Zeit und Geschichte Time and History - Austrian Ludwig Wittgenstein ...

means of conventions and designating it by a single name.
At this first step of concept formation, the relation of
concepts to experiences remains a close one: our definitions
are tied to qualitative experiences and identifying
an object designated by a concretely defined concept
implies having recourse to specific sensory experiences.
The second step then consists in devising purely
conceptual definitions. Concepts are defined solely by
means of other concepts. As a consequence, the structure
of knowledge consists in purely conceptual relations and is
insofar freed from qualitative experience: it has a status of
its own, essentially distinct from intuition. This idea of a
breach between the formal and the experiential, meaning
that the first doesn’t enter in the determination of the
second, is also to be found in Einstein’s writings, as we
have already seen. Thus both Schlick and Einstein agree
that the conceptual system of knowledge has a specific
status insofar as it is formal. This is a constant idea in
Schlick’s thinking, which remains primordial during his
Viennese period: Einstein’s later critics against Schlick’s
thinking having become too positivistic should be
tempered by this fact.
The question of the determination of the system of
knowledge and the one of its constitution should however
be distinguished here. If Schlick and Einstein agree on its
specific formal character, they disagree regarding the way
we arrive at it and its relation to sensory data. We have
outlined that Einstein sees the fundamental concepts of a
theory as pure theoretical constructions, and that for him
the question of the relation between experience and the
theoretical system of science arises only after the latter
has been fully developed. For Schlick on the contrary the
purely formal system of knowledge is not something we
begin with: it is rather the result of an evolution from a
concretely defined system of concepts and it presupposes
this former state. To be more precise the more advanced
state of knowledge corresponds to theoretical physics,
where physical magnitudes are conceptually defined without
any recourse to qualitative experience (cf. Schlick
1925 as well as Schlick 1932).
Moreover Schlick maintains that even if the scientist
seeks to define concepts by eliminating qualitative
experience from his definitions, he nonetheless has in
mind the idea of preserving the link between the formally
determined system of science and experience. Theory,
even if formal, is not developed at the purely abstract level
of mathematics but at the level of theoretical physics,
meaning that the physical concepts are always defined so
as to designate objects in nature. Now it is a specific kind
of experience which warrants that the concepts belonging
to the system of knowledge actually designate real objects,
it is namely the observation of spatio-temporal
coincidences. Verifiable statements which predict the
occurrence of measurable events must indeed be
derivable from the formal definitions of physical concepts if
they are to designate real objects. Every measurement
finally ends up in the observation of the coincidence of two
points: one on the measured body, the other on the
measuring rod. Thus point-coincidences alone can warrant
the link between the formal system of concepts and the
real objects.
It must be noticed that the observed coincidences
have nothing in common with the qualitative experiences
delivered by one particular sense. Observation of
coincidences exemplifies a kind of experience which
retains nothing of the qualitative and subjective
characteristics of ordinary sensory experience as defined
by Schlick. This explains that the recourse to this kind of
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What is Physically Real? Schlick vs. Einstein - Delphine Chapuis-Schmitz
experience doesn’t threaten the objectivity of knowledge
nor its specific status towards intuition.
The difference between Schlick and Einstein’s
conception of the status of physical concepts can be further
exemplified by the way each of them conceive of the pointcoincidence
concept. As Einstein himself explains (see
Einstein 1963 for instance) the defining of points of the
space-time manifold as coincidences of world-lines is the
result of a conceptual inquiry. Formulating the general
covariant equations which form the general theory of
relativity implied to redefine the concept of point in the
space-time manifold so as to be able to individuate
univocally the points of this manifold. In the special relativity,
a point of the manifold is determined by his coordinates in a
specific system of coordination. But under the general
relativistic postulate, the system of coordination itself is not
invariant under the class of general transformations: the
determination of a point of the manifold in terms of its
coordinates in a particular system is then not sufficient
anymore to individuate it univocally. These formal
considerations finally led Einstein to redefine the point of the
manifold as the coincidence of two world lines. Only such a
definition permits an invariant determination of a point under
any general transformation. It is furthermore devised by
purely conceptual means and without being primarily guided
by the requirement of a possible experiential interpretation: it
therefore designate specifically physical objects.
On the other hand Schlick takes the idea of observed
coincidences as a fundamental one. After explaining in 1922
that space and time are not themselves objects of
measurement but rather a schema we can set up and use to
order physical objects, he locates the requirement of
preserving the coincidences that we observe in every
measurement at the very beginning of our building of the
spatio-temporal schema in physics (see Schlick 1922, and
also Schlick 1925, § 31). This doesn’t prevent him from
recognizing rightly the specificity of the physical definition of
point-coincidences in terms of coincidences of world lines.
But the physical objects thus defined are not different from
what is observed when measuring: it is the same objects
which are conceptually defined in physics and grasped
through observation. Coincidences thus stand at the
interface between the physical (conceptual) and the
psychological (intuitive) apprehension of reality.
The identification of the physically defined pointcoincidences
and the coincidences apprehended by
observation exemplifies a fundamental idea of Schlick’s
epistemology, namely that the way we relate to reality
doesn’t interfere in what reality is. Knowing by means of
concepts and experiencing through intuition are two ways of
relating to the same reality (see Schlick 1932 for a clear
statement of this idea). Against Einstein, Schlick makes a
clear distinction between reality itself and our knowledge of it
by means of concepts.
Moreover, if the epistemological distinction between
conceptually defined objects and the objects of sensory
experience doesn’t lead Schlick, as opposed to Einstein, to
distinguish between two kinds of reality, it’s finally thanks to
his particular use of the coincidence concept which, lying at
the interface between the physical and the psychological,
warrants that both refer to the same reality. Coincidences
are absolutely necessary to bridge the gap between the two
kinds of access to reality that Schlick identifies. This doesn’t
mean that for him our knowledge of reality is entirely
determined by real facts, since conventions also have a role
to play in the formation of scientific systems; but this means
that they do not play a constitutive role in the einsteinian
sense of the word.