy had wanted to publicly
debate the matter with Galileo, but Galileo had deliberately avoided them, and had even changed
108 KGW 16:597: ―Miram et spectabilem occursationem; cum ille exsultanti vultu, et veluti
triumphato Galilaeo me ut consentientem alloqueretur, ego vero responderem ex formula
Epistolii, quo ipsi amicitiam renunciaveram. Id tanto utrumque magis perturbavit; quod nec ille
de mea renunciatione sciebat (quippe literae meae Bononiam perlatae sunt post ipsius
discessum) neque ego aliter, quam lectum ipsi Epistolium, animum indixeram.‖
109 Ibid.: ―Caeterum doluit pessime, cum ipsi recenserem, quid ad te scripsissem.‖
110 Ibid.: ―…sic respondebat: obsecundatam se hic publicae famae, doctissimis in Academia
Bononiensi professoribus non paucis, aliisque per Italiam: de quorum consensu fidem mihi fecit
documentis manifestissimis.‖
181

his residence because he feared the confrontation, allowing the authority of his prince to protect
him from even the deserving queries of fellow scholars.
Horky had argued that it was therefore only a matter of time before someone came forth
with a book like his—he had only happened to be the first. In the end, Kepler confessed to
Galileo, Horky had convinced him—not that Galileo‘s claims were flawed or problematic, but
rather that Horky‘s own behavior had not been entirely unjustified. Horky had ―persuaded me,‖
he wrote; ―I recognized the allure of rash behavior, and I forgave him; we became friends once
again.‖ 111 They ended their meeting cordially, but Horky promised that ―as soon as he, with me
demonstrating, has seen and recognized the satellites of Jupiter, he will change his mind.‖ 112
As
Horky needed to leave to travel to his father, this joint telescopic adventure would take place the
next time that Horky returned to Prague.
Because of Kepler‘s newly reached understanding with Horky, Kepler also asked Galileo
to refrain from publishing the letter denouncing Horky that he had sent to Galileo earlier, and
that he had given Galileo permission to broadcast widely. If Galileo felt that he could improve
his reputation and counter the attacks against him by publishing Kepler‘s letter, Kepler assured
him that ―they glory of your triumph will be greater, if, as I hope, I send to you a voluntary
confession of your enemy.‖ 113
Moreover, since sending Galileo that letter, Kepler had also
published his Narratio, recounting his own personal experiences with the telescope which had
procured in the interim, and he noted that this might be the best way for Galileo to refute those
who denied his discoveries. Regardless, Kepler urged Galileo to have some compassion for poor
111 Ibid.: ―…expugnavit me, agnovi temeritatis illecebras, ignovi; rediimus in gratiam.‖
112 Ibid.: ―…ut ille primum atque me monstrante visurus et agniturus sit Joviales satellites,
sententia sua cessurum profiteretur.‖
113 Ibid.: ―Major erit gloria triumphi, si tibi, uti spero, hostis tui confessionem ultroneam
transmisero.‖
182

Horky, and to avoid addressing Horky‘s work directly. ―Consider his youth,‖ he wrote.
―Nothing is more common at this age than to agree passionately with one‘s teacher‘s ideas, and
from them to dash ahead in a fit of rash courage as if from some rampart, in order to engage in
battle with an enemy.‖ 114
With this in mind, Kepler argued, Horky‘s antics should be dismissed
as the excesses of youth, nothing more—and certainly nothing worth openly combating. Not
only would it be beneath Galileo‘s dignity to address the intemperate claims of someone so far
beneath him both intellectual and professionally, but it would only make others pay more
credence to those claims. Moreover, it would open the floodgates for other similarly
meaningless attacks, by making it clear that Galileo deemed them worthy of reply. While
Galileo ought to support those truly interested in understanding and verifying his discoveries,
Kepler argued, baseless condemnations were best ignored. Kepler noted that having left the
university, Galileo had thankfully left behind the world of the disputation, and need reply only to
the questions that had merit, not to every meritless critique. ―Leave their manners to the schools
that you have left,‖ he wrote. 115
As Galileo may have noted from the earlier part of Kepler‘s letter, Kepler no longer felt
that Horky‘s behavior had been truly baseless. Indeed, Horky had persuaded him to change his
mind by citing the very fact that Galileo had ignored the calls of all those Italian scholars
interested in debating his discoveries with him. Kepler was thus not advocating that Galileo
ignore all those who questioned his claims, but merely that he respond only to those genuinely
interested in debate, and only to those whose tone was properly scholarly and respectful. Horky,
young, brash, and not yet a real scholar, would not be the best choice of a target, Kepler insisted.
114 Ibid.: ―Si adolscentiam ipsius respicis; nihil est in hac aetate familiarius, quam in placita
praeceptorum fervide transire, exque iis veluti ex aliquo propugnaculo temerario ausu
procurrere, et manus cum hoste conserere.‖
115 Ibid.: ―…relinque igitur scholae, qua de exiisti, mores suos.‖
183

If Galileo did decide to respond personally to Horky anyway, Kepler asked that his own letter be
left out of the public sphere. And finally, if Galileo felt that it was absolutely necessary to refer
to Kepler‘s letter in some way given that Horky had cited Kepler in his attack, Kepler asked that
he refer only generally to the theme of the letter, while leaving out the particulars. In this case,
Kepler wrote, Galileo should,
remove the personal names and insulting words….[such as] when I attributed petulance
to him, called him a sputum of a man, accused him of destruction, called him a sycophant
and a buffoon…[or spoke of] ignorance, temerity, stupidity, and other most unfortunate
turns of phrase. 116
Kepler noted that the other terms he had used were more acceptable; these extreme words had
been appropriate only given Horky‘s seeming exploitation of his own words. Yet once Kepler
realized that Horky had meant no harm and had thought himself true to Kepler‘s intentions,
Kepler felt that his own insults were no longer appropriate. The Republic of Letters ought to be
characterized by civility, after all. If Horky had truly twisted Kepler‘s words on the public stage,
he had placed himself outside the boundaries of the Republic of Letters, and Kepler would have
been justified in responding in kind. 117
But Kepler had come to realize that Horky‘s words
stemmed not from ―vice or the disgraces of life, but rather the faults of character or age.‖ 118
Kepler‘s change in attitude toward Horky stemmed in large part, it is clear, from his
realization that Horky was simply a well-intentioned and injudicious youth, rather than someone
116 Ibid.: ―Denique si ne hoc quidem obtineo, saltem titulos personales, et probra verborum,
justissima quidem sed jam remissa, expungas: cuiusmodi sunt, quod aio, nondum ipsum famae
suae curam habere (contra quod ipse totam vitam suam ad eximanandum proposuit) quod
petulantiam illi tribuo, quod sputum hominis vocito, quod perditionem incuso, quod
sycophantem, quod scurram appello. Imperitiam, temeritatem, stupiditatem, infoelicissimum
meorum verborum intellectum, et quae alia huius classis, tolerabiliora existimo.‖
117 For examples of the ways that ―impolite‖ or other unruly behavior altered the landscape of the
otherwise civil Republic of Letters, see Martin Mulsow, Die Unanständige Gelehrtenrepublik
(Stuttgart: Metzlersche J.b. Verlagsb, 2007).
118 KGW 16:597: ―…quia non Animi morbi, non vitae probra, sed vel Naturae vel aetatis vitia.‖
184

who had deliberately set out to wrong Kepler or Galileo. At the same time, it stemmed from his
growing frustration with Galileo himself. After the initial letter that Kepler had received from
Galileo in 1597, in which he learned of Galileo‘s Copernicanism, Kepler had rejoiced to meet a
fellow scholar with whom he might share his honest ideas and opinions. Yet while Galileo had
ultimately not disappointed him when it came to supports for the Copernican enterprise, he had
disappointed him as a fellow member of the scholarly community. After the first letter, there had
been no word from Galileo at all for thirteen years. When Galileo had finally reached out to
Kepler once again, it was with thrilling news—a new instrument that revealed new bodies in the
heavens, bodies that themselves seemed to support the theories of Copernicus. Kepler, once
again, wrote to Galileo in full support, immediately publishing his thoughts for all to see. Yet
Galileo continued to be less than forthcoming. Kepler repeatedly begged Galileo for a copy of
his telescope. ―You have inflamed me with a great desire to see your instrument,‖ he wrote in
one letter to Galileo. 119
The telescopes available in Prague were far inferior to Galileo‘s, and
made it impossible to verify Galileo‘s discoveries. The Tuscan ambassador to Prague himself
asked Galileo to make a telescope available to Kepler, but Galileo claimed that none was to be
had. He wrote to Kepler that he had already given some to his patrons, and that the construction
of others was ―very laborious,‖ 120 and simply not possible at the present time. Kepler waited
until the next time he planned to write to Galileo, and asked in a post-script that Galileo ―free us
at the first possible moment from the desire for your new discovery.‖ 121
Sensing that Galileo
hesitated to reveal his secrets to others—indeed, aware that this was the very reason that so many
had challenged Galileo‘s results to begin with—Kepler emphasized that ―there is no one whom
119 KGW 16:584: ―Magno me desiderio incendisti videndi tui instrumenti.‖
120 KGW 16:587: ―…paris excellentiae nullum aliud construxi, praxis enim est valde
laboriosa…‖
121 KGW 16:597: ―…nos primo quoque tempore desiderio tuae novae inventionis leva.‖
185

you should fear as a rival.‖ 122
Even so, Kepler‘s telescope was to come not from Galileo, but
from the Elector of Cologne; he was one of the noble patrons to whom Galileo had given a
telescope, and he temporarily loaned it to the court in Prague during a visit there.
Similarly, even when Galileo made new discoveries with his telescope, he did not share
them immediately. Twice he sent to Kepler anagrams which contained hidden within them the
nature of his discoveries—one about the triple-form of Saturn, and one about the phases of
Venus—which Kepler tried desperately to solve. To the second anagram, Kepler sent Galileo
back a full eight guesses, none of which hit the mark. ―I implore you,‖ he wrote in his letter,
―do not keep the matter hidden from us any longer. See that you are dealing with real Germans.
I come away impatient from your various literary secrets. Do you see the misery in which you
cast me with your silence?‖ 123 Kepler continued to speak highly of Galileo in all his writings—
particularly in the Dioptrics which he published the same year, and which contained the
solutions to the anagrams that Galileo had finally revealed to him. Yet he never felt comfortable
with the secretiveness of Galileo. He surely recognized that Galileo had crafted his work ―to
maximize the credit [he] could expect from readers while minimizing the information given out
to potential competitors,‖ 124 and knew that Galileo put all his fellow scholars into this class.
Kepler, by contrast, viewed his own ideas and innovations not as personal products to be
guarded secretively, but rather as contributions to the general store of public knowledge. If
Galileo saw himself writing not to any coherent community but rather to a diverse and
122 Ibid.: ―…neminem habes, quem metuas aemulum.‖
123 KGW 16:604: ―Obsecro id ne nos diu celes quicquid est: vides tibi rem esse cum Germanis
germanis. Ego impatientia occulti literas varie digessi. Videre in quas me conjicias miserias
tua reticentia? Itaque desinam de his: ad tuarum literarum reliqua venio.‖
124 Bialgioli, Galileo‘s Instruments of Credit, 81.
186

disconnected field, 125 Kepler‘s goal was the deliberate construction of just such a community.
This perhaps explains Kepler‘s insistence in 1597 that Galileo share his thoughts to a much
broader audience, alongside Galileo‘s own silence after that lone initial letter. Indeed, until the
publication of the Sidereus Nuncius in 1610, ―Galileo seemed content to limit his audience to
small groups of Paduan academics, Venetian patricians, and Florentine courtiers with whom he
discussed philosophy, music, mathematics, and literature.‖ 126
And when he did reach to a
broader audience, it was in order to secure his status an inventor, not because he had agreed to
join the community that Kepler struggled to create. Indeed, part of the reason that Kepler‘s
Dissertatio was seen as an attack on Galileo lay precisely in the fact that Kepler strove to draw
attention to that broader community, and to highlight the larger efforts amidst which Galileo had
made his own discoveries.
Kepler believed that the open exchange of information and discoveries was the only way
that a community of scholars might succeed; if he shared freely, he hoped others would share
freely with him. As he once wrote to Magini (later to be Horky‘s host in Italy, as it happened),
―I am so passionate for the astronomical arts that I cannot refrain from communicating my ideas
to expert practitioners, so that through their advice I may make subsequent achievements in this
divine art.‖ 127
The question of priority and personal credit had already been raised for Kepler
years before with regard to Galileo himself. When, in 1603, Kepler‘s friend Edmund Bruce
125 See Ibid. 97-98.
126 Ibid. 119.
127 KGW 14:190: ―Sum artis astronomiae cupidissimus et temperare mihi non possum, quin
artificibus consilia mea communicem, ut illorum admonitionibus subinde in hac divine arte
proficiam.‖
187

wrote to him that Galileo was supposedly claiming Kepler‘s ideas as his own, 128 Kepler urged
Bruce not simply let it go. ―I am not worried that Galileo claims my ideas,‖ wrote Kepler.
…There are those who emphasize truth and the glory of God the creator rather than their
own reputations. Let the Garamantes and Indians hear these and other mysteries of God,
let my enemies make them known, let my name also perish in the meantime, so long as
the name of God, the Father of minds, is thus promoted. 129
Kepler knew how to act the courtier, to be sure—he fashioned his ideas into products tailored to
his patrons, as we saw earlier with Duke Frederick, as surely as Galileo fashioned the moons of
Jupiter into emblems of the power of the Medici. 130
Yet like his deceptions of the vulgus, he
reserved this behavior for those outside the Republic of Letters. Fellow scholars, he felt, should
be treated with openness and candor, not subterfuge or cunning. Likewise, the kind of insults he
had leveled at Horky were appropriate only for those who had deliberately placed themselves
outside the Republic and its guiding precepts—for those who adhered to the norms of scholarly
decorum and civility, only civility could be returned in kind. Both Horky‘s earnest attempt to
justify his own behavior and Galileo‘s continued evasiveness moved Kepler to reevaluate his
condemnation of Horky‘s behavior toward Galileo. Though he continued to approve of Galileo
the Copernican, his evaluation of Galileo the courtier was less positive.
128 Though it is unclear to what exactly Bruce alluded, Stillman Drake has speculated that it was
likely Galileo's own discussion of the relationship between planetary periods and orbital
distances, which he made on the basis of the table from Kepler's Mysterium Cosmographicum.
See ―Galileo‘s ‗Platonic‘ Cosmogony and Kepler‘s Prodromus,‖ pp. 364-379, in Essays on
Galileo and the History and Philosophy of Science, Volume 1, eds. Noel M. Swerdlow and
Trevor Harvey Levere (Toronto: University of Toronto Press, 199), p. 367-374.
129 KGW 14:268: ―Galilaeum nihil moror, mea sibi vindicare…illi praesertim, cui veritas deique
conditoris gloria potius, quam sua fama proposita est. Audiant haec et alia dei Mysteria
Garamantes et Indi; praedicent vel hostes mei, pereat interim et nomen meum: tantum ut Deo et
Patri mentium suum inde nomen crescat.‖
130 See Mario Biagioli, Galileo, Courtier: The Practice of Science in the Culture of Absolutism
(Chicago: University of Chicago Press, 1994).
188

Conclusion
The story of Kepler and Galileo thus provides us with a window onto Kepler‘s attempts
to construct an astronomical community centered on the theories of Copernicus. In many ways,
that community was modeled on the larger Republic of Letters. Kepler reached out to Galileo as
a fellow scholar, one whom he hoped would welcome his ideas, criticize them honestly, offer his
own ideas in kind, and contribute to his attempts to strengthen their communal enterprise.
Though he was thrilled to have Galileo join the ranks of Copernicans, and delighted that
Galileo‘s telescopic discoveries further supported the truth of heliocentrism, he found himself
troubled by Galileo‘s secretive behavior. For Kepler, who labeled his very first book with the
word ―mystery,‖ or ―secret,‖ nature‘s secrets meant its inner workings. These were to be
plumbed and then shared, not kept hidden; nature‘s surface secrecy did not correspond with any
kind of secrecy or concealment on the part of its investigators. Kepler, that is, firmly believed in
the ideal of public knowledge that was to characterize many early modern scholars of his time, in
contrast with the hermetic exclusivity of many of his predecessors. 131
While Galileo, too, had no interest in limiting his discoveries to a select few initiates, he
emphasized secrecy in the sense of privacy and priority. Always concerned that others might
take advantage of him and claim credit for his discoveries, Galileo‘s refusal to share his
telescopes or his plans for their construction greatly frustrated Kepler, as did his sending of
ciphers rather than clear and immediate news of his discoveries. Indeed, in the end Galileo‘s
secretiveness was among the reasons Kepler withdrew his condemnation of Horky. Though
Kepler continued to support Galileo and to argue on his behalf, he also believed that since
131 On the evolving connotations of the ―secrets of nature,‖ see William Eamon, Science and the
Secrets of Nature: Books of Secrets in Medieval and Early Modern Culture (Princeton: Princeton
University Press, 1996).
189

Galileo had not been truly open about spreading or defending his ideas, he could not expect his
work to go unchallenged. Likewise, Kepler tried to model his behavior toward Horky in
accordance with the guidelines of civil behavior that characterized both the larger Republic of
Letters and the mathematical Republic within it. When Horky‘s own behavior placed himself
outside those guidelines, Kepler‘s response was harsh and his break with Horky decisive. Yet
when Horky convinced Kepler that his own behavior had been justified, Kepler immediately
retracted his negative words about Horky and sought to ensure that they would not be publicized,
despite his continued disagreement with Horky‘s stance. In other words, while the ideas of
Copernicanism that were to undergird Kepler‘s conception of scientific community were very
important to him, the ideals of civility and shared knowledge were critical as well.
The interactions between Kepler and Horky also reveal that those ideals could be difficult
to uphold in the face of the practical constraints of an imagined Republic spread across
geographic boundaries. If scholars were to be united across Europe, the communications that
undergirded their union might be slow in coming and easily misunderstood. The situation in
which Kepler and Horky found themselves was due as much to the fact that their letters kept
crossing paths as it was to their intellectual disagreement. Horky‘s negative letters to Kepler
about Galileo were not answered quickly enough to prevent his misconstruing Kepler‘s own
feelings on the subject. And Kepler‘s angry condemnation of Horky‘s work completely missed
Horky, who arrived at Kepler‘s home eager to revel in their mutual disapproval of Galileo.
Likewise Kepler‘s own efforts to support Galileo through his Dissertatio were complicated by
the fact that readers often completely misunderstood his tone. The problems of communication
at a distance—delay, crossed paths, and misconstrued tone—were as much a challenge to
Kepler‘s attempts at establishing community as Galileo‘s emphasis on secrecy and priority.
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Additionally, though Kepler certainly argued for public knowledge, we need to clarify
what kind of ―public‖ he meant. Among scholars, to be sure, Kepler advocated for openness and
honesty. Yet when it came to the unlearned or moderately learned public, Kepler was willing to
be less forthcoming. In her analysis of the Republic of Letters, Ann Goldgar has written that
―the ‗public‘ my scholars cared about was each other.‖ 132
For Kepler, this was not strictly the
case—he certainly cared what the larger public thought, and his Copernican campaign was aimed
as much at this larger public as at the more limited Republic of scholars. Yet when it came to
addressing this public, Kepler was willing to be less than open. This larger public, Kepler felt,
would not be swayed by the open sharing of knowledge—other methods would have to suffice,
methods that might be secretive, or even deceptive.
Kepler, like Galileo, could be the consummate courtier if he so chose. He was certainly
equipped with the right tools to act the part; as a trained humanist, Kepler relied on a long history
of rhetorical techniques first described by the ancient Greeks and taught in the universities of his
own time as well. 133
Those techniques could be used alongside traditional logical or
mathematical arguments to further bolster one‘s argument, and they could be targeted at scholars
and non-scholars alike. Even the letters of the theoretically open and transparent Republic of
Letters were themselves crafted with great care and attention to rhetoric; letters were, after all, as
much self-conscious attempts at the fashioning of one‘s persona as they were methods of
communication. 134
Kepler‘s Astronomia Nova was likewise targeted specifically toward the
132 Ann Goldgar, Impolite Learning: Conduct and Community in the Republic of Letters (New
Haven: Yale University Press, 1995), 6.
133 See, for example, Carlo Ginzburg, History, Rhetoric, and Proof (Hanover: University of New
England Press, 1999).
134 See, for example, Adam Mosley, Nicholas Jardine, and Karin Tybjerg, ―Epistolary Culture,
Editorial Practices, and the Propriety of Tycho‘s Astronomical Letters,‖ Journal for the History
191

scholarly reader, and was itself a masterpiece of rhetorical persuasion. 135
Yet the very specific
strategies that Kepler labeled as deliberately deceptive were aimed at a non-scholarly audience in
particular, and relied heavily on the manipulation of opinion through an emphasis on authority.
These deceptions were only appropriate, in Kepler‘s view, because they were addressed to
outsiders; he faulted Galileo for playing the courtier even to his intellectual colleagues.
Of course, these deceptive strategies were not always successful, nor did they always
reach the appropriate targets. As the reception of Kepler‘s Dissertatio demonstrated, his
attempts to use the weight of authority to bolster Galileo‘s arguments were completely
misunderstood. And the people who misunderstood them were the very scholars whom Kepler
hoped would be convinced without the need for such deceptions. In the face of such
misunderstanding—and in light of the fact that Galileo‘s discoveries could not be proven via
deduction nor experienced by the majority of readers who did not possess a telescope—Kepler
began to employ a different sort of rhetorical strategy. From an emphasis on the weight of
authority he moved instead to an emphasis on the weight of the law. He argued, in the aftermath
of the Dissertatio, that the proper standards for credible testimony and the legal idea of fides
meant that Galileo‘s claims had to be accepted, and he targeted these arguments at the scholar
and non-scholar alike.
This latter rhetoric of law seems more immediately understandable to the modern reader
as a buttress for the scientific enterprise; the idea of deceptive rhetoric, by contrast, seems less
consonant both with our typical understanding of the ideals of science and also with the persona
of Kepler himself, who characteristically argued for candor and truthfulness. Indeed, his very
of Astronomy 34 (2003): 419-51. See also Lisa Jardine, Erasmus, Man of Letters: The
Construction of Charisma in Print (Princeton: Princeton University Press, 1993).
135 See the discussion in Voelkel, The Composition of Kepler‘s Astronomia Nova.
192

efusal to dissimulate when it came to matters of religion led directly, as we saw in the previous
chapters, to his exclusion from the Lutheran communion and his refusal to go along with the
Jesuits who continually urged him to convert to Catholicism. Why, then, did Kepler specifically
advocate a strategy of dissimulation when it came to the spread of Copernicanism? And what
did dissimulation mean to him?
To answer this question, we need to remind ourselves that although dissimulation has
overwhelmingly negative valences today, it was a prominent and often accepted feature of early
modern life. Rosario Villari, for instance, has highlighted the ways that dissimulation in early
modern Italy was used as an important form of political resistance and innovation. 136
Likewise,
although Calvin railed against the Nicodemites—a term he coined to refer to those who, while
accepting a new faith in their hearts, did not alter their public professions of religious belief—the
practice was widespread and the dissimulation that underpinned it widely recognized. 137
Selffashioning,
as well, relied upon deception, and the supposedly artless sprezzatura to which
Castiglione‘s courtier aspired was, of course, a laboriously acquired façade. 138
Also ubiquitous
was the early modern belief—and the allegorical style of reading that sustained it—that God had
disguised the truth in densely complex texts in order to protect it from the foolish ignorant, and
that the pagan ancients had likewise deceptively hidden the truth under layers of myth such that
136 Rosario Villari, Elogio della Dissimulazione: La Lotta Politica nel Seicento (Rome, 1987).
137 Though there is some debate as to its true nature; Carlo Ginzburg portrays it as a unified
movement (see his Il Nicodemismo: Simulazione e Dissimulazione Religiosa nell‘Europa del
‘500 (Turin: Guilio Einaudi, 1970) while Carlos Eire describes it as a large-scale and
heterogeneous attitude (see his ―Calvin and Nicodemism: A reappraisal,‖The Sixteenth Century
Journal 10 (1979): 45–69).
138 Baldassare Castiglione, Il Cortegiano (Venice, 1524).
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only the truly wise could decipher it. 139
Kepler was immersed in and drew on all these modes of
thought; his campaign of deception, that is, while rooted in ancient rhetorical traditions, was also
a strategy of its time.
Yet many of the forms of deception noted above were ways of hiding what one truly
thought, not of deliberately disseminating falsehood in order to eventually further a larger truth.
Hence a closer analogue to Kepler‘s approach lies not in allegorical modes of reading or in the
masking of religious belief, but in religious approaches to the spreading of true doctrine among
the uninitiated. As I noted in the previous chapter, Kepler was well acquainted with Jesuit
strategies for propagating the Catholic faith, and at times deliberately likened his own
Copernican campaign to their religious campaigns. The Jesuits hoped to win their audiences
over to the truths of the Catholic faith, and were willing to ―accommodate‖ false beliefs in order
to do so; many felt that any deception required was ultimately justified by the winning of new
souls to worship in the community of the true Church. 140 Kepler‘s attitude nicely mirrors this
approach; by dissimulating and projecting the illusion of authority, he hoped to win his audience
over to the truth of Copernicanism and create his own kind of community of believers. Kepler
thought of Copernicanism not merely as a scientific truth, but as an all-encompassing one, a
paramount truth to which he needed to devote the full-strength of his persuasive energies.
―Because I am completely persuaded by the opinion of Copernicus,‖ he wrote, ―I am religiously
prevented from proposing anything different…This glory suffices, that with my discovery I can
139 See Hankins, Plato in the Italian Renaissance, and Don Cameron Allen, Mysteriously Meant:
The Rediscovery of Pagan Symbolism and Allegorical Interpretation in the Renaissance
(Baltimore: Johns Hopkins University Press, 1970).
140 See, for example, Adriano Prosperi, ―The Missionary‖, in Ed. Rosario Villari, Baroque
Personae (Chicago: University of Chicago Press 1995), 160–94. See also John W. O‘Malley et
al. (eds), The Jesuits: Cultures, sciences, and the arts, 1540–1773 (Toronto: University of
Toronto Press, 1999), in particular ―Part Four: Encounters with the other: Between assimilation
and domination‖, and ―Part Five: Tradition, innovation, and accommodation.‖
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guard the gate of the temple in which Copernicus celebrates at the high altar.‖ 141
The words
Kepler used to describe Copernican theory were rife with theological overtones. And though
Kepler could never bring himself to dissimulate when it came to questions of confession, as we
saw in the earlier two chapters, this was in part because he felt that those questions would never
be settled in with any degree of unanimity in his lifetime. If the only way to achieve churchly
harmony was through negotiation and compromise, dissimulation was counterproductive—it
would only make things more difficult. By contrast, as we‘ve seen, Kepler felt that the
Copernican question could be conclusively settled, via deductive reason and in ways that were
inarguably evident. Indeed, all his books—from his Mysterium Cosmographicum to his
Harmonice Mundi—were attempts to do just this. The evidence provided in the books
themselves, he hoped, would convince all scholars capable of truly reasoned thought. For the
rest, if dissimulation was required to bring them around, then it was surely warranted in his view.
If God‘s Church could not be aligned with any one confession, so be it—after all, as Kepler had
written, ―Christ the Lord, who spoke this word, neither was nor is Lutheran, nor Calvinist, nor
Catholic.‖ 142
Yet God‘s Church might still be a Church of Copernicans, and Kepler did his best
to see that it would be. For God had imprinted the world with his harmonic blueprint, clear for
all to see—and God was a Copernican. 143
141 KGW 13:91: ―Atque etiam mihi, cui persuasissima est Copernicj sententia religio est aliud
proponere, vel in laudem ingenij, vel ad gratiam hominum, qui absurditate sententiae plurimj
offenduntur: sufficit haec gloria, posse Copernico ad magnam aram sacra facientj portas templj
mea inventione custodire.‖
142 KGW 12.26: ―Aber Gott lob das Christus der Herr, welcher diese Wort aussgesprochen, auff
diesen ihren schalg, weder Lutehrisch noch Calvinisch, noch Papistisch gewest, noch ist.‖
143 See Peter Barker, ―The Role of Religion in the Lutheran Response to Copernicus,‖ in
Rethinking the Scientific Revolution, Ed. Margaret J. Osler (Cambridge: Cambridge University
Press, 2000): 59-88. Barker also ends his essay with the phrase ―God was a Copernican.‖
195

Chapter 4:
“Your Copernican Book”:
The Targets of Kepler’s Epitome
Kepler‘s interactions with Galileo, as I argued in the previous chapter, reveal the ways
that Kepler aimed his Copernican campaign both at the scholarly public of astronomers and
mathematicians as well as at the unlearned or moderately learned public. With the publication of
his Epitome of Copernican Astronomy, Kepler hoped to further that effort. The rhetorical tactics
that he had described to Galileo and enacted in his Dissertatio with the Sidereus Nuncius were
ways to try and sway a public who did not have the skills or capacities to be won over with true
knowledge and mathematical demonstrations. Yet with the Epitome, Kepler tried another tactic,
and one that he clearly preferred. The Epitome was to be a textbook, a way for the young and
ignorant to acquaint themselves with the rudiments of Copernican astronomy when they were
still receptive and malleable. In this way, Kepler hoped to reach that crowd of unlearned men
before they had gotten to such a state, and to craft them into the kind of public who might
appreciate his arguments. He hoped to provide young students with the foundational knowledge
and skills to become true members of the community of Copernicans in the future, able to
appreciate the arguments he offered in favor of Copernicus without the need for subterfuge or
deception.
This idea would not be as easy to implement as Kepler had hoped, however, and not just
because Copernican astronomy was no easy subject to master. Rather, Kepler‘s efforts to target
his Epitome to the young and unlearned were frustrated by two external events: the banning of
the first three books of his Epitome in Italy, and the outbreak of the Thirty Years‘ war. Both
these events, I argue in this chapter, caused Kepler to dramatically reconceptualize his Epitome
and reframe its target audience. By the time he published the later books of the Epitome, that is,
196

Kepler argued that he had targeted the book specifically not for students, but rather for expert or
powerful readers alone. In this chapter, I will tell the story of how these changes came about,
and of the ways that both the banning of the Epitome and the outbreak of war altered Kepler‘s
conception of his work and its purpose. Much like Kepler‘s interaction with the work of Galileo
discussed in the previous chapter, I argue, Kepler‘s changing attitude toward the Epitome sheds
light on his understanding of what it meant to be a Copernican, and on how Copernicans might
best seek to enlarge their communal ranks.
Kepler’s Epitome as Copernican Primer
Kepler‘s Epitome of Copernican Astronomy was a dense and lengthy exposition of
Copernican theory, written in question-and-answer format, and published in three octavo
volumes between 1618 and 1621. Scholars typically tend to see the book as an elementary
Copernican textbook targeted toward the unschooled student reader. 1
Many recognize, however,
that the book sits uneasily in this genre, and thus descriptions of the book are often qualified—it
is, one scholar notes, an ―idiosyncratic textbook.‖ 2
Caspar, the preeminent biographer of Kepler,
goes so far as to say ―it is not doing justice to it to designate it as a textbook, even though it is in
the form of one; it is not to be compared with the other textbooks of astronomy then in use.‖ 3
One problem in categorizing the book as a Copernican textbook is that it is not, in point of fact,
1 For example, Rhonda Martens writes that ―it was written for a more general audience [than
Kepler‘s other books],‖ (Kepler‘s Philosophy and the New Astronomy [Princeton: Princeton
Princeton University Press, 2000], 142); Judith Field describes it as an ―elementary textbook of
Copernican astronomy,‖ (―Renaissance Mathematics: Diagrams for Geometry, Astronomy and
Music,‖Interdisciplinary Science Reviews 29.3 [2004]: 259-277, at 275); and Bruce Stephenson
writes that it was ―intended for the student‖ (see Kepler‘s Physical Astronomy [Dordrecht:
Springer, 1994], 138).
2 Stephenson, 138.
3 Kepler, Trans. and Ed. Doris Hellman (New York: Dover, 1993), 297.
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strictly Copernican—it is more an epitome of Keplerian astronomy, or of Copernican astronomy
as interpreted and made physical by Kepler. Yet still more problematic is the Epitome‘s
incredible complexity. It is a detailed and mathematically sophisticated account of Kepler‘s
physical system—it is, in fact, the most detailed exposition of that system that Kepler produced.
It is difficult to imagine the average student—or even, for that matter, the advanced student—
using such a book to learn the basics of theoretical astronomy. Indeed, we have evidence that
even university mathematics professors struggled with the text. Peter Crüger, Professor of
Mathematics at Danzig, read Book IV of the Epitome and reported that ―the Poet says that a
reading repeated ten times should be pleasing. But I still don‘t understand this after one hundred
repetitions. The author seems to deliberately obscure the matter, as is his custom.‖ 4
Of course, a book‘s complexity does not necessarily discourage its use as a textbook.
Early modern textbooks came in many shapes and sizes, and ―what look to us like massive,
erudite reference works sometimes functioned, thanks to the practices of readers, as elementary
textbooks.‖ 5
Although historians previously assumed, for example, that nobody read
Copernicus‘s De Revolutionibus due to its complexity, Owen Gingerich‘s detective work has
revealed that it was a remarkably successful textbook. 6
Some scholars claim similar prominence
for Kepler‘s Epitome, noting that it ―attained a relatively wide readership‖ 7 among a general
4 KGW 18:937: ―Librum Astronomiae Kepplerianae quartum accepi...Legi, nec semel, quae de
proportione Orbium et Corporum Planetariorum Kepplerus citatis a te locis infert. Lectio decies
repetita placebit, ait Poeta. Sed haec vel centies repetita nondum intelligo. Et videtur autor
more suo rem obscurare de industria.‖
5 Anthony Grafton, ―Textbooks and the Disciplines,‖ in Scholarly Knowledge: Textbooks in
Early Modern Europe, Eds. Emidio Campi, Simone De Angelis ,Anja-Silvia Goeing and
Anthony T. Grafton (Geneva: Librairie Droz S. A., 2008), 28.
6 The Book Nobody Read: Chasing the Revolutions of Nicolaus Copernicus (New York: Walker
and Company, 2004).
7 Martens, 142
198

audience or that it ―acquired considerable popularity as a textbook.‖ 8
Yet the historian who
resurrected Copernicus as a textbook does not do the same for Kepler; Gingerich rightly notes
that since the Epitome only went through two printings in the seventeenth century, it is unlikely
that it was a very popular university text—the Epitome Astronomiae of Kepler‘s teacher Michael
Maestlin, by contrast, went through seven editions. 9
And so we have a picture of a textbook which even university professors struggled to
comprehend, a book seemingly targeted toward students which appears not to have been taught
at universities. Could Kepler have simply drastically overestimated his audience, intending to
teach beginners but presenting them with a book impossible for them to understand? This is
indeed a possibility, yet Kepler was a skilled rhetorician who possessed a keen sense of his
potential readers and a remarkable ability to adapt his books to a variety of audiences. 10
This
was the man, after all, who wrote yearly popular astrology almanacs, a fantastical account of a
voyage to the moon, and letters to experts and amateurs, nobles and commoners alike.
Perhaps, then, the problem is not that Kepler missed the mark with his textbook, but that
the Epitome should not be read as a textbook at all, or at least not a textbook for the beginner.
8 Stephenson,138. As evidence, Stephenson cites J. L. Russell, ―Kepler's Laws of Planetary
Motion: 1609-1666,‖ The British Journal for the History of Science 2.1 (1964): 1-24, at 8. Yet
though Russell does demonstrate increasing interest in the Epitome in the latter half of the
seventeenth century, this is interest on the part of other expert practitioners—mathematicians and
astronomers. Russell does not address the popularity of the Epitome as a textbook for students.
9 ―Five Centuries of Astronomical Textbooks and Their Role in Teaching,‖ in The Teaching of
Astronomy: Proceedings of IAU Colloq. 105, Eds. J.M. Pasachoff and J.R. Percy (Cambridge:
Cambridge University Press, 1990), 192. To quote Gingerich, ―Kepler himself ultimately
produced a squat, fat textbook containing more words than any of his other writings. Called The
Epitome of Copernican Astronomy, it is generally believed by historians of science to have been
one of the most widely used texts of the early seventeenth century, but they are wrong. Just
because a historian of astronomy once said so does not make it true.‖
10 See Anthony Grafton, ―Humanism and Science in Rudolfine Prague: Kepler in Context,‖ in
Defenders of the Text: The Traditions of Scholarship in an Age of Science, 1450-1800
(Cambridge: Harvard University Press, 1991).
199

Why, after all, have scholars begun by assuming the book to be an elementary textbook when its
content is so much more advanced than one would expect of such a book? The fact that Kepler
called the book an ―Epitome‖ is not itself indicative of its target audience. Possibly the most
famous astronomical Epitome of the period, Peurbach and Regiomontanus‘s Epitome of the
Almagest, did purport to summarize Ptolemaic astronomy, but it did far more than that—it took a
critical look at Ptolemy‘s work and considered theoretical and observational developments in
astronomy since Ptolemy, and was a primary resource for all practicing astronomers of the
period. 11
Peurbach‘s and Regionmontanus‘s Epitome was still used in university classrooms of
the sixteenth century, as it was easier to follow than the Almagest itself. Yet it was a resource for
more advanced astronomy students, as opposed to the simpler elementary astronomical texts
widely used for beginning students, like Sacrobosco‘s Sphere or Peter Apian‘s Cosmographia.
By contrast, another famous astronomical Epitome, the Epitome astronomiae of Kepler‘s
teacher, Michael Maestlin, was intended not for practicing astronomers or advanced students but
specifically for non-specialists. Maestlin dedicated the book to Duke Ludwig of Würrtemberg,
and explained in the preface that he intended it for beginning students in the arts—all of whom
were required to study some astronomy, a subject of the traditional quadrivium—and particularly
for those unskilled in mathematics. He strove to use only simple methods and accepted theories,
leaving out anything of interest to experts alone. This is likely the reason that Maestlin‘s
Epitome did not adopt the Copernican system, though Maestlin himself was a Copernican—this
new theory would be of interest to the more advanced student of astronomy, not the beginner
11 See Noel Swerdlow, ―Astronomy in the Renaissance,‖ in Astronomy before the Telescope, Ed.
C. Walker (London: British Museum Press, 1996): 187-230, at 190.
200

who would soon leave the study of astronomy behind. 12
By the end of the sixteenth century,
Maestlin‘s Epitome was among the most popular of astronomical textbooks, along with
Christoph Clavius‘s commentary on Sacrobosco‘s Sphere.
When he began working on his own Epitome, Kepler described it as a book of
astronomical principles that he had crafted ―in imitation of the first book on the spheres by
Maestlin.‖ 13
Indeed, on the surface Kepler‘s Epitome seems much more an imitation of the work
of his teacher than of Peurbach and Regiomontanus. The title of Kepler‘s book, the Epitome of
Copernican Astronomy, is a clear reference to Maestlin‘s own textbook, with the simple addition
of the word ―Copernican.‖ Maestlin had written his Epitome as a series of questions and
answers, a format relatively unique for astronomical textbooks of the time, and one which Kepler
adopted for his Epitome as well. Also, like Maestlin‘s Epitome but unlike the Epitome of
Peurbach and Regiomontanus, Kepler‘s book was published in cheap, octavo form. Finally,
unlike many of the other textbooks widely used in the classroom, Maestlin had structured his
book as a comprehensive survey of astronomy, which included both material on the sphere and
on planetary theory, and Kepler followed this model for the content of his book as well.
Kepler‘s adoption of Maestlin‘s Epitome as a model for his own book suggests that, like
Maestlin, Kepler intended his book for the beginning student in astronomy. Indeed, like
Maestlin, Kepler made this clear at the very start of his book. In his dedication to the first three
12 See Charlotte Methuen, ―Maestlin's Teaching of Copernicus: The Evidence of His University
Textbook and Disputations,‖ Isis 87.2 (1996): 230-247.
13 KGW 16:619,‖Vellem igitur Marius refutationis suae materiam habere posset ex libello meo
de principijs astronomiae, quem ad imitationem libri primi Sphaericorum Maestlini concinnavi.‖
201

ooks of the Epitome, he explained that he conceived of the book as a summary of the new
astronomy adapted for ―children at the school-bench.‖ 14
Since, he wrote,
this science cannot be successfully learned unless those who want to reap the fruit of it as
adults can sow a seed in it as children, they should be aided by its ease of comprehension,
its low price, and the proper abundance of examples. 15
He explained his use of the question and answer format along similar lines—the style, he wrote,
was one which eliminated tedium, by diverting the reader and making the argument easier for the
beginner to follow. Books I-III of the Epitome focused on the doctrine of the sphere, something
he noted that any beginning student in astronomy would expect to learn.
Kepler admitted that there were many other books that focused on this material—
particularly the immensely popular textbook of Sacrobosco, and the textbook of his own teacher,
Maestlin. He was adding his own contribution, he explained, since ―there are varied styles of
learning, and all students are not suited to the same teacher.‖ 16
More importantly, he emphasized
that the doctrine of the sphere needed serious revision if one adopted the theories of Copernicus.
And unlike Maestlin, who left Copernican theory out of his Epitome because it was unsuited to
the beginner, Kepler maintained that Copernicanism was particularly appropriate for a beginner
text, since it made astronomical theory easier to grasp, by eliminating needless embellishments
like epicycles and eccentrics. Indeed, he argued that the reader would be inspired to adopt the
theory of Copernicus purely because of the ways in which it simplified astronomical theory.
14 KGW 7.7, 4-8: ―Quod jamdudum post edita mea de motibus stellae Martis commentaria,
suadentibus amicis, Astronomiae peritis, factitare coepi, vt novam illam Astronomiae sub
RVDOLPHO Caesare restauratae formam compendio complecterer, et minoribus quasi
subselliis accommodarem.‖
15 Ibid., 8-11: ―…vt quia non foelicius discitur haec scientia, quàm si qui fructum eius adulti
percipere cupiunt, in eâ sementem pueri faciant; simul illi et facilitate comprehensionis, et pretij
diminutione, copiâque iustâ exemplarium iuvarentur.‖
16 Ibid., 39-42: ―Nam primò etsi nihil accessisset novi ad doctrinam Veterum, tamen illam ipsam
expedit à variis authoribus tradi, cùm sint ingenia discentium varia, nec eidem omnes magistro
apti discipuli, nec idem omnibus discentibus stilus, nec eadem methodus commoda…‖
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Kepler thus not only envisioned his book as a primer due to its format and price, he saw its
content, as well, as suited toward the beginning student.
Though Maestlin had crafted a traditional, non-Copernican Epitome, he responded
positively to Kepler‘s idea of a Copernican textbook in a letter of 1616, urging Kepler only to
tread carefully, since Copernicanism had many opponents. He found more problematic Kepler‘s
contention that the book would focus on the physical causes of astronomical phenomena, like the
variations of the moon. He wrote,
I don‘t fully understand what you wrote about the moon—that you had converted all its
variations to physical causes. Moreover, I think, in the present circumstances, that one
must avoid physical causes, and that astronomical things must be handled astronomically,
through astronomical causes and hypotheses, not physical ones. For, as is clear to
everybody, the calculations demand for their support astronomical foundations from
geometry and arithmetic, not physical conjectures, which confuse the reader rather than
informing him. 17
Maestlin, it appears, understood Kepler to be aiming for a teaching text, and worried that the
novel idea of ―physical astronomy‖ would confuse Kepler‘s target readers and in this way
undermine the purpose of the book. Kepler was unwilling to abandon an idea so central to his
own conception of astronomy, yet he emphasized that the idea of physical astronomy need not
affect the status of his book as a teaching text. His approach should not confuse readers, he
contended, since he would treat astronomical things both physically and astronomically, by
clearly explaining how to compute all the motions from the hypotheses.
A surface look at the opening pages of Kepler‘s the Epitome also indicates that the book
was intended to be read by those first beginning to study the discipline of astronomy. Maestlin
17 KGW 17:744: ―De Luna quod scribis, te omnes eius varietates ad causas Physicas traduxisse:
hoc non plane intelligo. Existimo autem hîc a causis physicis abstinendum esse, et Astronomica
astronmice, per causas et hypotheses astronomicas, non physicas esse tractanda. Calculus enim
fundamenta Astronomica ex Geometria et Arithmetica, suis videlicet alis, postulat, non
coniecturas physicas, quae lectorem magis perturbant, quam informant.‖
203

had opened his Epitome with a definition of astronomy and a description of its goals; Kepler‘s
book, as well, begins with the simple question ―what is astronomy?‖ and the explanation that ―it
is a science which relates the causes of those things which appear from the heavens and the stars
to us who dwell on earth, and which produce the changes of the seasons….‖ 18
other basic questions like ―What is the relation of this science with others?‖ 19
It then raises
(In answer, Kepler
describes its relationship to physics, geography and hydrography, chronology, meteorology,
optics, geometry, and arithmetic.) The nature of astronomical observations, hypotheses, tables,
and instruments are addressed in turn. The book is filled with images, some of which are printed
multiple times, when relevant. The images often serve to further simplify the text, and though
some are sophisticated geometrical diagrams, many others are quite rough, with a whimsical
character that reinforces the idea of the Epitome as a textbook for young readers. 20
Maestlin‘s approach in his Epitome astronomiae seems to have worked; his ideas were
presented in a relatively simple manner, and his textbook was indeed popular in its time. While
the first three books of Kepler‘s textbook were the simplest and most relevant to beginners, even
here Kepler received word that his arguments, particularly the ones relating to the diurnal motion
of the earth, were too wide-ranging to fit properly in a beginner‘s Epitome. 21
By the later books,
Kepler‘s textbook clearly required a sophisticated understanding of mathematics and astronomy
and seemed particularly unsuited to the beginner. This is evident, for instance, in Kepler‘s
18 KGW 7, 23, 6-8: ―Quid est Astronomia? Est scientia, causas tradens eorum, quae nobis in
Terra versantibus de coelo et stellis apparent, Temporumque vicissitudines pariunt…‖
19 Ibid., 14: ―Quae est cognatio hujus Scientiae cum caeteris?‖
20 For a discussion of the images in the Epitome, see Pantin, Isabelle, ―Kepler‘s Epitome: New
Images for an Innovative Book,‖ in Transmitting Knowledge: Words, Images, and Instruments in
Early Modern Europe, Eds. Sachiko Kusukawa and Ian Maclean (Oxford: Oxford University
Press, 2006): 217-237.
21 KGW 7, 252, 12-13: ―…diffusior visus sum, in disputatione de motu vel quiete Terrae diurna,
quam pro ratione Epitomes.‖
204

discussion of the thorny issue of lunar theory, with which he had struggled for years before
explicating it for the first time in the Epitome. In addition to explaining how the earth, and not
just the sun, could also take on the role of a central body in a planetary system, Kepler also had
to explain the lunar inequalities, not present in other planetary motions. 22
In describing the
effects of sunlight on the motion of the moon, Kepler noted that ―no part of celestial physics was
more difficult than this to explain.‖ 23
Notably, these issues would be of interest to practicing
astronomers, but were far too complex and specialized to be included in a typical course of
astronomy for beginning students. Indeed, Kepler‘s Epitome did attract a great deal of notice
among advanced astronomers and mathematicians, who cited it often, particularly after the
publication of the Rudolfine Tables. 24
We might simply conclude that Kepler‘s book missed its intended mark, but had an
important impact nonetheless. This may very well be part of the story, but it is not the full story.
For Kepler‘s comments framing the book as a teaching text for the unlearned student were all
made early on, either while he worked on the first sections of the Epitome, or surrounding the
publication of Books I-III in 1618. By contrast, Kepler himself portrayed the texts quite
differently with the publication of the later Books in 1620 and 1621. This suggests that
something happened to alter his conception of the text between the first and the last stages of the
publication. Indeed, two highly significant events that directly affected Kepler‘s work on and
conception of the Epitome occurred in just those years. The first was banning of the book by the
22 For a detailed description of some of the more complicated issues in the later books of the
Epitome, and for a step-by-step explanation of his account of lunar theory in particular, see
Stephenson, 173-201.
23 KGW 7, 322, 33
24 See Russell, ―Kepler‘s Laws of Planetary Motion.‖
205

Congregation of the Index in Italy, an occurrence which seemed to take Kepler completely by
surprise.
Kepler, Ingoli, and the Banning of the Epitome 25
From his home in Linz, Austria, Kepler struggled to keep abreast of developments in the
Republic of Letters. He was interested particularly in developments in Italy, and he solicited his
friends for news, noting that ―we Germans lack letters relating to Italy.‖ 26 In September of 1617,
Kepler wrote to Thomas Mingonius, chief physician for the Imperial court in Prague, asking for
news of a rumored Church decree against Copernicanism. Though Mingonius had extensive
contacts in Italy, he responded that he knew ―nothing about the pope having made a new decree
against philosophical teachings and the liberty of philosophers.‖ 27
He promised to send more
news if he heard anything further, and urged Kepler to send him an opinion on the question of
the motion of the earth in the meantime. Two months later, another letter from Mingonius
finally clarified the situation in Italy. Mingonius wrote of a friend in Padua who was interested
in selling copies of Kepler‘s latest ephemerides on the Italian market. However, before doing so
he had asked to see whatever parts of the ephemerides referred to philosophical matters, ―lest the
theologians introduce some impediment to selling it, and harm to the seller.‖ ―For in Italy,‖
25 Much of the correspondence detailed in this section is also described by Massimo Bucciantini
in Contro Galileo : Alle Origini Dell‘Affaire (Florence: Leo S. Olschki, 1995). Bucciantini also
provides a transcription and an Italian translation of Ingoli‘s Replicationes.
26 KGW 17:810: ―Literae enim apud nos Germanos…carent Italico.‖ The problem was mutual,
for Kepler‘s works were very difficult to obtain in Italy. As Vincenzo Bianchi wrote to him in
1619, ―your works cannot be found without great labor in either Venice or in Rome, or in the
other flourishing cities of Italy. For my part, if I wanted your Ephemerides, I would have to
write to Frankfort.‖ (―Mirum dictu, nec Venetijs, nec Romae, nec florentibus alijs in urbibus
Italiae, Opera tua nisi maximo labore, uel casu reperiri. Mihi, tuas si ego uolui Ephemerides,
fuit necesse scribere Francfordiam.‖ KGW 17:825.)
27 KGW 17:768: ―Nihil scio quod summus Pontifex decreuerit aliquid de nouo contra
Philosophica dogmata, et libertatem philosophorum.‖
206

explained Mingonius, ―certain limits have been established for philosophers, beyond which a
Catholic is not able to wander by law.‖ 28
Though the Church‘s formal condemnation of the
Copernican system had been issued in March of 1616, this was the first real confirmation that
Kepler received of it.
In his letter, Mingonius requested once again that Kepler send him an opinion on the
Copernican doctrine. In particular, he sent Kepler a tract against the motion of the earth written
by ―an Italian mathematician and theologian,‖ and he asked Kepler to tailor his response directly
to the objections made there. The document in question was Francesco Ingoli‘s Disputatio de
situ et quiete terrae contra Copernici systema, which sought to counter the Copernicanism of
Galileo by arguing for the rest and centrality of the earth. Ingoli was a consultant to the
Congregation of the Index in Rome, and he composed his Disputatio after Galileo‘s visit to
Rome, in which Galileo had argued forcefully for the Copernican system. 29
Ingoli framed this
Disputatio as an open letter to Galileo, a continuation of the oral conversations that took place in
Rome; he asked Galileo to respond to the text ―for the investigation of the truth‖ and prove him
wrong by refuting the anti-Copernican arguments he has offered. 30
Galileo responded to Ingoli
in a brief letter of 1624, but did not fully take up the challenge until the publication of his 1632
Dialogi. By contrast, Kepler, upon reading the Disputatio, decided to act the role of Copernican
defender himself. He composed a Responsio ad Ingoli Disputationem de Systemate, which he
returned to Mingonius along with several copies of the newly printed first three books of the
28 KGW 17:772: ―…vellet libenter eam partem Ephemeridum uidere quae discursus et res
philosophicas continet ne fortasse a Theologis aliquod impedimentum et damnum emptori
inferatur. Nam in Italia sunt quidam limites philosophis conclusi, extra quos catholicus non
potest iure expatiari et iustissimas ob causas.‖
29 On Galileo‘s debates in Rome, see William Shea, Galileo in Rome: The Rise and Fall of a
Troublesome Genius (Oxford: Oxford University Press, 2003).
30 See Bucciantini 97.
207

Epitome of Copernican Astronomy. 31
In the Responsio Kepler adopted Ingoli‘s division of his
criticism into mathematical, physical, and theological problems and responded to each in kind. 32
He made frequent reference to the arguments of the Epitome, often pointing directly to page
numbers in the Epitome where he felt he had definitively settled some of the challenges to
Copernicanism posed by Ingoli‘s Disputatio. Upon receiving Kepler‘s response, Mingonius
promptly forwarded the Responsio and a copy of the Epitome itself both to Padua and to Rome,
to be read by Ingoli. 33
At the same time, Kepler wrote directly to Vincenzo Bianchi, one of his Venetian
correspondents, asking for more information on the Church‘s position. Kepler worried for his
newly printed Epitome and still more for his forthcoming Harmonice Mundi, a book which he
saw as the culmination of all his efforts thus far. He wanted to know whether the Harmonice
Mundi could be printed in Italy, for though it didn‘t have a special ecclesiastical license, it was
printed with the Imperial privilege. Moreover, he explained, there was nothing in it which was
contrary to Catholicism. In fact, he had asked some of the Catholic advisors at the Imperial court
to review the book, and they had concluded that there was nothing theologically problematic
about it. He added that they had reached this conclusion despite the fact that—as he had heard—
elsewhere opposition to Copernicanism had been registered in a churchly censure, though that
censure was ―still private.‖ 34
Kepler, it seems, still did not fully comprehend the nature of the
31 For the text of the Responsio, see KGW 20.1, 168-180.
32 By contrast, Galileo in the Dialogi only responded to the mathematical and physical
arguments, claiming that the theological ones ―are not subject to refutations but are liable only to
interpretations.‖ See Maurice Finocchairo, The Galileo Affair: A Documentary History
(Berkeley: University of California Press, 1989), 155.
33 See KGW 17:792.
34 KGW 17:810: ―Verum rogati super hoc Consiliarii Aulici Caesarei Catholici negarunt videri
contra Catholicam quod naturalibus rationibus salvis superioribus et supernaturalibus
208

church ban on the Copernican doctrine, and viewed it as a private matter still being deliberated.
He also noted that the Harmonice Mundi was not the only book of his that made Copernican
arguments—the same could be said of the Astronomia Nova, the Optics, the De Stella Nova, and
the Epitome. Yet these books had not attracted any negative attention on the part of Italian
theologians, so perhaps there was no need to worry for the Harmonice Mundi either.
Bianchi replied with both bad and good news. The bad news, he explained, was that the
church was very serious in its opposition to Copernicanism. Since the office of the censor was
―in a fury,‖ he advised Kepler to omit any further mention of the Copernican system, lest his
books be attacked by those in Rome. 35
Yet he also reassured him that though books of
―illustrious German authors‖ like Kepler had been banned, they were ―nevertheless secretly sold,
and read attentively.‖ 36
A future ban on Kepler‘s books, that is, might actually increase interest
in them and cause them to circulate more widely, though secretly. This news did little to comfort
Kepler. Bianchi‘s letter had finally conveyed to him the gravity of the Copernican situation in
Italy. ―I see that you, from whom nothing can remain secret, also mention that the decree of the
censor is edited and published,‖ he wrote, ―and otherwise I had believed until now that it was in
deliberation, and had not yet been reinforced by the authority of the Pope.‖ 37
He was in a
quandary as to the best course of action at this point. Should he, he wondered, actively take up
the Copernican crusade, acting ―as an advocate of Copernicus to the censors, and moreover an
disputatur de motu terrae, licet haec sententia nuper notata fuerit aliqua censura, sed quae sit
adhuc privata.‖
35 KGW 17:825: ―Quoniam recens est in Copernicum animaduersio, et feruescente adhuc
censura, ne libri mutilarentur Romae, praetermitterem hanc quaestionem.‖
36 Ibid.: ―Illustrium tamen Authorum Germanorum libri, etsi quandoque uetantur, clam
nihilominus uenduntur, et attentius leguntur.‖
37 KGW 17:827: ―De motu Terrae maior difficultas, cum videam censuram editam et publicatam
etiam a te ipso perhiberi, quem nihil horum latere potest. Atqui secus ego credideram adhuc
illam in deliberatione esse, necdum Summi Pontificis authoritate roboratam.‖
209

advocate of his disciples, not even for myself or for Germans, who do not follow the Roman
Church, but for Italians, are subject to another Roman one‖? 38
Or should he remain silent, lest he
attract the attention of the censors to his own books, which had so far escaped their notice?
This question was posed a bit late, however. He soon received yet another letter from
Italy, this one from Johannes Remus Quietanus, a German physician and astronomer who had
studied in Padua and then moved to Rome. Remus wrote with the news that ― your Copernican
book‖ had been placed on the Index of Forbidden Books, and that as a result Galileo had been
unable to obtain a copy to read. 39
Kepler responded first to Remus‘s description of the book. ―I
don‘t completely understand which Copernican book you speak of,‖ he wrote, ―for all of my
books are Copernican, even the prologues of the ephemerides. Moreover, the Harmonica is not
yet published…I therefore suspect that your discussion was about the Epitome of Copernican
Astronomy.‖ 40
Kepler begged Remus for the exact wording of the censure, and wondered
whether the ban might be applied in Austria as well, making it extremely difficult for him both to
earn a living and to practice the kind of astronomy that depended on ―the freedom of
philosophy.‖ 41
38 Ibid.: ―…quid si advocatum agerem Copernici ad censores, aduocatum etiam eius
discipulorum; non meum quidem aut Germanorum, qui Romanam Ecclesiam non sequuntur, sed
Italorum, qui alii Romanae subsunt….‖
39 KGW 17:845: ―Desiderat Galilaeus habere librum tuum Copernicanum quia est prohibitus et
Florentiae non haberi potest, unde petijt a Serenissimo nostro eundem librum, se enim facile
habiturum licentiam asserit.‖
40 KGW 17:846: ―…nec satis capio, quem tu librum Copernicanum dicas; omnes enim mei sunt
Copernicani, etiam Ephemeridum Prolegomena. Harmonica quidem nondum sunt
edita….Suspicor igitur, de Epitoma Astronomiae Copernicae tibi sermonem esse.‖
41 Ibid.: ―Quin imo dabitur mihi intelligendum, renunciandum mihi professioni Astronomicae,
postquam jam fere consenui in hujus dogmatis doctrina, nemine tamdiu contradicente
tandemque renunciandum ipsi provinciae Austriae, si in ea non sit futurus locus libertati
philosophicae.‖
210

Kepler‘s suspicion that the ―Copernican book‖ of Remus‘s letter was his Epitome was
accurate. The Epitome had been recently reviewed for the Congregation of the Index by
Francesco Ingoli, who wrote up the official formula of censure in 1619. It is highly likely that
Kepler inadvertently set the ban in motion by responding to Ingoli‘s Disputatio with a heavy
reliance on the Epitome, and indeed, by sending along a copy of the Epitome itself to further the
argument. Once he received both the Responsio and the Epitome, Ingoli wrote a response of his
own, the Replicationes de situ et motu terrae. The Replicationes made frequent reference to the
arguments of the Epitome, and was the precursor to the formal ban on the text. Ingoli was not
wholly unsympathetic to Kepler; he began his censure by noting that the Epitome‘s author
seemed an upstanding sort of fellow, who ―although of the highest integrity in character, has
unfortunately been deceived by the ministers of Luther and is held prisoner in the heresy of
Luther.‖ 42
Ingoli seemed somewhat well-disposed not only to Kepler himself but to the Epitome as
well, which he described as ―most curious and beautiful.‖ 43
He summarized the content of the
Epitome, both the first three books, already published, and the promised books to come. He then
noted that the reason for the book‘s prohibition lay in two errors which it put forth. The first was
its Copernicanism—Kepler, wrote Ingoli, not only ―believes and defends as very true the system
of Copernicus concerning the position and motion of the earth, against the sacred scriptures and
42 ―Author ut audivi, licet summa quoad mores vivat integritate, miserabiliter a Ministris
Lutheranis deceptus in haeresi Lutheri detinetur.‖ Quoted in Pierre-No l Mayaud, La
Condamnation des Livres Coperniciens et sa Révocation à la Lumi re de Documents Inédits des
Congrégations de l'Index et de l'Inquisition (Rome: Editrice pontificia Universitata Gregoriana,
1997), 64-67. Ingoli‘s attitude toward Kepler here is similar to that of many of Kepler‘s other
Catholic acquaintances, who often greatly admired him despite their disagreements and struggled
repeatedly to convert him to Catholicism. See, Chapter 2 of this dissertation, as well as M. W.
Burke-Gaffney, S. J., Kepler and the Jesuits (Milwaukee: The Bruce Publishing Company,
1944).
43 Ibid.: ―Liber curiosissimus et pulcherrimus est.‖
211

the determination made by this sacred congregation,‖ 44 but did so likely with the full knowledge
of the Church‘s prohibition, since the book was published two years after the 1616 condemnation
of Copernicus. (Ingoli was wrong here; as we saw earlier, Kepler did not become aware of the
Church‘s prohibition until after he had published the first books of the Epitome.) Ingoli
described how Kepler had attempted to avoid the scriptural problems with Copernicanism by
arguing that Scripture spoke according to the appearances of things to humans, rather than
according to the truth of things, and how Kepler had not only defied the Church, but ―with
obscure words insults theologians and all those scholars who condemn the theory of Copernicus
as false.‖ 45
The second error pointed to by Ingoli was the fact that Kepler had adopted one of the
ancient errors of Origen, condemned by the fifth general council of Constantinople—namely, ―he
asserts that the sun is animate.‖ 46 This error, Ingoli emphasized, had cropped up with increasing
frequency in recent years, and Ingoli himself had ―several times had the opportunity of debating
against those who hold that the heavens and the heavenly bodies are animated by a soul and
intelligence.‖ 47
Ingoli therefore emphasized that the Church ought to deal with the matter
44 Ibid.: ―…systema Copernici de situ et motu terrae ut verissimum credit et defendit contra
scripturas sacras et determinationem factam ab hac Sacra Congregatione de qua verisimile est
quod notitiam habuerit, quia liber est impressus post prohibitionem Copernici anno secundo ut
ego existimo.‖
45 Ibid.: ―…obscuris verbis suggillat theologos, et quoscumque literatos damnantes dogma
copernici, ut falsum.‖
46 Ibid.: ―Secundus error, quod solem asserit esse animatum pag. 126, quod se probaturum in
theoricis pollicetur.‖
47 Ibid.: ―Quem errorem apud aliquos etiam 67 adhuc pullulare scio, cum non semel mihi
occasio evenerit disputandi contra tenentes coelos et corpora colestia animata esse anima et
intelligentia.‖
212

expeditiously, ―so that innovating natural philosophers, of whom today there are many, are
prevented from progressing further.‖ 48
It seems, from the wording of Ingoli‘s censure, that he was most concerned with the
second error. 49
After all, Ingoli was aware of the merits of Copernicanism as an astronomical
theory, though he disagreed with it as a true description of the heavens. He had personally
emphasized to the Congregation of the Index that the book of Copernicus ―was very useful and
necessary to astronomy and on account of this sought after by all,‖ and for this reason he had
proposed ―that it could be corrected and emended, in order that thus emended and corrected it
could afterward be permitted.‖ 50
The fact that he urged the outright banning of Kepler‘s book,
rather than its suspension donec corrigatur, as was the case with the De revolutionibus, likely
owed much to Kepler‘s belief in the ensouled sun, an error which Ingoli believed was gaining in
prominence.
Remus seems not to have read the specific formula of censure, however, and he
confirmed Kepler‘s suspicions that the book would only be prohibited
because of the fact that it may speak against a decree of the Holy Office from two years
ago, whose cause was a certain devout Neapolitan [Foscarini] 51 who was spreading this
48 Ibid.: ―…unde non esset fortasse extra propositum de hac mature deliberare, ut praecludatur
via novatoribus physicis quorum magna hodie est copia, ulterius progrediendi.‖
49 See Mayaud, 68-69, who also emphasizes the significance of this second error to the specific
banning of the Epitome.
50 Notes from the meeting of the Congregation of the Index of April 2, 1618: ―…in qua facta
prius relatione per Illustrissimum Dominum Franciscum Ingolum, qualiter liber Copernici jam
prohibitus (eo quod falso asserat terram mobilem et coelum immobilem) valde utilis et
necessarius ad Astronomiam erat atque ob id ab omnibus desideratus, ob idque proposuit ipse
modum aliquem ab eo excogitatum quomodo corrigi atque emendari posset, ut sic emendatus et
correctus permitti postmodum valeat.‖ Cited in Mayaud, 56.
51 Paolo Antonio Foscarini (1565-1616), provincial head of the Carmelites in Calabria, had
published a work in Italian entitled ―Letter concerning the Opinion of the Pythagoreans and
Copernicus about the Mobility of the Earth and Stability of the Sun, and about the New
Pythagorean System of the World,‖ intended as a theological defense of Copernicanism. When
Copernicanism was banned in 1616, Foscarini‘s book was immediately placed on the Index. See
213

opinion among the public through vernacular writing, which gave rise to dangerous
consequences and opinions, while at the same time Galileo was urging his cause at Rome
with too much inflexibility. And in this manner Copernicus was corrected, at least in the
beginning of his first book for a few lines. 52
Remus emphasized here that the Holy Office decided to ban Copernicus not only for the content
of his books but also for the manner in which his ideas were propagated by his followers. Remus
highlighted the fact that Foscarini had chosen to advocate for Copernicus by writing in Italian,
clearly targeting a broad public audience, not simply learned men who would be used to reading
their books in Latin. The fact that Foscarini sought to publicize Copernican theories more
broadly had led to ―dangerous consequences and opinions‖ among the unlearned masses.
Likewise, with his claim that Galileo argued for Copernicanism ―with too much inflexibility,‖
Remus blamed Galileo primarily for his uncompromising and fractious attitude—he implied that
had Galileo proceeded more modestly, both in his personal attitude toward his opponents and in
his attitude to Copernican theory more generally, things may have gone differently. 53
Remus was right to emphasize the significance of Foscarini‘s vernacular defense of
Copernicanism. The censors of the Index generally tried to effect a clear demarcation between
high and low culture, and popular or scholarly audiences. Worried that the unlearned layman
might be easily corrupted by problematic vernacular content, for instance, the Index was willing
Richard J. Blackwell, Galileo, Bellarmine, and the Bible (Notre Dame: University of Notre
Dame Press, 1991), 217-251 and Maurice Finocchiaro, Defending Copernicus and Galileo:
Critical Reasoning in the Two Affairs (Dordrecht: Springer, 2010), 76-79.
52 KGW 17:848: ―…nec alio modo ut credo prohibitus erit iste liber quam quod Contra Diploma
Sancti Officij ante biennium affixum loquatur (In causa erat quidam Religiosus Neopolitanus qui
Italice spargebat in vulgus hanc opinionem publico scripto unde periculosae consequentiae et
opinones nascebantur, tum Galilaeus etiam nimis rigorose causam suam pertractabat eodem
tempore Romae). Eodem modo et Copernicus correctus est saltem in principio primi libri per
aliquot lineas.‖
53 Giucciardini, the Tuscan ambassador to Rome, also emphasized the negative effects of
Galileo‘s attitude, and wrote to the Secretary of State Curzio Picchena in Florence asking him to
recall Galileo to Florence and end ―his determination to castrate the friars.‖ See Shea, 92-93.
214

to allow Ovid‘s Metamorphoses to be printed in Latin, but not in Italian—who was to know how
the simple reader might be confused by its messages? 54
It was not the idea of the vernacular
itself that troubled the censors, but the kinds of men who might be reading the vernacular
editions of texts. Scholars typically read in Latin, and their manner of reading was sophisticated;
they could be trusted to take from Ovid his important stylistic contributions, and to reject his
pagan lessons. The uneducated reader could not necessarily be trusted to make this kind of
distinction. Likewise, censor Francisco Pena allowed an expurgated version of Jean Bodin‘s
1580 Denonomanie des Sorciers to be printed, but refused to allow the vernacular version of the
text any such leniency. Such a version might fall into the hands of the unlearned, and of women,
in particular, who could easily fall prey to the appeal of the forbidden ideas described by Bodin.
At the same time, however, the censors of the Index were well aware that vernacular
editions were typically more limited in their reach than Latin editions of the same text. Though a
vernacular text might reach a larger group of people within a particular region, it was usually
unable to travel beyond that region. Latin, by contrast, was an international language with a far
reach; though only scholars could typically understand it, it could be read by scholars in England
and France, the Holy Roman Empire and Italy alike. Even such educated men would likely not
know the vernacular tongues of other lands—there simply was no need for them to do so. For
this reason, in some instances the censors might deem a Latin version of a text more dangerous
than its vernacular counterpart, if it was clear that the vernacular would reach few readers. In
this case, they might simply ignore the vernacular text or ban it without much enforcement,
while taking great care to either correct the Latin version or ensure that the ban on it was
54 Peter Godman, The Saint as Censor: Robert Bellarmine between Inquisition and Index
(Leiden: Brill, 200), 157.
215

enforced. 55
In all cases, the Church censors responsible for evaluating texts were guided by a
keen sense of audience. They tried at once to ensure that dangerous ideas would stay away from
unwary and vulnerable lay audiences, and that Latin texts with international reach would convey
only the ideas that the Church deemed appropriate for mass consumption.
Finally, the Church had an additional way that it distinguished between high and low
culture, and lay and scholarly audiences. While books with dangerous ideas were generally
prohibited, the Church was willing to grant reading licenses for specific prohibited books to
scholars and experts, so long as they were ―respectable men, renowned for their piety and
scholarship.‖ 56
Such people, even more than the general Latin-reading public, might be trusted
to take from those books ideas that were relevant to their own studies, while rejecting the ideas
that the Church had deemed problematic. After noting that the ban on Copernicanism had
initially been linked to the problem of the vernacular, Remus referred to this policy in particular
and tried to reassure Kepler about the future of his Epitome. Despite the official prohibition of
all things Copernican, Remus noted, Copernican books continued to circulate, as could Kepler‘s
own book. He explained that Copernican books,
and your book the Epitome also, I think, can be read with a license by scholars and
experts in this science, in Rome and throughout Italy. Therefore there is no reason why
you should be afraid, either about Italy or Austria. Only keep yourself within your limits,
and control your emotions. 57
Kepler could avoid the pitfalls of Foscarini if he directed his book toward these sorts of men,
rather than a public who might read his ideas with ―dangerous consequences.‖ Though the book
55 Ibid.. 226.
56 Frangnito Gigliola, ―The Central and Peripheral Organization of Censorship,‖ 46, in Church,
Censorship and Culture in Early Modern Italy, ed. Gigliola Fragnito, trans. Adrian Belton
(Cambridge: Cambridge University Press, 2001).
57 Ibid.: ―…possunt tamen ijdem et hic quoque liber (uti puto) Epitome scilicet legi cum licentia
a doctis et peritis in hac arte Romae et per totam Italiam. Vnde non est quod tibi timeas nec in
Italia nec Austria modo intra tuos limites te contineas, et affectibus proprijs imperes.‖
216

might not be permitted to beginning students without the real power of discernment, scholars and
experts in astronomy might be trusted to use it wisely. Finally, Remus reminded Kepler of the
advice of the Stoics—all would be well, he claimed, if Kepler would only stay within his limits
and control his emotions, in contrast to the behavior of Galileo that had started the trouble to
begin with.
The New Italian Targets of the Harmonice Mundi and the Epitome
The news from Bianchi about the severity of the Copernican ban in Italy, and the news
from Remus about the banning of the first three books of the Epitome, both coincided with the
impending publication of Kepler‘s Harmonice Mundi, the culmination of his life‘s work. Kepler
worried that the book, which also contained many arguments for the theories of Copernicus,
might raise the ire of the censors in Italy. In a letter to Bianchi, Kepler discussed ways that he
might forestall this possibility. He considered addressing the Copernican ban directly at the end
of the Harmonice Mundi, or perhaps printing a separate letter addressing the ban. 58
Bianchi
urged him not to address the ban in the book itself, as this would only raise the interest of the
censors and open the book to further criticism. Rather, Bianchi advised Kepler to restrict his
defense of Copernicanism to isolated individuals, and noted that as a general rule, ―I would
ignore in silence that which has been done with so much noise in Rome.‖ 59
Taking the advice of Bianchi and adopting the more circumspect approach, Kepler left
the issue unaddressed in the Harmonice Mundi itself, and composed a short letter directly to the
booksellers of Italy, labeled an Admonitio ad Bibliopolas exteros, praesertim Italos drucken zu
58 See KGW 17:827.
59 KGW 17.834: ―Dissimularem silentio quae tanto Romae sunt acta rumore. Satis est,
superque, caussam suam coactos sustinere.‖
217

lassen und auszusenden. He printed the letter on a sheet of paper, which was to be inserted
directly into the copies of the Harmonice Mundi. In the letter, Kepler appealed to the booksellers
as fellow Christians and lovers of philosophy. He began the letter by describing himself as ―a
German man, [writing] with typical German outspokenness.‖ 60
Yet despite this, he argued, he
was still ―a Christian, a son of the church; and I not only willingly embrace Catholic doctrine
insofar as I am able to understand it at this point in my life, but I also judge it to be true.‖ 61
The
booksellers should rest assured, therefore, that his books would not contain anything which
would provoke the anger or censure of the church—anything, that is, beyond the argument about
the motion of the earth.
Addressing this contentious issue directly, Kepler noted that the Church had deemed
Copernicus unproblematic at the start—the book was, after all, dedicated to Pope Paul III—and
that he, a disciple of Copernicus from the age of 26, had only recently learned of the Church‘s
decision to ban the book ―donec emendetur.‖ He wrote, alluding to Remus‘s letter, that the door
had not been permanently barred against Copernicus—there were ―men from the most illustrious
orders, political and ecclesiastical, who direct astronomers to hope well: they insist that this
censure is neither enforced, nor does it seek to oppose the freedom to debate concerning purely
natural things and to illustrate the works of God.‖ 62
Indeed, wrote Kepler—abandoning his
typical modesty—the ban on Copernicanism may well have been partly his own fault, for he had
delayed too long in the production of his own books, in this way depriving Copernicus of a
60 KGW 6, Nachbericht, #296, 543-544: ―Scripsi haec homo Germanus, more et liberate
Germanicâ.‖
61 Ibid.: ―Christianus tamen sum, Ecclesiae filius, et doctrinam Catholicam, quantum ejus ad
hanc usque meam aetatem capere potuj, non voluntate tantum amplector, sed et judicio
comprobo.‖
62 Ibid.: ―Quanquam non desunt virj ex clarissimis ordinibus, politicis et Ecclesiasticis, qui
Astronomos bene sperare jubeant: eo quòd nec perlatam hanc censuram, nec libertatj disputandj
de rebus mere naturalibus illustrandique Dei opera oppositam pro repagulo dictitent.‖
218

suitable defense. 63
For if those who opposed Copernicus would read Kepler‘s books, and
particularly if they understood the full harmonic argument laid out in his Harmonice Mundi, they
would undoubtedly recognize the true majesty of the sun-centered heavens, and realize that
―Copernicus could by no means sufficiently be understood before the promulgation of this
work.‖ 64
Copernicus thus required a new judgment, one which took into account the
explanations which Kepler himself had provided too late.
Kepler entreated the booksellers to aid him in his task because of their own dedication to
true philosophy. He reassured them that they would not need to contravene the ban by the
Church by selling his books to just anybody. Instead, he urged, ―sell copies to no one except the
highest theologians, the most famous of philosophers, the most practiced of mathematicians, the
most profound of metaphysicians.‖ 65
The latter categories, wrote Kepler, would be able to use
his books to consider whether the ideas of Copernicus were mere fictions or were drawn out
from nature itself; the theologians would use them to decide whether the glory of God revealed
through Copernican theory would be best served spread among the public or suppressed by
decrees of censorship. Indeed, the church had already handed over the matter of Copernicus to
its mathematicians, asking them to emend it appropriately. Kepler was certain, he wrote, that
after reading his books it would be clear even to the Church‘s mathematicians that the
miraculous harmony he had described could not be maintained if one substituted the motion of
the earth for the motion of the sun.
63 Ibid.: ―…culpam ego meam ingenue fateor, qui cunctatione nimia meorum operum
Philosphiam defensione suâ destitutam praeveniri sum passus.‖
64 Ibid.: ―…tantam esse majestatem, tantam sublimitatem hujus Operum divinorum dispositionis
Harmonicae ut Copernicus ante promulgationem hujus operis sufficienter audiri nequaquam
potuerit.‖
65 Ibid.: ―…itaque vendetis exemplaria non nisj Theologis summis, non nisj philosophorum
clarissimis, Mathematicorum exercitatissimis, Methaphysicorum profundissimis.‖
219

In his Admonitio to the Italian booksellers, we see Kepler forcefully advancing the notion
that his books were targeted toward expert rather than lay readers. Kepler argued that his books
should only be sold to those with the skill and learning to appreciate them—to scholars skilled in
their respective disciplines, who could properly evaluate how those disciplines were addressed in
his books. This emphasis on expert readers was clear to Bianchi, to whom Kepler forwarded a
copy of the Admonitio. Like Ingoli, Bianchi noted the two issues in Kepler‘s works which might
raise the ire of the Church—the motion of the earth and the idea that the heavenly bodies were
animate. Bianchi, who enthusiastically agreed with both ideas, worried that Kepler would be
prevented from promulgating them because of the foolish reaction of unlearned readers, and
urged Kepler to avoid that scenario. ―What?‖ he asked rhetorically, ―because the rough and
unlearned do not easily grasp your lessons, you may not teach the wise either?‖ 66
Kepler ought
to follow the example of Aristotle, who ―wrote the books of Physics not for the dull Greek
public, but for the special philosophers of Athens.‖ 67
He was pleased to see, he noted, that
Kepler already intended to target his Harmonice ―not toward the common men, but toward the
best among them, which…you indicated in your admonition to the booksellers, full of eloquence,
dignity, and religion.‖ 68
Though Bianchi approved of Kepler‘s target readers as articulated in the Admonitio, it is
doubtful that Kepler himself really wanted to reach only so narrow an audience. It was rather
Kepler‘s habit to cast a very wide net in his Copernican campaign, targeting experts and general
66 KGW 17:834: ―Quod, quia documenta non facile capient tua rudes, et indocti, tu propterea
sapientes non magis edoceas?‖
67 Ibid.: ―Aristoteles Physicorum libros non ad stolidum Graeciae uulgus, sed ad praecipuos
Athenarum Philosophos scripsit.‖
68 Ibid.: ―Sic tu, non uulgaribus hominibus, sed summis uiris Harmonicorum uolumina
mandabis. Quod iam uideo te ipsum annuisse in tua Admonitione ad Bibliopolas, plena
eloquentiae, plena grauitatis et religionis.‖
220

eaders alike. As we saw in the previous chapter, Kepler openly speculated on the best ways to
convert the lay public to the Copernican worldview, and fashioned specific strategies to not only
the scholarly elite but also the vulgus and the moderately learned to the side of Copernicus. He
included Copernican speculations in the prefaces to his annual Ephemerides, books clearly
targeted toward a general, rather than a scholarly audience—a decision for which he was
criticized by Michael Maestlin, who believed that such material should be reserved for the
learned. 69
As the Harmonice Mundi was the culmination of his efforts to explain and promulgate
Copernican theory, it is unlikely that Kepler would have wished to restrict the book only to
expert practitioners. On the contrary, in the Harmonice Mundi itself he explicitly addressed a
general audience. ―I wish I could have made my discussion still more popular,‖ he wrote,
―provided that it was also clearer and more accessible…I relate geometrical materials in a
popular way.‖ 70 He encouraged his readers to continue on with the book even if they had no
expertise in the materials; they should not, he exhorted, ―be frightened off by the difficulty of the
geometrical arguments and deprive themselves of the very great enjoyment of harmonic
studies.‖ 71
Only in the Admonitio to the booksellers of Italy did Kepler specifically emphasize
that his book was intended for experts alone.
Unlike Copernicus‘s dictum that ―mathemata mathematicis scribuntur,‖ therefore,
Kepler‘s emphasis on expert readers did not stem from any deeply held belief. Rather, his
articulation of his target audience was a specific response to a difficult situation. Faced with the
banning of Copernican books in Italy, Kepler was in a quandary. How could he assure that his
books would reach their targets, and not incur the wrath of the Church? Kepler, it appears, took
69 See KGW 13:210.
70 The Harmony of the World, Ed. E.J. Aiton, J.V. Field, and A.M. Duncan (Philadelphia:
American Philosophical Society, 1997), pp. 14-15.
71 Harmony of the World, 15.
221

the advice of Remus to heart. Remus had urged him to keep himself within bounds, and had
noted that the Church willingly granted licenses for prohibited books to scholarly readers. In
reaching out to an audience in Italy, then, Kepler made the practical decision to target not
beginners and students but rather specialists. He performed his own act of censorship, in other
words, not on the text itself but rather on the text‘s framing, reorienting it toward a far more
limited public. 72
This reorientation would serve two purposes: first, very simply, these were the
only individuals who could conceivably obtain licenses to read the book in the first place. Better
a limited number of readers, in other words, than no readers at all. But equally important, Kepler
hoped that by reaching out to those at the top and explaining the true meaning of Copernican
theory, he could convert his readers to the Copernican view, or at least alleviate some of their
concerns about it. He would, as he had mentioned earlier in his letter to Bianchi, act as
Copernicus‘s advocate for the censors in Italy. His hope was that this would result in the
eventual lifting of the ban on Copernican texts.
That Kepler‘s targeting of expert readers was a conscious response to the situation in
Italy comes through even more clearly when one considers the Epitome. The Admonitio to the
Italian booksellers, focusing on the Harmonice Mundi, was written after Kepler learned of the
Copernican ban. Yet the first books of the Epitome were written before Kepler worried about the
reception of his books in Italy, while the later books were published after he had learned of the
72 As Amnon Raz-Krakotzkin has noted in his discussion of early modern censorship more
generally, ―Various kinds of relations existed among the various agents—the author, the editor,
the bookseller, the censor, and the reader—which together determined the boundaries of
readings. These relations also generated strategies of writing and a series of ‗subterfuges‘
designed to create ambiguity while reshaping the codes of the reader. The dialectics of
censorship is based on the mutual relationship between all of these actors—the various agents
shaping the text and the different readings possible in a particular context.‖ See The Censor, the
Editor, and the Text: the Catholic Church and the Shaping of the Jewish Canon in the Sixteenth
Century (Philadelphia: The University of Pennsylvania Press, 2007), 9-10.
222

Copernican ban, and in particular, after he had learned of the banning of the Epitome‘s first
books. Crucially, we see a clear about-face in Kepler‘s description of the target readers of the
Epitome between the first three books and the later books, with the first books framed as sections
of a textbook for young and unschooled readers, and the later ones framed as texts intended
specifically for experts.
As noted above, Kepler made it clear in the opening of the first books of the Epitome that
he intended the book as a teaching text for beginning students. There, he further emphasized his
desire to reach a general audience, specifically so that he might convince them of the truth of
Copernican theory. ―I understand with certainty that I have this duty…to defend [Copernicus]
openly to my readers with all the powers of my talent,‖ he wrote in the preface to Book I of the
Epitome. 73
possible.‖ 74
―…Therefore I dedicate the work to this: that I might persuade as many people as
Kepler viewed all his books, as we have seen in the previous chapters, as persuasive
arguments for the truths of Copernicanism. The Mysterium Cosmographicum, his first book,
furthered the Copernican cause by relating Kepler‘s own discovery, while his Dissertatio with
Galileo‘s Siderius Nuncius and his subsequent Narratio and Dioptrice did the same by providing
support for the discoveries of Galileo. In writing these books, Kepler had endeavored to reach
both a lay and a scholarly audience; indeed, he had discussed with Galileo as early as 1597 the
best ways that a lay audience might be swayed to the Copernican cause, and he had fashioned his
Dissertatio as a text that might begin to do so. Yet he recognized that there was no book that the
non-expert reader might turn to for a general introduction to the principles of Copernican
astronomy, aside from Copernicus‘s own De revolutionibus, which itself was quite unwieldy.
73 KGW 7.8, 26-29: ―ego certe hoc illi officii me debere intelligo…eandem etiam foras ad
lectores omnibus ingenii viribus defendam.‖
74 Ibid., 43-44: ―…eoque id operam do, ut quod in re inest, quamplurimis persuadeam..‖
223

He envisioned his Epitome of Copernican Astronomy at the start as just such a book; through it,
he might acquaint the beginning student with the rudiments of Copernican astronomy. In so
doing, he would not only begin the project of converting the larger lay public to the Copernican
cause, but also potentially transform some of that public into an audience better positioned to
judge the Copernican claims on their merits. Through the Epitome, that is, he might reach
members of the vulgus or the moderately learned at an early stage, and transform them into truly
learned readers.
A very different picture of Kepler‘s imagined readers comes through immediately in the
later books of the Epitome, published in 1620. In the preface to Book IV, Kepler described the
history of the first three books of the Epitome, published two years earlier. He had begun writing
the Epitome, he explained, after the publication of his New Astronomy, a complicated text which
had ―concealed the doctrine of celestial causes among thickets of numbers and further
astronomical trappings, and scared off the poorer [readers] by the price of the book.‖ 75
Friends
had urged him to write a summary of the new astronomy ―in plain and simple speech, with the
boredom of the demonstrations cut back.‖ 76
Kepler had tried to do just that, yet even so he had
received reports that he seemed ―to be more expansive in the debate about the diurnal motion or
rest of the earth than is appropriate to the nature of an Epitome.‖ 77
If this was the case for the
first books, which were relatively simple and contained material found in most epitomes of
astronomy, then Book IV, ―which unfurls so many new and unforeseen things concerning the
75 KGW 7.251, 3-5: ―Qui liber…doctrinamque de causis coelestium inter spineta numerorum et
reliqui apparatus Astronomici velut abscondisset; cum et pretio libri tenuiores absterrerentur…‖
76 Ibid, 6-8: ―…visum est amicis, recte me et ex officio facturum, si Epitomen conscriberem, in
qua summa doctrinae tam physicae de coelo, quam astronomicae, resectis demonstrationum
taediis, oratione simplici et plana proponerentur.‖
77 Ibid, 12-13: ―…diffusior visus sum, in disputatione de motu vel quiete Terrae diurna, quam
pro ratione Epitomes.‖
224

whole nature of the heavens,‖ 78 would seem especially difficult and strange. Therefore,
explained Kepler, he had decided to publish the later books separately, so that ―according to the
decision of the astronomer-purchaser, they could be omitted, or inserted into the rest of the
Epitome.‖ 79
Not only did Kepler emphasize the difficulty of the material in the later books, he
emphasized as well that the imagined purchaser was an ―astronomer‖—not a student, in other
words—and that even this astronomer might choose to bypass the books because of their
complexity.
Kepler then went on to counter the theoretical objection that the philosophy expressed in
the Epitome was so obscure and novel as to be useless; he hoped, he wrote, to ―vindicate [it]
from the trite accusations of excess curiosity and novelty.‖ 80
Kepler employed a number of
strategies to justify his book from these charges; for our purposes, the notable one is his claim
that though a book may seem obscure and challenging to beginners, it serves an important
purpose when it reaches its proper expert readers. ―If some subtle and difficult to grasp things
should not be related to beginners, or should not be preferred to accepted and necessary things,‖
he argued, ―it does not mean that therefore those things should not be written or read
privately.‖ 81
He likened his Epitome to Aristotle‘s Metaphysics; though few universities would
find it appropriate to teach the Metaphysics to beginners, no one would discount its value. On
the contrary, the Metaphysics was typically considered ―most useful by professors on all the
78 Ibid, 15-16: ―…libellus iste Quartus, qui tam multa de omni coelorum Natura nova et
inopinata ventilat….‖
79 Ibid, 31-32: ―…ut pro arbitrio emptoris Astronomi, vel omitti, vel inseri possit in reliquam
epitome.‖
80 Ibid, 38-39: ―…vel Philosophia a curiositatis et novationis protritis criminationibus
vindicator.‖
81 Ibid. 253, 13-15: ―Non igitur si subtilia nonnulla et captu difficilia proponi non debent
incipientibus, aut si non praeferenda receptis et necessariis, illa propterea neque scribi, neque
privatim legi debent.‖
225

faculties who judged it.‖ 82
The Epitome should be viewed through this lens. It was not as a text
intended to be taught to just anybody, but as a book for experts, professors, and the like—for
people who might understand and appreciate it.
This later framing of the Epitome, as a text targeted toward practicing mathematicians
and astronomers, is thus exactly opposed to the earlier framing of the first three books, which
explicitly addressed the beginning student. The material Kepler intended to tackle was surely
more complicated in the later books, yet he had planned his proposed topics when he first began
the book, and he could have endeavored to relate his findings throughout in plain and simple
speech, with minimal calculations and demonstrations. Instead, Kepler chose to downplay the
work as a beginner‘s textbook, and to reach out to a different audience entirely. This shift
becomes more understandable when one considers the immediate context of the Epitome—the
letters to Remus and Bianchi, the banning of the first three books of the work, and the Admonitio
to the booksellers of Italy. Kepler‘s late framing of the Epitome as a book for experts—and the
consequently complicated presentation of the material in the later books, so much so that even
experts struggled with the text—were linked not only to the more complicated subject matter of
the later books, but also with Kepler‘s desire to get around the censure of the book by the
Congregation of the Index, a censure which contained loopholes for expert readers. If he made it
clear that his book had this expert audience in mind, Kepler hoped, the censors might allow his
book to be printed, or at least to be read by a more limited audience.
Moreover, Kepler hoped not only to ensure that his book would be read despite its
Copernican content, but also to use it as a means by which the Copernican ban might eventually
be lifted. His goal in reaching expert readers, and in explaining Copernican theory in all its
82 Ibid., 17-18: ―scripsit tamen et Metaphysicam Aristoteles; eamque, judicibus omnium
facultatum Doctoribus, utilissimam.‖
226

complexity, was in part to reveal how wrongly Copernicanism had been banned by the Catholic
Church. Kepler ended his preface to Book IV by making this very point. He argued forcefully
that ―the boundary posts of investigation should not be set up in the narrow minds of a few
men…the boundary posts of true speculation are the same as those of the fabric of the world.‖ 83
Kepler lamented the Church‘s creation of false ―boundary posts,‖ and noted that ―antiquity
teaches us by examples how vainly man sets up boundary posts where God has not set them
up.‖ 84
He cited Eusebius‘s example of an astronomer who chose to abandon Christianity rather
than his astronomy, since the two were at odds, and the examples of Augustine and Tertullian,
who opposed the existence of the antipodes. ―Yet today,‖ he wrote, ―we set up academies
everywhere: we order that philosophy be taught, that astronomy be taught, that the antipodes be
taught.‖ 85
Banning Copernicanism would only be repeating the errors of old, argued Kepler; his
books were an attempt to forestall the Church from this disastrous path, by providing them with
unassailable arguments for lifting the ban. The Church itself, as he had noted earlier, had
recognized that the question of Copernicanism could be decided only by the experts, and
therefore had asked its mathematicians to decide the issue. Though those mathematicians had
decided against heliocentrism at present, Kepler hoped that he might change their mind—in
many ways, these were the most important of his new target readers.
Kepler had recognized that his Copernican campaign was in danger of stalling—with no
possibility of publishing his works, how was he to convince others of the truths that Copernicus
had revealed? Though the idea of working from the bottom up had been an attractive one—what
83 Ibid. 254, 22-25: ―Nec enim figendae sunt indagationi metae in paucorum hominum angustis
ingeniis…Verae quidem speculationis metae sunt eaedem, quae et operis Mundani…‖
84 Ibid. 27-28: ―Docuit nos exemplo Antiquitas, quam frustra metas homo figat, ubi Deus non
fixit.‖
85 Ibid., 35-37: ―Nos tamen hodie Academias ubique constituimus, Philosophiam doceri,
Astronomiam doceri, Antipodas doceri, jubemus.‖
227

etter way to convince readers to accept the evidence for Copernicanism than to equip them at a
young age with the tools to do so?—this no longer seemed like a viable option. Instead, Kepler
would work from the top down, first convincing those with power to overturn the Copernican
ban, and only later addressing other, non-expert readers. He emphasized this yet again in the
second edition of the Mysterium Cosmographicum, published in 1621. Referencing the ban on
Copernicus, he described his attempts to see it overturned. ―I have explained Copernicus‘s
words more clearly at the end of Book I of the Epitome of Astronomy,‖ he wrote.
In those places I hope that I have sastisfied the devout, provided that they bring to their
judgement of this enough mental prowess and knowledge of astronomy for the glory of
God's visible works to be able to be entrusted to their safe protection....Certainly God has
some kind of tongue, but he also has some kind of finger...Therefore, in matters which
are most evident, the very devout should take greatest care that they do not twist the
tongue of God so that it refutes the finger of God in nature. 86
Kepler hoped that the mathematicians of the Catholic Church would use his explanations in the
Epitome to make a new and informed decision about Copernican theory, one which took care to
support both the Book of Scripture and the Book of Nature.
The Thirty Years’ War and the Purpose of the Epitome
Though the banning of the Epitome in Italy was very distressing to Kepler, a far more
destructive event also separated the publication of Books I-III in 1618 from the publication of
Books IV-VII in 1620 and 1621. The year 1619 marked the start of the Thirty Years‘ War, a
civil war of unprecedented brutality and suffering, which saw towns destroyed, communities
86 KGW 8.39, 29-35: ―Psius etiam Copernici verba explicaui dilucidius in fine libri I. Epitomes
Astronomiae: quibus locis spero religiosis satisfactum iri: dummodo et ingenium et
cognititionem Astronomiae talem ad hoc iudicium afferant, vt gloria diuinorum operum
visibilium ipsorum patrocinio tuto credit possit. Est sane aliqua lingua Dei, sed est etiam aliquis
digitus Dei....In rebus igitur euidentissimis torquere Dei linguam, vt illa digitum Dei in natura
refutet, id religiosissimus quisque maxime cauebit.‖
228

uprooted, and scores of people devastated by the effects of violence and disease. The years
leading up to the war, too, were far from peaceful—in 1616, one of Kepler‘s correspondents
already fretted that ―there is no corner of the world where the seeds of war are not dispersed and
growing.‖ 87
Yet after 1619 the ravages of war seemed ever-present. ―The fires of civil war are
raging in Germany,‖ wrote Kepler in 1621. ―…Everything in my neighborhood seems
abandoned to flame and destruction.‖ 88
So staggering were the effects of war that many believed
that the end of the world was near—or at least, the end of the world as they knew it. ―Europe is
our Europe no more,‖ lamented a friend to Kepler in 1622. 89
Kepler focused heavily on the war and its effects in the dedication to Book V of the
Epitome. There, he noted the way that the war had disrupted his life and the lives of those
around him, delaying the publication of the later books of the Epitome. ―Alas!‖ he wrote,
If I consider the circumstances of time, this edition is exceedingly late, on account of the
suffering caused by the start of a very destructive war, and after the groups of students for
whom these things were written have either been scattered by the military turmoil or
diminished and destroyed by the expectation of war: after Austria, thus far my nourisher
and benefactor, has been crushed against a very hard rock, and seems to be called away
from the guardianship of these beautiful things to the serious care of its own safety: and
after I myself, on account of the cruelty of a private enemy of mine, hav been away from
my home in Linz for almost a year. 90
The ―cruelty of a private enemy‖ to which Kepler referred was the witch trial of his mother,
which culminated in 1620. Kepler acted as her legal defense, and eventually succeeded in
87 KGW 17:747: ―…nec angulum esse in orbe puto, ubi non bellorum semina dispersa sint et
excrescent.‖
88 KGw 18:909: ―Flagrare vides incendium belli civilis in Germania…corripi proxima, grassari
flammam.‖
89 KGW 18:941: ―Europa enim nostra Europa amplius non est.‖
90 KGW 7.359, 11-17: ―Si temporis circumstantias respicio, sera est oppido proh dolor editio
ista postquam bello coorto perniciosissimo coetus discentium quibus ista scribuntur, vel dissipati
sunt turbis bellicis, vel attenuati emactatique belli expectatione: postquam Austria, hactenus
altrix et benefactrix mea, durissimum in scopulum illisa, a decorum istorum tutela, ad seriam
salutis suae curam auocari videtur: postquam ipse quoque priuati meorum hostis atrocitate,
domicilio meo Linciano excitus annum pene totum foris discursito.‖
229

obtaining her acquittal. The trial forced him to travel from Linz to Würrtemberg, and made a
sustained focus on the publication of the Epitome very difficult. Yet Kepler presented this
personal hardship as secondary to the hardships suffered by all those dealing with the effects of
war, from the students for whom he had initially written the Epitome to the patrons who had
initially supported it. He described his own efforts to publish the later books of the Epitome ―in
the middle of the Bavarian armies, and the constant disease and death of as many soliders as
civilians.‖ 91
War, in Kepler‘s portrayal, formed a relentless backdrop to the completion of the
Epitome, one which could not but color his conception of the book.
Though this situation was far from ideal, Kepler noted that it did have some positive side
effects. He highlighted the fact that delayed publication of the later books, both due to the trial
of his mother and the difficulties of the war, gave him time to reconsider some of the ideas in
those books. ―The fact that this publication has been prevented till now calls for thanks, not
blame,‖ he asserted.
Certainly the computation of the Ephemeride and the publication of the many books of
the Harmonies, the work of the intermediate time, warned me that although much of what
pertained to the six planetas had either been established or at least aimed at twelve years
earlier in the Commentaries on Mars; and althogh they had been taken up from there and
arranged into the form of an instructional [book], they clung to my desk for seven years,
in anticipation of the work of the supervisor and printer. Nevertheless, as often as I
reread them, either because of additions or explanations or textual transpositions, it was
clear that I needed a new plan. This was so much the case that not a trace remained of
the original in the copy finally presented to the printer. 92
91 Ibid. 360, 9: ―…media inter arma Bauarica, crebrosque morbos et mortes tam militum quam
ciuium.‖
92 Ibid. 359, 20-37: ―…beneficium est non culpa, quod hactenus impedita fuit haec editio...Multa
scilicet me monuit computatio Ephemiridum, multa editio librorum harmonicorum, intermedii
temporis opera: vt quamuis pleraque quae ad sex planetas pertinent, jam ante annos duodecim
in Commentariis martis vel constituta, vel saltem affecta essent; quamuis inde transsumpta,
inque formam institutionis composita jam a septem annis haererent in scriniis meis, operas
expectantia Curatoris et Chalcographi: quotiescunque tamen illa relegebam, vel
augmentationibus, vel dilucidationibus, vel transpositionibus textus, necessitas imponeretur
230

Had the publication of the later books not been delayed, explained Kepler, they would likely
have recapitulated much of the material from his New Astronomy, published in 1609. Yet in the
intervening period—and specifically, after the publication of Books I-III in 1618—he had
completed both his masterpiece, the Harmonice Mundi of 1619, and a series of Ephemerides for
the years 1617-1620. Both these works, he argued, caused him to rethink the material that he
had compiled for his textbook, and eventually forced him to rework it, to such a degree that ―not
a trace remained of the original‖ in the final copy.
Along a similar vein, Kepler described how his frequent travels, particularly after the
publication of Book IV of the Epitome in 1620, actually gave him additional leisure time to work
on the final books of the text, since he could not fulfill his official duties as district
mathematician in Linz. ―Although since the publication of Book IV I am away from home, and
spend a great deal of time traveling and dealing with the courts,‖ he wrote, ―nevertheless it has
been permitted to me to rest awhile for the better part of my time, and I have devoted all of that
time to the care of this publication.‖ 93
In particular, along his travels he was able to stop in
Tübingen at the end of 1620, where he spoke with Maestlin about his new lunar theories. In
preparing for his talk with Maestlin, he wrote down questions about the relationship of his lunar
theory to the theories of the other planets, and about the physical causes of planetary motions
more generally. When he returned home, he reread his questions and then reread the material he
had prepared for Book VI, in order to finish preparing it for publication. He had hoped such
preparation would be simple, but instead, he wrote, ―I discovered it to be laborious, not so much
nouae descriptionis. Ita factum, vt de primo exemplari, ne vestigium quidem superesset in eo,
quod exhibitum est Chalcographo.‖
93 Ibid. 360, 16-18: ―…etsi post editum librum IV. Domo absum, nec parum temporis itineribus,
curisque forensibus insumo: potiori tamen temporis parte mihi licuit interquiescere: atque illam
omnem ego in curam hujus editionis impendi.‖
231

ecause of difficulty as because of the multitude and variety of the questions, and the concern for
method.‖ 94
He mulled over the material still further, and ―immediately when I returned to
Tübingen, I saw that the fourth part of Book VI, on the moon, would have to be furbished with
repeated work, on account of the fact that the definitions derived in words did not exactly
represent the force of my physical hypotheses.‖ 95
The extra time he devoted to thinking about
the material, his additional conversations with Maestlin, and his ability to peruse additional
books at Tübingen which he could not obtain at Linz all resulted in a transformation of the
material in the later books. In this way, the many hindrances to publication had a positive
result—for ―if the printing had not been delayed until now, these things would necessarily have
been omitted.‖ 96
The difference between the earlier and the later books of the Epitome thus stemmed from
many sources. On the one hand, Kepler consciously reframes the later books following the
banning of the initial books in Italy, targeting them to experts rather than beginners. At the same
time, the many delays in publishing the later books, delays brought on by the exigencies of the
Thirty Years‘ War and the witch trial of Kepler‘s own mother, caused Kepler to reconsider not
merely the framing of the books, but also the content. He read more widely than he had done
before, and incorporated material into the later books of the Epitome from his Harmonice Mundi
94 Ibid. 22-25: ―…et ipsam deprehendi laboriosam, non tam difficultate, quam multitudine et
varietate quaestionum, et cura methodi.‖
95 Ibid. 27-30: ―Statimque, vt Tubingam redii, etiam partem libri VI quartam, de Luna, repetito
labore interpolandam vidi; propterea, quod definitiones verbis conceptae, vim Hypotheseos
meae physicae nondum exacte repraesentarent.‖
96 Ibid. 36-39: ―Multa tamen, occasione conuersationis cum Maestlini, veteri duce meo ad
cepssendum hoc iter Astronomiae Copernicanae, multa per lectionem libroru, quos hactenus in
Austria nancisci non poteram, inciderunt; quae nisi hucusque dilata fuisset editio, necessario
praetermittenda fuerunt.‖
232

and Ephemerides, along with the results of his extensive conversations with Maestlin. All this,
as he made clear, resulted in a dramatically different text than he had initially envisioned, one
whose ideas had been refined and perfected over time. Kepler used the later books of the
Epitome, that is, both to review material that was already available and to articulate his latest
conceptions of his own physical theories, in ways that he had not done before. The first books,
which were intended more as summary than as innovation, fit more cleanly into the form of a
textbook; the later books, which Kepler used to fully work out his own physical theories and to
advance new arguments, were consequently far more complicated. This helps to explain the
disjunction we noted at the start of the chapter, between Kepler‘s initial presentation of the
Epitome as a textbook for beginners, and the later presentation of the book as a text for experts.
It also explains the discrepancy between Kepler‘s initial assertion that he would present the
material in the text as simply as possible, and the struggles of even his expert readers to
understand the material in the later books of the Epitome.
Yet something still more is at play beyond the changes to the content of the later books.
If Kepler consciously reframed the Epitome in light of its banning in Italy, he did so as well in
light of the changes wrought by the start of the Thirty Years‘ War. As he noted at the start of
Book V‘s dedication, the war had led to the dispersal of the ―students for whom these things are
written.‖ Indeed, the Thirty Years‘ War put a halt to the normal workings of universities
throughout the Empire, as libraries were depleted, teachers dismissed, and students forced to flee
for their lives. 97
With the disruption to both Kepler‘s own teaching and to scholarly life in
97 See C.V. Wedgewood, The Thirty Years War (New York: New York Review of Books, 2005).
Wedgewood recounts, for example, that with the Catholic capture of Heidelberg in 1622, "the
Protestant churches of Heidelberg itself had been closed, the University dissolved, and the
superb library packed into boxes and trundled in wagon loads over the Alps to Rome,
Maximilian's thankoffering to the Vatican." 156.
233

general, the idea of the Epitome as a teaching text began to seem far less relevant. With no
students to teach, and no one to do the teaching, the necessity of yet another beginner‘s Epitome
of astronomy was dubious, at best.
At the same time, all those in the Empire who had previously supported Kepler‘s work,
and on natural philosophy more generally, were forced to focus on more pressing matters
instead—were called, as Kepler wrote, ―from the guardianship of these beautiful things to the
serious care of its own safety.‖ Indeed, many people argued that esoteric discussions of the
heavens had no place in a world ravaged by war. Kepler had heard such arguments before. As
far back as 1599, when Kepler lived in a Graz beset by escalating religious tensions, he had been
scolded angrily for his attention to obscure astronomical questions by the city authorities.
―Those men,‖ he had written then to Michael Maestlin, ―as people did once in Florence against
Philelphus, shout against me today (or certainly mutter) that now is not a time for learning, but
for waging war.‖ 98
Indeed, they had urged him to focus instead on a field that might be
potentially useful in a time of war: ―They urged,‖ he wrote later to Herwart von Hohenberg, ―but
really ordered under the threat of dismissal, that I put aside astronomy for the present, and
embrace medicine, and that I transfer my interest from speculations which were more lovely than
useful in this difficult time, to seeing to the public utility.‖ 99
Kepler had not had to make that kind of decision at the time; ultimately banished from
Graz with his fellow Protestants in 1600, he had made his way to Tycho Brahe and continued his
98 KGW 14:132: ‖Penes quos cum sit rej summa, nescio quam diu me tutatura sit Inspectorum
authoritas contra illorum invidiam, qui, ut olim Florentinj contra Phielphum sic hodie contra me
clamitant, vel certe mussitant, non jam tempus esse discendj, sed belligerandj.‖‖
99 KGW 14:168: ―Domo discessi cum venia Magistratus mej: reditum meum ubi illis significavj,
diligentiam quidem collaudarunt, caeterum verbotenus suaserunt, reipsâ sub dimissionis
interminatione imperarunt, ut sepositâ in praesens Astronomiâ, Medicinam amplecterer,
animumque a speculationibus pulchris magis, quam hoc difficili tempore salutaribus, ad curam
utilitatis publicae traducerem.‖
234

astronomical studies. Now, however, with the war full-blown and raging, Kepler anticipated a
similar objection to his work, and took care to opposite it directly in his work. Hence he argued
both in the preface to the later books of the Epitome and in the Harmonice Mundi that quite the
opposite was true. In a world characterized by chaos and disharmony, Kepler believed,
discussions of heavenly order and harmony were not only important, but necessary. Earthly life
was merely a microcosm of the heavenly macrocosm; in understanding the harmony that
characterized the heavenly sphere, Kepler believed, people could better act harmoniously in their
own lives, using the heavenly harmony as a model for harmony on earth. He had therefore
opened his Harmonice Mundi with an illusion to the start of the Thirty Years‘ War, ―this slightly
too harsh discord,‖ 100 and with the hope that ―the examples of concord in the visible works of
God [would]…strengthen and stir up the zeal for concord and for peace in church and state.‖ 101
In a similar vein, Kepler used the preface to Book V of the Epitome to argue for the
book‘s relevance during a time of war. He had persevered in ―pursuing the footsteps of divine
providence in an indefatigable chase,‖ he wrote, and he had done so with his patrons in mind; ―I
am not frightened by your adversities, Princes, which have meanwhile assailed you and your
wretched province, or which seem to threaten in the distance, so as to not fulfill my plan and my
promise to you.‖ 102
The completion of his book, he explained, was the payment of a debt to all
those who had supported him and his work in the past. This was not merely because the book
100 Harmony of the World 2
101 Ibid. 5
102 KGW 7.361, 6-12: ―Atque ipse quoque, vestigia diuinae prouidentiae, cui equidem artes istas
(diuinorum scilicet Operum praeconia) curae esse credo, indefessa prosecutus indagine,
postquam, quid utliitatis hauserit libellus ex mora ista temporis ad mentem reuoco; non terreor
aduersitatibus vestris, Proceres, quae interea vos et prouiniciam miseram vel sunt adortae, vel
imminere porro videntur quo minus et pensum meum absoluam et promissum vobis…‖
235

itself was an embodiment of princely honor and erudition, but because it contained much which
Kepler believed could help his patrons in a time of adversity. Kepler continued,
For I hope that so much divine mercy remains in the treasure chamber that he wants this
horrible storm to be calmed, the clouds to be dissipated, and the sun to shine earnestly
again on those who have repented, peace to be restored, and some place remain in Austria
too for these peaceful arts, whose elaboration He does not stop caring for, and for some
number of people to gather there who learn to obtain from these arts of praises of God the
Creator. I hope that this little book will be useful to them. 103
Kepler prayed that God would bring peace to a war-torn Europe, but he believed that this would
happen far more speedily if people used his books as a model of peace, and ―learn[ed] to obtain
from these arts the praises of God the Creator.‖ His book, he argued, ―will be useful‖ to all those
people who hoped to put a stop to the conflicts that surrounded them and return to an era of
peace. Mathematics, right religion, and peaceful living went hand in hand, in Kepler‘s view. He
therefore ended his preface with the entreaty each reader who both valued mathematics and
devoted himself to God ―very frequently join his prayers to the most merciful God with mine:
that with the tumults of war calmed, the desolation restored, the hatred quenched, and golden
peace returned, he might revive [these lands] with the fertile shower of his grace.‖ 104
If the
readers of the Epitome—like the readers of the Harmonice Mundi, and indeed, of all of Kepler‘s
books—truly took its lessons to heart, Kepler believed that they would be impelled to seek a
peace on earth that followed the model of the harmony of the heavens.
103 Ibid. 13-18: ―Spero namque superesse tantum de misericordiae diuinae thesauris; vt sedata
hac horribili procella, dissipatis nubibus, Solem serio poenitentibus iterum lucere, pacem
reducere, locumque aliquem his pacis artibus vt quarum elaboriationem procurare non desinit,
in Austria quoque superesse, et in illa numerum aliquem eorum qui ex his artibus laudes Dei
Creatoris sui addiscant colligi porro quoque velit: quibus libellum hunc profuturum spero.‖
104 Ibid. 27-33: ―…ita frequentissime vota sua ad Deum misericordissimum cum meis coniunget:
vt sedatis bellorum tumultibus, resarcita vastitate, extinctis odiis, pax aurea reuersa, Serenissimi
Potentissimique D. Ferdinandi II Roman. Imperatoris Augusti Domini nostri, Imperium serenet,
prouinicias Maiest. S. omnes, imprimis Austriam supr-Anisanam, foecundo Gratiae suae imbre
refocillet…‖
236

This idea—of the Epitome as a model for earthly peace—provides us with another
explanation for Kepler‘s later reframing of the text, and his targeting of a different sort of reader.
Initially, Kepler hoped to spread the Copernican message as broadly as possible, and crafted his
Epitome as a book for the beginning student. Yet with university life disrupted and war
continuing to rage with no apparent end in sight, Kepler began to target readers at the top of the
social and political hierarchy, rather than the bottom. Instead of reaching out to students, as he
had done in the earlier prefaces, Kepler used his later prefaces to reach out to his princely patrons
and others of similar standing. With his hope that one day ―there be gathered together in Austria
once again some number of those who learn from these arts the praises of God their Creator,‖ he
painted a picture of a more select group of readers—not all those with a passing interest in
astronomy, but rather all those with both the desire and, crucially, with the ability to apply the
very deep lessons contained in Kepler‘s text. Since Kepler saw his Epitome, like his other
books, as a model for earthly harmony, he used his later prefaces to reach out to those readers
with the potential to take such a model to heart and affect the course of the war to some degree.
Not students, then, but princes, generals, and diplomats, who might directly harness his model to
real action, and theologians and mathematicians, who might supply additional material to aid in
the quest for peace. This was the very reason why Kepler had dedicated his Harmonice Mundi
to King James I of England; seeing how James had taken England and Scotland and ―from the
combination of both provinces…produced one kingdom and one harmony,‖ Kepler hoped that
James would read his book and use it as a model to pursue harmony and peace on a more global
scale, so that ―abroad also, as a king among kings…[James] would perform some greater and
more excellent, and also more lasting work.‖ 105
105 Harmony of the World 3
237

At the start of his career, in his Mysterium Cosmographicum, Kepler had also tried to
attract patrons to his work. Then, in answer to the objection that astronomy had little value,
Kepler had emphasized precisely its lack of utility as the reason for its attraction to noble
readers. ―Why must one value the advantage of divine things in cash, like food?‖ he had written
then.
For how is knowledge of natural things useful to a hungry stomach, how is the whole rest
of astronomy useful? Nevertheless wise men do not listen to the barbarity that shouts
that these studies must therefore be abandoned. We receive painters, who delight our
eyes; orchestras, which delight our ears, although they bring no benefit to our affairs.
And the pleasure received from either of these works is deemed not only civilized but
also honorable. What incivility, what stupidity, therefore, to begrudge the mind its
honorable delight, but not the eyes and ears! 106
Then, he had likened his work to art or music, emphasizing the pleasure it provided, pleasure
which was not base and barbaric but rather civilized, even honorable. Still further, he had argued
that it was lack of utility that made his work particularly suited to a princely patron. Common
people focused on the useful and the commonplace, while nobles were interested in the rare, the
beautiful, and the pleasurable. According to Kepler, the book‗s merit was inversely proportional
to the number of ―common‖ people who praised it. True knowledge be appreciated best by those
with discriminating tastes, and the less linked a subject was to common, earthly concerns, the
more noble and pure it was. By contrast, in a time of violence and upheaval, Kepler emphasized
that his book did have utility. Yet that very utility was of a high and noble character—for while
106 KGW 8.17, 14-22: ―Quanquam quid necesset est, diuinarum rerum vsus instar obsonij
nummo aestimare? Nam quid quaeso prodest ventri faemlico cognitio rerum naturalim, quid
tota reliqua Astronomia? Neque tamen audiunt cordati homines illam barbariem, quae
deserenda proterea ista studia clamitat. Pictores ferimus, qui oculos, Symphoniacos, qui aures
oblectant: quamuis nullum rebus nostris emolumentum afferant. Et non tantum humana sed
etiam honesta conesetur voluptas, quae ex vtrorumque operibus capitur. Quae igitur
inhumanitas, qua stultitia, menti suum inuidere honestum gaudium, oculis et auribus non
inuidere?‖
238

the weapons of war seemed to offer no end to the troubles plaguing Europe, Kepler insisted that
the weapons of astronomy had the power to point the way to peace.
Conclusion
Kepler‘s changing attitude toward the Epitome and its readership underscores the fact that
Kepler was no ivory tower scholar, producing obscure academic texts with little regard for the
world around him. He responded quickly and decisively to new political and religious
developments, molding his work in response to the changing world around him. And more
importantly, Kepler‘s approach to the Epitome helps us understand how he saw himself with
respect to that world, and what it meant to be a Copernican in Kepler‘s view, and how a true
community of Copernicans ought to look. Kepler, a Copernican but also a Lutheran and a
German, reshaped the Epitome specifically so that it would reach Catholics in Italy. He could
easily have given up on such readers, targeting instead sympathetic Lutherans and fellow
Germans. The Copernican ban, after all, would be unlikely to affect his work outside of Italy,
and his books could still be taught at Lutheran universities, which adopted a very practical
approach to Copernican theory. 107
Yet Kepler specifically took on the mantle of Copernican
advocate for Italians and Catholics, bringing himself and his work to the attention of the
Congregation of the Index in the process. Such a role was important to him because the
Copernican community, in his view, was not restricted by nationality or confession. It included
all those who studied the natural world and recognized it for what it was—a system characterized
by divine harmony. It was incumbent on members of the community to act as allies in the search
for truth, as Kepler had written to Galileo years earlier, and to vocally further the Copernican
107 See Robert Westman, ―The Melanchthon Circle, Rheticus, and the Wittenberg Interpretation
of the Copernican Theory,‖ Isis 66 (1975): 165–193, and the discussion in Chapter 1.
239

cause, setting themselves and their work up as examples to follow. Still further, the community
of Copernicans not only transcended the limitations of religion and state, but served as a means
by which the enmity engendered by those limitations could be healed. Thus Kepler also
repositioned the Epitome in the wake of the start of the Thirty Years‘ War, reaching out in
particular to those at the top of the religious and political hierarchy—those, that is, whose
decisions could directly affect the outcome of the war. Reading his explanations of heavenly
harmony would provide them with a model for earthly harmony, and learning the details of
mathematical astronomy would provide them with a means by which they might foster concord
and virtue. For mathematics, as Kepler explained in the Harmonice Mundi, ―perfects us in moral
philosophy, implanting in our behavior order, propriety, and harmony in social relations.‖ 108
Kepler‘s decision to act as Copernican advocate for Italians and Catholics likewise
reveals how deeply he took his identity as Copernican to heart. He lived his life at odds with the
community of Lutherans and as a wanderer from one place to another, but this existence on the
margins was not by choice. ―I have been denounced as unprincipled, agreeing with all…I have
been called a godless scorner of the word of God…I have been denounced as a doubter…I have
been denounced as unstable,‖ he wrote. ―But I bear witness before God that I am neither pleased
nor satisfied in this role, nor do I like to be considered as a man apart.‖ 109
Though his fellow
Lutherans doubted his devotion, and though he was never permitted to return to his home
province of Würrtemberg, his dedication to the Copernican cause was clear for all to see. In
108 Harmony of the World, 129, cited from Proclus, Commentary on Book I of Euclid. See also
Chapter 5 of this dissertation, and Matthew Jones, The Good Life in the Scientific Revolution:
Descartes, Pascal, Leibniz, and the Cultivation of Virtue (Chicago: University of Chicago Press,
2006).
109 Glaubensbekkentnis, KGW 12, 27.
240

eaching out to fellow Copernicans and in struggling to convert others to the Copernican cause,
Kepler was seeking, once again, to strengthen the one community to which he truly belonged.
Of course, despite his dedication to Copernicus, Kepler did not simply parrot the ideas of
his predecessor. He reshaped Copernican astronomy, gave it a physical basis, and, with his
description of planetary orbits as ellipses, transformed it into something else entirely. All this
comes through quite clearly in the Epitome, so much so that its title presents something of a
puzzle, for the book is less a description of Copernican astronomy than of Keplerian astronomy.
Kepler himself was aware of this problem, and he addressed the issue directly in Book V of the
Epitome. He posed the question as follows: ―By what right do you make this also a part of
Copernican astronomy, when nevertheless that author continued in the opinion of the ancients
concerning perfect circles?‖ 110
His answer reveals a great deal about his conception of himself
and his work with respect to that of Copernicus. He wrote,
I admit that this form of the hypotheses is not Copernican. But because that part
concerning the eccentric is secondary to the general hypothesis which uses the annual
motion of the Earth and the rest of the sun; therefore the name [Copernican] comes from
the more important [aspect]. Add the fact that this small part of the hypothesis is bound
to the Copernican doctrines with necessary physical arguments [which come] from the
rest of the sun and motion of the Earth. Thus these things can be referred to with good
merit as Copernican. 111
According to Kepler, all of his work was ―bound to the Copernican doctrines with necessary
physical arguments‖—he had merely taken Copernicus to his logical conclusion, allowing the
110 KGW 7.364, 36-37: ―Quo iure hanc quoque partem facis Copernicanae Astronomiae; cum
tamen is author manserit in sentential veterum, de perfectis circulis?‖
111 Ibid., 38-40; 365, 1-3: ―Fateor formam hanc hypothesium non esse Copernicanam. At quia
pars ista de Eccentrico seruit Hypothesi vniuersali, quae motu Telluris annuo, et quiete Solis
vtitur: fit igitur a potiori denominatio. Adde quod ista particula Hypotheseos, necessariis
argumentis physicis ex illa quiete Solis et motu terrae, dogmatibus Copernicanis, nectitur; itaque
bono titulo etiam haec ad COPERNICVM referri possunt.‖
241

seed planted by Copernicus to germinate. He saw himself, that is, as clarifying and interpreting
the work of the master, rather than fundamentally changing it.
With this in mind, another genre suggests itself to which we might fruitfully assign
Kepler‘s Epitome—rather than a Copernican textbook, it is perhaps best seen as a Copernican
commentary, or exegesis. Peurbach‘s and Regionmontanus‘s Epitome of the Almagest was itself
as much a commentary on Ptolemy than a textbook, and Kepler likely had this model as much as
Maestlin‘s own Epitome in mind as he crafted his own book. Still further, as a former theology
student at Tübingen, Kepler was well acquainted with the exegeses of the Church Fathers. And
along with theological commentaries, during the sixteenth century some of the philosophical
commentaries of the ancients were newly available; Proclus's commentary on the first book of
Euclid's Elements, to which Kepler referred throughout his Harmonice Mundi, was first printed
in its Greek edition in 1533, and in Latin translation in 1560. Moreover, the commentary
tradition continued to flourish in sixteenth- and seventeenth-century Europe; Aristotelian
commentaries were still the primary stock of university teaching, and commentaries on the Bible
were still produced in remarkable profusion. Those biblical commentaries were themselves a
highly versatile genre, which could cover an enormous range of subjects under the auspices of a
gloss on the scriptural text. And they were rare among theological texts in that they traveled
relatively freely between Catholics and Protestants, given that their subject matter was typically
not doctrinal or confessional in nature. 112
Kepler was well acquainted with both the philosophical and the theological commentary
traditions, and he clearly linked the two. Along these lines, he argued in his Harmonice Mundi
that Plato‘s Timaeus should be understood as ―a kind of commentary on the first chapter of
112 See Kevin Killeen, Biblical Scholarship, Science and Politics in Early Modern England:
Thomas Browne and the thorny place of knowledge (Burlington: Ashgate, 2009), 74.
242

Genesis, converting it to the Pythagorean philosophy, as is readily apparent to the attentive
reader, who compares the actual words of Moses in detail.‖ 113
Likewise, Kepler‘s theological
outlook permeated his own study of the heavens; he described himself, as astronomer, as ―a
priest of God with respect to the book of nature.‖ 114
Because of this, some scholars have
fruitfully employed the exegesis genre as a way to better understand Kepler‘s books, arguing that
much of his work can be read as an exegesis of the book of nature. 115
Yet if Kepler assumed the
mantle of astronomer-priest, he cast Copernicus in the role of high priest. ―This glory is
sufficient,‖ he asserted, ―that I can wield my discovery to guard the gates of the temple where
Copernicus offers sacrifices at the high altar.‖ 116
For Kepler, Copernicus had first revealed the
true meaning of God‘s creation; he himself had then further explained and elaborated that
meaning. Thus if some of Kepler‘s work are exegeses of God‘s book, the Epitome is an exegesis
of the book of Copernicus—an explanation of what Copernicus really meant, conveyed so
forcefully and clearly that all who read it, even the Italian clergy who seemed so set against
Copernicanism, would be compelled to worship at the same altar as Kepler did.
113 Harmony of the World, marginal note to 301.
114 KGW 13:89, ―Ego vero sic censeo, cum Astronomj, sacerdotes dej altissimj ex parte librj
Naturae simus.‖
115 See Kenneth Howell, God's two books: Copernican cosmology and biblical interpretation in
early modern science (Notre Dame: University of Notre Dame Press, 2002), p. 115.
116 KGW 13:91: ―…sufficit haec gloria, posse Copernico ad magnam aram sacra facientj portas
templj mea inventione custodire.‖
243

Chapter 5:
A “Political Digression”: Kepler and the Politics of Harmony
In 1623, Kepler argued that the prudent man should eschew politics in favor of
philosophy. Referencing the recent popularity of utopian texts, which encased their political
messages in allegory, Kepler mused about the possibility of turning his Somnium—a description
of the earth as viewed from the moon—into a utopia. ―Campanella wrote a City of the Sun,‖ he
wrote to Matthias Bernegger. ―What if I wrote one of the moon? Would it not be a wonderful
deed to paint the barbarous habits of this time in vivid colors, but for the sake of caution to leave
the earth with such a work and to withdraw to the moon?‖ Yet Kepler decided against such an
approach. Politics was contentious enough, he believed, that even the writing of a political
allegory could be a dangerous undertaking. ―How would it help to hold back in this way?‖ he
continued. ―Neither More in his Utopia nor Erasmus in his Praise of Folly were safe, but each
needed to defend themselves. Therefore let leave the vicissitudes of politics alone and remain in
the pleasant greenery of philosophy.‖ 1
While Kepler may have been able to leave any overtly political discussions out of his
Sominum, he certainly could not avoid the political sphere entirely. He knew well that his post
as Imperial mathematician and advisor to the Holy Roman Emperor was a highly political one,
and he referred to himself alternately as both a mathematicus and a politicus. He discussed
political questions in his published astrological works, in letters to friends and patrons, in
nativities which he was commissioned to produce, in reports which the emperor requested of
1 KGW 18: 963: ―Scripsit Campanella civitatem Solis, quid si nos Lunae? Anne egregium
facinus Cyclopicos hujus temporis mores vivis coloribus depingere, sed cautionis causa terris
cum tali scriptione ecedere, inque Lunam secedere? Quanquam quid tergiversari juvabit? cum
nec Morus in Utopia nec Erasmus in encomio Moriae, tuti fuerint, quin utrisque fuit apologia
opus. Missam igitur penitus faciamus picem hanc politicam, nosque in amoenis Philosophiae
viretis plane contineamus.‖
244

him, in the prefaces and dedications to many of his astronomical or cosmological books, and
even in a ―political digression‖ to his masterpiece, the Harmonice Mundi. In the previous two
chapters, I focused most closely on Kepler‘s conception of himself as a mathematicus, and as a
Copernican in particular. In this chapter, I will turn to Kepler‘s conception of politics, of himself
as a homo politicus, and of the relationship between his political thought and his (natural)
philosophical beliefs more broadly. I will first focus on the tradition of astrology as an art with
great political resonance, and consider how Kepler modified this tradition in his own conception
of the field. Kepler drew much, I will argue, from the political ideas of the neo-Tacitists of his
time, and argued that while astrologers often offered political predictions, these only had a hope
of accuracy if they were grounded on political experience and personal discretion. He
emphasized that his own astrological reports often drew on his political awareness as much as his
knowledge of the motions of the heavens, and argued that such political awareness often dictated
that he hide or alter the message of the stars if that message seemed politically dangerous. When
it came to questions of astrology, I will demonstrate, Kepler played the role of the consummate
politician.
Next, I will move from astrology to mathematics and cosmology, and focus on Kepler‘s
discussions of politics and political harmony in his Harmonice Mundi. I will examine the
reasons why Kepler dedicated the book to King James I of England, and focus at length on the
―political digression‖ which Kepler placed at its midpoint and based on the ideas of Jean Bodin.
Kepler, I will argue, believed that the mathematical harmony of nature which he had explicated
in his book could, and should, provide a blueprint for political harmony, particularly in a world
as characterized by political discord as his own. He saw in King James someone with the desire
and the power to take such a model to heart and implement it on the ground. Yet while he
245

elieved that the mathematics of harmony might lead to a politics of harmony, he did not provide
a specific formula for political organization, and avoided the model of Bodin, which tried to
bolster a particular form of government with the claim of mathematical certainty. Much as in his
discussions of astrology, Kepler emphasized the subjective nature of politics and of political
harmony. Though there were certain broad principles upon which he insisted—in particular, the
preeminence of the public good and the welfare of the state—Kepler implied that multiple kinds
of political configurations were equally valid, so long as they agreed on these principles. While
the harmony of nature could point the way to political harmony on earth, it needed to do so
indirectly, for politics was too complex and subjective an art to be grounded on the certain truths
of geometry.
The Astrologer as Politician
The close linkages between astrology and politics with which Kepler struggled were not
new to the Holy Roman Empire of the early modern period. On the contrary, astrology had long
been ―profoundly involved with action and power in the world.‖ 2
The emperors in ancient Rome
had relied on the advice of astrologers, and French and English rulers of the late Middle Ages
had paid astrologers for their genitures. 3
Yet the value that rulers assigned to astrological advice
and the potential for advancement that astrological expertise afforded its practitioners were both
particularly great in sixteenth- and seventeenth-century Germany. 4
Kepler‘s own employer,
2 See ―Astrology‖ in The Classical Tradition, Eds. Anthony Grafton, Glenn W. Most, and
Salvatore Settis (Cambridge: Harvard University Press, 2010), 86.
3 See Anthony Grafton, Cardano‘s Cosmos: the worlds and works of a Renaissance astrologer
(Cambridge: Harvard University Press, 1999), p. 118.
4 See Darin Hayton, ―Astrology as Political Propaganda: Humanist Responses to the Turkish
Threat in Early Sixteenth Century Vienna,‖ Austrian History Yearbook 38 (2007): 61-91. See
also Grafton, Cardano‘s Cosmos, 110.
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Rudolf II, placed a high premium on astrology and astrological advice because of the tense
political climate that characterized his reign. The empire was divided, both by faith and by
increasing political disputes; Rudolf felt increasingly threatened by his brother Matthias, who
gained the crowns of Austria, Hungary, and Moravia in 1608—and who would force Rudolf‘s
abdication in 1611. The papacy had begun an attempt to regain some of its old positions in the
Empire, while Spain started to reassert its own Imperial interests, particularly in Bohemia. In
1591, the Ottoman Empire had also begun a prolonged assault on the Hungarian front, which
lasted well into Rudolf‘s reign. Faced with both the internal political rivalries of the empire and
the outside threat from European and Turkish forces alike, Rudolf increasingly relied on advisors
who were independent, without ties to any rival power. 5
Astrology, in particular, seemed to offer
an objective and more certain source of advice and guidance, and Rudolf, following in the
footsteps of Imperial rulers before him, turned to astrology with high hopes, and often relied on
astrologers to assist him in the difficult political decisions he faced.
While for Rudolf, as for his Imperial predecessors, astrology had an important place at
court, the astrologer could occupy a range of positions. Some astrologers, like Kepler, held
permanent official positions at court, while others with distinguished reputations, like Cardano,
were consulted as outside experts, or given temporary appointments at court. These men did
not merely provide abstract theoretical explanations of the heavenly bodies which might be used
by the rulers to infer their own political conclusions. Rather, astrologers typically offered
detailed and specific advice, and often even propaganda, to support an individual ruler‘s claim to
5 See R. J. Evans, Rudolf II and his World: A Study in Intellectual History, 1576–1612 (Oxford:
Oxford University Press, 1984), Chapter 2: ―The Politics of Rudolf.‖ See also Jaroslava
Hausenblasová, Der Hof Kaiser Rudolfs II.: eine Edition der Hofstaatsverzeichnisse, 1576-1612
(Praha: Artefactum, 2002) and Peter Marshall, The Magic Circle of Rudolf II: Alchemy and
Astrology in Renaissance Prague (New York: Bloomsbury Publishing USA, 2006).
247

the throne, to ascertain the result of a forthcoming battle, or to advance a particular political
agenda. 6 Astrology thus had ―an immediate and almost palpable role in politics.‖ 7
When Rudolf II designated Kepler his Imperial mathematician, he expected him to
provide astrological advice that was specifically political in nature. He expected this advice to
take full account not only of the positions of the heavenly bodies but also of the earthly situation
both in the Empire and abroad, and to include tangible conclusions about the best course of
action. Kepler therefore wrote reports for Rudolf on subjects ranging from the dispute between
Venice and Rome in 1605, the political situation in Hungary, and the pressing Turkish threat. He
provided horoscopes and astrological advice to Rudolf as well as to other powerful figures who
sought his expertise, including Rudolf‘s rival and eventual successor, Archduke Matthias; Count
Wallenstein, both before and after he became a general; and Bavarian Chancellor Herwart von
Hohenburg. Likewise, even before his promotion to Imperial mathematician, Kepler composed
annual predictions as part of his calendars, which often included political components. 8
Kepler knew well, in other words, that the astrologus was in many ways a politicus as
well. In fact, in his treatise ―On the More Certain Foundations of Astrology‖ of 1601, he argued
explicitly that ―in matters of politics and war, the astrologer clearly has an opinion to express.‖ 9
Yet he quickly limited this statement, and explained that
it is really the height of folly to look for predictions about specific matters….Nothing can
be looked for from Astrology except the prediction of some excess in the inclination of
souls. What this inclination will lead to in future realities is determined by man‘s choices
6 See Grafton, Cardano‘s Cosmos, Chapter 7: ―The Astrologer as Political Counselor.‖
7 Hayton, ―Astrology as Political Propaganda,‖ 63
8 See H. Darrel Rutkin, ―Various Uses of Horoscopes: Astrological Practices in Early Modern
Europe,‖ in Horoscopes and Public Spheres: Essays on the History of Astrology (Berlin: Walter
de Gruyter, 2005): 167-182, especially 170.
9 I have used J.V. Field‘s translation of ―On the More Certain Foundations of Astrology‖
included in ―A Lutheran Astrologer: Johannes Kepler,‖ Archive for History of Exact Sciences,
31.3 (1983): 189-272, section LXVIII.
248

in political matters—for man is the image of God, not merely the offspring of Nature—as
well as by other causes. Thus whether there will be peace or war in some particular
region is a matter for the judgment of those who are experienced in politics, for their
power of prediction is no less than that of the Astrologer. 10
Kepler himself had to offer the very predictions that at first dismissed as ―the height of folly,‖
and hence he argued not that such predictions should be avoided, but instead that they should be
based as much as possible on political knowledge and experience. Though the astrologer did
have some special insight into political affairs, Kepler maintained, that insight was limited—as
was astrology itself. The advice of a true politicus ought to be based on his understanding of
war, peace, and political affairs, rather than in the study of the heavens alone.
Kepler tried to take his own advice, and his astrological reports to the emperor were often
based on his personal political assessments of current events, rather than on the heavenly
positions and trajectories alone. When Rudolf requested that his Imperial mathematician supply
him with a report on the situation in Hungary, Kepler emphasized in the official report that
…since I was asked about the particularities of Hungary, I cannot do otherwise but focus
on earthly causes, with as much knowledge as I have of them. For I have often made
clear to the emperor my opinion that is a bad and groundless thing to judge by the
heavenly signs alone what will happen to the condition of his lands—rather, heavenly
signs should be subservient to common perception. 11
Though Kepler‘s own position hinged on both his astrological expertise and his ability to offer
sound political counsel, Kepler sought to emphasize his political skills and give them precedence
over his astrological expertise. Astrology was often unsuited to interpreting the specifics of a
10 Ibid., LXI.
11 Judicium astrologicum de Hungaria, in Johannes Kepler Opera Omnia, ed. Christian Frisch
(Frankfurt: 1858-1871), VIII.2, 335-338 at 335: ―Weil aber E. Mt. in sonderhaitt von Ungaru
fragen, kan Ich nit umb, sondern muss die Irdische Ursachen darzuziehen, sovil Ich darvon
wissenschafft habe. Dann E. K. M. Ich nun zum offtermahl meine mainung entdeckht, das es
einen sehr schlechten vnd nichtigen grund habe, wan man nur allain auss den Zaichen wil
vrtheilen, was es mit denen lendern fuer einen Zustand haben werde, die den Zaichen nach dem
gmainen Wahn vnderworffen sein sollen.‖
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messy political situation, particularly one with so many unknowns. Along similar lines, Kepler
emphasized in the same report that as he lacked the nativity of the Turkish emperor, he would
have to rely on political causes in his analysis of the Turkish threat as well. A good astrologus,
Kepler made clear in this report, did not automatically make a good politicus. If an astrologer
wanted to provide good counsel for his sovereign, he would have to broaden his perspective, and
take account of the local political forces in any given situation.
In a later ―Discourse on the Great Conjunction of 1623,‖ Kepler again argued that ―ein
gueter Politicus‖ should acquire a detailed knowledge of earthly circumstances, and that such
knowledge provided far more accurate predictions about ―particularfragen‖ than the motions of
the heavens. He further specified that
the more expert a politicus is, the more he will keep secret his suspicions—not only
because even he cannot offer a determinate truth about future contingencies, but also
because he knows that it does no service to the butcher for someone to tell the ox when it
will be slaughtered. 12
With this, Kepler went beyond his earlier assertion that astrologers should base their claims on
political knowledge. To be a good politicus, Kepler argued here, an astrologer who hoped to
offer helpful political counsel might need to conceal his astrological knowledge when that
knowledge was potentially damaging to his sovereign. Astrology, in this view, was not simply
an uncertain art when it came to the political sphere, but also a potentially dangerous one. Since
it seemed to offer independent guidance that stemmed directly from the heavens, it had the
power to do more serious damage than political advice from more mundane sources.
12 Discurs von der grossen conjunction, 1623, KOO VII, 685-713, at 708. ―Je besser aber ein
solcher in Politicis beritten vnd practiciert ist, je mehr er seine vermutungen verschweigen wirdt,
nicht nur darumb, weil de futuris contingenitibus ne apud illum quidem est determinata veritas,
sondern auch weil er weiss, dass dem Fleischhaker in dem kein dienst geschehe, wann einer dem
Ochsen sagte, zu welcher stunde er solte geschlachtet werden, dann ob jener schon dem Ochsen
gescheid genug, so gibt es doch weniger muehe, wanns dieser nicht weiss.‖
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This claim echoes one that Kepler made at far greater length in a private letter earlier in
his career. In 1611, Kepler wrote worriedly to an anonymous nobleman—whom Barbara Bauer
tentatively identified as Johann Anton Barwitz, secretary and close confidant of the emperor 13 —
about the dangers that astrology posed in the fraught political times leading up to Rudolf‘s
abdication. Kepler began the letter with the belief that like him, the recipient was a man loyal to
the German empire and the emperor, rather than to the Austrian or Bohemian factions who
opposed him. He then boldly stated the main purpose of his letter: to convince its recipient that
―astrology could do great harm to a monarch if some clever astrologer wanted to dupe him based
on his gullibility.‖ 14
Kepler hoped to join forces with the recipient of his letter so that ―this does
not happen to our emperor, [since]…the emperor is gullible.‖ 15
Kepler continued to explain that he referred not simply to popular astrology, of the sort
which he felt had little basis in nature, and which could easily be twisted to please either party in
a dispute. Rather, he felt that even the astrology which he had placed on more certain natural
foundations in his own work could cause political damage. People placed too much stock in the
word of astrologers, Kepler believed. While malicious astrologers might twist an astrological
report to suit their own purposes, even the report of an honest astrologer could lead to
undesirable political outcomes. Kepler clarified what he meant by referring to his own recent
experience—he had been asked by both the supporters of Matthias and the supporters of Rudolf
for an astrological analysis of the political situation and their respective fortunes. In reply to the
supporters of Matthias, whom he took to be enemies of the emperor, Kepler explained that he
13 See Barbara Bauer, ―Die Rolle des Hofastrologen und Hofmathematicus als fürstlicher
Berater,‖ in Hoefischer Humanismus, ed. A. Buck (Weinheim: VCH, 1989): 93-117. Much of
my discussion in this section and the next takes Bauer‘s article as its starting point.
14 KGW 16:612: ―Inter caetera hesterni colloquii, dixi uno verbo Astrologiam ingentia damna
afferre Monarchis, si catus aliquis astrologus illudere velit hominum credulitati.‖
15 Ibid.: ―Id ne Caesari nostro eveniat, operam mihi dandam puto. Caesar credulus est.‖
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had deliberately altered his astrological interpretation, since he felt that the real astrological
forecast would only cause damage to the emperor‘s cause and inspire his enemies. Instead, he
had given them a report which supported the emperor‘s position and undermined their own, in
the hopes that it might forestall an imminent escalation of the political conflict. As he wrote,
When asked about the decrees of the stars by those whom I know to be enemies of the
emperor, I did not respond with that which I assessed to be of some importance, but
rather with that which would demoralize the credulous: I said that the emperor would live
a long time, and that there were no bad directions....On the other hand, for Matthias I
predicted imminent unrest...I said this to the enemies of the emperor, because even if it
does not instill fear in them, certainly it will not inspire confidence either. 16
Likewise, he explained that he preferred to give the emperor no report at all on the question,
since the actual astrological indications were ―not of such importance that one ought to place
faith in them,‖ and that they might cause the emperor to ignore the ordinary means by which he
might improve his situation. Thus ―astrology would put him into a much worse situation than he
is in now.‖ 17
Kepler summarized the actual astrological prognosis for his correspondent, so he would
have all the information at hand. He emphasized that though he felt it was insignificant, most
astrologers would interpret it by placing their confidence in Matthias and deeming the position of
the emperor to be very alarming. Accordingly, he insisted,
16 Ibid.: ―Ego rogatus a partibus, quas Caesari scio adversas, super astrorum decretis, respondi,
non quae per se alicujus momenti esse censeam, sed quae credulos percellant: nimirum
longaevam Caesaris aetatem, directiones malas nullas, Revolutiones quidem malas et Eclipses,
sed illas jam praeteritas ante annum biennium et triennium: Contra Matthiae turbas imminentes,
quia Saturnus ad Solem ipsius accedit, et quia fiet oppositio magna Saturni et Jovis, in loco Solis
ipsius. Haec dico hostibus Caesaris, quia si metum illis non incutiunt, certe confidentes non
reddunt.‖
17 Ibid.: ―Caesari ipsi nolim ista dicere quia non tanti sunt momenti, ut iis fidendum putem: et
vero metuo ut Caesarem praeter rationem obfirment, ut negligat media mediocria, quae
Principum fidelium intercessionibus habere fortasse potest: quo pacto Astrologia illum in multo
majus malum conjiceret, atque nunc est. ―
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I believe that astrology ought to be banished entirely, not only from the Senate, but also
from the minds of those who want to daily advise Caesar of what is best for him: indeed,
it must be fully hidden from the emperor‘s sight. 18
Even those who have the emperor‘s best interests at heart might be negatively influenced by
astrological rumors and conjectures, Kepler believed. The only way to safeguard the emperor
and ensure that his best interests were served would be to eliminate astrology from the political
sphere entirely.
In his emphasis on the benefits of political dissimulation, of course, Kepler was
embracing his role as politicus, rather than discounting it. The simple astrologer would offer his
interpretation of the heavens without worry of—or perhaps without knowledge of—its potential
consequences. That astrologer, however, would be doing a political disservice to his rulers.
Likewise, the simple astrologer who based his predictions on the heavens alone would miss
much of the political texture of the times and thus offer predictions that were incomplete or
simply wrong. Kepler did not deny that astrology could offer some political guidance, though he
did emphasize that that guidance was general at best, on the level of ―inclinations‖ rather than
necessities. Moreover, he emphasized that the guidance afforded by astrology needed to be
weighed heavily against the potential damage it could cause. In all this, Kepler emphasized that
the successful court astrologer needed to be more of a politician, rather than less of one. And in
hic conception of the scope and possibilities of politics, Kepler drew on a political tradition that
had become particularly popular in the decades before he assumed his post as Imperial
mathematician—the tradition of Tacitism.
18 Ibid.: ―Breviter, censeo Astrologiam exire debere non tantum e senatu, sed etiam ex animis
ipsis eorum, qui hodie Caesari optima suadere volunt, adeoque arcendam penitus a conspectu
Caesaris.‖
253

Kepler, Tacitus, and Tacitism
Throughout the sixteenth and much of the seventeenth centuries, commentaries on
Tacitus formed ―the common currency of political discourse.‖ 19
The writings of Tacitus seemed
to speak with particular relevancy to the men of early modern Europe—they too, navigated a
world that seemed characterized by violent conflict and that demanded a great deal of skillful
maneuvering from the successful courtier. Moreover, since Tacitus had kept his own political
views ambiguous, his writings could be mobilized to bolster multiple political perspectives in the
early modern period, including both the supporters and opponents of absolute monarchy. The
sheer number of books published on Tacitus in the sixteenth and seventeenth centuries bears
witness to his popularity for rulers, courtiers, and political theorists: more than 100
commentaries—mostly political—appeared between 1580 and 1700, along with sixty-seven
editions of the Annals and the Histories between 1600 and 1649. 20
Part of Tacitus‘s popularity lay in the fact that his writings were easily assimilated into
the reason-of-state (ratio status) tradition, an approach to politics which had become popular in
the sixteenth century, and in which Machiavelli could be appropriated. This tradition posited
that the ruler should be above the law, in certain instances, and able to override it. There were
typically deemed ―good‖ and ―bad‖ reasons-of-state: good reason of state allowed the ruler to
serve the public good, while bad reason of state served self-interest alone. Alongside this focus
on the power of the ruler to serve the common good, theorists also emphasized the idea of
political prudence, which applied both to rulers and their courtiers and demanded a degree of
19 See ―Commentary,‖ in The Classical Tradition, Eds. Anthony Grafton, Glenn W. Most, and
Salvatore Settis (Harvard University Press, 2010), 231.
20 Peter Burke, ―Tacitism, Skepticism and Reason of State,‖ in The Cambridge History of
Political Thought, 1450-1700, ed. J.H. Burns (Cambridge: Cambridge University Press, 1994):
479-498, at 484.
254

(warranted) dissimulation and state secrets (arcana imperii). Additionally, adherents to the
reason-of-state tradition argued that politics was a learned skill, or art, which could be acquired
via experience, whether gleaned personally or through a careful study of history. Particularly
since Machiavelli was often deemed too problematic to rely upon, Tacitus‘s work was used to
buttress this tradition. In this manner, Justus Lipsius, one of the most prominent early modern
Taciteans, devoted the fourth book of his Six Books of Politics to a discussion of how to best
promote the good of a kingdom, and the different kinds of dissimulation necessary to do so. 21
Several of Kepler‘s frequent correspondents—among them Christoph Besold and
Matthias Bernegger—were noted Tacitists of their time. Like them, Kepler too read Tacitus
politically. While serving in Prague as Imperial mathematician, he produced his own German
translation of the first book of Tacitus‘s Histories. Like most of his work, Kepler probably
intended this for eventual publication, but he first used it as a tool in the Latin instruction of his
son, Ludwig. Every week for three years, from when he was six years old, Ludwig read through
sections of Kepler‘s German text and translated them back into Latin. He and Kepler then
compared his Latin translation with Tacitus‘s original. 22
At the age of eighteen, Ludwig lent a
copy of Kepler‘s translation to Duchess Herberstorff, who—evidently finding much that was
useful in it—asked him for a copy for her son, Gottfried Heinrich von Pappenheim, who later
became an officer in Wallenstein‘s army. Instead of simply lending her a copy, Ludwig
decided—with Kepler‘s agreement—to publish the translation in 1625, with a dedication to the
Duchess. He described it much as Kepler seemed to understand it—as a book ―full of admirable
21 Ibid. esp. 482-483.
22 See the commentary by Friederike Boockmann on the ―Tacitus Uebersetztung‖ in KGW XII,
pp. 367-383.
255

discussions of regiments and wars, which are no less useful for the present time to read as the
general comparison of the old word to the new.‖ 23
In a letter to an anonymous woman, Kepler had once described himself as a
―mathematicus, philosophicus, and historicus.‖ Historia, he explained there, ―concerns itself
with old histories and church histories, and also with providing instruction to people of all
times‖—instruction which, he continued, ―today‘s preachers take to heart less than is fitting, else
there would be fewer conflicts.‖ 24
Kepler clearly felt that history could provide lessons for his
own time—lessons which would demonstrate ways to eliminate conflict, and which were
consequently particularly useful in the realms of politics and religion. He intended his Tacitus
translation to be read at court, by those with an interest in modern day governance. Though
Kepler approached Tacitus with the sophisticated and contextualizing eye of a humanist scholar,
and though he ―warned the reader not to look for simple, schoolboy lessons about political
prudence,‖ 25 his highly political focus on Tacitus—much like his astrological reports for the
emperor—marked him as a politicus, one interested in and conversant with the political trends of
his day.
Barbara Bauer has astutely noted, however, that Kepler focused on Tacitus both in his
translation of Book I of the Histories and in his Tertius Interveniens—and that the latter
23 Title page of Tacitus Ubersetzung, KGW XII, p. 103: ―…Voller trefflicher Regiments- und
Kriegs Discursen, Diser Zeit nit weniger nutzlich als von Vergleichung wegen der alten und
newen Welt annemblich zulesen.
24 KGW 17:643: ―Nu wolan Ich bin ein Mathematicus Philosophus und Historicus….die
Historica gehet auff alte geschichten und Kirchenhistori, auch was man Jeder zeitt fuer lehren
gefuehrt habe, darumben die Prediger heuettiges tags sich weniger annemen dan guett ist, sonst
waeren nit sovil streitte.‖
25 Anthony Grafton, ―Kepler as Reader,‖ in Journal of the History of Ideas 53.4 (1992): 561-
572, at 567.
256

discussion may reveal even more about Kepler‘s conception of himself as politicus. 26
In Tertius
Interveniens, Kepler responded to a wholesale repudiation of astrology by Philip Feselius,
physician to Margrave Georg Friedrich von Baden. Kepler, who had previously argued at length
against the wholesale adoption of astrology by Helisaeus Roeslin, here positioned himself as a
mediating figure who rejected both astrology‘s complete embrace and its complete rejection. In
the book, he argued that while much of astrology was foolish, much of it still had value—that
―no one should consider unbelievable that out of astrological foolishness and godlessness can be
found also useful wit and holiness.‖ 27
Toward the end of Tertius Interveniens, Kepler reflected on the prohibition in Leviticus
against consulting magi and arioli, or seers and astrologers, and asked what kind of astrology
this biblical prohibition encompassed. In answer, he referred broadly to the central role of the
astrologer in the Roman Empire—for instance, the fact that astrology guided every step of the
army. This, Kepler argued, was the sort of thing that the Bible forbade. He then referred
specifically to the story of Otho and Galba, as relayed by Tacitus in his Histories. According to
Tacitus, astrologers had inspired Otho to murder Galba and seek the throne of the Empire
himself, by telling him that his future foretold glory in the coming year. Tacitus had therefore
labeled astrologers, whom he called ―mathematici,‖ ―a group of men disloyal to those in power
and treacherous to those who aspire to it‖ 28 —a sentiment on which, Kepler noted, Feselius had
based his own anti-astrology tract.
26 See Bauer, ―Die Rolle des Hofastrologen.‖
27 Tertius Interveniens, KGW IV, 145-258 at 161: ―niemandt fuer unglaeublich halten / dass
auss der Astrologischen Narrheit und Gottlosigkeit / nicht auch eine nuetzliche Witz und
Heyligthumb…gefunden werden koendte.‖
28 KGW 12.238, 25-30: ―Welcher Historien Beschreibung dem Cornelio Tacito zu dem jenigen
Spruch Ursach geben, den Feselius fornen auffs Buch gesetzt: Dass nemlich die
Mathematici…seyen ‗genus hominum, potentibus infidum sperantibus fallax.‘‖
257

Kepler, however, wanted his book to distinguish between good and bad uses of astrology,
and thus he paused to consider what broader implications this Tacitean story truly had. He
concluded that if someone were to approach him with specific yes or no questions about the
coming year, such as whether a friend lived or died abroad or whether he would recover or die
from an illness, and if he were to respond by using a nativity to offer specific answers to those
questions, ―then I would be an ariolus, and a violator of God‘s law.‖ The entire process here,
Kepler argued—the decision of specific future actions on the basis of a nativity—was groundless
and unnatural. If, however, argued Kepler—taking up Tacitus‘s story—Otho had approached
him and simply asked how his nativity currently looked—without asking any specific questions,
and without revealing anything of his future plans—then Kepler, or any astrologer, could have
told him of the same ―good revolution‖ and lucky tidings that his astrologers had without any
negative compunctions. In this instance, Kepler wrote, ―I would not be guilty in [his plans],
because I had only told him that which was natural, with as good a conscience, as if he had
brought me the urine of Galba‖ 29 and asked for a medical prognosis on its basis.
On the one hand, Kepler‘s reflections here are significant for his differentiation between
the kind of astrology that was ―natural‖ and the kind that was groundless. He highlighted the
fact that astrologers who tried to predict specific events in the future based on the positions and
motions of the heavenly bodies were not practicing an art based in nature, but were instead
creating foolish fantasies—or worse, violating the word of God. By contrast, he insisted that the
positions of the heavenly bodies, and nativities in particular, did have more limited uses, and
29 Ibid. 239, 2-4 : ―Ich aber were an demselben unschlutig, dann ich ihme nur das gesagt hette,
was natuerlich, mit so gutem Gewissen, als hetter er mir urinam Galbae gebracht, fragendt, ob
er nicht kranck, und bald sterben wuerde.‖ Of course, critics of uroscopy took it as a primary
example of a theoretically inconsistent and empirically invalid procedure, as Kepler no doubt
knew. See M. Stolberg, ―The decline of uroscopy in early modern learned medicine (1500-
1650),‖ Early Sci Med. 2007;12 (3):313-36.
258

could reveal general patterns for the coming year. More importantly, however, Kepler‘s
reflections reveal a great deal about his conception of the role of the astrologer as politician. As
Barbara Bauer notes, Kepler invoked Tacitus‘s irresponsible ―ariolus‖ as a means for him to
relay his own sense of professional ethics. It was clear to Kepler that astrologers had the power
to cause great political upheaval, as in the case of Otho and Galba. The ethical astrologer, who
wanted to avoid Tacitus‘s charges of disloyalty and treachery, had two choices. On the one
hand, he could opt for the path that Kepler outlined in the Tertius Interveniens: he could,
essentially, opt out of politics entirely. As Kepler argued, if the astrologer were to base his
words solely on that which was naturally warranted, and if he were fully unaware of their
potential political ramifications, he could not be held accountable for whatever followed. He
could insist not only on his political neutrality, but also on his political naiveté, and in this way
absolve himself of all political responsibility.
Yet this choice was clearly unsatisfactory to Kepler. He wanted not just to avoid the
charge of irresponsibility, but to effect positive change; not merely to watch from the sidelines as
the political situation deteriorated on its own, but also to try and help improve it. He wanted to
be a better politicus, not to deny his political role. In this case, the ethical astrologer, fully aware
of the political situation and the potential ramifications of his words, needed to think carefully
about what he said, and to whom he said it. If telling Otho of his good revolution might lead him
to murder Galba, perhaps it would be better to tell him something different. Kepler took this
approach in his 1611 letter to the anonymous advisor to Rudolf. There, aware of the tense
situation between Matthias and Rudolf, he knew that a good astrological report to Matthias and a
bad report to Rudolf could lead to disastrous results. In order to avoid exacerbating the conflict,
Kepler felt that it was most appropriate to conceal his astrological knowledge and dissimulate to
259

Matthias, while trying to convince Rudolf to avoid astrology entirely. Moreover, in order to
make the right decision about when to dissimulate and when to speak the truth, the responsible
astrologer needed not to lessen his political involvement, but to broaden it—to learn as much as
possible about the political situation, and to gather experience, whether personal or historical,
that would enable him to act wisely and appropriately, for the good of both the ruler and the
state.
Kepler‘s Tacitism thus manifested itself on two levels. On the one hand, like many
others of his time, Kepler found in Tacitus a font of wisdom relevant to modern times, and
particularly to the troubled Empire of the early seventeenth century. Like other Tacitists, and
other adherents of the reason-of-state philosophy more generally, Kepler conceived of politics as
an art grounded in a rich context of personal and historical experience. Generals tended to make
better politicians than astrologers, Kepler believed, because their experiences on the ground
made them experts; absent this kind of experience, Kepler relied on his interactions at court, and
the historical insights and experiences of Tacitus. At the same time, like many other Tacitists,
Kepler believed that politics had an ethics that underpinned it. That ethics privileged the public
good over personal interest, and held that the public good could not be pinned down by prewritten
laws, but needed to be judged on a case by case basis. Moreover, it admitted—even
required—deception, if such deception furthered the public good.
The idea of the public good was not incidental to Kepler‘s political worldview—it was an
essential component of it. More than his political work for Rudolf, more than his astrology,
more even that his astronomy, Kepler valued his work on harmony. As he wrote to Christopher
Heydon in London in 1605, ―May God free me from astronomy, so that I might turn to the care
260

of my work on the harmony of the world.‖ 30
That work, he believed, had ramifications for all
aspects of life, including the political sphere. Indeed, in his Harmonice Mundi, Kepler included
his only lengthy theoretical examination of politics—an examination which also drew on his
knowledge of Tacitism, and particularly on the idea of the public good.
Kepler, King James I, and the Politics of the Harmonice Mundi
As Kepler wrote to Christoper Heydon, the Harmonice Mundi represented his own
personal passion. In that work, he planned to demonstrate the way that harmony underpinned
everything in nature, from the realm of music to the foundations of astrology and the motions of
the heavens. Moreover, he knew from the start to whom he would dedicate the book: King
James I of England. He continued to write to Heydon that ―already some time ago I silently
determined that [the Harmonice Mundi] would be for your king, not so much out of a desire to
become known to him, as for my ardent prayer that he might help to establish the harmony of the
church.‖ 31
King James, Kepler believed, had already proven his interest in harmony by his own
writings and deeds, and for this reason Kepler‘s dedication and his hopes that James might help
bring about churchly harmony seemed to Kepler ―not unsuited or disharmonious.‖ 32
The
Harmoncie Mundi was therefore conceived from the start as work with important religious and
political implications.
Kepler was not alone in his belief that James was uniquely positioned to help repair the
breaches in Christendom that had already led to so much violence and bloodshed. James had
30 KGW 15:357: ―Deus me ex Astronomia expediat, vt ad curam operis mei de harmonia mundi
conuertar.‖
31 Ibid.: ―Equidem illud opus iam pridem tacite Regi vestro destinaui, non tam studio ei
innotescendi, quam voto ardentissimo, vt in ipso coalescat harmonia Ecclesiae.‖
32 Ibid.: ―Is enim talia scripsit, talia facit, vt non inconueniens aut άνάρμοστος videatur
huiusmodi, vel dedicatio vel estistimatio.‖
261

personally witnessed the havoc that religious divisions could wreak on his own country, and
already in his speech to the first Parliament of his reign in March of 1604, he had made clear his
commitment to religious unification and harmony. ―I could wish from my heart,‖ he said, ―that
it would please God to make me one of the members of such a generall Christian vnion in
Religion, as laying wilfulnesse aside on both hands, wee might meete in the middest, which is
the Center and perfection of all things.‖ 33
Later, in his Premonition of 1609, the preface to a
reissue of his Apologie for the Oath of Allegiance of 1609, James had argued more specifically
that Christian princes should take it upon themselves to reunify their faith by calling for a general
council, in which a certain baseline of common beliefs could be identified, and all points of
division discussed and resolved.
Given James‘s clear interest in resolving a situation that seemed dangerously explosive,
others with similar interests in churchly unity or religious peace flocked to his court. Among
them were Isaac Casaubon, Georg Calixtus, and Hugo Grotius, all of whom argued for some
form of religious irenicism or conciliation. Casaubon stayed in England from 1610 to 1614,
during which time Calixtus and Grotius also visited; like James‘s own words and the letters, the
books of these three men ―helped to make England a center of irenic activity…and kept the idea
of a religious concord before a European audience.‖ 34
Moreover, James did not confine his
irenic ideals to words alone; the Jacobean Church reached out to Protestant Churches on the
continent and tried to establish contacts with the Eastern Orthodox Church as well. At the start
of the Thirty Years‘ War, James sent emissaries to the Empire to help the Protestants in Bohemia
and the Austrian Hapsburgs arrive at a peaceful resolution to their conflict. James did not hope
33 W. B. Patterson, King James VI and I and the Reunion of Christendom (Cambridge:
Cambridge University Press, 1997), 36.
34 Ibid. 152
262

for a universal Church in which everyone agreed an all points; rather, he envisioned ―a series of
national or particular churches, most of them directed by temporal authorities; some of them
recognized the spiritual jurisdiction of Rome while others did not.‖ 35
He believed that only by
this kind of compromise, with a baseline of agreement set by the ancient Church and room for
some divergence on the particulars, could there ever be a lasting European peace on both
religious and political fronts.
Kepler had reached out to James I even before he published his Harmonice Mundi. In
1607, he presented a special copy of his De Stella Nova, a book on the new star of 1604, to the
English king. He personally inscribed the copy of De Stella Nova, which he sent to James via his
Imperial ambassador, with the words ―To a philosopher king a servant philosopher/ To a Plato a
Diogenes/ To the master of Britain one who at Prague begs for a small offering from Alexander/
From his hired tub sends and recommends this, his philosophical demonstration.‖ 36
He also
wrote a letter to James, where he included a prayer for James‘s success in seeking both personal
and communal harmony:
May God bring it about that your Majesty govern Britain with such good fortune that you
are never forced to bid philosophy farewell because of the heavy weight of business.
May the thoughts and plans you undertake for the peace and improvement of the Church
be led to the safety of Christendom and the prosperity of the kingdom. 37
James had already, Kepler believed, shown his commitment to the principle of harmony as
35 Ibid. 362
36 ―Regi philosophanti, philosophus serviens, Platoni Diogenes, Britannias tententi, Pragae
stipem mendicans ab Alexandro, e dolio conductitio, hoc suum philosophema misit et
commendavit.‖ The copy to King James, with this inscription, is currently housed at the British
Library.
37 KGW 16:470: ―Faxit Deus Opt: Max: ut S. M. V. ea faelicitate Britanniam gubernet, ne
unquam negociorum mole oppressa, philosophiae valedicere cogatur. Idem S. M. V. studia
incepta, imperia cogitationesque ad Ecclesiae suae difficilime renascentis tranquillitatem
emendationemque, ad Reip: christianae incolumitatem, et subditorum regnorum salutem
dirigat.‖
263

applied to church and state. Philosophy, hoped Kepler—including the kind that he wrote in his
own books—would help James further understand and implement God‘s harmonic model. The
harmony of nature, in other words, could help provide James with model for harmony on earth,
and equip him with the tools necessary to achieve his harmonic vision.
When Kepler finally did complete his Harmonice Mundi, he wrote to Christoph Besold of
his plans to dedicate the book to King James. Besold agreed with Kepler‘s vision of the
monarch, and heartily endorsed the planned dedication. He too believed, he wrote, that James
was ―special among rulers and among scholars, and alone in our generation is one who most
happily joins together and harmonizes letters of every kind and expertise in ruling: thus this new
work of harmonies is owed to him.‖ 38
James was, of course, a Calvinist and the son of a
Catholic, yet the Lutheran Besold, like Kepler clearly felt him to be an ally in the cause of
religious peace. Moreover, Besold endorsed Kepler‘s planned dedication despite the fact that it
may have seemed politically risky, given Kepler‘s own position as a servant to the emperor. In
1613, James‘s daughter had married Frederick, ruler of the Palatine and leader of the German
Protestants. Just as Kepler‘s Harmonice Mundi was set to appear in print in 1619, Frederick
joined the cause of the Bohemians against the emperor by accepting their crown. Dedicating his
book openly to a monarch with close ties to the emperor‘s enemies was a political gamble for
Kepler, yet one both he and Besold clearly felt was worth taking.
In the dedication to the Harmonice Mundi, Kepler once again expounded on his reasons
for linking James to the cause of world harmony. He first clarified why it was not inappropriate
for him to dedicate the book to a foreign monarch, ―away from the court of the most august
38 KGW 17:799: ―Dedicationem ad Angliae Regem, suadeo omnino: argumentum sumerem ego
ex eo, quod is praecipuus inter magnates, praecipuus inter Litteras, et unicus seculi nostri, qui
felicissime litteras omnigenas et peritiam imperandi conjunxerit, et concordArit: cui itaque
novum hoc harmonicorum opus, debeatur.‖
264

emperor, my lord, from his kingdoms and hereditary Austrian provinces, and in fact away from
Germany.‖ 39
On the one hand, he argued that it would only benefit the Holy Roman Emperor if
his Kepler demonstrated to world outside the empire that the emperor had wisely allocated his
resources for the ―divine study‖ of mathematics, and had therefore directly supported the work
that Kepler published here. It would also be clear to the world ―from the uninterrupted progress
of the ornaments of peace throughout these provinces‖ that the rumors of civil war would surely
soon give way to peace in the Empire, and that ―that this slightly too harsh discord, as in an
emotional melody, is on the very point of resolution into a pleasing cadence.‖ 40
Given that the
Thirty Years‘ War had only just begun, and Rudolf had just abdicated the throne to his brother
Matthias, it is likely that Kepler‘s gesture toward a peaceful resolution of the conflict was
rhetorical in the short term. In the long term, however, he did believe that his Harmonice Mundi
supplied a true blueprint for harmony on earth, and consequently that its publication could
indeed help lead to a resolution of the political and religious troubles plaguing the Empire.
Kepler also argued that it was appropriate to select James as the dedicatee of the book on
his own merits as well. James himself obviously appreciated philosophical studies, as his own
writings and the opinion of his subjects made clear. In particular, he had proven himself wise
when it came to studies of the heavens—he had ―deemed the astronomy of Tycho
Brahe…worthy of the ornaments of his talent‖ and had visited Brahe‘s observatory in Denmark,
and he had ―marked the excesses of astrology with public censure‖ 41 in a book he had authored.
James would thus be able to truly evaluate and appreciate Kepler‘s masterpiece, since he would
39 The Harmony of the World, Ed. and trans. E. J. Aiton, A.M. Duncan, and J.V. Field
(Philadelphia: American Philosophical Society: 1997), p. 2.
40 Ibid.
41 Ibid., 3.
265

have ―complete understanding of the whole of this work and of all its parts.‖ 42
Yet even James‘s
philosophical acumen, unusual for a ruler, was not the main reason for Kepler‘s dedication to
him. Instead, Kepler‘s choice of James as dedicatee of the Harmonice Mundi stemmed from
―that manifold dissonance in human affairs.‖ 43
Though Kepler believed that ―it was God who
regulated all the melody of human life,‖ 44 and therefore that all dissonance served a purpose in
the grand harmony that God had orchestrated, he still yearned for peace in his own time. He had
turned to James, he explained, because ―my longings prompted me to look for some basis for
reconstructing consonance from your Davidic harp.‖ 45
In James‘s union of England and
Scotland he had ―produced one kingdom and one harmony (for what else is a kingdom but a
harmony?).‖ 46
This had proven, in Kepler‘s mind, that James was destined for even greater and
grander undertakings in the service of world harmony. Accordingly, Kepler felt that it was his
duty to reach out to James and provide him with the model whereby he could reproduce his
domestic successes on an international scale.
Here Kepler paused in his dedication to bemoan the personal circumstances that
prevented him from fully dedicating himself to the cause of world harmony. ―I should wish
here,‖ he wrote, ―for the three-part public dissonance of clamoring voices to show me a little
more moderation so that I could make the results of my own thinking publicly heard.‖ 47
Here
Kepler referred to the disputes between the three major confessions, and the fact that his private
attempts at moderation or conciliation had let not to personal harmony, but rather to his own
42 Ibid.
43 Ibid.
44 Ibid.
45 Ibid., 4
46 Ibid.
47 Ibid.
266

exclusion from the Lutheran communion. While he struggled for harmony in his personal life,
he believed that he had a higher, more public calling. ―What use will it be,‖ he wrote,
if in striving for harmony with my private clamor I do not overcome the public roaring,
through the weakness of my support, and in addition I increase the annoyance of the
absurd chorus to my ears? For my part I must confess—ah! What sorrow—that the crisscross
wound is still swollen, or if we prefer a more sacred and more felicitous word, the
cross-shaped wound is swollen…[and] the medicine has so far been useless, jeered at
from all sides….Yet I am invigorated by the very thought that the supreme Healer of our
wounds is sure in his art, and applies no remedy in vain. Therefore, he who embarked on
that care, who has now brought forward, has now shown to the world that confirmation,
but meanwhile encounters impairment through public calamities….[believes that] at last
this enduring dissonance (to revert to the metaphor which was suggested) will end in pure
and abiding harmony. 48
Kepler‘s sense of his own mission comes through clearly here: in his work, he hoped to provide a
remedy for the religious and political strife that he conceived of as a public illness, and a model
of harmony for a world only increasing in dissonance. In his view, his own excommunication
was both a personal misfortune and a threat to his larger, public mission. Hence he struggled to
transcend the ―private clamor,‖ and aim directly at the ―public roaring,‖ hopeful that such a
strategy would lead to a world harmony that might eventually heal his private wounds. With this
in mind, he reached out to James I as a ruler who might use his harmonic model effectively. He
prayed in his dedication that James would ―look upon this work on harmony…[and] stir up in
[himself] by the examples of the brilliance of concord in the visible works of God the zeal for
concord and for peace in church and state.‖ 49
In the five books of the Harmonice Mundi, Kepler offered a grand theory which used
geometry as the foundation for an analysis of harmony on multiple levels, among them musical,
astrological, and astronomical. In so doing, Kepler joined his voice to a discussion of harmony
that had originated in antiquity, a discussion begun by Pythagoras and continued by Plato and
48 Ibid. 4-5
49 Ibid., 5.
267

Ptolemy. Kepler blended the ideas of the three, by adopting Plato‘s realist view of geometry,
joining it to the Pythagorean notion of the harmony of the spheres, and using Ptolemy‘s musical
system as its basis. 50
Moreover, he hoped to offer not simply a poetic and rhetorical discussion
of harmony but also a physical system, ―a detailed and coherent explanation of the structure of
the cosmos in terms of a divine harmony based on geometry.‖ 51
At the same time, Kepler saw
harmony both as something created by God, and—as he had written to James—as something
which men ought to model on the ethical and communal levels. Throughout the text, he often
referenced the social implications of his notion of harmony. He began Book III, in which he
moved from the geometrical basis of his argument to the actual discussion of harmony in music,
with a quote from Proclus‘s commentary on the Elements of Euclid on the usefulness of
mathematical learning. Mathematics, Proclus had written,
perfects us in moral philosophy, implanting in our behavior order, propriety and harmony
in social relations. It also informs us what figures, what songs, what motions are
appropriate to virtue; and also the teaching by which the Athenian would have those who
will play attention to moral virtues from their youth cultivated and perfected.
Furthermore [Plato] makes plain the proportions of numbers which are associated with
the virtues, some in arithmetic, some in geometry, and others in harmony; and he shows
the excesses and deficiencies of the vices. By all of these we are guided to the middle
way in behavior and in morals. 52
Harmony, Kepler cited Proclus to demonstrate, connected the physical macrocosm to the
microcosm, and further connected both to the moral microcosm. Geometry provided the lexicon
for the harmony one could see or hear, as well as for the harmony that ought to govern virtuous
behavior and relations between men.
50 For a discussion of Kepler‘s musical theories of harmony, see H. F. Cohen, Quantifying
Music: The Science of Music at the First Stage of the Scientific Revolution, 1580-1650
(Dordrecht: Springer, 1984), particularly 13-34.
51 Ibid., ―Introduction,‖ xxxviii.
52 Ibid., 128.
268

Kepler was not unique in his focus on the social overtones of harmony. Pythagoras had
been known to argue that music directly affected the senses, and still further that certain musical
arrangements could lead men to fury and even murder, while others could transform ―into their
opposites all the maladies of the soul‖; likewise, the Pythagoreans were said to declare that
―virtue is harmony.‖ 53
With the rediscovery in the fifteenth and sixteenth centuries of many of
the ancient writings on music, the idea that music was somehow linked with moral behavior
gained new traction. Castiglione, Ficino, Shakespeare, and Milton were among those who saw
music not merely a source of knowledge about the world but also a ―moral force that seemed to
rectify the relationships between outside and inside, between the body and soul, between sense
and reason, between matter and understanding, and between subject and sovereign.‖ 54
The very
language of music took on moral overtones in this period, as individuals and communities were
described as ―justly proportioned,‖ ―well tempered,‖ ―measured,‖ and ―in tune.‖
One primary application of music‘s moral significance, and the one on which Kepler
focused when he dedicated his Harmonice Mundi to James, was political. Plato had placed
central importance on the role of music in his ideal state, and argued that ―musical training is a
more potent instrument than any other, because rhythm and harmony find their way into the
inward places of the soul.‖ 55
Many early modern thinkers went further still, and posited both that
music directly affected the moral behavior of members of the polis and that its harmonic order
provided a blueprint for the harmonic ordering of the state at large. Shakespeare echoed a
53 See Kristin Rygg, Masked Mysteries: Early Modern Music Theater and its Pythagorean
Subtext (Hillsdale: Pendragon Press, 2000), Chapter 5: ―Music and the Arts in the Pythagorean
Worldview,‖ 75-98, esp. 77.
54 See Kate van Orden, Music, Discipline, and Arms in Early Modern France (Chicago:
University of Chicago Press, 2005), Chapter 2: ―Juste Proportion: Music as the Measure of All
Things,‖ 37-80, citation from 78.
55 Plato, Republic, Book III
269

sentiment shared by many of his contemporaries when he compared governments to music, and
wrote that ―government, though high and low and loer, / Put into parts, doth keep in one consent.
/ Congreeing in a full and natural close, / Like music.‖ 56 Good government, that is, was a wellordered
hierarchy that could be likened to musical harmony; as Kepler had written in his preface
to James, ―what else is a kingdom but a harmony?‖ It followed that political disorder and strife
could be likened to musical dissonance; thus Shakespeare also wrote that if one were to ―take but
degree away, untune that string, / …hark, what discord follows.‖ 57
While Shakespeare used the
language of harmony largely as a political metaphor, others applied musical harmony to politics
far more directly. Perhaps the most prominent early modern example of the politics of harmony
can be found in the work of Jean Bodin—work on which Kepler focused directly in his
Harmonice Mundi.
Jean Bodin and Political Harmony
Jean Bodin—humanist, politician, jurist, and political philosopher—is today most famous
for his theory of absolute sovereignty. In the Six Books of the Republic of 1576, in which he first
articulated this theory, Bodin hoped to help resolve the civil unrest in France that had begun with
the start of the Wars of Religion in 1562. He would do so, he argued, by demonstrating how to
best organize the state, drawing on the teachings of both history and philosophy for guidance.
Moreover, his argument would not be of an ideal nature that could never be realized in actuality:
―we do not intend,‖ he wrote ―to describe a purely ideal and unrealizable commonwealth, such as
56 Shakespeare, Henry V, I, ii, 180-183.
57 Shakespeare, Troilus and Cressida, act 1, sc. 3, l. 109-10
270

that imagined by Plato or Thomas More, Chancellor of England.‖ 58
Rather, he argued for the
best kind of state that might actually thrive, and in particular, that might actually help to solve
the political problems of his day. His description of such a state hinged largely on the figure of
the absolute monarch: of ―the sovereign prince‖ who, he argued, ―is accountable only to God.‖
His arguments clearly reverberated with sixteenth-century readers, particularly given that they
were written in French, rather than Latin: seventeen French editions of his book appeared
between 1576 and 1596. In 1586, Bodin translated the book into Latin, and nine editions of the
Latin translation appeared between 1586 and 1641. 59
Bodin had first argued that the absolute sovereignty of the monarch was apparent from
daily experience of the natural world. ―There is no need to insist further that monarchy is the
best form,‖ he wrote,
seeing that the family, which is the true image of the commonwealth, has only one head,
as we have shown. All the laws of nature point towards monarchy, whether we regard
the microcosm of the body, all of whose members are subject to a single head on which
depend will, motion, and feeling, or whether we regard the macrocosm of the world,
subject to the one Almighty God. If we look at the heavens we see only one sun. We see
that gregarious animals never submit to many leaders, however godd they may be….The
true monarchical state, like a strong and healthy body, can easily maintain itself. But the
popular state and the aristocracy are weak and subject to many ills…. 60
Though this kind of natural verification of the superiority of monarchy was persuasive, Bodin
felt that something more than mere persuasion was warranted, given the tumultuous political
situation of his time. Indeed, the question of the ideal commonwealth was being hotly debated
by Bodin‘s contemporaries. In the Francogallia of 1573, Hueguenot Francois Hotman had used
58 Jean Bodin, Six Books of the Commonwealth, Ed. and trans. M. J. Tooley (Oxford: Blackwell,
1955), 2.
59 Van Orden, Music, Discipline, and Arms, 68.
60 Bodin, Book 6, Chapter 4, p. 199
271

historical arguments to demonstrate the superiority of popular sovereignty in France. 61
According to Hotman, the constitution of the ancient Francogallia supported a blend of
democracy, aristocracy, and monarchy, in which decisions were made by a common council with
supreme authority—a council which Hotman had explicitly linked to the modern day Estates
General. In order to support his claims, Hotman had relied on the musical metaphor and in
particular on the notion of harmony. He quoted from Cicero‘s Republic to prove that
harmonious and agreeable concord is produced…from the regular arrangement of
dissimilar sounds. In the same way a commonwealth which is regulated by reason
produces harmony through the consent of dissimilar elements, drawn, like the sounds,
from the highest and the middling orders, from the lowest and the intermediate estates.
What is called harmony in song by musicians, is called concord in a commonwealth. 62
Both in music and in government, Hotman had argued, harmony required the coming together of
different voices—and consequently could not be achieved via one absolute sovereign alone.
Bodin took up Hotman‘s challenge in his Republic, and argued not merely that Hotman‘s
understanding of political harmony was flawed, but that harmonic theory supplied a
mathematical—and therefore demonstrably certain—foundation for absolute monarchy. Hotman
had argued that political harmony necessarily implied that the Estate General should hold the
most power in France. Bodin, by contrasted, demonstrated even if one wanted to follow the
patterns supplied by musical theory, there were three different mathematical methods, or musical
means, by which one could organize a government—arithmetic, geometric, and harmonic. The
means, initially defined by Pythagoras, had traditionally been used to establish the proportional
relationships between intervals like the octave, fourth, and fifth. The arithmetic mean was
defined as m=(a+b)/2, the geometric mean as a/m=m/b, and the harmonic mean as m=2ab/(a+b).
61 For an expanded version of the discussion of Hotman and Bodin that follows, see van Orden,
Music, Discipline and Arms, Chapter 2.
62 Ibid. 72.
272

Thus, for example, for the octave, where a=1 and b=2, the arithmetic mean would be 3/2, or a
fifth, while the harmonic mean would be 4/3, or a fourth.
Bodin first used the idea of the means to describe three different ways to apply justice
and order a government. The arithmetic means, he explained, created sets in which the numbers
differed by equal amounts, but not proportions. In the arithmetic set 3, 9, 15, 21, for example,
each number is separated equally by 6, but the proportions between them are different.
According to Bodin, this corresponded to commutative justice, or the principle of equality, in
which justice is ―regulated by fixed and invariable laws, not susceptible of any equitable
interpretation nor admitting any privilege or exception of persons.‖ 63
The geometric means, by
contrast, created sets in which numbers differed by the same ratios, but unequal amounts. Thus
in the geometric set 3, 9, 27, 81, all members of the state are related by the ratio of 1:3, but not
by the equal addition of numbers. According to Bodin, this corresponded to distributive justice,
or the principle of similarity, in which different levels of society were subject to different laws,
such that ―it is agreed that the execution of the law ought to be adapted to the circumstances of
each case.‖ 64
The harmonic means, in Bodin‘s view, united the two. Rather than rely on
Pythagoras‘s definition, Bodin instead opted for a notion of the harmonic series that directly
combined elements of the arithmetic and geometric. For example, in the series 3, 4, 6, 8, 12, 16,
the arithmetic mean is inserted between each of the terms of a geometric set. Bodin argued that
this harmonic ―blending‖ of the two series corresponds to a harmonic justice that avoids ―the
unmitigated rigidity of the commutative principle, and the variability and uncertainty of the
distributive.‖ 65
63 Bodin, 205.
64 Ibid., 206.
65 Ibid.
273

More broadly, these means corresponded to different forms of government. The
arithmetic means, or the principle of equality without proportion, corresponded to a democracy,
or popular government, a society where the nobility were given no special privileges, and
equality under the law reigned supreme. The geometric means, or proportionality without
equality, corresponded to an aristocracy, where some individuals were privileged over others,
and the law was able to take these privileges into account. Finally, the harmonic means, which
combined the principles of equality and proportionality, corresponded to a monarchy with an
absolute sovereign. In such a system, the laws allowed for a measure of equality, but some
distinctions between nobles and commoners remained, and the sovereign was given the power to
supersede the law to achieve the best results for his people. Indeed, in Bodin‘s view the person
of the sovereign guaranteed the harmonious blending of the commutative and distributive
principles. According to Bodin, ―the wise king ought therefore to govern his kingdom
harmoniously, subtly combining nobles and commons, rich and poor...In doing this the prince
reconciles his subjects to one another, and all alike to the state.‖ 66
Bodin focused on the numerical and harmonic foundations of government again when he
stressed why this sovereign must be absolute. The orders of society in a harmonic government,
he argued, corresponded to the numbers 1 to 4. The king ―exalted above all his subjects, whose
majesty does not admit of any division, represents the principle of unity, from which all the rest
derive their force and cohesion.‖ 67
Below him, representing 2 to 4, were the three estates—the
clergy, the military, and the people. Bodin maintained that in order to have a truly harmonious
relationship between these groups, ―the union of its members depends on unity under a single
ruler, on whom the effectiveness of all the rest depends. A sovereign prince is therefore
66 Ibid., 211.
67 Ibid., 212.
274

indispensable, for it is his power which informs all the members of the commonwealth.‖ 68
Since
the king represented the number 1, his sovereignty and authority needed to be absolute and
indivisible, just as he needed to be above the law in order to properly blend the different kinds of
justice. Moreover, since all harmonic consonances could be produced with the ratios of the
numbers 1 to 4, the monarchical system was complete—any change would ―mar the harmony,
and make an intolerable discord.‖
With his discussion of the politics of harmony, Bodin hoped to provide a model of
political certainty in a world where state, religion, and philosophy all seemed increasingly
uncertain. Indeed, his discussion of harmonic justice had much in common with his approach to
both natural philosophy and religion, which all hinged on the notion of harmony. According to
Bodin, in the principle of harmony, whether in politics, religion, or the natural world, entailed the
mediation of opposites. In his Theater of all Nature, Bodin detailed a complicated chain of
being, in which all categories were linked to one another by intermediate elements: stones and
plants were linked by coral, while stones and earth were linked by clay. The middle term in each
case was not distinct from the extremes—it participated in their natures and in so doing brought
them together. The four elements held the entire natural world together, and though they were
opposites, their interconnectedness led to the harmony of nature. 69
As Bodin wrote, ―far from
causing the ruin of the world, the contrariety of the elements would by its absence destroy the
world, just as harmony is altogether lost if the intermediates between the high and low voices are
removed.‖ 70
68 Ibid.
69 See Ann Blair, The Theater of Nature: Jean Bodin and the Reanissance (Princeton: Princeton
University Press, 1997), 126-142.
70 Ibid.
275

Similarly, in Bodin‘s Colloquium Heptaplomeres, a religious dialogue between seven
men of differing religious views, harmony figures centrally. At the start of Book IV of the
dialogue, the participants discuss the nature of harmony in color, taste, music, and the motions of
the heavens, and the natural philosopher asserts that
this is very apparent in all of nature: opposites when united by the interpolation of certain
middle links present a remarkable harmony of the whole which otherwise would perish
completely if this whole world were fire or moisture. In like manner tones in unison
would take away all sweetness of harmony. 71
Similarly, he asserts that in a state, justice is only apparent when there are both good and wicked
men, both rich and poor, and both common and noble. The participants begin to debate whether
it is good for a state to include multiple religions, and from there they move to a discussion of
which religion is most true. In neither case do they rich a definitive conclusion. Indeed, the
debate continues until the very end of the text, in which Coronaeus, the Catholic, ends the
discussion with the following praise: ―Low, how good and pleasing it is for brothers to live in
unity, arranged not in common diatonics or chromatics, but in enharmonics, with a certain, more
divine modulation.‖ 72
With this statement, all the participants withdraw to their respective
homes,
having embraced each other in mutual love. Henceforth, they nourished their piety in
remarkable harmony and their integrity of life in common pursuits and intimacy.
However, afterwards they held no other conversation about religions, although each one
defended his own religion with the supreme sanctity of his life. 73
Though the participants reach no agreement on the nature of religious harmony, Bodin implicitly
71 Jean Bodin, Colloquium of the seven about secrets of the sublime, Ed. and Trans. Marion
Leathers Daniels Kuntz (Princeton: Princeton University Press, 1975), 146. The book was
highly unorthodox and circulated only in manuscript—see Noel Malcolm, ―Jean Bodin and the
Authorship of the "Colloquium Heptaplomeres,‖ Journal of the Warburg and Courtauld
Institutes 69, (2006): 95-150.
72 Ibid., p. 471.
73 Ibid.
276

offered his own perspective through this very ending. As in politics and in nature, so too in
religion, Bodin believed, harmony could be achieved via the blending of many opposite voices,
all linked in mutual appreciation of God and his world. For Bodin, the actualization of this
principle meant religious toleration in the state.
Many of Bodin‘s views share clear similarities to Kepler‘s own. In particular, Kepler and
Bodin both insisted on the centrality of harmony to spheres of nature, religion, and politics.
Kepler, like Bodin, hoped to highlight the points of commonality among the varying confessions,
and to achieve some kind of religious unity. His Harmonice Mundi highlighted, as did Bodin‘s
Theatrum, the centrality of harmony to all of nature, though Kepler‘s definition of harmony
differed from Bodin‘s in key respects. Likewise, Kepler also highlighted the political valences
of harmony—in fact, he did so by basing his discussion directly on the relevant sections of
Bodin‘s Republic. This discussion, which Kepler included as a brief ―political digression‖ at the
end of Book III of his Harmonice Mundi, reveals at the very outset Kepler‘s ―harmonious‖
embrace of differing perspectives, as the reliance on a Catholic and controversial thinker like
Bodin was itself highly unusual for someone in Kepler‘s position. And the ways that Kepler
both drew on and diverged from the views of Bodin reveals even more about Kepler‘s own view
of harmony, both natural and political.
Kepler, Bodin, and the Digressio Politica
At the very end of Book III of the Harmonice Mundi, Kepler included a ―Political
Digression on the Three Means.‖ This digression was a late addition to the text; Kepler opened
it by explaining that when he had first prepared the text, he had included only a brief paragraph
in the midst of Book III on the idea of ―harmonic proportions‖ in the state. There, he had written
277

a marginal note pointing to ―the splendid passage in Bodin on the state.‖ However, this
paragraph was accidentally omitted, because the pages of the original had been ―carelessly
distributed‖ during the printing. Upon recognizing the omission, Kepler wrote, he decided
instead to add the paragraph to the very end of Book III, and then to expand upon it into a longer
discussion of the politics of harmony. And instead of merely a brief reference to Bodin in the
margins, Kepler decided ―to transcribe from Bodin himself the main heads of this political
dissertation, shaping the words and arrangement as far as possible from my understanding of that
passage.‖ 74
He focused on Bodin, he explained, to clarify and correct Bodin‘s own discussion of
political harmony which he felt was both obscure and mathematically faulty, and he focused on
politics more generally in order ―to lighten the tedium of dour mathematical demonstrations, of
which the whole book consists, by the interpolation of some enjoyable popular material, and to
display a foretaste of its considerable usefulness in understanding the State.‖ 75
By titling this section a ―digression,‖ Kepler invoked the classical rhetorical technique
most closely associated with Cicero, and described at length by Quintilian in his Institutio
Oratoria. Quintillian had defined digressio as ―the handling of some theme which must however
have some bearing on the case, in a passage that involves digression from the logical order of our
speech.‖ 76
Rhetorical digressions were somewhat paradoxically titled—while departing from the
main subject of the speech and seemingly irrelevant, they were actually designed in order to
directly affect the reception of the speech as a whole. While Quintilian enumerated several
potential uses of the digressio, most centered on manipulating the emotions of the audience in
order to make them more receptive to the larger discussion. This was particularly the case when
74 Harmony of the World, 256.
75 Ibid.
76 The Institutio Oratoria of Quintilian, Trans. H.E. Butler, Loeb Classical Library (Cambridge:
Harvard University Press, 1980), IV. 3.14.
278

the topic being discussed was one to which the audience may have been unreceptive, or
unprepared to accept. In order to accomplish this, the digressio usually involved a topic that was
interesting or diverting; as Quintilian wrote, rhetoricians might digress ―to some pleasant and
attractive topic with a view to securing the utmost amount of favor from their audience.‖ 77
Kepler drew on this rhetorical tradition both in his use of the title ―Digressio politica‖
and in his explanation at its opening. He emphasized that the material he planned to discuss
departed from his primarily argument about harmony in nature in order to discuss Bodin‘s
application of harmony to the political realm. He likewise emphasized that this topic was
supposed to be a more generally pleasing topic to readers—indeed, unlike the rest of the
material, he deemed it ―popular‖ material, intended for the non-specialist. This popularity
should serve, he hoped, to convince his readers—some of whom, he implied, were not
themselves overly concerned with purely philosophical debates—that his seemingly esoteric
discussions of harmony were actually quite useful, particularly when it came to questions of
politics. It is likely that these readers were the rulers and patrons—like James I of England—
whom Kepler hoped to reach with his text. Earlier, at the start of his 1596 Mysterium
Cosmographicum Kepler had argued that it was unnecessary to focus on the utility of his
cosmological work, and that noble men in particular would delight in it as pleasurable in its own
right. ―Why must one value the advantage of divine things in cash, like food?‖ he had asked
there. ―For how is knowledge of natural things useful to a hungry stomach, how is the whole rest
of astronomy useful? Nevertheless wise men do not listen to the barbarity that shouts that these
studies must therefore be abandoned.‖ 78 However here, in the political digression to his
77 Ibid., IV., 3.1-2.
78 KGW 8.17, 14-22: ―Quanquam quid necesset est, diuinarum rerum vsus instar obsonij nummo
aestimare? Nam quid quaeso prodest ventri faemlico cognitio rerum naturalim, quid tota
279

Harmonice Mundi, he emphasized exactly the opposite: that this book had clear relevance, of
which he would only demonstrate a brief ―foretaste.‖ Kepler not only changed his own tune by
emphasizing the book‘s political utility, but he went against what would likely be the prevailing
opinion of the reader opening the text—that it had little practical import. The use of the
digressio technique would thus have allowed Kepler not only to try and sway the reader to agree
with him, but also to demonstrate how something seemingly off-topic—here political theory—
was actually centrally relevant to the larger themes of the book.
Since he geared his political digression toward the general reader, Kepler began with an
explanation of the musical means, or proportions, ―which is rather extended and more suited to
the understanding of the reader who is not a mathematician.‖ 79
He offered a detailed explanation
of geometric and arithmetic proportions and the series that they produced, and then moved on to
the harmonic proportion. According to Bodin, the harmonic proportion was a combination of the
arithmetic and the geometric, yet Kepler disagreed with Bodin‘s definition. On the one hand, he
noted that there were many instances in which the arithmetic and geometric proportions could be
combined in the manner described by Bodin, yet would not yield a harmonic series. On the other
hand, there were harmonic series which were also only geometric or only arithmetic, with no
combination of the two—and some which were neither. Kepler referenced his own earlier
discussion of musical harmony in Harmony of the World which provided examples of such
series, and emphasized that harmony was a unique principle, rather than merely combination of
others, and that it could not simply be arrived at via recourse to the old mathematical theories of
reliqua Astronomia? Neque tamen audiunt cordati homines illam barbariem, quae deserenda
proterea ista studia clamitat. Pictores ferimus, qui oculos, Symphoniacos, qui aures oblectant:
quamuis nullum rebus nostris emolumentum afferant. Et non tantum humana sed etiam honesta
conesetur voluptas, quae ex vtrorumque operibus capitur. Quae igitur inhumanitas, qua
stultitia, menti suum inuidere honestum gaudium, oculis et auribus non inuidere?‖
79 Harmony of the World, 256.
280

the ancients. Experience of the senses, too, needed to play a role in the determination of what
constituted a harmony; Bodin, in his attempt to link harmony only to the combination of the
geometric and the arithmetic, had ―rebel[ed] on the authority of the ancients against the sense of
hearing.‖ 80
After this mathematical explanation, Kepler proceeded to assess Bodin‘s application of
harmony to the moral and political spheres. Though he generally approved of Bodin‘s attempt to
link musical and political harmony, his disagreement with Bodin‘s definition of harmony led him
to differ with the particulars of Bodin‘s effort. Bodin had insisted that in justice and government,
as in music, harmony was produced by the blending of the arithmetic and the geometric—that is,
by the blending of the principles of equality and similarity. Kepler, by contrast, argued that
oftentimes such blending simply destroyed both principles and did not arrive at true harmony. In
order for true harmony to be achieved, Kepler insisted, it had to be thought of as a principle in its
own right, one which superseded both the ideas of equality and similarity. When it came to
issues of justice or morality, Kepler therefore maintained that the principle of harmony
symbolized the common or public good: ―the public good,‖ he wrote, ―has a certain
correspondence with the way in which singing in harmonic parts is pleasing.‖ 81
In politics,
Kepler maintained that the principle of harmony stood for the good of the state. He explained
that
this one supreme law, the mother of all laws—that anything on which the safety of the
state depends is ordered to be sacred and lawful—is…consistent…with harmonic
ratios…even if that law contains nothing further similar either to geometric or arithmetic
proportions. 82
80 Ibid. 257.
81 Ibid. 268.
82 Ibid.
281

In both instances, if one argued for the harmonic proportion, one implied that the common good
or public welfare stood above and beyond the needs of individuals.
In order to elaborate on both Bodin‘s and his own understanding of harmonic justice,
Kepler referred to one example brought by Bodin with which he agreed, though not for the same
reason as Bodin. Bodin had retold a story from the childhood of Cyrus of Persia, in which Cyrus
had observed a tall man wearing a short tunic standing near a dwarf with an overly long tunic. 83
Cyrus had argued that the two should exchange garments to obtain what would be best for them
both. His master had instead ordered that each should keep his own garment. Cyrus, according
to Bodin, had focused on the geometric proportion, or the principle of similarity, where justice
ought to take account of what was best for each individual. His master, by contrast, had focused
on the arithmetic proportion, or the principle of equality, where each individual ought to keep
what was rightfully his. Bodin suggested that the harmonic principle of justice could be
achieved if the tall man had paid the dwarf money in order to exchange garments. For Bodin,
this was harmonic because it combined the specific needs of each individual with the equality of
their resources—that is, it was a combination of both earlier suggestions. Kepler agreed that this
was a harmonic resolution, but argued that it was so because it arrived at the greatest common
benefit—―taking away from the one as much of his clothing as was superfluous, and from the
other money….for the common benefit of both is compared with the pleasantness of singing in
harmony.‖ 84
Kepler continued to discuss Bodin‘s ideas on harmonic justice, and argued that often in
Bodin‘s examples of the harmonic ―combination‖ of geometric and arithmetic justice he had
offered ―not a combination of intact kinds, but to a certain extent an infringement of them, to set
83 Bodin derived this story from Xenophon, Cyopaedia, 1, 3.
84 Harmony of the World, 261
282

up a harmonic proportion.‖ 85
Thus Kepler insisted that his own definition was preferable to
Bodin‘s, as it allowed harmonic justice to stand on its own merits. To demonstrate, Kepler again
offered an example in which he agreed with Bodin‘s result but not his rationale. Bodin had
noted that punishments for murder tended to accord with harmonic justice, since ―in the divine
law all murderers are punished by death with arithmetic equality, but the kind of death to be
inflicted is within the power of the judge in geometric correspondence with the dissimilar facts
and variety of circumstances.‖ 86
In particular, the punishment for killing a head of state was far
greater than for killing a peasant. Kepler agreed with Bodin that this was an instance of
harmonic justice, but not because it sought to combine the arithmetic and the geometric. ―This
inequality in punishments,‖ Kepler wrote,
is due not so much to the individual persons injured as to the safety of the whole republic
which permits all enemies of the fatherland to be killed with impunity, and at the same
time safeguards the well being of all the citizens in the security of the leader and the
aristocracy and in the preservation of public tranquility. 87
This was harmonic justice, Kepler argued, not because it combined elements of the arithmetic
and the geometric, but rather because it sought to preserve the public good above all else, by
preserving those who were charged with safeguarding it.
Here Kepler included a further example of Bodin‘s ―harmonic‖ justice, only to distance
himself from it. According to Bodin, a physician often took more money for curing a rich man
in order to subsidize the car of a poor man—in the harmonic ratio, Bodin argued, ―the wealth of
the latter and the health of the former are compared‖ (―not, I think, with the same certainty,‖
inserted Kepler glibly). 88
Bodin related this practice to the custom of judges in assigning fees for
85 Ibid. 263
86 Ibid. 267
87 Ibid. 268
88 Ibid. 272
283

their cases. Often, he noted, cases that required the most effort were the least profitable;
therefore harmonic justice allowed judges to assess their cases and demand appropriate fees from
the litigants, particularly in cases where the fee from the republic was insufficient for the effort
required by the case. Kepler, by contrast, found this practice highly distasteful. ―I leave this
harmonic part-song to its author Bodin as a Frenchman,‖ he wrote. ―Among us Germans justice
in the chief states and provinces is kept far away from meanness of that kind, and it is not lawful
to demand anything beyond what is prescribed by law.‖ 89
Kepler then moved on to assess not merely Bodin‘s approach to justice, but also to the
various forms of government. He first described Bodin‘s linkage between the arithmetic
proportion and democracy, the geometric proportion and aristocracy, and the harmonic
proportion and monarchy. While Kepler did not follow Bodin in specifically endorsing
monarchy as the ideal form of state, he approved of Bodin‘s use of the term ―harmonic‖ in his
description of monarchy, and believed that here Bodin had followed Kepler‘s definition of the
term inasmuch as he ―relates all policies not so much to individual orders or men, as to the whole
body of the state, and its safety and mutual love and peace.‖ 90
Yet though he approved of this
focus on the good of the state, Kepler argued against the kind of mathematized politics that
Bodin sought to establish as the foundation for the state—one in which a harmonic series could
be broken down into its component geometric and arithmetic parts in order to yield a specific
formula by which the state should be governed. ―If the harmonic proportions of numbers bring
any light to bear on the understanding of politics,‖ he wrote, ―they do it on their own account,
89 Ibid.
90 Ibid. 260
284

independently of any relation with geometric proportions.‖ 91
Harmony was a sui generis
principle, Kepler believed, and the lessons it yielded for statecraft were also sui generis.
What, then, were those lessons? Kepler remained vague on the particulars, and chose to
focus on the larger concept of political harmony as public good. He demurred that he himself
was not so politically experienced, nor did his book focus primarily on politics. ―Certainly if I
had acquired knowledge of the state, and was dealing with politics in this book,‖ he wrote,
―…Bodin would have learnt from this Harmony of mine…how to be a better political
philosopher.‖ 92
Yet Kepler could, perhaps, offer some brief pointers. In particular, while he
had earlier discussed Bodin‘s theory of arithmetic, geometric, and harmonic justice without
betraying his own preference, his claim that German judges, unlike their French counterparts,
were above the kind of ―harmonic‖ fee-gathering that Bodin described was telling. He argued
here more generally that harmonic proportions were best applied only to the ruling of the state,
and not to the realm of justice. ―I should say,‖ he wrote,
that the condition of the state and the pattern of its government were one thing, and the
administration of justice another, for they differ as part and whole; just as in mathematics
geometric and arithmetic proportions in numbers are one thing, and musical harmonies
expressed in numbers another. 93
Judges, that is, ought to be wholly separated from rulers, and they ought to administer justice
strictly according to either the geometric and arithmetic proportions—that is, with careful
consideration for the letter of the law or for fairness. The ruler, by contrast, was ―exercising a
higher office, safeguarding the state and its individual limbs,‖ and thus ought to be guided by
harmonic proportions—he should, that is, have the prerogative to depart from all considerations
91 Ibid. 275
92 Ibid.
93 Ibid.
285

legality or individual fairness at will, and to focus solely on public harmony and the welfare of
the state.
Here, Kepler was deliberately vague on what sort of ruler he had in mind—and by
extension, on what he felt was the ideal form of government. While Bodin had argued that
mathematics had definitively pointed to the royal state as the ideal, Kepler instead described his
ruler simply as ―this regent, whether he be king, or the aristocracy, or the entire people‖ 94 —for
all of these could, in principle, be guided by the notion of political harmony as Kepler had
described it. Kepler further emphasized the fact that harmony, when it came to government, was
not a objective mathematical blueprint for how to govern, but rather an argument for the free and
subjective judgments of the ruler. If those responsible for the welfare of the state were bound by
detailed mathematical guidelines, by the intimate details of the law, or the demands of fairness,
Kepler argued ―for God‘s sake, what a crop of arguments there would be!‖ 95
Though it was
appropriate for the decisions of judges to be subjected to intense scrutiny, and to be ―turned
inside out and subjected to the most detailed examination by those learned in the law,‖ the
direction and condition of the state at large, ―unfettered by such great compulsions, should be
adapted to the general well-being at the will of the ruler, according to the circumstances, without
a great commotion.‖ 96
His own vagueness on the ideal form of the state and the appropriate
decisions of the ruler was itself a political stance guided by harmony, as it left the ruler with the
freedom and discretion to guide the state to safety and security. Though it might in theory be
possible to associate particular kinds of harmony with the acts and duties of the ruler—for
example, Kepler noted that soft harmony (the minor scale) was linked with peace, and hard (the
94 Ibid. 276
95 Ibid.
96 Ibid.
286

major scale) with war—Kepler himself avoided detailing these associations, writing that he
wished instead to ―leave these matters to others to take care of, whose style of life is more
appropriate for them: I myself now hurry to the themes belonging to my profession which
follow.‖ 97
Kepler ended his brief political digression with a consideration of Bodin‘s linkage
between the state and God‘s creation. Here, he wrote, ―I agree with his purpose as much as
anyone‖ 98 —if not with all of his specifics—in linking the idea of harmony to the natural world.
He briefly noted some of the harmonies which Bodin pointed to in the natural world, and then
ended with a list of ―discords,‖ which also existed both in the government of men and in
the government of the world: faults in the soul; monsters among animals; eclipses in the
heaven; inexpressibles in geometry....; in the works of providence examples of divine
anger and vengeance; among rational beings the devil. All of which are arranged by God
the supreme Regent for good end, and the most complete harmony of all things. 99
With this list of natural types of discord that ultimately resulted in harmony, Kepler reminded his
reader at the very end of his digression that as in nature, so in politics—communal discord too
could end in concord and harmony. He then closed his digression with the prayer that he could
continue to serve God through his work in whatever ways possible.
In his analysis of Kepler‘s political digression, August Nitschke has emphasized that
though Kepler‘s appeal to political harmony seems to allow for the arbitrary and uncontrolled
power of the ruler, in fact Kepler offers certain clear guidelines for rulers to follow. 100
Harmony
for Kepler, Nitschke reminds us, is not only an analogy, but also a cause. It has clear and visible
effects throughout nature. Kepler had explained earlier in the Harmonice Mundi that the
97 Ibid. 276-77
98 Ibid. 278
99 Ibid. 279
100 August Nitschke, ―Keplers Staats- und Rechtslehre,‖in Internationales Kepler-Symposium,
Band I, Weil der Stadt, 1971, (Hildesheim: HA Gerstenberg, 1973): 409-424.
287

heavenly bodies moved as an expression of harmony, astrological influences were harmonic, and
human souls
take joy in the harmonic proportions in musical notes which they perceive…they move
their bodies in dancing, their tongues in speaking, in accordance with the same laws.
Workmen adjust the blows of their hammers to it, soldiers their pace. Everything is
lively while the harmonies persist, and drowsy when they are disrupted. 101
In nature, Kepler argued, harmony led to motion, to action, and to joy. In politics, too, harmony
for Kepler was a cause in its own right, not simply a rhetorical excuse for arbitrary rule. When
Kepler wrote that the harmonic ruler was concerned with the welfare of the state above all else,
Nitschke argues, he relied on the idea of harmony as a political cause—as that which fashioned
men into a united political community. Consequently, in Kepler‘s view rulers did not have
unlimited power to make whatever arbitrary decisions they chose; rather, the good ruler followed
the principle of harmony only if all his actions contributed to political unity and the public good.
The function of the ruler, that is, was both to follow the model of harmony as a political ideal,
and also to create harmony in the state.
Conclusion: Political Harmony and the Nature of Politics
Bodin and Kepler had much in common in their focus on harmony. Both saw it as a
central principle that underpinned the natural world, and both sought to link the harmony of
nature to the harmony of church and state. Both lived in a world beset by uncertainty, violence,
and strife, and both hoped to use their work to improve that world and pave the way for peace.
Yet when it came to linking natural and political harmony, Bodin and Kepler opted for two very
different strategies. Bodin emphasized the mathematical foundations of his harmonic theory in
101 Ibid. 147. This is also the period in which military music came to be used as a way to keep
soldiers marching in unison. See William H. McNeill, Keeping Together in Time: Dance and
Drill in Human History (Cambridge: Harvard University Press, 1997), 86.
288

order to highlight its certainty. As the foundations for law and the monarchical state were
increasingly shaken, Bodin attempted to provide a new, stable basis for the French monarchy.
He argued that both the idea of monarchy and of absolute sovereignty were demonstrably rooted
in the mathematics of harmony, and hence that mathematics provided clear and direct rules, or
laws, by which politics ought to be organized and conducted. By ending his Republic with a
discussion of harmonic theory, Bodin sought to support his entire discussion of politics with a
mathematical foundation: ―in order to safeguard the monarchy against the chaos of the Wars of
Religion…he restructured government to correspond with universal laws that were as
mathematically sound as they were musically sensible.‖ 102
By highlighting Bodin‘s work in his own political digression, Kepler associated his own
ideas with those of Bodin; indeed, he noted that when it came to the general linkage between the
harmony of nature and the harmony of the state ―I agree with his purpose as much as anyone.‖
Kepler, too, was deeply troubled by the political instability and uncertainty of his own time, and
hoped that by his work he might provide a way for rulers to achieve and new and more lasting
political harmony. Indeed, even in praising Bodin so highly Kepler highlighted the practical goal
of worldly harmony, for few of his fellow Protestants would have had anything positive to say
about the work of Bodin. Yet though Kepler linked his mathematical and musical arguments to
his political discussion, he did so in a manner that differed dramatically from that of Bodin.
Bodin had sought to demonstrate that harmony was a mathematical combination of the geometric
and arithmetic means, and that that combination provided a mathematical formula by which
political harmony could be understood. Kepler disagreed with Bodin‘s mathematical
explanation, and argued that harmony was a principle unto itself. And while that principle might
102 Van Orden, Music, Discipline, and Arms, 78.
289

e mathematically described when it came to music, when it came to politics harmony provided
no specifics for governance. Harmony when applied to politics, Kepler argued, pointed only to
the fact that the public good and the welfare of the state should be preeminent. It offered a
relatively free reign to rulers—royal, democratic, or aristocratic, as the case may be—so long as
they sought to actively foster the good of the state above all else. In fact, establishing too
specific a model for government would only hinder this goal in Kepler‘s view, and lead to
further disagreement.
Kepler had long felt that his work should benefit not just his direct employers, and not
just individual expert readers, but rather the world at large. ―I go about my business,‖ he wrote
to Michael Maestlin in 1605, ―as if I did not serve the emperor but mankind and posterity.‖ 103
In
the Harmonice Mundi, the book he deemed his most important contribution and pinnacle of all
his previous work, he hoped to make the benefit of his labors especially clear to his readers. In
order to do so, he hoped to clearly demonstrate the nature of harmony in all its manifestations—
mathematical, musical, astrological, and astronomical. To this he added political and religious
harmony, and he dearly hoped that his book might point the way to the harmony of church and
state. To this end, he dedicated the book to James I of England, with the belief that James was
the sort of ruler who could take the lessons of the book to heart and implement them. He also
included a ―political digression‖ at the very middle of the book, and gestured toward the classical
rhetorical tradition in which ―digressions‖ were both separate from and central to the message
that a rhetorician hoped to convey. Politics, he implied here, was distinct from the mathematical
and natural harmony of the world, but could also be informed by it in important ways. Yet those
ways were highly general, and very unlike the detailed mathematical support for monarchy that
103 KGW 15:335: ―…sic me comparo, ac si non Caesarj sed generj humano posterisque
serviam.‖
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Bodin sought to locate in the mathematics of harmony. Mathematical and natural harmony could
provide a model for political and religious harmony, according to Kepler, yet such a model did
not preference one kind of government over another. Instead, it focused on the end results of
political action, while leaving the means to the discretion of the political actors.
That Kepler‘s idea of political harmony encompassed many different potential political
models was clear not merely from the content of the political digression, but from the framing of
the Harmonice Mundi as a whole. Kepler dedicated the book to the James as King of England,
yet was explicit in that dedication about his own position as advisor to the Holy Roman Emperor.
He wrote appreciatively of the political work of Bodin, who supported monarchy in France,
while also referring within his discussion of Bodin to his own identity as a German, and to at
least one area where the German approach to justice ought to be preferred. In framing the book
with reference to England, France, and the Holy Roman Empire, Kepler demonstrated the fact
that his approach to political harmony might, in theory, embrace all three, so long as their rulers
heeded his lessons. If the end result was political harmony and peace, then Kepler deemed it a
positive one, regardless of the specific form and constitution of the government.
At the same time, in citing Bodin, a Catholic, and dedicating his book to James, a
Calvinist, Kepler, as a Lutheran, sought to demonstrate that one specific confession was not
essential to the establishment of political harmony. Unlike Bodin, who in his writings focused
more on natural theology than on the particularities of confession, Kepler vocally identified as a
Lutheran—despite his excommunication—and did discuss the details of confessional disputes in
his writings. Yet though Kepler embraced a specific confessional stance, he—like Bodin—did
not want to tie it to the state. Exiled from Graz himself when the Catholic rulers decided to expel
the Protestant residents of the city, Kepler had suffered from the close linkage of politics and
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eligion, and in his discussions of the state, as in those of Bodin, religion is noticeably absent.
Though he did believe that political and religious harmony went hand in hand, this was because
he hoped for a more large-scale reunion of the confessions alongside the political stabilization of
the European states, rather than the imposition of one particular confessional stance on the state
itself.
In the end, Kepler‘s approach to politics drew in large part on his own experiences at
court and the ideas of neo-Tacitism so popular at the time. This approach to politics
―implied…a broader and more flexible conception of social structure and change and the limits
of policy and legislation.‖ 104
It implied a degree of relativism, a belief that politics was
subjective, a focus on public utility, and a belief that the welfare of the state, however it might
achieved, ought to take precedence over pre-conceived ideas of ―just government.‖ It also
emphasized that politics was an art, a skill learned via experience rather than via abstract
mathematical models. Indeed, throughout the sixteenth century the subjective nature of politics
was often explicitly contrasted with the objective certainty of mathematics. Tacitus was viewed
as the preeminent political thinker precisely because his writings were based on observation and
experience, rather than theoretical speculation. Plutarch had gotten it right when he emphasized
in his Moralia that while the rules of geometry were clear and unchanging, politics dealt with
―things that varie…and never meddleth with those that are firme, stable, and
immutable…[rather, it] descendeth to things full of varietie, error, trouble, and confusion.‖ 105
This is not to say that Kepler sought to distance himself from the uncertainties of politics.
As Imperial mathematician—a role which, at Kepler‘s time, was primarily astrological and
104 Donald Kelley, The Beginning of Ideology: Consciousness and Society in the French
Reformation (Cambridge: Cambridge University Press, 1981), 206.
105 Jessica Wolfe, Humanism, Machinery, and Renaissance Literature (Cambridge: Cambridge
University Press, 2004), 23.
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astronomical—Kepler knew that he needed to provide political advice to his employers. He
argued that astrology in and of itself could not provide a clear basis for political action, and
warned his patrons about the dangers inherent in political astrology—yet at the same time he
provided detailed political advice of his own. In doing so, he sought to rely on his knowledge of
politics as an art in itself—on his experiences at court, his readings of historical and political
works like those of Tacitus, and his knowledge of the current and ever-changing political
situation. In emphasizing that the successful court astrologer needed a firm grounding in politics
if he hoped to provide accurate predictions, Kepler essentially made the astrologer more of a
politician, rather than less of one. Astrology could not hope to be politically useful if it
pretended to stand on its own merits—only in combination with political acumen and experience
could it play a serious and helpful role in court life.
While Kepler sought to strengthen the linkage between astrology and politics, he sought
at the same time to deemphasize the linkage between mathematics and politics. In contrast to
Bodin and to later thinkers like Grotius and Hobbes who hoped to establish a ―mathematics of
politics‖, Kepler deliberately avoided a notion of political harmony that was too directly and
explicitly mathematical. While mathematics could provide a model of harmony that was
relevant to the political sphere, and even a kind of general blueprint, it could not—and indeed, it
should not—provide a detailed set of laws or rules by which states should be structured and run.
Kepler‘s understood politics as too much of a subjective art to be susceptible to explanation via
mathematical formulae. Though astrology itself spoke only of possibilities or inclinations, in
Kepler‘s view, and thus might possibly be merged with an understanding of politics,
mathematics by its nature spoke of certainties and incontrovertible truths, truths which were
incompatible with the ambiguity that characterized political affairs. If Kepler made the
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astrologer more of a politician, in other words, he made the mathematician less of one. And
much as the decision to avoid politics is itself a political decision, this very decoupling of
mathematics and politics had important political ramifications for Kepler, as we shall see in the
next chapter. It allowed him to construct the figure of the mathematician so as to make him
uniquely suited to mediate political disputes and provide solutions that might be acceptable to all
parties.
I opened this chapter with Kepler‘s claim that while men like Campanella and More
wrote political utopias, he would avoid politics in favor of philosophy. He wrote this in
reference to his Somnium, in which Duracotus, the main character of the short text, journeys to
the moon and considers the earth from a new vantage point. Though Kepler certainly did not
avoid politics in many of his other writings, it is true that the Somnium does not discuss political
issues explicitly, and focuses instead on questions of astronomy and natural philosophy like the
motion of the earth or the effects of the atmosphere. Yet there is a way, too, in which the
Somnium can be deemed a utopia with political relevance, for it does highlight—albeit
indirectly—Kepler‘s own perspective when it came to the state and to issues of communal
relations more broadly. Kepler described in his own footnotes to the Somnium what he deemed
―the thesis of this book‖:
What are for us among the main features of the entire universe: the twelve celestial signs,
solstices, equinoxes, tropical years, sidereal years, equator, colures, tropics, arctic circles,
and celestial poles, are all restricted to the very tiny terrestrial globe, and exist only in the
imagination of the earth dwellers. Hence, if we transfer the imagination to another
sphere, everything must be understood in an altered form. 106
The main thesis of the Somnium, in other words, is that much of what we take for granted as
natural and necessary is actually only happenstance, or a result of our personal and limited
106 Kepler's Somnium: The Dream, or Posthumous Work on Lunar Astronomy, Ed. and Trans.
Edward Rosen (Madison: University of Wisconsin Press, 1967), 85.
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perspectives. By moving from the earth to the moon, Kepler forced his narrator, and his readers,
to see the world differently, to challenge their preconceptions, and to recognize the inherent
subjectivity of much of their situations. 107
This lesson was in part astronomical—Kepler hoped
to demonstrate that the seeming centrality of the earth was merely a question of our limited
terrestrial perspective. Yet it was also political. As Kepler emphasized throughout his writings
on politics, in order to create a stable and peaceful state rulers and their advisors needed to
consider each situation on its own merits, to rely on their judgment and experience, and to place
the welfare of the state and the public good above the law. Still more, politicians needed to
foster their ability to see beyond the obvious, to imagine alternative possibilities and outcomes,
and to alter the truth, if necessary, if it furthered the greater good. The lessons of the Sominum,
while perhaps not political at the level of More or Campanella, were in this way still uniquely
suited to the political realm.
Kepler deemed himself a public servant and focused most of his political writings on the
global community, but he applied those lessons on a personal level as well. While Kepler
yearned for the harmony of the world, he yearned at the same time for the personal harmony that
seemed again and again to elude him. Cast out of his church, the community that meant the
most to him, Kepler found solace in the friendships he sustained with other scholars in the
Republic of Letters. Through letters and meetings with these men—many of whom, too,
struggled to find their place in the communities that overlapped with their idealized scholarly
republic—Kepler found a measure of the harmony that he devoted his life to elucidating. In the
107 See also Elizabeth Spiller, ―Reading through Galileo's Telescope: Johannes Kepler's Dream
for Reading Knowledge,‖ in Science, Reading, and Renaissance Literature. The Art of Making
Knowledge, 1580-1670 (Cambridge: Cambridge University Press, 2007), esp. 119-136.
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middle of his political digression to the Harmonice Mundi, he paused to consider this kind of
personal harmony. ―Friendships are given life by harmonic tempering,‖ he wrote.
For what concord is to proportion, that love, which is the foundation of friendship, is to
the whole compass of human life…Although friendship cannot survive frequent
injustices, yet it rejects laws, and refers everything to the sound and sober judgment of
love, dispensing now equality, now proportionality, and when neither, always dispensing
what seems in the immediate situation to make for the preservation of love, which is also
goaded on, as harmony is by discords, and as fire is by an iron poker, by a few injustices
and renews its strength by free forgiveness of them. 108
The harmony of the world, Kepler firmly believed, existed everywhere in nature—in the motions
of the heavenly bodies, in two voices raised in song, and in the soul of man, attuned to the
harmony of the creator in whose image he was fashioned. It ought to exist in church and state as
well, and Kepler bitterly bemoaned the discord that characterized his own time. The harmony of
personal friendship was one intermediate step between nature and community, and though it was
characterized by occasional discord, it could overcome that discord all the stronger. Kepler‘s
personal life was characterized by the same kind of strife that seemed to exist all around him. ―I
am a guest, a foreigner, almost unknown,‖ he wrote to Matthais Bernegger from Sagan. ―I am
all but deaf to the local language, I am in turn considered a barbarian….There is no house of my
own here, and I have no place in the church, from whose gate I have departed.‖ 109
What
consoled him were his friendships with men like Bernegger, and the hope that in his own life, as
in the world at large, discord would ultimately lead to an even greater harmony.
108 Harmony of the World, 263
109 KGW 18:1111: ―Hospes, peregrinus, pene ignotus, et tantum non surdus sum ad idioma
vicissimque barbarus habeor. Mos hic est, in aedibus parentum sponsae nuptias instituere
triduanas: mihi propria domus nulla; in templo sedes nulla, ex quo ab ejus ostio aberro.‖
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Chapter 6:
“The Christian Resolution of the Calendar”:
Kepler and Calendar Reform
In 1588, Michel de Montaigne grumbled about the effects of the calendar reforms
instituted by Pope Gregory several years earlier. ―The recent eclipse by the pope of ten days has
taken me so low that I cannot well get used to it,‖ he wrote. ―I grit my teeth, but my mind is
always ten days ahead or ten days behind.‖ 1
Though confusion about the Gregorian calendar
reform was widespread, acceptance of its legitimacy tended to fall along confessional lines;
Catholics typically supported the new calendar, while Protestants tended to reject it because of
its papal origins. Kepler, along with Tycho Brahe, is often cited as an exception to this rule.
Conventional wisdom holds that Kepler was one of the few Protestants able to rise above his
confessional allegiance and recognize the superiority of the Gregorian calendar; this is taken to
reveal the extent to which Kepler placed more value on astronomical precision than on
theological wrangling. 2 Yet such a claim greatly oversimplifies Kepler‘s approach to the
complex issue of calendar reform, an approach which evolved from his days as a schoolteacher
in Graz to his tenure as Imperial mathematician. At the same time, such a claim ignores the
1 Essays, Book III, Chapter XI: ―Of Cripples‖
2 See H. M Nobis, ―The Reaction of Astronomers to the Gregorian Calendar,‖ in Gregorian
Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th
Anniversary, 1582-1992, Eds. G. V. Coyne, M. A. Hoskin, and O. Pedersen (Vatican City:
Pontifical Academy of Sciences, Specolo Vaticano, 1983), 244; Gerald J. Whitrow, Time in
History: Views of Time from Prehistory to the Present Day (Oxford: Oxford University Press,
1990), 118; Johannes Janssen; History of the German People at the Close of the Middle Ages,
Volume 10, trans. A. M. Christie, M. A. Mitchell (London: K. Paul, Trench, Trübner, & co., ltd.,
1905), 55. Indeed, Kepler‘s preference for the Gregorian calendar is even cited—wrongly—as
the basis for his excommunication in Linz. (See, for example, Roscoe Lamont, ―The Reform of
the Julian Calendar,‖ 18-32, in Popular Astronomy 28 [Berkeley: University of California,
1920].)
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centrality of theology both to Kepler‘s life generally, and more specifically to his evolving
approach to the particular question of the calendar.
In this chapter, I offer an account of Kepler‘s approach to the reform of the calendar and
the manner in which that approached changed over time. Beginning with a short survey of the
state of the calendar debates at the end of the sixteenth century, I move first to a 1597 letter of
Kepler‘s to Michael Maestlin, in which he argued strongly for the adoption of the Gregorian
calendar by its Protestant opponents. I then focus the majority of the chapter on an unpublished
dialogue Kepler wrote around the year 1604, in which he proposed not the adoption of the
Gregorian calendar, but rather a differently reformed Julian calendar. Finally, I briefly consider
some of the documents that Kepler drafted for his Imperial employers on the question of the
calendar between 1607 and 1613, which once again urged the adoption of the Gregorian
calendar, but with certain key changes.
My central claim in this chapter is that Kepler‘s changing approach to the question of
calendar reform was closely tied with his growing awareness of the raging confessional conflicts
in early seventeenth-century Europe, and his desire to help resolve those conflicts. Many of
Kepler‘s contemporaries saw the Kalenderstreit as an essentially religious dispute, and historians
have typically portrayed the calendar dispute as a microcosm of the broader confessional discord
dividing Catholics and Protestants. 3
Kepler, too, recognized the theological underpinnings of the
issue, yet took them one step further, arguing that the calendar debate could be seen not only as a
3 See, for example, Ferdinand Kaltenbrunner, ―Die Polemik über die Gregorianische
Kalenderreform,‖ Sitzungsberichte der Kaiserlichen Akademie von Wissenschaften zu Wien,
Philosophisch-historische Klasse 87 (1877): 485-586; Felix Stieve, ―Der Kalenderstreit des 16.
Jahrhunderts,‖ Abhandlungen der Bayerischen Akademie der Wissenschaften, Historische Classe
15 (1880); and Bernd Roeck, Eine Stadt in Krieg und Frieden. Studien zur Geschichte der
Reichstadt Augsburg zwischen Kalenderstreit und Parität, vol. 1 (Göttingen: Vandenhoeck &
Ruprecht, 1989).
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microcosm of confessional conflict, but also as a model for confessional reconciliation. In his
1604 dialogue, in particular, he used the issue of calendar reform both to suggest the manner in
which the fissures in Christendom could be repaired, and also to offer a specific model for a kind
of churchly unity, one that did not depend on absolute agreement on points of doctrine between
the confessions. Resolving the problem of the calendar would provide both a step on the path to
a reunified Christendom, in Kepler‘s view, and a vision of what such a reunified Christendom
might look like.
Closely intertwined with this argument, my second claim in this chapter is that Kepler
used the issue of calendar reform and its resolution to articulate his conception of the proper
political and social role of the mathematician. Specifically, he portrayed the mathematician as a
vital mediator and conciliator, who through his craft provided not only a model of harmony, but
also a resolution to the specifics of certain controversies which led to disharmony in church and
state. At the same time, he took care to emphasize that in order for mathematicians to
successfully embrace this role, they needed to cultivate their detachment from political and
religious ties. Mathematicians could only effect real compromise on religious and political
issues, Kepler argued, if they made clear that they were governed by the rules of their discipline
alone, and not by the ordinances of the emperor or the pope, nor by their own personal biases.
Kepler‘s arguments about the proper role of the mathematician were inextricably linked
with his own personal role as Imperial mathematician, a political position which I examined in
some depth in the previous chapter. They also offer some insight into the larger story of the
relationship between science and court in early modern Europe. Much of the literature on early
modern astronomy emphasizes the court as a crucial new locale, the mid-point in a gradual move
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from the university to the scientific society or academy. 4
In this view, the court provided
astronomers with a more open and constructive space in which to practice their art, a space
unhindered by the intellectual constraints and disciplinary hierarchies of the university. By
extension, by linking their practices with the social prestige of the court, astronomers could
legitimate their work and enhance the status of a discipline previously deemed secondary to
natural philosophy. Galileo is cited as the preeminent example of someone who thrived in a
courtly environment, and cleverly used the court culture of patronage and exchange in order to
gain support and legitimacy for his astronomical work, earning the title of ―court philosopher and
mathematician‖ in the process. 5
Kepler certainly has a place in this story; after he was expelled from Graz and refused his
request for a faculty position at Tübingen, the court provided him with a place of refuge and the
opportunity to pursue his astronomical interests. Yet though Kepler embraced the chance offered
to him by Tycho and Rudolf, this chapter, like the last, reveals the extent to which he accepted
the mantle of Imperial mathematician with some apprehension, and uneasily negotiated the
boundary between his role as politicus and his role as mathematicus. Pamela Smith describes the
sharp contrasts felt by seventeenth-century scholars between the values of the Republic of
Letters and the values of court society; for her protagonists, ―the tension they felt between court
4 See, for example, Robert Westman, ―The Astronomer‘s Role in the Sixteenth Century: A
Preliminary Study,‖ History of Science 18(1980): 105-147. See also Bruce Moran, ―Patronage
and Institutions: Courts, Universities, and Academies in Germany: An Overview 1500-1750,‖ in
Patronage and Institutions: Science, Technology, and Medicine at the European Court, 1500-
1750, Ed. Bruce Moran, et al. (Rochester: Boydell and Brewer, 1991); Mario Biagioli,
―Scientific Revolution, Social Bricolage, and Etiquette,‖ in The Scientific Revolution in National
Context, eds. Roy Porter and Mikulas Teich (Cambridge: Cambridge University Press, 1992);
and Nicholas Jardine, ―The Places of Astronomy in Early Modern Culture,‖ Journal for the
History of Astronomy 29 (1998): 49-62.
5 See Mario Biagioli, Galileo, Courtier: The Practice of Science in the Culture of Absolutism
(Chicago: University of Chicago Press, 1993).
300

privileges and the life of the mind was palpable in their work.‖ 6
Kepler, too, worried more
generally about the damage caused to the discipline of mathematics and to the reputation of
mathematicians by their ties to politics, damage which could limit their potential for good. He
believed that this worry was born out by the calendar conflict, as each side‘s mathematical
integrity was compromised by its political and religious allegiances. Kepler‘s uncertainties
about his courtly role are an important reminder that the move from university to court was not
simply a move from a restricted to a freer environment—the court setting came with restrictions
of its own.
In the face of his uncertainties about his role as political advisor, Kepler used his 1604
dialogue to illustrate what he believed to be the ideal—mathematicians unhampered by political
ties, free to follow the rules of their craft alone, and thus to act as true and unbiased mediators
and conciliators. In reality, of course, Kepler could not escape his political duties, and he served
as the voice of the emperor when it came to the question of the calendar, eventually advancing an
official proposal which differed in some respects from his own views. Even that proposal was
ultimately unsuccessful, and the calendar conflict continued, as the confessional divide became
only more entrenched and violent over the course of his lifetime. Yet by examining his writings
on the calendar conflict, we gain a clearer picture of the kind of community Kepler hoped to
create, and the role he hoped to fill in order to bring it about.
6 Pamela Smith, The Business of Alchemy: Science and Culture in the Holy Roman Empire
(Princeton: Princeton University Press, 1997), 43.
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The Gregorian Calendar Reform and Protestant Reactions: A Brief History 7
The solar Julian calendar was introduced by Julius Caesar in 46 BC as the civil calendar
of the Roman Empire, and it subsequently became the civil calendar of Christian Europe. Since
it assumed the average year length to be 365 ¼ days, it divided the year into 365 days, with a
leap day added to February every four years to account for the extra quarter days. The vernal
equinox was assumed to be March 25. In addition to this civil calendar, the church needed a
method by which to correlate lunar and solar time, in order to properly set the dates for moveable
feasts like Easter, which were tied to particular seasons of the year. For this purpose, the church
used the 19-year Metonic luni-solar cycle, which helped to determine on what solar dates the
new moons of a given year would occur. 8
There were two problems with this overall arrangement. First, the periods of revolution
of the lunar and solar years are incommensurable, so that the Julian year is somewhat longer than
the year in the Metonic cycle. This introduced an error in the age of the moon of approximately
one day in 300 years. Second, the Julian length of the solar year is slightly longer than the actual
7 On the larger topic of the Gregorian calendar reform, see Ferdinand Kaltenbrunner, ―Die
Vorgeschichte der Gregorianischen Kalenderreform,‖ Sitzungsberichte der kaiserlichen
Akademie von Wissenschaften zu Wien, Philosophisch-historische Klasse, 82 (1876): 289-414;
and Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to
Commemorate its 400th Anniversary, 1582-1992, Eds. G. V. Coyne, M. A. Hoskin, and O.
Pedersen (Vatican City: Pontifical Academy of Sciences, Specolo Vaticano, 1983). In particular,
on the state of the calendar before the reform, see O. Pederson, ―The Ecclesiastical Calendar and
the Life of the Church,‖ 17-74, and J. D. North, ―The Western Calendar—‗Intolerabilis,
Horribilis, et Derisibilis.‘Four Centuries of Discontent,‖ 75-113, all in that volume. Also in the
same volume, for the specifics of the Gregorian Reform, see Gordon Moyer, ―Aloysius Lilius
and the ‗Compendium Novae Rationis Restituendi Kalendarium,‘‖ 171-188. On the reaction of
Protestants to the Gregorian reforms, see H. M Nobis, ―The Reaction of Astronomers to the
Gregorian Calendar,‖ 243-251; and Michael Hoskin, ―The Reception of the Calendar by Other
Churches,‖ 255-264. See also Kaltenbrunner, ―Die Polemik‖ and Stieve, ―Der Kalenderstreit.‖
8 The Metonic cycle contains 235 lunations, or new moons, over 19 years, with seven
intercalated half days and one omitted day, or saltus lunae, at the end of the cycle; in addition,
seven solar years of the cycle are embolistic years, with an intercalated month.
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tropical year (the time it takes the sun to return to the same position along the ecliptic), leading to
an error of 11 minutes and 14 seconds each year, or one day in 129 years. Both of these errors
were principally problematic because of the need to accurately calculate the date of Easter.
According to the Council of Nicaea in 325 AD, Easter Sunday was established as the first
Sunday after the first full moon occurring immediately after the vernal equinox. The Council,
recognizing that some slippage had already occurred since the time of Julius Caesar, fixed the
date of the vernal equinox to March 21, rather than 25, but did not establish measures to correct
for the faulty length of the Julian year; consequently, the astronomical vernal equinox continued
to move forward in time. Likewise, nothing was done to better correlate the lunar and solar
years and allow for a more accurate determination of the date of the new moon. By the midsixteenth
century, the astronomical vernal equinox was occurring on March 11, ten days earlier
than the set date of March 21, and astronomical new moons were occurring four days before
ecclesiastical new moons.
Of course, the problems with the Julian calendar were apparent even before the sixteenth
century, and attempts at reform were initiated, though never completed. Pope Clement VI had
briefly considered the question of calendar reform in 1344, as had the Council of Constance in
1417—both times without resolution. Nicholas of Cusa sought to reform the calendar at the
Council of Basle shortly thereafter, also unsuccessfully, while in 1476, Regiomontanus was
called to Rome to consult on the question of the calendar, but died before the question could be
seriously addressed. At the Lateran Council, Paul of Middelburg took up the reform of the
calendar, and recruited other expert opinions on the subject. Copernicus, asked for his views,
declined to comment, arguing that the motions of the sun and moon were not yet well enough
understood to successfully reform the calendar, and the Council ended with no conclusion
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eached. The Council of Trent finally jump-started the reform process in 1563, with the decision
to amend the missal and breviary, which included the calendar on which they were based. And
the reform process was finally completed in 1582, when Pope Gregory XIII created a
commission, headed by the Jesuit mathematician Christoph Clavius, to reform the calendar based
on the recommendations of astronomer Aloysius Lilius. The commission wrote up their plan in
the Compendium novae rationis restituendi Kalendarii, which they sent out to mathematicians at
Catholic universities throughout Europe for feedback. After some change based on the feedback,
Gregory XIII enacted the reforms in his Bull Inter Gravissimas on February 24, 1582, published
along with the Canones in Kalendarium Gregorianum Perpetuum.
The Gregorian reform encompassed several changes. First, in order to remedy the fact
that there were approximately three days too many in each 400 years, the new calendar dropped
three leap years in that amount of time, by allowing that the last year of a century would only be
a leap year if it were divisible by 400. This too left an error of one day in 3333 years, which the
reformers recognized, but deemed small enough to be acceptable. The new calendar also
reestablished March 21 as the true vernal equinox, in accordance with the decree of the Council
of Nicaea, by dropping ten days from the calendar. Thus the papal Bull specified that October 4,
1582 would be followed by October 15. Finally, Lilius‘s primary achievement in reforming the
calendar was his correction of the epact cycle. In brief, there were two methods by which the
lunar phases could be tabulated in the Metonic cycle in order to easily determine on what solar
date a new moon would occur, and by extension to set the date of Easter—the epacts were one,
and the Golden Numbers another. 9
Both methods were in error by the time of the Gregorian
9 The Golden Number represented the number of the year within the nineteen year cycle; they
thus ran from I to XIX and were assigned to successive years, such that all years with the same
Golden Number had the first full moon on the same date; likewise, a year with Golden Number
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Reforms. In Lilius‘s calendrical modifications, the Golden Number, then considered most
important for the calculation of Easter, was replaced by an improved epact cycle, which adjusted
both for the discrepancy between the ecclesiastical and astronomical new moons and the changes
to the solar calendar made in the Gregorian reforms. 10
The Gregorian calendar was accepted immediately in Catholic Europe, yet was received
by Protestants with suspicion and hostility. This was due in large part to the manner in which the
reform had been conducted, and in particular to its papal origins, rather than to any strong
opposition to the idea of calendar reform in itself. After all, Luther himself had recognized the
problems of the Julian calendar in his 1539 Von den Konziliis und Kirchen. Yet he had argued
first that it was unnecessary to tie the solar date of Easter to the lunar calendar at all, and
recommended instead a fixed date for Easter, following the example of Christmas. And more
II would have its first full moon 11 days earlier than years with Golden Number I. One could
simply calculate the golden number as 1 + A.D. mod 19, that is, by adding 1 to the year date and
dividing the sum by 19, with the remainder representing the Golden Number for that year. The
epact number was a related calculating device. The epact of a given year signified the age of the
moon on either January 1 or March 22, the earliest possible date for Easter (this varied
historically). Based on the epact number of a given year, the date of the first new moon and the
first full moon could be calculated, and from this one could calculate the dates of the moons of
the following months. The epact increased by 11 days each year, because of the 11 day
difference between the solar and lunar year. When the epact number was greater than 30 days,
one subtracted 30 to get the epact number for the next year, and intercalated a lunar month to that
year. The epact could be calculated as AD mod 19 X 11 mod 30; as is clear, it was closely
linked with the golden number. Indeed, before the Gregorian Reform it was supplied specifically
by the golden number, such that if one knew the golden number one automatically arrived at the
epact. In supplying a corrected epact cycle, Lilius essentially broke the link between the epacts
and the golden numbers.
10 This was done via a solar equation, which expressed the difference between the Julian and
Gregorian calendars, and increased by 1 every hundred years not divisible by 400, and a lunar
equation, which expressed the difference between the Julian calendar and the Metonic cycle, and
increased by 8 days every 2500 years. In order to express all this simply, a table was provided
for each month of the year, along with an expanded table of the epacts for successive years. The
entire cycle was to repeat every 7000 years. Even with the correction, the astronomical and
ecclesiastical new moons still differed, both because Lilius‘s cycle relied on the mean, rather
than the true moon, and to ensure that Easter and Passover did not coincide.
305

importantly for the matter at hand, he argued that reform of the civil calendar ought to be left to
political, rather than religious authorities. Following Luther‘s lead, German Protestants objected
to the Pope‘s meddling in what they saw as political business, suitable for the emperor alone.
In fact, the issue of the calendar had come under discussion in the empire shortly after the
introduction of the papal calendar in 1582, at the Reichstag in Augsburg of the same year.
There, Rudolf had requested reports on the question of the calendar reform from all of his
electors. Protestant electors like the Langrave of Hesse and Augustus of Saxony had argued
against the new introduction of the new calendar, but Rudolf ultimately decided to introduce the
reform throughout the empire. He issued a proclamation in September of 1583 which ordered
the adoption of the Gregorian calendar, starting in January of 1584; in it, he took care to avoid
any reference to its religious character or its papal author, noting only that it was necessary for
the empire to conform to the dating of other lands. Yet Protestants in the Empire were well
aware of the papal bull and—convinced that this was a religious issue—refused to adopt the new
calendar.
The city of Augsburg presents one particularly noteworthy example of the calendar
conflict and its effects. 11
When the new calendar was first issue by the pope, Augsburg was a biconfessional
city, ruled by Catholics but with Protestants forming the majority of the populace.
Even before the emperor‘s general proclamation, the city council of Augsburg decided in
January of 1583 to introduce the new calendar, and maintained that it did so ―for purely civic and
political reasons...without the least intention, however, of obstructing or interfering in any way in
11 See, for example, C. Scott Dixon, ―Urban Order and Religious Coexistence in the German
Imperial City: Augsburg and Donauwörth, 1548–1608,‖ Central European History 40 (2007): 1–
33.
306

the teaching, belief, order, or ceremonies of one or the other of the two religions.‖ 12
Yet the
Lutherans were not convinced; preachers argued against the new calendar from the pulpit, and
the Lutheran residents continued to conspicuously observe holidays according to the Julian
calendar. Butchers refused to slaughter according to the times of Gregorian-calendar holidays,
and Lutheran members of the city court refused to appear during Julian-calendar holidays. The
issue became violent when the Catholic city council attempted to banish Georg Müller, the
leading Lutheran preacher in Augsburg and a strident opponent of the new calendar. Müller was
freed by the city‘s Lutherans as he was being escorted out of town, and an armed riot ensued.
Eventually, Lutheran clergymen ordered the people to lay down arms and return home, but the
conflict itself was anything but resolved.
In addition to public sermons, Protestant theologians across the empire published short
pamphlets and longer tomes arguing against the Gregorian calendar reform. One noteworthy
example is Jacob Heerbrand, Professor of Theology at Tübingen, who published the 1584
Disputatio de adiaphoris, et calendario Gregoriano. In it, he referred to the new calendar as a
product of the ―"the anti-Christ and the devil,‖ and argued that if German Protestants accepted
the calendar, they would ultimately be accepting the religious authority of the Catholic pope. 13
―We do not recognize this legislator, this calendar-maker,‖ he wrote, ―just as we do not hear the
shepherd of the flock of the Lord, but a howling wolf.‖ 14
Likewise, the theologians at the
University of Tübingen issued an opinion on the calendar in 1583, in which they recommended
12 Ibid. 12.
13 On the particular reactions of Heerbrand and Maestlin to the Gregorian reforms, see Charlotte
Methuen, ―Time Human or Time Divine: Theological Aspects in Opposing the Gregorian
Calendar Reform,‖ in Science and Theology in the Reformation: Studies in Theological
Interpretation and Astronomical Observation in Sixteenth-Century Germany (London: T & T
Clark International, 2008): 61-73.
14 Hoskin, Gregorian Reform, 260.
307

to Duke Louis of Würrtemberg in the strongest terms possible that the new calendar be rejected.
The new calendar, they wrote,
has manifestly been devised for the furtherance of the idolatrous popish system.…If we
adopt his calendar, we must go into the church we he rings for us. Shall we have
fellowship with the Antichrist?....Should he succeed, through the imperial authority, in
fastening his calendar about our necks, he would bring the cord in such a way about our
horn that we could no longer defend ourselves against his tyranny in the church of God.
The Pope hereby grasps also at the electoral hats of the princes of the empire. If the new
calendar be not generally adopted, the world will not go to ruin on that account. Summer
will not come sooner or later if the vernal equinox should be set a few days farther back
or forward in the calendar; no peasant will be so simple as, on account of the calendar, to
send out his reapers at Whitsuntide, or the gatherers into his vineyard at St. James's Day.
These are merely the pretexts of people who stroke at the fox-tail of the Pope, and would
not be thought to do so. Satan is driven out of the Christian Church. We will not let him
slip in again through his representative, the Pope. 15
Acceptance of the new calendar, they argued, would imply their acceptance of the authority of
the pope. Since it was clear that the new calendar served no agricultural or commercial purpose,
the only reason for the pope to seek calendrical reform was to extend his own religious or
political power, both of which were unacceptable to the majority of Protestant Germans.
Though most of the arguments against the calendar reforms were religious ones offered
by theologians , the new calendar was criticized by astronomers and mathematicians as well.
Some, like Scaliger or Calvisius, accepted that calendar reform was necessary and timely, but
objected to the details of the Gregorian reform, and offered alternative reform plans of their own.
Others, like Michael Maestlin, Kepler‘s mentor and teacher of mathematics and astronomy at
Tübingen, argued both against the reforms of Pope Gregory in particular and against the very
idea of calendar reform more generally—or at least, against the present need for calendar
15 ―Kepler and his Discoveries,‖ National Quarterly Review, Eds. Edward Isidore Sears, et al.,
Volume 8, (New York: Pudney and Russell, 1864), 341.
308

eform. 16
In his 1583 Aussführlicher und Gründtlicher Bericht, Maestlin began by describing the
history of the Julian and ecclesiastical calendars, and enumerating the many problems that he
knew they contained. Yet he argued that ―although in the old Roman calendar, still employed by
us, some defects have crept in, they have not yet spread so far, nor by no means are they so
important that they need a correction.‖ Maestlin argued that reform was unnecessary for the dayto-day
business of life in the empire—by contrast, calendar reform would only confuse the
common people, making life more, not less difficult. Though the old calendar was not perfect, it
had sufficed until then, and would continue to suffice for a while yet. Indeed, argued Maestlin,
the Last Judgment was swiftly approaching, making calendar reform pointless, for the errors in
the calendar—only a few days at present—would not increase so much before the end of time
that they required imminent correction. Maestlin also claimed, like Heerbrand and the Senate of
Würrtemberg, that even if correction were warranted, the pope had no authority to institute what
was essentially a political reform, and that he did so only to increase his power in Protestant
regions.
Maestlin‘s mathematical and astronomical objections to the new calendar, though
discussed briefly in the Aussführlicher und Gründtlicher Bericht, were considered in more detail
in his 1586 Alterum Examen. There, Maestlin noted that even in the new calendar the vernal
equinox would not always fall on March 21, and thus it was foolish to affix it permanently to that
date. He argued that the current available astronomical tables—the Alfonsine and Prutenic—
were imperfect, and therefore that it would have been sensible to wait for improved tables before
establishing what Clavius and Gregory had vainly called a ―perpetual‖ calendar. He likewise
16 On Maestlin‘s approach to the Gregorian calendar reforms, see Richard A. Jarrell, ―The Life
and Scientific Work of the Tübingen Astronomer Michael Maestlin,‖ (Dissertion: University of
Toronto, 1971), 46-64.
309

objected to the fact that the new calendar relied on the mean, rather than the true motions of the
sun—any good calendar, he felt, should stick as closely to the true astronomical facts as possible.
He attacked the new epact cycle of Lilius as riddled with errors, resulting in an often incorrect
date for Easter. He concluded that rather than calling it a perpetual calendar, ―if you wish to find
a worthy epithet to apply to the Gregorian Calendar, a very correct one would be A VILE
MEDLEY OF ALL ERRORS.‖ 17
Since the Pope and his mathematicians could not have been
unaware that their reform contained so many errors, Maestlin believed, they clearly had ulterior
motives at heart.
Kepler and Calendar Reform c. 1597
The calendar debates still raged furiously in 1596, as Kepler, a young teacher and district
mathematician in Graz, finished writing his first book, the Mysterium Cosmographicum. Kepler
was eager to see the book in print, yet this was no simple proposition, for Graz was at some
distance from the main centers of printing, and Kepler had not yet made the sort of contacts there
who could easily help him with the task. Instead, he relied on his old teacher and friend Michael
Maestlin to see the work readied for publication at Tübingen. Maestlin undertook the task
gladly; he was, after all, a strong supporter of Kepler and a great admirer of the book. Yet he did
so at some cost to himself, for the efforts he expended on Kepler‘s behalf caused him to delay
the completion of his own work—in particular, he noted in a letter to Kepler, ―I couldn‘t finish
my work against the new calendar before the book fair, on account of which I received very great
criticism from the Senate.‖ 18
The work in question was Maestlin‘s Examina eorumdemque
17 Ibid. 59.
18 KGW 13:63: ―…meum contra Kalendarium nouum scriptum ante nundinas absolui non
potuerit, cuius gratia in magnam apud Senatum amplissimum reprehensionem incidi.‖
310

apologia, the latest of his polemical works against the Gregorian calendar reform, in which he
responded to Clavius‘s 1588 rebuttal of some of his previous arguments.
Kepler and Maestlin had much in common—from their national and religious allegiances
to their belief that the Copernican system truly represented the state of the cosmos. Yet on the
question of calendar reform, the 26-year old Kepler parted ways with his mentor—and with the
majority of his fellow Protestants—and believed that the Gregorian calendar ought to be adopted
by Protestant Germany. Though Kepler had never publicly addressed the issue of calendar
reform, he took up the issue in his reply to Maestlin, using Maestlin‘s off-hand mention of his
own work against the calendar to express his disagreement with Maestlin‘s approach. To ease
his criticism of Maestlin‘s position, he first took pains to note those areas in which he and
Maestlin were in agreement. The Gregorian calendar was not error-free, he admitted, and many
of Maestlin‘s own mathematical or astronomical arguments were sound—so much so, Kepler
punned, that ―neither a Clavi, 19 nor a wedge, nor indeed, not even the whole machinery of the
heavens will resolve [them].‖ 20
Kepler added that he himself was not fully satisfied with the
details of the new calendar; in particular, he found the Gregorian calendar‘s removal of ten days
of little advantage. Though he did not believe, like some, that the end of the world was
immediately at hand, 21 he knew it would come eventually, and hence he was not overly worried
that the date of Easter might change over time—by the ―empty fear,‖, as he mockingly put it,
―that the world will endure so long that Easter will fall in autumn, and the heavens will fall into
19 A nail, or a reference to Clavius, the calendar‘s chief promoter.
20 KGW 13:64: ―Novj equidem, quae tu suscepisti defendenda, ejusmodj firmata esse
argumentis, quae non Clavi neque cunej, imo ne tota quidem coelj machina solvet.‖
21 Much of his work takes for granted the notion of future progress in astronomy, and the
existence of future readers of his books. In the Harmonice Mundi, Kepler refers to readers 100
years in the future, while in the Astronomia Nova, he addresses a more general ―posterity,‖ and
hopes that God will allow the world to exist long enough for the questions he has not yet
resolved to be worked through by others.
311

the earth.‖ 22
Moreover, he felt that the calendar reforms were not needed from the perspective of
practical governance—the new calendar, he wrote, was as necessary for the political order ―as a
fifth wheel to a carriage.‖ 23
Finally, Kepler admitted that the fears of the Protestant theologians
about this Catholic innovation were not totally groundless—the theologians were right, he
averred, to ―look around and make sure that there isn't a snake lying in the grass.‖ 24
Kepler agreed with Maestlin in many respects, in other words. Yet here they parted
ways—―though I support all this,‖ wrote Kepler, ―as for the rest, my position is highly
heretical.‖ 25
That is, despite his objections, he firmly believed that the new calendar ought to be
embraced by its opponents—by individual Protestants, and by Germany more broadly. In
explaining why he felt this way, Kepler focused on the fact that the new calendar had already
been widely accepted, and was clearly there to stay. The objections he had raised at the start of
the letter, he implied, may well have been sufficient reasons to reject the new calendar in 1582,
but were no longer relevant in 1597. With the new calendar already a fixture throughout most of
Europe, Protestant Germany remained one of the few places to persist in refusing the reform, and
doing so put it at a distinct disadvantage. ―What should half of Germany do?‖ he asked. ―How
long will it separate from the rest of Europe?‖ 26
In contrast to Maestlin, Kepler argued that the
reform of the calendar would not lead to widespread confusion; it should be relatively easy to
change calendars at this late date, since the way had been paved by all those who had already
done so.
22 KGW 13:64: ―Neque sum in illo inani metu, ne mundus eo usque duret, dum pascha in
autumnum et caelum in terram cadat.‖
23 Ibid.: ―Quinimo hoc esse puto correctionem hanc ordini politico, quod quinta rota currui.‖
24 Ibid.: ―Illud etiam cum Theologis sentio: circumspiciendum fuisse non frustra, ne quA lateat
anguis in herba.‖
25 Ibid.: ―Haec cum ita teneam: in caeteris in magna sum haeresj.‖
26 Ibid.: ―Quid enim agat Germaniae dimidium? Quamdiu dissidebit ab Europa reliqua?‖
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In addition, Kepler argued, it was unclear what alternative the opponents to the Gregorian
calendar really anticipated. Unless they waited to see ―whether some deus ex machina comes,
and illuminates all those magistrates [who have accepted the new calendar] with the light of the
gospel,‖ 27 there were really only two other options to accepting the Gregorian reforms. For one,
they could simply stick with the old Julian calendar. Yet he noted that all the great astronomers
of the past 150 years, and even Luther himself, had argued that the calendar needed some
correction, and it would be foolish to ignore this. One the other hand, the opponents of the
Gregorian reforms could theoretically propose a new calendar of their own—and indeed, many
did just this—yet Kepler doubted that a better alternative would really surface. This was likely
in part due to the astronomical difficulties involved in the issue of calendar reform, but also, as
he explained, because once one alternative had been widely accepted, introducing another one
would certainly lead to only greater confusion. Therefore the only real solution at this point,
argued Kepler, was to reform the calendar following the Gregorian model. Even if it was not the
ideal solution, it was a workable solution for the present—and this was sufficient, for ―we are not
afraid for remote centuries.‖ 28
Kepler also responded directly to one of Maestlin‘s arguments—that astronomers should
avoid assisting in the reform of the calendar, since it made no practical difference to them what
calendar was widely accepted. Calendars were simply a convention for the ordering of time,
Maestlin had asserted, and though astronomers needed to agree on what convention they used,
the details were unimportant for their work. In response, Kepler emphasized one of the primary
27 Ibid., ―Quid expectamus? Num ut Deus aliquis e machina prodiens, omnes illos magistratus
Evengelij luce illuminet?‖
28 Ibid., ―…Gregorianam emendationem jam propagatam approbent: non quidem ut optimam,
sed ut non omnino pessimam proximis praesertim saeculis: nam remotiorum nos nullus tenet
metus.‖
313

arguments of his Mysterium Cosmographicum, the book which Maestlin had delayed his
calendar publication to support—that astronomers ―are concerned not only with utility but also
with order and beauty.‖ 29
In the dedication of the Mysterium Cosmographicum, as we have seen
in the previous chapters, Kepler had argued at length against those who argued that the book was
not ―useful.‖ ―Why must one value the advantage of divine things in cash, like food?‖ he wrote
there. 30
His book had revealed the beauty of the cosmos and provided a source of delight for
the mind; consequently no one should accuse him of undertaking anything useless. In a similar
vein, he argued here that even if the calendar had no bearing on the practical pursuit of
astronomy, the Gregorian calendar was still more astronomically pleasing than the Julian, and for
this reason it should be supported by astronomers. ―For if it pleased God to decorate the word
with perfect quantities,‖ he reasoned, ―why should not some perfection in the calendars also
please astronomers?‖ 31
Kepler likewise noted that noted that though Protestants worried about the theological
consequences of accepting the new calendar, they would be wise to note the theological
consequences of rejecting it as well. The opponents of the reform had argued that adopting the
pope‘s calendar would be tantamount to submitting to the theological authority of the pope. Yet
Kepler claimed that this was no longer the case. Having rejected the calendar already for nearly
20 years, Protestants had made it clear that they did not need to obey the Pope‘s decrees; if they
willingly accepted the calendar now, without additional compulsion, it would be clear that they
did so not because of the Pope‘s authority, but simply because they judged the reformed calendar
29 Ibid.: ―Astronomj non tantum ad utilitatem sed etiam ad ordinem et pulchritudinem intentj
sunt.‖
30 KGW 8.17, 14-15: ―Quanquam quid necesset est, diuinarum rerum vsus instar obsonij nummo
aestimare?‖
31 KGW 13:64: ―Nam si Deo mundum placuit ornare perfectis quantitatibus, cur non et
astronomis aliqua etiam perfectio placeat in fastis.‖
314

to be better than the old. By continuing to reject the Gregorian calendar, however, they ran the
risk that in the future, an emperor more hostile to Lutherans than Rudolf II would arise. Such an
emperor could easily seize on the rejection of the political edict to adopt the new calendar as a
reason for war, and in such a war Lutherans could lose their prized religious freedom in the
empire. ―It would preferable,‖ he wrote, ―to voluntarily accept it while there is still no
constraint,‖ 32 both to forestall this possibility and to make it clear that they did so by their own
choice, and not because of compulsion by an outside power.
Kepler ended his letter to Maestlin by noting that the turn of the century approached,
which could be used as an ideal time to adopt the new calendar—1600 was, after all, a more
appropriate year to inaugurate a new reckoning of time than 1582. He suggested that if the
emperor framed the edict for the new calendar as a political matter alone, and did so in open
consultation with his mathematicians, it would make clear that Protestant Germany had accepted
not Pope Gregory‘s bull, but rather the advice of their own mathematicians and the decree of
their emperor. He sincerely hoped that this would happen soon, for the good of his country and
the pride of his country-men; ―it is a disgrace to Germany,‖ he wrote, ―having restored the art of
reformation, to alone lack reform.‖ 33
Kepler was not unique among Protestants in his support of the Gregorian calendar.
Tycho Brahe, his soon-to-be employer in Prague, also felt that the Gregorian calendar was
preferable to the Julian, and he recognized that opposition to the calendar reform hinged largely
on its papal origins. 34
Yet Tycho felt that this was misguided, since the calendar was political,
rather than theological; indeed, he argued that its introduction by the pope was warranted, since
32 Ibid., ―Satius esset sponte aliquid adire dum nulla adhuc coactio pro foribus.‖
33 Ibid.: ―Turpe Germaniae, cum artem corrigendj restaurarit, solam correctione carere. ―
34 On Tycho‘s approach to the Gregorian calendar, see Kaltenbrunner, Die Polemik, 574.
315

only the pope had the kind of authority necessary for such a universal change. Additionally,
Tycho emphasized that there would always be problems inherent in any calendar, for no calendar
could perfectly represent the movements of the heavens. Kepler‘s position in his 1597 letter to
Maestlin was similar to Tycho‘s, in some respects. Like Tycho, Kepler argued that the
Gregorian calendar was not perfect, but was the best option available. He coupled this with his
belief, just emphasized in the Mysterium Cosmographicum, that astronomers ought to concern
themselves with beauty rather than merely with utility. The clear faults in the Julian calendar, he
felt, made it incumbent on astronomers to support whatever calendar best corrected those
faults—and if the only option were the calendar introduced by the Catholic pope, so be it.
Moreover, Kepler was similar to Tycho in his attempts to distinguish between religion and
politics when it came to the new calendar. Tycho had emphasized that the question of the
calendar was strictly political, rather than theological. Kepler, while recognizing that there were
theological issues at stake when the new calendar was first proposed in 1582, argued that fifteen
years after the calendar‘s widespread acceptance the question had become a political one. In
refusing to adopt the new calendar, Germany hurt itself politically, damaging its reputation in the
eyes of the world.
The damage to Germany‘s image caused by the rejection of the new calendar was
particularly upsetting to Kepler, because he believed that that image was specifically tied to the
issue of mathematics—as he once wrote, ―mathematics is the true pride of Germany alone.‖ 35
And if Kepler upheld Germany as the pinnacle of mathematical aptitude and innovation, he often
represented Italy as exactly the opposite. When Galileo wrote in 1597 of his hesitation to
publish his Copernican ideas, Kepler noted that Germany presented fewer impediments than
35 KGW 13:112: ―Decus autem Germaniae mihi quilibet est cuj tantum tribuo, quantum illj
tribuebam: quia nempe Mathemata verum decus sunt unius Germaniae.‖
316

Italy to its mathematicians. 36
Likewise, when he heard that Galileo‘s telescopic observations
were rejected in Italy in 1610, he noted such foolishness was only to be expected in a country
whose astronomers rejected parallax, a phenomenon almost universally accepted elsewhere. 37
When writing to congratulate Samuel Harenreffer—the son of theology professor Matthias—on
a mathematical disputation he had written, Kepler noted that he had done both Tübingen
University and the German nation proud with his work. ―Look at the nations,‖ he wrote in his
congratulatory letter. Unlike the Germans, ―the Italians [do nothing but] dream.‖ Kepler named
only two mathematicians of merit in Italy, Federico Commandinus and Giambattista Benedetti;
―for [even] Clavius,‖ he noted, ―is a German.‖ 38
And Kepler cited the fact that he himself was ―a
German, in nationality and character,‖ 39 as a reason why he could not move to Bologna when
offered the chair of mathematics there after the death of Magini. Germany was where
mathematics flourished, Kepler believed, and Germans were particularly known for their
36 KGW 13:76: ―Si tibi Italia minus est idonea ad publicationem, et si aliqua habiturus es
impedimenta, forsan Germania nobis hanc libertatem concedet.‖
37 KGW 16:584: ―Quid mirum, Professores Academiarum promiscuos opponere sese inventinoi
rei novae in illa Provincia, in qua rei tritissimae et apud omnes Astronomos contestatissimae,
Parallaxium scilicet, extant oppugnatores loco eminentissimi, eruditionis fama celeberrimi?‖
38 KGW 15:400: ―Circumspice nationes. Itali somniant (praeter unum Commandinum et Joh.
Baptistam Benedictum, Clavius enim Germanus est).‖ Interestingly, Christoph Scheiner lodged
the same complaint against the Holy Roman Empire that Kepler lodged against Italy, citing
Kepler himself as the only exception to the sad state of mathematics he found upon his visit to
Prague. Writing about his visit, he noted that ―the muses of mathematicians mourn on the shores
here: there is no mathematician of any name in Prague, none in Bohemia, none in Moravia, no
one in Austria (excepting Kepler, living in Linz, whom I will visit in my ascent).‖ [KGW
17:755: ―Sed Musae Mathematicorum hisce in oris lugent: nullus est Pragae alicuius nominis
Mathematicus, nullus in Bhohemia, in Morauia nullus, nemo I nAustria (excipio Keplerum Lincij
degentem, quem in ascensu meo adibo). Habet haec prouincia hoc tempore nullum; dolendum
sane est, studium hoc in nostra Societate ita languere.‖] Yet while for Scheiner this is simply a
comment about the problems found in a given location, for Kepler it seems to have been more
about national character, as he even included Clavius on the side of the Germans.
39 KGW 17:761: ―Ego natione, animoque Germanus sum, Germanorum moribus imbutus, ijs
vitae, hoc est (more Germanico inter literatos etiam recepto,) conjugij necessitatibus innexus, ut
si vel ipse Imperator annuat, non nisi difficilime domicilium ex Germania sim translaturus in
Italiam.‖
317

mathematical aptitude and the freedom to pursue their craft, while Italy was known for its
backwardness when it came to mathematical pursuits. Yet when it came to the question of the
calendar, Kepler found the situation suddenly reversed—Italy had pioneered a mathematically
advanced new calendar, while Germany refused to adopt it, and persisted with the old calendar
despite its errors. That the country known for its mathematical expertise should refuse to accept
an obvious mathematical improvement—and one originating from Italy, no less—was a disgrace,
in Kepler‘s eyes.
Yet behind Kepler‘s arguments to Maestlin there is also a clear element of religious and
political naïveté. He wrote to Maestlin that ―the path to renovation is very easy for us,‖ 40 clearly
not realizing quite how contentious an issue the adoption of the new calendar really was. Having
only recently moved from Tübingen University to Graz, and still only an unknown
schoolteacher, Kepler had not yet felt the full effects of the raging confessional disputes, nor had
he yet had any exposure to the complications of political debates in the empire. The following
years brought some dramatic changes to Kepler‘s life. Expelled from Graz because of his refusal
to convert to Catholicism, Kepler moved to the cosmopolitan city of Prague, to work for Tycho
Brahe at the court of Rudolf II. Within only a few short years he found himself granted the
position of Imperial mathematician following the death of Tycho Brahe. His personal exposure
to the violent effects of the fiercely entrenched confessional disputes was thus quickly coupled
with his immersion in the world of politics. Both these factors would affect his views on the
question of the calendar.
40 KGW 13:64:―Facilimus est nobis aditus ad novationem…‖
318

Kepler’s Dialogue on Calendar Reform, c. 1604
As Imperial mathematician, Kepler was often asked by Rudolf and other members of the
ruling elite both for astrological prognostications and for his opinion on issues of political
importance that pertained to mathematics. The new Gregorian calendar was clearly such an
issue, and between 1603 and 1613 Kepler received numerous requests for reports or opinions on
the question of the calendar. Of course, Kepler was not at liberty to respond in any way he
chose, for the emperor had his own views on the question of the calendar, particularly after his
early attempt to introduce the Gregorian calendar failed in the Protestant areas of the empire. I
will consider Kepler‘s official reports on the calendar shortly; first, I will focus on an
unpublished dialogue which Kepler drafted in 1604 on the question of the calendar, and which he
modified in successive drafts over a number of years.
Written during his tenure as Imperial mathematician, the dialogue reflects Kepler‘s
growing awareness of the difficult political and religious issues at stake in the calendar debates.
In fact, the immediate impetus for the work, which Kepler titled ―Ein Gespräch von der
Reformation des alten Calenders,‖ was likely the 1603 Reichstag convened by Matthias, then
Archduke of Austria (and later to become emperor after Rudolf II), during which he invited
discussion on the question of calendar reform. 41
Kepler may have drafted the work in
preparation for some of his official reports for the emperor and his electors, though it differs in
41 For a discussion of the dating of the dialogue, Friederike Boockmann‘s commentary on
Kepler‘s calendar manuscripts in KGW 21.1, 642-667, in particularly 649. Since Kepler
mentions a recent Reichstag in the dialogue, Frisch and others have conventionally assigned it to
1613, following the Reichstag in Regensburg of Rudolf II. Yet Boockmann notes that Kepler
refers to his time with Tycho as relatively recent, and Tycho died in 1601. Likewise, Kepler
refers to works written through 1603, and relies upon datings of the equinox through 1604.
Finally, he writes that it has been ―around twenty years‖ since the empire has operated with two
different calendars—and counting from Easter of 1603, this implies a date of 1603 or 1604. The
later drafts seem to date from 1604-1609.
319

some key respects from those reports—or he may have used it simply as a way to think through
the issues for himself and his correspondents in the Republic of Letters. In either case, the fact
that it does differ from those official documents, and that Kepler never published it or even
showed it to the emperor 42 —though he felt it important enough to return to it multiple times over
the years, and mentioned it in letters to his correspondents—suggests that, like his earlier letter to
Maestlin, it offers us some insight into his personal perspective on the question of calendar
reform.
As the title of the work indicates, Kepler intended it not simply as a discussion of the
already reformed Gregorian calendar, but rather as a more general ―dialogue on the reformation
of the old calendar‖—that is, a discussion about how to reform the Julian calendar, one which
does not take the Gregorian reforms as a given. Kepler clarified in subtitles that the dialogue
would actually consider three separate options—whether the states of the Holy Roman Empire
should adopt the Gregorian calendar, remain with the Julian calendar, or should adopt a third,
newly reformed Julian calendar, one which differed in important respects from the calendar
proposed by Pope Gregory. Kepler crafted the work as literary dialogue, with each position
represented by speakers who would debate them at length over the course of the work. It might
have made sense, Kepler noted in the preface, to name the characters in the dialogue after the
principal figures in the calendar reform debates—Clavius, who supported the Gregorian reforms
on behalf of the pope, and Maestlin, who argued against them on behalf of his fellow Protestants.
Yet Kepler worried that because the tenor of the debate between the two had become so hostile,
42 KGW 17:629: ―Est mihi ad manus manuscriptum colloqiuum de Calendario lingua Teutonica,
quem Caesari nunquam tradidi.‖
320

doing so would awaken old grudges, which would ―agitate my friendly dialogue.‖ 43
Therefore
he decided to create two fictional characters on each side of the debate, one political and one
religious. In support of the Gregorian calendar reforms—representing the Catholic side, that
is—he introduced the political Cancellarius and the religious Confessarius, and in opposition to
the Gregorian reforms—representing the Protestant side—he introduced the political Syndicus
and the religious Ecclesiastes. To these four characters he added a fifth, the young
Mathematicus—who, it soon becomes clear, was intended to represent Kepler himself.
The dialogue begins with each character making one of the stock claims often cited either
in support of or against the Gregorian calendar reform. Cancellarius first asserts the need for the
Holy Roman Empire to finally adopt the reformed calendar, since the maintenance of two
different calendars in the empire has led to ―unrest in political affairs.‖ 44
Confessarius supports
him by noting that only by adopting the new calendar can its opponents return to obedience of
the Church. By contrast, Syndicus argues that Protestant mathematicians have demonstrated a
great many defects in the Gregorian calendar, and Ecclesiastes maintains that only if the
emperor, and not the pope, reforms the calendar could Protestants possibly accept it, ―since we
differ from one another in doctrine.‖ 45
The four characters then debate whether or not the
calendar is a religious or political artifact, with each side using the examples of antiquity—
particularly that of Julius Caesar and the emperor Constantine—to support its claims. The
Catholics, who argue that it is religious, maintain that it is a matter for papal correction, while the
43 KGW 21.1, 351, 27-29: ―Ich hab mich aber besorget, wail sie baide einander vor disem in
gengeschriften unfreundtlich tractirt: möchte auß dem alten grollen ein feindselighkheitt
erwachsen, und mir mein vertrawliches gespr ch verunruewigen.‖
44 Ibid., 352, 1-3: ―…wir der gorssen ungleichheitt in halting der feyr und festtäge, wölliche nun
uber zwantzig Jahr im Römischen Reich allerley zerrütlicheitt und unruhe in Politischen
geschäfften angerichtet, dermahlen eins abkhämen.‖
45 Ibid., 9-10: ―Doch das der Keyser das ganze Wesen moderirte und nit der Bapst, sonst
khöndten wir gewissens halber nichts endern, weil wir in der lehr wider einander seind.‖
321

Protestants, who argue that it is political, deem it a matter of Imperial concern. Amidst this
debate, Cancellarius raises another question which he proposes they not discuss immediately, but
keep in mind for consideration: ―If a similar reformation would be done anew, could it be done
better than the one done already [by Pope Gregory]?‖ 46
It is at this point that the Mathematicus first enters the discussion. Syndicus calls on the
Mathematicus to speak his mind about the questions they‘ve been discussing, because ―you are
younger…[and thus] will not be partisan‖ (Kepler himself was just over thirty at the time), and
also because ―today‘s astronomy is better.‖ 47
Rather than take up the debate, the Mathematicus
denies that the entire discussion has any relevance to him. He asserts that
if clever and overly hot-tempered and idle individuals in Germany would spend enough
time on their studies that they would learn to understand these things themselves, and not
to force us mathematicians, who are generally thought to be worthless and neglectful, to
advise them, not only would they forgo the heat and haze of quarrel on this account, but
also they would finally see that they have no reason to debate the matter so much. Our
studies are not partisan, but are devoted to the utility of mankind, to quiet, peace, and
unity. You theologians have confused so much—thus decide things without the
mathematicians and don‘t mix us into it, and thereby make our studies hated. It doesn‘t
matter to us at all whether we calculate according to Egyptian, Chaldean, Greek, or Julian
years, or according to Gregorian years, when our work is already piled high for us, and
needs careful attention. 48
46 Ibid., 353, 41-43: ―Hiervon wöllen wir nit redden, sondern das geb Ich eüch jetz
zubedenckhen, wan gleich ein solliche Reformation von newem angestelt warden solte ob mans
auch füeglicher angreiffen wurde khönden, als es Jetzo beschehen?‖
47 Ibid., 354, 1-2: ―Ir sendt der Jungen einer, Ich vermain Ir sollet nit Parthenisch sein. So hatt
man auch heüttiges tags die Astronomiam besser, wie fiindet Irs?‖
48 Ibid, 354,4-13: ―Wan die scharffsinnige und zuvil hitzige oder müessige köpffe in teuüschland
sich sovil mit den studijs bemüeheten, das sie dieses ach selber verstehen lehrneten, und nit uns
Mathematicos, die wir gmeinglich schlechte unachtsame personen seind, drumben fragen
müessen, so würd Inen hierzwischen nit allein die hitz und Zanckhdunst vergehen, sondern
würden auch entlich sehen, das sie nit Ursach hetten sich so sehr yber disem werckh zuzwayen.
Unsere Studia seind unpartheyisch, dem menschen nutzlich; der rhue, fridens, und einigkheitt
begirig: habt Ir Theologj vil verworren, so schlichtet es, ohne die Mathematicos und menget uns
nit drein, macht unsere studia darmit verhasst. ES gehet uns nichts auff oder ab, Wir rechnen
nach den annis aegyptijs, Chaldaicis, Graecis, Julianis oder Gregorianis, wan uns schon die
arbaitt ein wenig geheüfft würd, es braucht yberal fleißiges aufsehens.‖
322

The Mathematicus here argues two things. First, he claims that the arguments about the new
calendar are not rooted in mathematics at all. In speaking to ―you theologians [who] disturb the
peace,‖ he implies that the calendar debates have become debates about theology. For this
reason, he argues, mathematicians should not be asked for advice nor embroiled in the
contentious debates at all; instead, the question of the calendar should be settled by the
quarreling parties themselves. In his view, mathematics is an essentially peaceful art, devoted
―to the utility of human kind…and the love of concord‖—accordingly, it would be particularly
out of place to invoke it in order to increase strife, as the calendar debate has done. Indeed, the
use of mathematical arguments in the calendar debate would serve to debase mathematics,
making others look on it with scorn rather than respect. The Mathematicus further argues that
the calendar question is not one that pertains to mathematicians because it is irrelevant to their
studies—for astronomical purposes, the calendar could be reckoned according to any number of
systems, with little practical difference.
The Mathematicus‘s claims here are surprising on a number of levels. For one, Maestlin
had made exactly the latter claim in his rejection of the Gregorian calendar—a claim which
Kepler himself had discounted in his 1597 letter, where he argued that even if there were no
practical astronomical difference between calendars, astronomers should still support the one that
was the most accurate and beautiful. More important still, however, is that fact that Kepler,
himself a mathematician, was already very clearly ―mixed in‖ to the debate on calendar reform;
he had earlier taken a clear position in his letter to Maestlin, and was obviously still engaged
with the debate, in his political role as Imperial mathematician. Indeed, the writing of the
dialogue itself represents an attempt, by a mathematician, to settle the issue. This might simply
suggest that the Mathematicus does not represent Kepler‘s view, yet the character, of an age and
323

profession with Kepler, is clearly intended as a medium for the author‘s own voice. Kepler‘s
initial stance in the dialogue must therefore be seen as a rhetorical strategy; in starting with an
exaggerated denial of the calendar debate‘s relevance to mathematicians, the Mathematicus can
slowly begin to articulate his ideal view of the exact role that mathematicians should serve in the
calendar debates. As becomes clear over the course of the dialogue, this role is on the one hand
far more restricted than the one conventionally assigned to them, for it relegates their
involvement to limited and specifically mathematical questions and issues. On the other hand, it
also concedes far greater authority to mathematicians, granting them a unique power to help
resolve both the calendar debates and religious conflict more broadly.
The process of slowly defining the role of the mathematician begins as all the parties in
the debate immediately attack the Mathematicus‘s refusal to participate. ―How can you push the
matter so far away from yourselves,‖ wonders Cancellarius. ―Who else first brought up the
matter two hundred years ago, but mathematicians?‖ 49
Confessarius likewise notes that all the
Catholic mathematicians of note were consulted in the drafting of the Gregorian calendar, while
Ecclesiastes points out that Protestant mathematicians are the very ones who have argued that the
Gregorian calendar is riddled with error and therefore should be rejected. Clearly, both Catholics
and Protestants argue, the debate is inextricably tied to mathematics. The Mathematicus does
concede that mathematicians have been closely involved with the correction of the calendar. But
he asks that the others concede to him that
mathematicians are not to blame in the calendar debate and conflict, for they did not state
their opinion so that people could quarrel on account of it—just as God cannot be
49 Ibid. 14-15: ―Wie schiebet Ir die sach so weitt von eüch. Wer hatt sonsten dise sach auff die
Baan gebracht als eben die Mathematicj von zwayhundert Jahren her?‖
324

assigned guilt for men who kill one another, as though he should have not let wine come
to be. 50
Mathematical arguments may have been used in the debate about the calendar, contends the
Mathematicus, yet this does not mean that mathematicians are at fault. He distinguishes, that is,
between the true purpose of mathematical claims and the uses to which such claims are put. He
insists that mathematics itself is pure and unassailable, as are its true practitioners—but like any
good thing, it can be wrongly used.
Yet even this argument is challenged by Syndicus, who maintains that ―you
mathematicians first began this controversy yourselves.‖ 51
The Mathematicus rejects this claim
by defining what it means to act as a mathematician:
I call someone a mathematician who speaks, writes, debates, and argues on the basis of
his art—that is, so long as he stays within his boundaries. However, when he disputes
outside of his art, and gets by with political or theological arguments, or is affected by his
appointed position in government, then I consider him a theologian or a politician, and in
this matter I have nothing in common with him. 52
A mathematician, to be worthy of the title, must rely on mathematical arguments alone, argues
Kepler through the Mathematicus. Once he begins to debate on the basis of political or
theological arguments, he abrogates the right to the title ―mathematician,‖ and becomes instead a
politician or a theologian. Crucially, the Mathematicus emphasizes that this occurs once he is
―affected by his appointed position in government‖—the key point is not whether he occupies
50 Ibid. 23-27: ―Aber das werdt Ir mir darneben zugeben müessen, das die Mathematici an dem
Calenderstreitt und Zwispalt nit schuldig, dansie Ire meinung nit darumb gesagt haben das man
sich drüber zanckhen soll: gleich wie man Gott dem hern khein schuld geben khan, das die volle
paurn einander zutodtschlagen gleich als solt er den Wein drum nit haben wachsen lassen.‖
51 Ibid., 28-29: ―Die gleichnus will sich ybel reimen, dan Ir Mathematicj habt den streitt selber
angefangen.‖
52 Ibid., 31-35: ―Ich nenne disen einen Mathematicum, wöllicher auß seiner kunst redet schreibet
streittet und argumentiret und das, so lang er in terminis pleibt. Wan er aber auß seiner kunst
schreittet udn sich mit Theologischen oder Politischen Argumentis behelffet, oder von einem der
ernenten stenden in rath gezogen wüt, als dan helt Ich ine fur einen Theologum oder Politicum;
und hab mit Ime in diser sach nichts gemein.‖
325

such a position, but once it affects his mathematical judgment. When this happens, he stresses,
―I have nothing in common with him.‖ Kepler thus used the Mathematicus not merely to
articulate the ideal role of the mathematician, but also to fashion such a role for himself, and to
set himself apart from those whose mathematical integrity has been influenced by their religious
or political stations. Though he too holds a political office, he emphasizes that he would not
allow himself to be influenced by such a role.
Though Kepler initially created the characters of his dialogue to avoid invoking the
animosity of the Clavius-Maestlin debates, he brings them into the picture now, as he is further
pressed to explain whether he views their involvement in the calendar debates to be
―mathematical.‖ Those mathematicians like Clavius who were involved in the reformation of the
calendar, responds the Mathematicus, were acting not only as mathematicians but ―either had
theological or political thoughts on their own, and then supplied them to the authorities, or were
summoned by the Pope and empowered by him.‖ 53
Likewise, Maestlin ―was also impelled by
his political authorities and theologians, so that he wrote about it not only mathematically but
also theologically and politically.‖ 54
Again, the key issue is not simply the political or religious
ties of Maestlin or Clavius, but the fact that they used those ties to further their mathematical
claims, and to bolster their mathematical authority. For mathematics is governed by its
53 Ibid., 43-45: ―…so seind sie nit nur Mathematicj gewest, sondern haben eintweder von Inen
selber Ire Theologische und Politische bedenckhen darneben gehabt, und soliche hernach den
Obrigkaietten heimgestellet, oder aber seind von dem Babst darzue bestellet udn gevolmaechtigt
worden.‖
54 Ibid., 355, 6-7: ―Er ist eben sowol von seinen Obrigkeitten und Theologis darzue angetriben
worden; das er nit allein Mathmatice, sondern auch Theologice und Politice darvon gescriben.
326

principles alone, the Mathematicus insists—―in mathematics one disputes neither based on the
authority of the pope nor on the authority of the emperor.‖ 55
As the debate in the dialogue continues, the Mathematicus is pressed about mathematical
involvement in the initial Gregorian reform of the calendar. He allows that this involvement was
warranted, since all mathematicians agreed that the Julian calendar was mathematically
problematic, and there was a clear need for some mathematical resolution. Though Syndicus
points out that Maestlin had observed similar errors in the Gregorian calendar, the Mathematicus
argues that such errors were far fewer in number than in the Julian calendar. More to the point,
he highlights the fact that the reformers of the calendar were aware that such errors existed, and
―knowingly allowed them.‖ 56
From this point on the question had ceased to be mathematical.
As he explains,
What then can a pure mathematician bring against that from his art? It is not appropriate
for an astronomer to command church and state, as though they ought to orient
themselves along with the times of the year according to the motion of the heavens.
Rather, one ought to leave the matter to the higher faculties [of the university], so that
then, when a conflict arises relating to the reform, they will prefer thereafter to leave the
mathematicians to themselves. 57
Mathematics can aid in the reform of the calendar, emphasizes the Mathematicus, but only when
pure mathematical questions are at issue. When it attempts to intervene in non-mathematical
questions, or stakes a claim in decisions made on the basis of extra-mathematical concerns, it
once again crosses the boundary to politics or religion. And in attempting to ―command church
55 Ibid., 15-16: ―…dan in der Mathematica disputirt man weder von Bäpstlichen noch
Khayserlichen rechten.‖
56 Ibid., 33-34: ―die Reformatores solliche zuvor außgesehen, und wissentlich zulassen…‖
57 Ibid., 37-41: ―Was khan dan nun Jetzo ein pur lautterer Mathematicus auß seiner kunst
darwider bringen? Es stehet Ja nit zu einem Astronomo, der khirchen und policey
fürzuschreiben, wie fer und genaw sie sich mit Iren Jahrzeitten nach des himmels lauff richten
sollen: sondern man mueß sich in den höhern Faculteten drüber zuvor vergleichen: als dan,
wöllicher stand erstritten, das Ime die Reformation zustehe, der mag hernach die Mathematicos
zu sich ziehen.‖
327

and state,‖ mathematics will ultimately be commanded by them—for in involving themselves in
issues beyond their purview at the outset, mathematicians will ultimately be called upon ―when a
conflict arises relating to the reform,‖ and will be forced to support the religious or political
stance of each side. By sticking only with mathematics from the start, however, they can make it
clear that these issues do not pertain to them, so that others ―will prefer to leave the
mathematicians to themselves.‖
The Catholics and Protestants press on, with each side claiming that they are right for
various political or religious reasons. The Mathematicus then interjects once more. ―Thank you,
my lords,‖ he exclaims. ―With these words you have demonstrated yourselves that a
mathematician has nothing to do with the calendar debate.‖ He contains to explain:
For both initially and now you could argue with one another without my mathematical
instruction. If only you would spare other [mathematicians] also, and not say, our
mathematicians have found things to be so, while ours have found it otherwise. Stay
closer to the truth of the matter, and say instead, whatever each of us wants, he can use
his mathematicians to achieve it. For they are our servants. 58
As before, the Mathematicus claims that mathematicians have not only improperly employed
political or theological arguments—they have become servants of church and state, who produce
arguments at the command of their political or religious superiors. Kepler levels this indictment
both generally at all those involved in the calendar debate, and at Clavius and Maestlin in
particular, whom the Mathematicus goes on to name specifically. Likewise, he makes clear that
his point is not that mathematicians should remain in an ivory tower, far removed from worldly
58 Ibid., 356, 10-15: ―Danckh habt meine Hern, hiermit erweiset Ir selber, das ein Mathematicus
nichts mit dem Calenerstreitt zuthun habe. Dan Ir anfangs und auch Jetzo ohn meinen
Mathematischen Underricht wider einander argumentiren khöndt. Wolte aber got, Ir
verschonetet unser auch sonsten, und sprächet nit, unsere Mathematicj habens so gefunden,
Unsere aber habens anderst gefunden: sondern griffet vilmehr näherzur sach und sprächet, wie
usner Jeder will, so khan er die Mathematicos brauchen und anführen, dan sie seind unsere
Knecht.‖
328

conflict; mathematics can help to resolve those conflicts, but only when it stays within its own
boundaries, and recognizes no master beyond its own principles.
By now the Mathematicus has finally convinced the various parties about the place of
mathematics in the reform of the calendar. ―You fill me with such wonder,‖ exclaims
Cancellarius, ―that I must believe that you are right. Please tell me the right and pure reasons for
establishing or reforming the calendar.‖ 59
Now that the Mathematicus is on firm ground with
regard to his proper role, and the dialogue unfolds in an extensive discussion of the purpose of
calendar reform and the various aspects that require reform, finally with his full participation.
Throughout the remainder of the dialogue, the Mathematicus acts as a referee of sorts, clarifying
what requires clarification and taking sides on specific mathematical or astronomical questions.
He makes clear that a new calendar is necessary for neither political nor agricultural reasons, but
only in order to properly calculate the date of Easter according to the rules established by the
Council of Nicaea. There is some disagreement, however, about how best to comply with those
rule, and the parties begin to debate the merits of the different calculation cycles, and the benefits
or detriments of relying on strict astronomical observations. Amidst this debate, in which
Ecclesiastes presses for strict astronomical observations and Confessarius for a cyclical and
mean method of calculation, Syndicus interjects. ―I would like to propose a plan to my most
gracious lords,‖ he says, ―which…would be useful for a long time, and would serve the interests
of obtaining peace between us.‖ ―That I would hear very much like to hear,‖ responds
59 Ibid., 27-29: ―Ir machete mir es wunder selzam, Ich mueß eüch recht vernemen. Lieber sagt
mir den rechten purlautteren Matehmatischen grudn darnach der Calender anzustellen oder
zureformiren?‖
329

Cancellarius. 60
Syndicus replies:
My thought is this. A communal decree should be instituted at a Reichstag, that Easter be
celebrated in the future according to the decree of the Council of Nicaea, and the
mathematicians should be charged with diligently computing it from the foundations of
astronomy, and not from the old and faded computus, according to which we find
ourselves celebrating Easter several days away from the intention of the council. I would
urge the Protestants most strongly to accept this decree…and thus both parties will have
it so that Easter will fall out almost always together in our lifetimes, but by different
decrees. 61
Cancellarius immediately objects that such a process would not be admissible under Pope
Gregory‘s bull, and the debate continues. Yet here Syndicus has outlined the basic operating
principle for Kepler‘s dialogue, one which the Protestants eventually work out in some detail,
though it differs from the particulars suggested here by Syndicus. The way to resolve the
conflict, Syndicus suggests and Kepler ultimately clarifies, is to devise a means by which
Catholics and Protestants can disagree about the details of calendrical reform, while still arriving
at synchronized dates for Easter.
The two sides move on to discuss the correct length of the solar year, and the need to
improve the solar calendar. The Mathematicus explains that based on the observations obtained
by Hipparchus in antiquity and Tycho Brahe in modern times, the Gregorian calendar stipulated
a largely correct length of the solar year—indeed, this is the reason, he notes, why Tycho Brahe
praised the Gregorian calendar reform. Yet it is still not perfect, notes the Mathematicus, who
60 Ibid., 360: ―Syndicus: Ich will meiner Gnädigen Obrigkheitt wol ein rath geben, der da wie
Ich auß dem Jenigen abnehmen khan, was Jetzo gesagt worden, eine Zeitt lang guett thuen udn
zwischen uns friden stifften w rtt… Cancellarius: Das will Ich gern hören.
61 Ibid.: ―Mein meinung ist, man soll auff einem Reichstag einen gemienen schluß machen,
hinfüro die Ostern nach einsetzung des h. Nicenischen Concilij zuhalten, und den Mathematicis
anbefehlen, das sie ex fundamentis astronomicis und nit auß dem alten verschoffenen Computo
vliessig nachrechnen sollen, wan und zu wöllichen tagen sich solliches fest nach des Concilij
mainung finde. Den Protestierenden will Ich meinstheils vleissig zureden, das sie in ein sollichen
schluß willigen…Dadurch warden bayden Partheyen auß underschidlichen decretis die Ostern
bey unsern Lebzeitten fast alweg zusammen fallen.‖
330

discusses attempts by Scaliger and others to arrive at an even more precise determination of the
solar year—an attempt made difficult by the lack of precise enough observations. The two
parties discuss as well the related issue of the moving equinox, and the best ways to comply with
the decrees of the Council of Nicaea on the proper date of the equinox. Here Kepler, as author,
incorporates a lengthy Digressio, not in dialogue form, on the solar year, complete with a
historical survey of the determination of the solar year since the time of the Old Testament, and a
discussion of various solar and lunar calendars, including the ancient Persian and Egyptian
calendars, the modern Mexican and Japanese calendars, and the Jewish calendar.
After the Digressio the dialogue picks up once more, as the participants continue to
debate the best way to resolve the date of the equinox, and the reasons for or against removing
ten days from the calendar, as the Gregorian commission had done with its reform. The
Protestants argue against the omission of 10 days from the calendar; likewise, the Mathematicus
agrees with the Protestants that since the actual equinox would take place in the coming years on
March 10, the Gregorian commission should rightly either have removed 11 days from the
calendar, or designated the equinox on March 20. He notes, however, that this may not be a
mathematical issue, for it depends on the rationale used in the determination of specific calendar
dates. If those establishing the calendar, he argues, ―maintain that today the equinox falls on the
11 or 21 of March, I can contradict them from my art.‖ 62 But if, knowing when it actually
happens, they chose to designate the equinox on the 21 for the purpose of calculating the date of
Easter, he admits that they have the full right to do so. ―What does it matter to an astronomer,‖
he asks, ―what day is pleasing to them for the terminus lunae quartae decimae of Easter? Easter
62 Ibid., 377, 35-36: ―Wann sie fürgeben, das aequinoctium sey heütt zu tag den 11 oder 21
Martii, da will Ich Inen auß meiner kunst widersprechen.‖
331

is a holiday, not a star.‖ 63
Here he emphasizes that mathematics can aid in the calibration of an
astronomically correct calendar, but it need not be invoked in all instances. The length of the
solar year and the specifics of the lunar cycle certainly have their source in astronomy—but the
decision about the specific date of Easter is ultimately a religious one. And as he emphasized at
the start of the dialogue, the Mathematicus emphasizes here again that it is inappropriate for
mathematicians to take a stand on issues that do not pertain to their discipline.
The Mathematicus is then asked to clarify how many times the Gregorian calendar would
differ from the true equinox—and hence from the date of Easter of the Protestants, following the
true equinox—in the coming years. To answer this question, he notes that four fundamental
points about the establishment of the calendar need to be settled: : 1) whether the vernal equinox
should be set to an exact time in hours and minutes, or more generally to a day; 2) whether the
day should be started from midnight, morning, or evening; 3) which meridian ought to be chosen
to represent zero; and 4) whether one should consider the true, the mean, or the cyclically
calculated full moon. These questions are debated at length by all the parties, with the
Protestants eventually settling on the following: 1) The equinox should be fixed astronomically,
and as an exact time in minutes and hours. (This is against the advice of the Mathematicus, who
notes the true equinox cannot possibly be observed with such precision without error, both
because the instruments are not precise enough and because of the uncertainty of solar parallax
and the specific variations caused by refraction.) 2) The day should start either at sundown in
Jerusalem or at midnight in Rome. 3) The prime meridian should be the one which goes through
the middle of Europe—appropriately, this meridian goes through Rome and Prague, which are
both the origin and the current seat of the Roman empire, and through Hven, from which Tycho
63 Ibid., 38 – 387, 1-2: ―Was gehet es einen Astronomum an, was Inen für ein tag zum Termino
Lunae quartae decimae Paschalis gefalle. Ostern ist ein fest und khein stern.‖
332

Brahe made his astronomical observations. Finally, with regard to 4), Ecclesiastes votes for the
true full moon, since they have decided to abide by the true observed equinox. Yet the
Mathematicus points out that the difference between the true and the mean full moon is far
greater than that between the true and the mean equinox; for this reason, Syndicus argues that
they should stick with the mean full moon. Ecclesiastes is willing to concede in part, but they do
not reach a firm decision.
Syndicus again tries to return the discussion to the Mathematicus, and asks how often it
will happen, with the four points mostly resolved, that the dates of their calendar will differ from
the Gregorian calendar when it comes to Easter. The Mathematicus replies that having decided
on the essential elements of their new calendar, he will ―gladly undertake this doubled labor,
with only this condition: that Lords Syndicus and Ecclesiastes embrace whichever form [of the
calendar] differs the least from the Gregorian Reform in the celebration of Easter, and thus this
controversy can be happily settled.‖ 64
Syndicus willingly agrees, yet Ecclesiastes is skeptical.
―In the name of God!,‖ he exclaims. ―We will not reform the world with our private
agreement!‖ 65
His suspicion extends to the Mathematicus himself, whom he admonishes to
―proceed, but calculate faithfully and without bias. My associates are also calendar makers, who
can easily refute you if you report wrongly.‖ 66
Before the Mathematicus can take up the
challenge, Confessarius and Ecclesiastes take a moment to discuss the requirements laid down by
64 Ibid., 386: ―Ich will die doppelte arbait gern Verrichten doch mit disem beding, wölliche form
der Gregorianischen reformation in halting der ostern am wenigsten zuwiderlaufft, das baide
herrn Syndicus und Ecclesiastes derselben beyfallen und die andere fahren lassen, und also der
streitt aufgehebt sey.‖
65 Ibid.: ―Im namen gottes, wir warden doch mit unserm Jetzigen privat Consensu die welt nit
reformiren.‖
66 Ibid.: ―So fahret fort Mathematice, doch rechnet getreülich und unpartheyisch, Meine
spiesgesellen khönden auch Calender machen, die warden eüch wol erdappen, wan Ir Unrecht
berichtet.‖
333

the Council of Nicaea for the calculation of Easter, and Bede‘s interpretation of those
requirements. Based on their discussion, Syndicus remarks: ―It‘s a wonderful thing—we almost
agree, that the true equinox and the mean full moon should be followed….What then, have we
accomplished with our argument?‖ 67
Ecclesiastes concedes that he agrees in some respects with the interpretations of the
Catholic side, yet asks them whether or not they believe that the Council of Nicaea requires them
to follow the nineteen year cycle. Though Confessarius first states that it does, Ecclesiastes
points out that the errors in the cycle have caused it to result in dates for the equinox and Easter
that depart from the guidelines set by the council. Confessarius agrees, and notes that this is
exactly why Clavius substituted a corrected epact cycle. To this Ecclesiastes counters that just
as the Catholics had rejected the original nineteen year cycle because it was imperfect and
substituted Clavius‘s new epact cycle, so the Protestants rejected the epact cycle because it was
imperfect too. Ecclesiastes then suggests to Syndicus that they might abide by the wishes of the
Council of Nicaea if they produced a corrected golden number cycle, in contrast to the epact
cycle of the Catholics.
To this end, the Mathematicus takes a moment to explain the history of the golden
number cycle and the current problems with it, and works with Ecclesiastes over several pages of
the dialogue to develop an improved calculation for the golden number. According to this
method, one divides the year number by 500, multiplies the integer result by 11, adds the result
to the year number, adds 1, and then divides the result by 19; the remainder is the corrected
golden number. In the example the Mathematicus gives, if one takes 1609, one multiples 11 by
67 Ibid., 387: ―Ein merckliche sach, wir seind fast einig gewest, das verum aequinoctium und
medium plenilunium zuerwehlen….Was haben wir dan bisshero verrichtet mit unserm langen
disputiren?‖
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3, adds one, adds that to 1609 to get 1643, divides that by 19, and arrives at a golden number of
9. Consulting the tables, one finds that this corresponds to new moons on January 25, February
23, and March 25. April 7 would thus be the luna decimaquarta, and the date of Easter would be
April 9.
Because the Protestants have not removed ten days from their calendar, and still take
March 10 for the equinox, there are times—specifically, when the full moon occurs on March
10—that with this method the Protestants can end up celebrating Easter one month earlier than
the Catholics, who set the equinox to March 21. Yet this would happen only five times in 100
years, according to the Mathematicus—and more importantly, for the remaining years, the date
of Easter calculated according to the corrected golden number cycle is almost always consistent
with the date of Easter calculated in the Gregorian calendar on the basis of the epacts. They
have arrived, essentially, at the solution articulated earlier in the dialogue by both Syndicus and
the Mathematicus—a different method of calculation from the Catholics which enables regular
agreement when it comes to the celebration of Easter.
This is not to say that the Catholics and Protestants then embrace with open arms. ―If
only,‖ Syndicus remarks, ―Pope Gregory had instituted this method of correcting Easter. For
then we would have followed his correction without contradiction.‖ 68
―I don‘t believe it at all,‖
counters Cancellarius. ―For you have too many quarrelsome people among you.‖ 69
The two
sides continue to argue for their own version of the calendar, though without excessive hostility.
Finally, as the dialogue winds down, the Mathematicus extends his ―blessing,‖ and reminds
68 Ibid., 395: ―Es Wär Zu Wünschen Bapst Gregorius hette die Correction mit den Ostern auff
disen schlag fürgenommen, da wolten wir ohn alle widerred nachgefolget sein…‖
69 Ibid.: ―Ich wills nit laichtlich glauben. Ir habt vil zu streittige köpffe under eüch.‖
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everybody that ―mathematicians are not at fault in the calendar debate, but rather each party uses
its mathematicians to achieve what it wants.‖ 70
With this in mind, he graciously offers the others
my services for the Christian resolution of the calendar, in part or in whole, as much as is
possible according my art, so that with this matter settled a beginning is made to settled
the other impending Christian conflicts, and henceforth to live with one another
peacefully and amicably. 71
Here he emphasizes once again that though mathematicians ought not to employ theological or
political arguments or to operate on the basis of on specific theological or political motivations,
their arguments can still have important theological or political effects. For mathematics—a
―peaceful art,‖ as he noted earlier—can be employed help to settle theological or political
disputes like the issue of calendar reform, presenting a solution that would be acceptable to all
parties and thus allowing Christians to live ―peacefully and amicably.‖ And with a final ―Amen‖
on the part of all, the dialogue comes to a close.
The calendar dialogue, though whimsical in character, clearly occupied Kepler seriously,
as he returned to and made corrections over a number of years. His position in the dialogue is
also clearly quite different than the one he articulated ten years earlier in his letter to Maestlin.
On the one hand, this change was tied to Kepler‘s growing frustrating with the calendar‘s main
explicator, Christoph Clavius. In 1603, Clavius had published his Romani calendarii a Gregorio
XIII restituti explication, a massive text in which he sought both to better explain the new
calendar and to defend it from attacks by its Protestant opponents. Kepler read the book, and
70 Ibid., 397, 27-28: ―…die Mathematici am Calenderstreitt nit schuldig seyen, sondern der
Partheyen Jede Ire Mathematicos brauchen, und anf hren khönde wie sie wolle.‖
71 Ibid., 28-32: ―Will aber eüch denstlich erbotten ahben, den herren sampt oder sonderlich zu
einer Christlichen fürhabenden vergleichung des Calenderwesens in parte vel toto mit meiner
kunst nach müglichaitt zudienen: Damit bey diser geringen Materij ein anfang gemacht werde,
die zwischen den partheyen schwebende zwiffälte Christlich hinzuleegn, und hinfort mit einander
fridlich und einvertreglich zu leben.‖
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wrote to Maestlin in 1607 that Clavius‘s approach had ―filled [him] with anger.‖ 72 Though he
had once urged Maestlin not to overthrow the Gregorian calendar, he continued, he had since
himself recommended a separate calendar, ―for the sake of a defense against the errors of
Clavius.‖ 73
Though he had no intention of ―overthrow[ing] the established customs of nations,‖
he also felt that it would be wrong to ―endure the corrupting mathematics of Clavius.‖ 74
In
particular, he believed that it was necessary to clarify the errors in the Gregorian calendar, and to
offer suggestions for alternatives, so that the Gregorian calendar could eventually be updated and
improved, though this would likely take place at some time in the future. Though Pope Gregory
had called the new calendar ―perpetual,‖ Kepler believed that with regard to particular questions,
like the relationship between the lunar and solar calendars or the omission of the leap days, ―the
pope himself reserved the judgment to posterity.‖ 75
He elaborated on his problems with Clavius‘s approach to the calendar in a short,
unpublished document, labeled an ―Explicationis Calendarij a Clavio Scripta Emaculatio.‖
These relate in particular to the manner in which the date of Easter was calculated, the unclear
designation of the equinox, the wrongly assumed length of the synodic month and the tropical
year, and the lack of sufficient reasons given for the rejection of the golden number. To these
Kepler added two additional objections; the first relates to the problematic labeling of the
calendar as ―perpetual.‖ Even supposing that in future years the astronomical knowledge of
72 KGW 15:417: ―Versor in lectione Clavij stomachabundus.‖
73 Ibid.: ―Ego etsi de Calendario ipso olim tibj scripsj, ne id nitereris convellere, tamen suaserim
separata Calendarij causa ab erroribus defensoris Clavij, in hos modeste stylum stringere‖
74 Ibid.: ―Calendarium receptum est, dies exemptj sunt, Pascha ad rationes Lunae propius
reductum est: quo consilio, quaelibet natio id fecerit, non amplius disputo, ut olim, cum de
recipiendo ageretur. Instituta Nationum postquam stabilita sunt non amplius convellam, fruatur
quilibet suo more. Sed Clavium corrumpentem Mathemata non propterea feram.‖
75 Ibid.: ―Pontifex ipse reservavit arbitrium posteritatj et de omittendis bissextis, et de Luna
aequanda.‖
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Kepler‘s time was still accepted as true, he wrote, there were still many things that the bull did
not—and indeed could not—anticipate, making the ―perpetual‖ label clearly problematic.
Clavius certainly knew this, and yet he deliberately wrote the bull ―very confusedly‖ so that it
would appear flattering to the pope, honored as the founder of a calendar so good it would last
for all time. Clavius, that is, ―was obliged to remain silent [about the problems with the
calendar] because of his office, and in this way garnered a reward.‖ 76
Similarly, Kepler
complained that in relating the reasons why the new calendar did not follow the true motions,
Clavius had omitted the real reason: ―the authority of the Church, which only and alone
established it thus.‖ 77
Clavius pretended, that is, that the new calendar was established on the
basis of mathematics alone, when it was clear that some of the key decisions at play were
influenced by theological, rather than astronomical, considerations.
Much as he had argued in the calendar dialogue, then, Kepler found Clavius‘s
involvement in the calendar problematic not merely because of specific mathematical and
astronomical errors he had introduced, but also because Clavius‘s approach was tainted by his
theological motivations, which influenced his mathematical judgment and caused him to obscure
the real issues at stake in the calendar reform. And his dissatisfaction with Clavius‘s approach
seems to be at least partially responsible for the change in his attitude between 1597 and 1604.
At the same time, Kepler‘s new attitude toward the calendar reform was likely also closely
linked with the changes in his life that accompanied it—his expulsion from Graz, and the
growing awareness of the intensity of the confessional dispute; and his new position as Imperial
76 KGW 21.1, p. 399: ―Fatendum confusius Paulo scriptam Bullam ab imperitiori, adulantibus
quorum erat revidendi opera. Id Clavius honoris causa tacere utique debuit, veniam igitur
meretur.‖
77 Ibid.: ―Rationes cur verso motus ecclesia non sequatur, non pugnant, genuine cuasa est
omissa, arbitrium ecclesiae, quae sola et unica causa id factum stability, caeterae facile
profligari possunt.‖
338

mathematician, and the political awareness that came with it as he watched the emperor struggle
to rule a divided empire. Unlike the younger, more naïve Kepler of 1597, Kepler had come to
realize that the solution to the calendar dispute could not be solved simply by noting the
superiority of the Gregorian calendar—the debate was too entrenched, and too tied to the larger
confessional conflict, for this approach to be successful. With time, Kepler had come to realize
that a more creative approach to the problem was warranted, one which took seriously the
hostility and inflexibility on both sides of the issue.
Yet though Kepler‘s approach to the calendar was influenced by his political connections,
it still differed in important ways from the approaches of Emperors Rudolf and Matthias, as is
apparent from the proposals he eventually drafted on their behalf. Specifically, both emperors
saw the removal of ten days from the calendar as essential for the preservation of unity in the
empire, while Kepler retained the ten days in his dialogue, as had been his preference since his
1597 correspondence with Maestlin. The difference between Kepler‘s own solution to the
calendar and the desires of Rudolf, his employer at the time, may explain Kepler‘s decision not
to publish his calendar dialogue—and indeed, not to show it to Rudolf at all. 78
Similarly,
Kepler‘s decision to keep the dialogue private may have been tied to his insistence, in the
dialogue, that mathematicians not act as ―servants‖ to church or state—for the emperor likely
saw him, the Imperial mathematician, as just that. Kepler‘s own view of the purity of
mathematics lay at odds, to some extent, with the political demands of his official position—
indeed, I have argued that it is this very tension which may have prompted him attempt to
delineate the appropriate intersections of mathematics, politics, and theology in the calendar
dialogue. Yet while this may have been a valuable personal exercise, and even one that might
78 Boockmann, too, cites this discrepancy between Kepler‘s own ideas and the ideas of Rudolf
and Matthias as the reason why he may not have published his dialogue.
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generate like-minded echoes among his colleagues in the Republic of Letters, one can imagine
that this was not a picture that he saw fit to advertise broadly while still within Imperial employ.
This is not to say that Kepler felt compelled to betray the principles he articulated in the dialogue
in his official position, but only that he may have recognized that it was not politically expedient
to declare publicly that he was a servant to no one.
Of course, Kepler‘s calendar dialogue was not simply an exercise in self-fashioning. Nor
was the specific suggestion of a newly reformed Julian calendar itself the primary purpose of the
dialogue—indeed, though the calendar reform was an issue of some astronomical and
mathematical complexity, there are few calculations in Kepler‘s calendar dialogue, and the
material is presented as clearly and simply as possible. The work therefore seems targeted
toward a non-expert audience, not the mathematicians who might evaluate and eventually
institute such a reform. The popular nature of the text is bolstered by the dialogue format, which
keeps the reading simple and entertaining. Yet the dialogue format is not intended merely to
entertain; on the contrary, it is tied very closely with the message Kepler intended to convey. As
it becomes clear over the course of the work, Kepler attempted, by means of the dialogue, to
present the reader not only with a potential solution to the issue of calendar reform, but also with
a model for how such reform could be achieved. His characters, that is, not only suggest specific
methods by which the conflict over the calendar might be resolved, but also, through their
interactions, exemplify the manner in which to resolve it. Although in the beginning all the
parties give stock speeches which show them to be entrenched in their respective positions, they
quickly develop a free and open dialogue, in which they consider each other‘s positions closely
and react thoughtfully. More importantly, they treat each other with great respect, never
resorting to the vitriol and ad hominem attacks that characterized the actual debates over the
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calendar in which Clavius and Maestlin were enmeshed. In this manner Kepler suggested,
through his literary dialogue, that true reform of the calendar could be achieved only if Catholics
and Protestants would abandon their polemics in favor of honest and respectful communication.
Kepler‘s dialogue thus offered both specific suggestions for reform of the calendar, and a
model for the kind of communication that might bring such reform about. At the same time, it
offered something still more far-reaching. The remarks of the Mathematicus clearly convey the
fact that Kepler viewed the calendar conflict, and its resolution as described in his dialogue, as a
model for inter-confessional communication more broadly, and indeed, for the possibility of
large-scale inter-confessional reconciliation. The possibility of a re-united church was one that
occupied Kepler throughout his life, and he often described himself as someone engaged in the
process of religious reconciliation. In the calendar dialogue, Kepler ended with the
Mathematicus‘s hope that by settling the calendar issue peacefully, the two parties could perhaps
begin to live together peacefully and harmoniously—they could begin, that is, to settle their other
differences in a like manner. This is not just because there would be one less issue of contention
on the table. Rather, Kepler portrayed the issue of calendar reform in particular as microcosm
for the larger confessional issues dividing Catholics and Protestants in the Empire—and more
importantly, he portrayed its resolution, as described in his dialogue, as a model for the means by
which other divisive issues might be settled.
Notably, by the end of Kepler‘s dialogue, the Catholics and Protestants don‘t actually
agree on any one solution to the question of the calendar. Instead, the Catholics remain
adherents of the Gregorian reform, while the Protestants support a differently reformed Julian
calendar. Yet the Mathematicus still clearly views this as a promising resolution, since the
newly reformed Julian calendar, while differing in many particulars from the Gregorian calendar,
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largely results in the same day for Easter as the Gregorian calendar. With this resolution, in
other words, Kepler crafted a method by which the two parties could differ in particulars, while
still coming together for issues of primary importance. Also significant is the fact that he
managed this without forcing either party to adopt a position that it deemed unpalatable. The
implication is clear—in other matters of religion, Kepler suggested, there were surely similar
points of commonality, where Catholics and Protestants might unite harmoniously, though still
committed to their own particular doctrines and practices. The idea of harmony is central to
Kepler‘s message; indeed, Kepler clearly drew the definition of harmony he later articulated in
his Harmonice Mundi in order to portray the kind of religious harmony he envisioned. Musical
harmony, he believed, was a pleasing and unified whole generated by a diversity of notes. As he
put it in his Harmonice Mundi, ―just as…individual consonances considered separately are
pleasing on account of the fact that they are plainly not identical notes, but in a way figured and
different notes…in the same way…the harmonious singing of parts…without any variety in them
ceases to be pleasing altogether.‖ 79
Diversity was essential to the unity of the harmony, and
Kepler held up this kind of unity, one which did not imply identity, as a model for a re-unified
Christendom which still allowed for diversity of opinion and practice.
The vital role played by the Mathematicus in the dialogue is also important for the larger
message Kepler hoped to convey. Through the voice of the Matehamticus, Kepler emphasized
throughout the dialogue that mathematics was a pure discipline, and that true mathematicians
ought to operate without bias, devoted to their craft alone and not to any particular political or
religious creed. He likewise highlighted the fact that mathematics was a discipline devoted to
harmony and peace, and opposed to conflict of any sort. Both these claims allow the two parties
79 The Harmony of the World, trans. and eds. E. J. Aiton et al. (Philadelphia: The American
Philosophical Society, 1997), 252.
342

in the dialogue to accept the Mathematicus as a mediator, and ultimately it is only with his
assistance that they come to any resolution at all. In this way, Kepler suggested that if
mathematicians on both the Catholic and Protestant sides could cultivate a similar purity of
purpose, they could act as crucial mediators in the confessional disputes more broadly, and
through their art provide models of harmony for others to follow. 80
He later cited Proclus, who
likewise argued that ―those features which to the uninitiated in the truth of divine matters seem
difficult to grasp and lofty are by mathematical reasoning shown to be trustworthy, manifest, and
uncontroversial.‖ 81
God was a geometer, after all, and the harmony he had instilled throughout
the cosmos was a geometric one. Mathematicians were therefore ideally suited to broadcast the
message of harmony to a war-torn world, and to provide models of ordered mathematical
reasoning which could be applied to other, more disorderly spheres.
Kepler further emphasized that mathematics could pave the way to reform and unity not
only by showing what true harmony looked like, but also by providing specific resolutions to
particularly thorny issues. In the dialogue, the Mathematicus ultimately solves the calendar
conflict with clever calculations, which enable the date of Easters in both calendars to coincide.
Similarly, as we saw in Chapter 1, Kepler had earlier argued that mathematics could point the
way to a resolution of one of the biggest issues dividing the confession—the problem of the
Eucharist. Though Kepler emphasized in the calendar dialogue that mathematicians needed to
steer clear of religious or political motivations and arguments, he clearly believed that pure
mathematics was still politically and religiously relevant, and could be marshaled to settle
80 Leibniz similarly argued for mathematicians as social mediators; see Christia Mercer, Leibniz's
Metaphysics: Its Origins and Development (Cambridge: Cambridge University Press, 2001), 49-
59; see also Matthew Jones, The Good Life in the Scientific Revolution: Descartes, Pascal,
Leibniz and the Cultivation of Virtue (Chicago: University of Chicago Press, 2006), 246-47.
81 Proclus, commentary on Book I of the Elements of Euclid, Book I, cited in The Harmony of
the World, Preface to Book III, 127.
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political or religious disputes. Yet in order for mathematicians to successfully function as
models and mediators, and to pave the way for a new reformation of the church, they needed to
make it clear that they stood apart from the theological conflicts surrounding them, and
intervened only when prompted by the dictates of their craft. And when they did so, they needed
to emphasize their desire to unite, rather than to divide. As Kepler would later emphasize, ―I do
not want to participate in the rage of the theologians. I will not judge my brothers; for whether
they stand or fall, they are my brothers with respect to the Lord.‖ 82
Kepler as Imperial Mathematician: Calendar Proposals, 1607-1613
After his failed attempt to introduce the Gregorian calendar throughout the empire in
1583, Rudolf continued to seek some way to resolve the calendar dispute, and he solicited the
advice of Kepler, his Imperial mathematician. He made clear that a unified empire was the goal;
if the Gregorian calendar remained an unacceptable option to the Protestant electors, he wanted
an option that came as close as possible, and that at the very least omitted ten days from the
calendar, to end the double-dating problem in the empire. In his official role of Imperial
mathematician, Kepler thus drafted a number of official proposals for reform of the calendar,
using as a starting point both his own ideas as articulated in his calendar dialogue, along with
Rudolf‘s request that ten days be omitted from the calendar. With the ten days omitted, the
calendar he developed on Rudolf‘s behalf was ultimately less a newly reformed Julian calendar,
as he had proposed in 1604, and more a modified Gregorian calendar, which some key changes.
On behalf of Rudolf, Kepler explained the details of this calendar in an official Imperial letter to
82 KGW 17:750: ―Ira Theologorum communicare nolo, fratres non judicabo, qui sive stent sive
cadant, dominj sunt, et fratres mej.‖
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the three Protestant electors in the empire, Christian II of Saxony, Friedrich IV of the Palatinate,
and Joachim Friedrich of Brandenburg.
At the start of the letter, Kepler enumerated five common Protestant objections to the
Gregorian calendar. These were 1) that the introduction of a new calendar would create
confusion; 2) that the calendar reform should not have been up to the Pope; 3) that it curtailed the
freedom of religion so prized in the empire; 4) that it would imply the acceptance by Protestants
of the decrees of the Council of Trent; and 5) that Protestant mathematicians had found the new
calendar problematic. Speaking for the emperor, Kepler argued that the fear of confusion was
unfounded, and that in fact the contrary was true— ―today the inequality of time in the Holy
Roman Empire causes great losses, confusion of commerce, and obstruction of justice.‖ 83
While
noting that ―in political matters the emperor bows to no one other than almighty God,‖ 84 Kepler
maintained that the emperor still took it to be a good thing that the reform of the calendar had
been conducted by the pope, as this allowed the new calendar to spread to those Christian
regions not subject to the authority of the empire. Moreover, he emphasized that the emperor
was aware of the religious anxiety raised by the issue of the calendar, and hence that the emperor
―does not want to speak about religious issues at all, but rather only about the political ordering
of time.‖ 85
Kepler focused particularly on the fact that the emperor ―desires from the start that
no one is forced,‖ and that he ―does not want to order anyone in his religion, or godly service, or
83 KGW 21.1, p. 423: ―Wie auch noch heüt zu tag die ungleichhaitt der Zeitt im Röm: raich
teutscher Nation grossen schaden und verwirrung der Commercien, sperrung der Justiten etc.
verursache…‖
84 Ibid.: ―Ob wol Ire K. Mt. ausser Gott dem Allmechtigen in disen politischen sachen…nimend
zurespectirn haben…‖
85 Ibid., p. 424: ―…das wöllen Ire K. Majestät an Jetzo, weil sie gar nit von gaistlichen aAchen
redden, sonder von der poiltischen Zeitordnung.‖
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matters of conscience.‖ 86
Rather, the emperor requested that his electors consider the matter
freely and come to a decision about how best to resolve the calendar conflict in the empire, while
avoiding issues of religion and focusing strictly on the political questions at stake. They need
not adopt the Gregorian calendar if they found it religiously or mathematically problematic, but
should instead consider other ways by which the empire could again be unified when it came to
questions of time.
To this end, Kepler, as Rudolf‘s spokesperson, put forth one such proposal. The new
calendar he described was essentially the same as the Gregorian calendar when it came to civil
dating—it followed the Gregorian calendar in removing ten days after February 13, 1608; and it
adopted the Gregorian approach to leap days, skipping in the years 1700, 1800, and 1900. Yet
the new calendar differed when it came to the method for the calculation of the date of Easter,
which was now based on the true observed equinox and the mean motions of the moon, with
provisions for calculating the date of Easter similar to the ones Kepler hadearlier described in his
calendar dialogue. Also as in the calendar dialogue, although at times this resulted in
discrepancies with the date of Easter in the Gregorian calendar, in most instances this resulted in
a concurrence of Easter dates. Moreover, Kepler recommended that aside from the method of
Easter dating, the new calendar should be kept strictly political—all religious terms should be
removed from the calendar, and fixed holidays should depend on the Gregorian calendar. He
also stipulated that the two calendars should always be printed side by side in the empire.
When Matthias became emperor after Rudolf‘s abdication in 1612, Kepler continued to
act as Imperial voice on the issue of the calendar. At Matthias‘s request he prepared a report on
the question of the calendar for the 1613 Reichstag at Regensburg. The calendar proposal he
86 Ibid.: ―begehren Ire Mt. anfangs niemand zuzwingen…so mainen Ire Mt. khains wegs Jemand
in seiner Religion, gottesdienst und gewissen Ordnung zugeben…‖
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submitted on behalf of Matthias was the same as the one he had drafted for Rudolf in 1607,
though Kepler modified the method by which the golden number would be calculated, to allow
an even greater agreement of Easter dates with the Gregorian calendar. In this version, the
Golden Number would be calculated as (12 + A.D. mod 19); this is also very similar to the
original rule for the Golden Number, in that only the first term is changed. As he had done
previously, in this report Kepler addressed the concerns of Protestants about the Gregorian
calendar, and emphasized that some decision needed to be made as soon as possible in order to
properly unify the empire. He made clear that the calendar he proposed on behalf of Matthias
would eliminate the double dates for Easter for at least the next 100 years, and allowed that after
that the issue could be taken up once again
Despite Kepler‘s best efforts, the calendar debate in the empire remained unresolved in
his lifetime. In fact, it was only in 1699 that the Protestant half of the empire adopted a new
calendar—though not the Gregorian one. Popularly known as the Verbesserte calendar, the
calendar eventually endorsed at the Regensburg Reichstag in September of 1699 followed spirit
of the model Kepler had advanced on behalf of Rudolf and Matthias years earlier. Ten days
were removed following February 18, 1700, and the rule for leap days would follow the
Gregorian calendar; however, the method for the calculation of Easter differed from the
Gregorian calendar, as it relied directly on astronomical observations and calculations for both
the equinox and the full moon. 87
Additionally, it relied on Kepler‘s Rudolfine Tables, rather than
the older Alfonsine or Prutenic tables; in this way, Kepler was able to play a central role (though
not the one he had hoped) in Germany‘s adoption of an updated calendar.
87 See Owen Gingerich, ―The Civil Reception of the Gregorian Calendar,‖ in Gregorian Reform,
265-279.
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The Kepler that comes through in the official proposals drafted for the emperors is an
Imperial servant, to be sure. He spoke clearly for the emperor, relating the emperor‘s desires and
needs. He even named Matthias as the source of the 1613 calendar proposal—it was, as he titled
it, a report ―which the Holy Roman Emperor, on August 13, 1613, introduced on the point of the
calendar for the electors and states of the Augsburg Confession‖; Kepler‘s own name is not
included in the report at all. Additionally, with these official proposals Kepler moved much
closer toward his position in the 1597 letter to Maestlin—though he did not urge the wholesale
adoption of the Gregorian calendar, he took pains to indicate why it should be preferred, and the
calendar he described was mostly identical with the calendar of the Gregorian reform. Yet the
difference between the Gregorian calendar and the one proposed by Kepler is not insignificant—
in allowing for a different method for the calculation of the dates of Easter, Kepler, and the
emperors, took seriously the concerns of Protestant opponents to the new calendar, and
recognized that the issue was not one that could be resolved by sampling noting the astronomical
superiority of one or the other calendar. The concern for unity and conciliation that come
through in the 1604 dialogue were shared by Kepler and his employers, and they come through
clearly in these official proposals as well. While Kepler, via his calendar dialogue, articulated
some discomfort at the idea of a mathematician serving as Imperial spokesperson, on this issue,
at least, he did not need to dramatically alter the position he felt would be most beneficial for all.
Conclusion
My focus throughout this chapter has been primarily on Kepler‘s depiction of calendar
reform as a microcosm for confessional reconciliation, and secondarily, on Kepler‘s conception
of the role of the mathematician as articulated through the issue of the calendar. In closing, I
348

want to return to this latter idea, which maps on to some larger narratives in the history of
science. One is the changing status of mathematical astronomy in the early modern period. As
scholars like Robert Westman and Nicholas Jardine have made clear, astronomers in the
sixteenth and seventeenth centuries began to posit a new relationship between mathematics and
natural philosophy, one which granted the astronomer the right not merely to calculate celestial
motions, but to demonstrate the causes of those motions. 88
Both Kepler and Copernicus before
him were central figures in the attempt to argue for a physical astronomy that could make claims
about the real world and penetrate into the true causes of things. In so doing, they argued that
they astronomer was a philosopher—indeed, because the astronomer mathematically explicated
the perfect works of God, he was the philosopher most able to speak with certainty about the
world around him. As noted earlier, both Westman and Jardine point to the court as a locale
which allowed astronomers bolster their status, legitimate their authority, and reformulate their
disciplinary roles. Though Kepler was wary of too close a linkage between politics and
mathematics, he used his 1604 dialogue to promote a similar goal. In it, he emphasized the
centrality of the mathematicus to the resolution of the politically charged calendar dispute. By
this means, Kepler portrayed the mathematician as a figure with unique insight into the world
around him, one whose skills were a crucial resource for all those struggling to resolve
seemingly intractable conflicts. He thereby recast mathematical astronomy, portraying it not
merely as a technical discipline of calculation and prediction but, rather, as Copernicus had once
argued, as ―the summit of the liberal arts,‖ a discipline ―most worthy of a free man.‖ 89
88 See Westman, ―The Astronomer‘s Role,‖and Nicholas Jardine, The Birth of History and
Philosophy of Science: Kepler's 'A Defence of Tycho Against Ursus' with Essays on Its
Provenance and Significance (Cambridge: University of Cambridge, 1988).
89 De revolutionibus, Introduction to Book 1, 7.
349

Alongside this reformulation of the astronomer‘s role, Copernicus had argued that the
distinctive expertise of mathematicians and the high status of their discipline meant that only
other mathematicians were qualified to evaluate each other‘s claims. ―Mathematics is written for
mathematicians,‖ he famously argued. He continued to discount the relevance of any critiques of
astronomical claims coming from those without mathematical expertise—and in particular,
coming from theologians. He wrote,
Perhaps there will be babblers who claim to be judges of mathematics although
completely ignorance of the subject and badly distorting some passage of Scripture to
their purpose, will dare to find fault with my understanding and censure it. I disregard
them even to the extent of despising their criticism as unfounded. 90
Kepler‘s arguments in the 1604 dialogue echoed those of Copernicus. In emphasizing the fact
that mathematicians ought not to employ theological or political arguments, Kepler argued at the
same time that theologians and politicians ought not to attempt to comment on mathematical
claims, and should instead ―leave the mathematicians to themselves.‖ Much of the authority of
the mathematician as mediator and conciliator stemmed, that is, not only from the
mathematician‘s unique insight into the world around him, but also from his privileged position
as expert—a position which served to shield him from the criticism of all those but other
mathematicians, who alone would be able to properly evaluate his claims.
This links our story to another larger narrative within the history of science—the rise of
the expert as an apolitical actor. In examining the emergence of the early modern notion of
expertise, Eric Ash notes that one criterion by which the expert came to be identified was his
perceived objectivity and independence: ―an expert was ideally one with a better understanding
and a superior position from which to give advice in part because he had no personal stake in the
90 Ibid., Preface, 5.
350

work itself, being above it all.‖ 91
While Ash applies this idea to a variety of disciplines, Ted
Porter‘s Trust in Numbers tells a later story of the process by which objectivity came to be
specifically invested in numbers and quantification. The reliance on impersonal numbers, Porter
argues, created a sense of objectivity which bridged gaps of distance and distrust in the
nineteenth and twentieth centuries; in this way, Porter posits quantification in part as a political
solution to a political problem. ―Scientific objectivity,‖ he writes, ―…provides an answer to a
moral demand for impartiality and fairness. Quantification is a way of making decisions without
seeming to decide. Objectivity lends authority to officials who have very little of their own.‖ 92
In Porter‘s narrative, mathematics is able to function as a political solution only by claiming to
occupy an apolitical zone; the supposed neutrality of numbers allows them to be mobilized as a
political tool. Though there are important differences—and several hundred years—between
Kepler and Porter‘s actors, Kepler‘s adoption of the mantle of the Mathematicus takes on new
meaning when considered in light of these later developments. Kepler‘s Mathematicus is
obviously a political actor, one who solves a very political problem. Yet he does so by
emphasizing the fact that he has no investment in the political issues at stake. ―Our studies are
not partisan,‖ he argues, while emphasizing that mathematicians can answer only mathematical
questions, using only the impartial tools provided by their art. Kepler‘s Mathematicus can be
viewed both as an early example of the scientific expert, and as an example of the ways in which
objectivity can be mobilized to serve specific political ends.
91 Eric H. Ash, ―Introduction: Expertise and the Early Modern State,‖ in Expertise: Practical
Knowledge and the Early Modern State, Ed. Eric H. Ash, Osiris 25 (Chicago: University of
Chicago Press, 2010), 8.
92 Theodore M. Porter, Trust in Numbers: The Pursuit of Objectivity in Science and Public Life
(Princeton: Princeton University Press, 1995), 8.
351

Porter‘s narrative is ultimately one of the move of science from close-knit and local
communities to far-flung and impersonal networks. For Kepler, however, the idea of
community—conceived very personally, in terms of brotherhood—remained central. Yet over
time he adjusted his conception of how that community ought to be constituted. At the start of
this chapter, I noted that Kepler‘s initial concern over Germany‘s refusal to adopt the Gregorian
calendar stemmed from his sense of national pride, and his distress that Germany, typically
renowned for its mathematics, should be seen as backward when it came to the mathematical
question of the calendar. Kepler argued in 1597 that the Lutherans in Germany ought to put
aside their religious fears, which he viewed as unfounded, and adopt the Gregorian calendar in
order to once again assert their mathematical superiority. Yet as Kepler came to see the calendar
conflict more and more as a religious dispute, and indeed, as a microcosm for confessional
conflict more broadly, he ceased focusing on Germany‘s reputation, and focused instead on the
need for a peaceful reconciliation between Catholics and Protestants. Therefore rather than
argue for the adoption of the Gregorian calendar, he argued instead for the adoption of a new
calendar, one which would be acceptable to Protestants and allow a degree of unity when it came
to the date when Easter would be celebrated. Kepler came, in other words, to deemphasize the
question of national identity in favor of the question of religious unity; when it came to his own
sense of belonging, it mattered more to him to belong to a unified Christendom than to a
Germany celebrated for its mathematical supremacy. Indeed, though he continued to emphasize
the ―love of [his] native country,‖ 93 he faulted his fellow Germans for the manner in which their
excessive pride contributed to the confessional conflict. ―The evil which oppresses Germany,‖
he wrote, ―arises chiefly from the pride of some divines, who would rather rule than teach…The
93 KGW 14:183: ―Ad vos me rapit amor patriae…‖
352

spirit of unity and mutual love is wanting.‖ 94
When national identity became a source of tension,
Kepler cast a broader net, reaching out to all those across Europe who shared his love of
mathematics and his desire for peace and unity. In the year before his death, he called on ―you
all, as many as there are, on whatever shores you live, that…have trained your minds thus far by
the study of mathematics.‖ 95
Politics was dangerous and divisive business, he knew by then, and
mathematics the only surety in a world beset by conflict. ―…The ship of the state is shaken by
dangerous storms,‖ he continued. ―….When the storms are raging and the shipwreck of the
state is frightening us, there is nothing nobler for us to be done than to let down the anchor of our
peaceful studies in the ground of eternity.‖ 96
94 Kepler to Mayer of Baden, 1614, cited in ―Kepler and his Discoveries,‖p. 342.
95 See Joannis Keppleri ad Epistolam D. Jacobi Bartschii Respnosio, Sagan, 1629; cited in
Johannes Kepler: life and letters, ed. Carola Baumgardt (London: Victor Gollancz, 1952).
96 Ibid.
353

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