Reduction and Elimination in Philosophy and the Sciences

“Downward Causation”: Emergent, Reducible or Non-Existent?
Peter P. Kirschenmann, Amsterdam, The Netherlands
1. Introduction
It is common to view reality as a hierarchy of levels, such
as the physical, biological, psychological level. Entities
(plus their properties) at higher levels (of “organization” or
“complexity”) consist of entities of lower levels, but are
supposed to be “emergent” – form “wholes that are more
than the sum of their parts” – and, possibly, have “downward
causal” influences on their parts.
All these views, often not well-articulated, are
contested. For hard-headed (eliminative) materialists or
physicalists, there is no emergence, let alone “downward
causation”. For reductionists, they are “nothing but”
material processes. Emergentists often rest content with
arguing for their possibility. “Non-reductive physicalists”
recognize emergent phenomena, but insist on their being
physically based.
I myself think that the occurrence of a hawk catching
a mouse is a macroscopic emergent phenomenon, though
I doubt that it involves “downward causation”. I used to be
a fan of layered ontologies (e.g. Nicolai Hartmann’s). Yet
lately, I think that we should avoid as much as possible
imposing a level structure on reality. Surely, a distinction
between macrolevel and microlevel often is very sensible,
but it can misfire.
I shall discuss two original views as well as the
muddled conceptualization and terminology, analyze two
examples, comment on the “causal exclusion argument”,
and conclude with a computer analogy.
2. The Muddle of ‘Downward Causation’
Donald T. Campbell, in 1974, first used the expression
‘downward causation’ (cf. Hulswit 2006, 266), for the view
that “all processes at the lower level of a hierarchy are
restrained by and act in conformity to the laws of the
higher levels”. His (biological) hierarchy ran from molecules
and cells up to populations and evolution. He noted
himself that the expression was at odds with our usual
concept of efficient causation: his higher-level “laws” selectively
restrain lower-level processes, unlike events causing
other events.
Around that time, Roger W. Sperry, after his splitbrain
investigations, started defending his “emergent
interactionism” (cf. Emmeche et al. 2000, Ripley 1984,
Hulswit 2006: 269). To clarify the “form of control” that
conscious phenomena exert over neural events he used
the examples of a wheel running downhill and an eddy in a
stream. The movement and fate of the constituent
molecules are “determined very largely by the holistic
properties of the whole wheel” or the whole eddy, though
without any change in the lower-level molecular laws.
Similarly, the component parts of “an excitatory neural
process are carried along and thus controlled by dynamic
properties of the whole system”, namely by unitary mental
experiences. Sperry was not quite happy with the term
‘interactionism’, as it smacked too much of a Cartesian
dualism.
What ‘downward causation’ or the downward part of
‘interaction’ is for these authors remains unclear.
Meanwhile, the terminological diversity has been
exploding. Thus, the higher level has been said to cause
inasmuch as it restrains, constrains, controls, organizes,
structures, determines, governs, delimits, bounds,
entrains, enslaves, harnesses or selects the lower-level
phenomena (cf. Hulswit 2006: 279f.), while said to emerge
from, cannot be explained by, reduced to, or predicted
from, them and their laws. Since several of those “causal
influences” hardly are examples of efficient causation,
some regard them as Aristotelian formal or final
(functional) causes. The most general and neutral term,
though in need of appropriate qualifications, is
‘determines’. Another disconcerting variation concerns the
relata of the alleged downward causality: entities,
substances, events, processes, states, types or
instantiations of properties, patterns, structures, laws or
regularities.
No doubt, novel things have diachronically
“emerged” during the evolution of the universe: stars,
heavy elements, planets, life, consciousness. We focus
here on synchronic emergence: “higher levels of reality” of
some permanence. Crucial in identifying emergent entities
or systems, I think, are their significant, possibly lawful
“horizontal” interactions with entities at the “same level”,
rather than “downward” influences.
A useful distinction is between three possible
meanings of ‘downward causation’ according to their
strength (cf. Hulswit 2006: 280, also Emmeche et al.
2000), all concerning an active system constituted by a set
of active elements:
weak – “downward explanation”: the behavior of the
elements cannot adequately be explained without
reference to the system;
medium – “downward determination”: it is partly determined
by the system;
strong – “downward causation”: it is partly brought
about by the system.
3. Examples – Analyzed
The most intriguing questions of emergence concern life
and mind. Yet, phenomena of the non-living world have
raised similar and more easily analyzable questions. They
often are supposed to attest to a continuity of emergence
and downward causation through all layers of reality (e.g.
Rockwell 1998). I have my doubts.
Sperry’s wheel is an example in point. The
macroscopic properties of the wheel, together with gravity,
slope etc., determine the movement of the wheel and thus
a fortiori that of its constituent molecules. Its stable circular
shape, due to the cohesive arrangement of its
constituents, is an emergent property – for not being a
property of the constituents – in an innocent sense, a
“structural emergence. It can thus be “explained”, without
getting reduced to properties and arrangement of
molecules. It is a factor in macroscopic causal relations, as
when the wheel should bump into a wall. Yet, pace Sperry,
there is no “interaction” between the wheel as a whole and
its constituents, let alone its “downwardly causing” their
movement, except in the weak sense of downward
explanation. Note, pace Campbell, that the laws of
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