Reichenbach on the relative a priori and

Synthese (2011) 181:79–93
DOI 10.1007/s11229-009-9588-7

Reichenbach on the relative a priori and the context
of discovery/justification distinction
Samet Bagce

Received: 13 May 2009 / Accepted: 8 June 2009 / Published online: 8 July 2009
© Springer Science+Business Media B.V. 2009

Abstract Hans Reichenbach introduced two seemingly separate sets of distinctions
in his epistemology at different times. One is between the axioms of coordination and
the axioms of connections. The other distinction is between the context of discovery
and the context of justification. The status and nature of each of these distinctions have
been subject-matter of an ongoing debate among philosophers of science. Thus, there
is a significant amount of works considering both distinctions separately. However,
the relevance of Reichenbach’s two distinctions to each other does not seem to have
enjoyed the same amount of interest so far. This is what I would like to consider in this
paper. In other words, I am concerned with the question: what kind of relationship is
there between his two distinctions, if there is any?
Keywords Hans Reichenbach · Philosophy of science · The axiom distinction · The

relative a priori · The context distinction
1 Introduction
Hans Reichenbach (1891–1953) introduced two seemingly separate sets of distinctions
in his epistemology at different times. One is between the axioms of coordination and
the axioms of connections he introduced in his The Theory of Relativity and A priori
Knowledge (TRAK) (1920). This distinction is introduced in the context of a given
scientific theory.

An earlier version of this paper was delivered at the conference, A Philosopher of Science in Istanbul:
Hans Reichenbach, Bogazici University, May 8–9, 2008.
S. Bagce (B)
Department of Philosophy, Middle East Technical University, 06531 Ankara, Turkey
e-mail: sbagce@metu.edu.tr

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The former are not empirical statements. One thus cannot test them empirically
alone. The axioms of coordination should be laid down before one can determine
empirically the relevant terms and concepts in the theory. The latter, on the other
hand, are empirical statements in the traditional sense, describing empirical regularities. He introduces this distinction in order to argue that the traditional empiricism
is at fault in not recognising the constitutive role in obtaining objective knowledge of
Kant’s notion of a priori. So, the axioms of coordination are to play that role. By doing
so, Reichenbach relativised Kant’s notion of a priori.
The other distinction is between the context of discovery and the context of justification he presented in his Experience and Prediction (E&P) (1938). Reichenbach in the
first chapter of his book E&P characterises epistemology as having three fundamental
tasks: the descriptive, critical and advisory tasks. In this section he describes what
these three tasks of epistemology are, and points to a particular difficulty of logical
empiricism. In order to overcome this difficulty, the difficulty how to construct a theory of knowledge being both “logically complete and in strict correspondence with
the psychological process of thought”, he distinguishes the task of epistemology from
that of psychology. He employs the term rational reconstruction to indicate the task
of epistemology. He then introduces “the terms context of discovery and context of
justification to mark this distinction”. He later identifies the context of justification as
the proper domain of epistemology.
The status and nature of each of these distinctions have been subject-matter of an
ongoing debate among philosophers of science. Thus, there is a significant amount of
works considering both distinctions separately. Some honour them by seeing them as

legitimate. Some try to abolish. There is no need to list here all the studies conducted
until now. However, the relevance of Reichenbach’s two distinctions to each other
does not seem to have enjoyed the same amount of interest so far. This is what I would
like to consider here. In other words, I am concerned with the question of what kind
of relationship there is between his two distinctions, if there is any.

2 The first distinction: TRAK and the philosophy of space and time
Especially after Eddington’s 1919 eclipse expedition yielding the empirical confirmation of the prediction by the relativity theory of bending of light passing near the sun,
the thread posed by the relativity theory to the standard views concerning space, time
and gravitation as well as the predominant methodology of science and epistemology
became acute. As a result a heated conflict between the neo-Kantians and the relativity
theory was resulted in. Einstein and Schlick, while trying to provide a philosophical
account of the general theory of relativity (GTR), were defending the theory against
Kantian attacks. There was certainly a need for a new philosophy of science, which
could establish the superiority of the theory over its predecessors, as well as which, in
turn, would be legitimised by its success in justifying the achievements of the relativity
theory. In order for this new account of scientific knowledge to do both required jobs,
it has to negotiate “a careful path between a crudely reductive Machian positivism and
the excesses of Kantian a priorism” (see Howard (1994), p. 47).

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Reichenbach’s TRAK grew out of such a need. In TRAK Reichenbach argues that
the theory of relativity makes it impossible for one to maintain the synthetic a priori
character of all the principles Kant had thought. So, one of the basic aims Reichenbach
has in TRAK is to refute Kant’s philosophy. The other one is to provide a reinterpretation of Kant’s philosophy so that it would still be compatible with the relativity theory,
as well as by means of which he would provide a good philosophical account of the
relativity theory.
But before going any further, let me ask the following question: what did Kant do
that required such a refutation? To answer the question requires us to consider Kant’s
philosophy briefly. Kant articulates an analysis of what counts as a genuine knowledge, i.e. scientific knowledge, in his Metaphysical Foundations of Natural Science
(MFNS) (1786/1970). He provides his account in terms of two particular theories,
Newtonian physics and Euclid’s geometry, which, in turn, is assumed as a background
by Newtonian physics. In other words, he considers these two theories as providing
us with what counts as genuine scientific knowledge.
Kant’s account of scientific knowledge is based upon a distinction between pure and

empirical, or form and content parts. Kant maintains that the pure part entirely consists
of synthetic a priori judgements. Synthetic a priori judgments are actually obtained
by the synthesis resulting from applying the pure concepts of the understanding to the
content provided by the pure intuitions of the faculty of (human) sensibility. The pure
forms of intuition together with the pure categories—yielding the synthetic a priori
judgements—which, in turn, constitute the pure part of knowledge, then represent the
very conditions of the possibility of the empirical part. Without the former, the latter
cannot have well defined meaning, and any relation to objects, that is, truth values.
So, one can have no judgement of experience, unless one has laid down the pure part
in the first place. Thus, the pure part really constitutes the objects of the judgements
of experience, i.e. genuine knowledge. This is why Kant regards them as constitutive.
However, they are not only constitutive; they are at the same time to make synthetic a
priori judgment as necessarily and unrevisable true for all times.
According to Kant, the pure part in the case of Newtonian physics contains Euclid’s
geometry, or more generally the whole applied mathematics required by the same theory, Galilean kinematics, or the absolute simultaneity and classical law of velocity
addition, and Newton’s laws of motions. These are to provide the very background
for Newtonian physics to formulate some specific laws of nature. As an example of
these specific laws of nature, the law of universal gravitation can be cited. Not only
this kind of laws, but any specific laws of motion that are to be obtained in terms of
the Newtonian laws of motion are, in turn, to form the empirical part (see Friedman

(1999), p. 61).
According to Reichenbach, this articulation of genuine knowledge provided by
Kant cannot be maintained in the light of the recent then developments in modern
physics, i.e. the discovery of the theory of relativity, and in the foundations of geometry, that is, the works conducted by Gauss, Helmholtz, Lie, Klein, Poincaré and Hilbert
concerning the foundations of geometry, which is culminated in the theory of relativity. This is because the relativity theory establishes that all the elements forming the
pure part cannot be a priori and thus necessarily and unrevisable true for all times.

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However, the book TRAK has a more interesting consequence that the theory of
relativity also makes possible to provide a reinterpretation of Kant’s conception of a
priori, and by such a reinterpretation one can see what is right in Kant’s epistemology
and at the same time what is wrong in the naïve empiricism, i.e. logical positivism.
Thereby Reichenbach differentiates two separate meanings of Kant’s notion of a
priori:
(i) necessarily and unrevisably true for all times;

(ii) constitutive of the concept of an object (see, 1920, p. 48).
Reichenbach rejects the first meaning of a priori, but considers the second one as
important. While he is clarifying these meanings, he introduces his famous distinction
between the axioms of coordination and the axioms of connection (see, 1920, p. 54).
By accepting the second meaning, he could provide a well articulated philosophical
account of the general theory of relativity. He thereby could protect the theory against
the neo-Kantians by maintaining that what Kant had once thought of some principles
as a priori is true, but in the restricted sense of the a priori: we need those principles just
to constitute the objects of experience, or better, these principles are just constitutive
principles. Moreover, this was quite befitting with his general philosophical aim: to
point out and account of the presence of the personal or subjective elements in human
knowledge contributed by human beings, or reason.
Reichenbach by his distinction between axioms of coordination and the axioms of
connection aims at providing a more specific account of the character and the status
of these constitutive principles. Briefly for Reichenbach, the axioms of coordination
are themselves not empirical statements and one cannot empirically test them alone.
However, they are the principles that make it possible for scientific theories to have any
relation to reality and empirical content. Therefore, before we lay down these axioms,
no meaningful question of truth or falsity of scientific theories can be raised. They are
necessary assumptions for doing any scientific investigation and for understanding the

world.
These axioms are necessary to determine what objects, properties and so on, our
scientific theories talk about. Therefore, they are to provide a framework for empirical
theorising, and thus, they are constitutive of the objects of experience. Once these
axioms are laid down and thereby a specific subject-matter is defined, one can then
formulate the axioms of connection that make specific empirical claims about the
subject-matter. The axioms of connection are empirical statements in the traditional
sense, describing empirical regularities.
When Reichenbach sees the axioms of coordination as being constitutive of the
objects of knowledge, he agrees with Kant on the presence of a priori elements or
principles in human knowledge. In other words, Reichenbach allows some subjective
elements in human knowledge provided by reason as only to constitute the objects of
knowledge, but not make our claims concerning these objects necessarily and unrevisably true.
According to Reichenbach, in the case of Newtonian physics, Euclid’s geometry,
Galilean kinematics, and the Newtonian laws of motion are all the axioms of coordination, and therefore constitutively a priori with respect to this theory. All the rest
of specific empirical laws that are formulated within this framework are the axioms

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of connection (see Friedman (1999), p. 61). This is Reichenbach thinks exactly what
Kant got right. So, Reichenbach believes that Kant’s articulation of human knowledge
is correct historically.1
In the case of the special theory of relativity (STR), Reichenbach maintains that
Euclidean geometry, Lorentzian kinematics, that is, the structure of Minkowski spacetime, are the axioms of coordination. On the other hand the axioms of connection in
this theory, theories of particular forces and fields formulated in this structure such as
Maxwell’s equations (see Friedman (1999), p. 62).
In the context of the general theory of relativity, Reichenbach says that we have
changed once again our framework and the axioms of coordination. “Now only the
infinitesimally Lorentzian manifold structure—space-time topology sufficient to admit some or another (semi-) Riemannian metric—is constitutively a priori: the particular (semi-) Riemannian metrical structure realized within this framework then is
determined empirically from the distribution of mass-energy, and thus the specific
principles of metrical geometry now count as axioms of connection” (see Friedman
(1999), p. 62).
This is also according to Reichenbach to point to what is wrong with the naïve
empiricism: they do not notice the role of the axioms of coordination in representing
the “subjective form” of knowledge, i.e. the contribution of reason, since they claim
that they can characterise all scientific statements indifferently as “derived from experience”; namely, as protocol sentences. In other words, Reichenbach does not hold

the view that ordinary physical objects can be constructed solely out of sense data;
instead, he thinks that to do so, some constitutive principles are also required. He does
not think that there is a set of privileged sense perceptions being independent of these
principles corresponding to physical objects.
However, for Reichenbach, the axioms of coordination are not adopted for once
and all. They can be developed, revised or given up with the progress of empirical
science, that is, in the light of, and under the pressure of empirical findings. This is in
fact what we have learnt from the theory of relativity: we have changed our axioms
of coordination and, therefore, our concept of object of knowledge in moving from
classical physics to relativity theory (1920, p. 94). As the development of relativity
theory shows, the axioms of coordination are not unrevisable fixed points of empirical
inquiry.
As for The Philosophy of Space and Time (PST), (1928), published eight years
after TRAK, is a book in which Reichenbach engages to unify certain ideas he had
previously held with some modifications. It is an elegant work, and by employing
better tools he provides his own account in addition to Helmholtz’s and Poincaré’s
views concerning geometry with an analysis of Einstein’s special and general theories
of relativity, some of which was already given in his Axiomatization of the Theory of
Relativity (ATR), (1924).
Some of these ideas include the distinction between universal and differential

forces,normal systems, the synonymy of equivalent descriptions, the principle of the
relativity of geometry, the distinction between inductive and descriptive simplicity, the

1 For more on this issue see, for example, Friedman (1999), pp. 59–79.

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requirement of postulating coordinative definitions beforehand, the conventionality of
coordinating definitions, the conventionality of metrical simultaneity, an analysis of
the logical structure of relativity theories in terms of causal relational properties.
Reichenbach begins his work by establishing the interdependence between alternative ways of measuring length and alternative geometries, and thereby maintaining the
same kind of relationship between properties and laws. This is to enable Reichenbach
to argue that alternative systems of definitions and laws that account for the same
empirical facts make the same claims and the same empirical content. In other words,
these descriptions provided by these alternative systems of definitions and laws are
equivalent ones. Thus, he no longer holds that relativity theory establishes a particular
geometry as a background to this physical theory. But here by definitions Reichenbach
means coordinative definitions, that is, they are specifying certain physical procedures
to determine the values of quantities.
Reichenbach also brings in Helmholtz’s idea of visualisation into discussion to
argue against the view that pure visualisation has some normative function by maintaining that “the normative function of visualization is not visual but of logical origin”
(1928, p. 91).
PST in general does not deviate much concerning Reichenbach’s treatment of space
and geometry from the one given in TRAK: each of the given theories, Newtonian, STR
and GTR has a certain group of transformations that leaves certain things invariant.
And each of such groups provides us with a range of possible and equivalent descriptions of nature. Reichenbach thinks that those elements remaining invariant are the
elements that mark out the range of these possible and equivalent descriptions, and are
the constitutive elements, the contributions of reason so to speak, that is, the definitions
of coordination. And they also indicate that within the range of possible descriptions,
the choice of one system over another one is arbitrary, that is, conventional.
For Newtonian physics the relevant group of transformations is the Galilean group,
and particular fields (of gravitational force, distribution of mass and etc.) formulated
in this structure are empirical statements. In STR, it is the Lorentz group and particular
fields defined in this structure such as the electromagnetic, the distribution of charge
and etc., are the axioms of connection. And in GTR, it includes one-one bi-differentiable transformations, i.e. the underlying topology is constitutive but the metric of
physical space is empirically determined (see Friedman (1999), p. 66).
In PST, there does seem to be one striking change in Reichenbach’s language
and epistemology. The term convention is not regarded as ill reputed any more, and
employed instead of a priori.2 All his references in PST to a priori are in critical
character. This may be taken to indicate a certain break with Kant’s epistemology.
In PST, Reichenbach seems to have given up his association with neo-Kantianism
(1928, p. xii). Thus, the epistemology underlying PST is intended to be basically more
empiricist: the conventional elements in science are just the non-observational or theoretical ones. The only facts are the observable facts; all the rest is the “contribution of
reason”. The distinction in TRAK between the elements of reason/facts, or if you like
the conventional/factual distinction, is transformed into the theoretical/observational

2 For this please see Hoyningen-Huene (1987) and Popper (1934).

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one. But in TRAK, the former part of the first distinction is not identical to that of
the latter’s; instead it is drawn within the realm of the theoretical: certain elements of
theoretical structure, for example the choice of rest system and of inertial system, are
conventional, other theoretical elements, such as the choice of metric, are not.
Reichenbach seems to have developed two different epistemological positions,
though they are complementary to each other:
i) the earlier one, given in TRAK and
ii) the later one, given in PST.
However, there is the same concern underlying both positions. This is his concern to
point to, and to account of, the presence of the elements in human knowledge contributed by reason, or subjective, conventional if you like—though Reichenbach does
not use this appellation to describe his position in TRAK. He holds in TRAK that the
form/content (convention/fact) distinction is essential for epistemology as well as the
philosophy of science. In E&P he says that “the presentation of volitional—conventional that is—decisions contained in the system of knowledge constitutes an integral
part of the critical task of epistemology” (1938, p. 9). Reichenbach’s positions both
in TRAK and PST are neither strictly Kantian nor strictly naïve empiricist but in PST
he seems to have liked to be less Kantian, and more empiricist.
3 The second distinction: experience and prediction
In Experience and Prediction Reichenbach spells out the epistemology underlying
PST and this is the book in which Reichenbach intends “to show the fundamental
place which is occupied in the system of knowledge by this concept [the concept
of probability] and to point out the consequences involved in a consideration of the
probability character of knowledge” (1938, p. vi).
In the very first section of the first chapter, Reichenbach characterizes epistemology
as having three fundamental tasks: the descriptive, critical and advisory tasks. In this
section he describes what these three tasks of epistemology are, and points to a particular difficulty of logical empiricism. In order to overcome this difficulty, the difficulty
how to construct a theory of knowledge being both “logically complete and in strict
correspondence with the psychological process of thought”, he distinguishes the task
of epistemology from that of psychology in the descriptive task of epistemology:
What epistemology intends to do is to construct thinking processes in a way
in which they ought to occur if they are to be ranged in a consistent system,
or to construct justifiable sets of operations which can be intercalated between
the starting point and the issue of thought-processes, replacing the real intermediate links. Epistemology, thus, considers a logical substitute rather than real
processes (1938, p. 5).
For this logical substitute Reichenbach employs the term rational reconstruction to
indicate this task of epistemology in its specific difference from that of psychology. He
then says that “in spite of its being performed on a fictive construction, we must retain
the notion of the descriptive task of epistemology. The construction to be given is not
arbitrary; it is bound to actual thinking by the postulate of correspondence” (1938, p. 6).

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To illustrate the point he appeals to an example:
The way, for instance, in which a mathematician publishes a new demonstration
or a physicist his logical reasoning in the foundation of a new theory, would
almost correspond to our concept of rational reconstruction; the well-known
difference between the thinker’s way of finding this theorem and his way of presenting it before a public may illustrate the difference in question (1938, p. 6).
He then introduces “the terms context of discovery and context of justification to mark
this distinction” (1938, pp. 6–7). He later identifies the context of justification as the
proper domain of epistemology (1938, p. 7 and 382).
However, he immediately warns off the reader by saying that “even the way of presenting scientific theories is only an approximation to what we mean by the context of
justification. Even in the written form scientific expositions do not always correspond
to the exigencies of logic or suppress the traces of subjective motivation from which
they started” (1938, p. 7).
This descriptive task a bit further down in the book is supplemented by the second
task of epistemology, that is, the critical task in which “the system of knowledge is
criticised; it is judged in respect of its validity and its reliability. This task is already
partially performed in the rational construction, for the fictive set of operations occurring here is chosen from the point of view of justifiability; we replace actual thinking by
such operations as are justifiable, that is, as can be demonstrated as valid” (1938, p. 7).
However, they are still different because “even the rational reconstruction contains
unjustifiable chains”.
It is interesting to see that the next time Reichenbach refers to this distinction is
nearly at the end of the final chapter on probability and induction of the book. Before
he brings in the distinction he talks about an objection to his account of induction
“as an interpolation, as a method of continual approximation by means of anticipations”, the objection that Reichenbach’s theory of induction “may be good enough for
the subordinate problems of scientific inquiry, for the completion and consolidation
of scientific theories. Let us leave this task to the artisans of scientific inquiry—the
genius follows other ways, unknown to us, unjustifiable a priori, but justified afterwards by the success of his predictions” (1938, pp. 379–381). The objection basically
amounts to be claiming that all the important works of great scientific minds cannot
be achieved only by the methods of simple induction and the employment of diagrams
and statistics.
To this objection Reichenbach’s reply runs as follows: “I know … that the working
of their [the great men of science] minds cannot be replaced by directions for use
of diagrams and statistics. I shall not venture any description of the ways of thought
followed by them in the moments of their great discoveries; the obscurity of the birth
of great ideas will never be satisfactorily cleared up by psychological investigation”
(1938, p. 381). However, he does not see these facts as constituting any objection to
his theory of induction “as the only means for an expansion of knowledge”.
At this juncture Reichenbach once more refers to the context distinction as a reason
why he does not see the facts mentioned above as a likely objection to his theory of
induction:

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We emphasized that epistemology cannot be concerned with the first but only
with the latter; we showed that the analysis of science is not directed toward
actual thinking processes but toward the rational reconstruction of knowledge.
It is this determination of the task of epistemology which we must remember if
we want to construct a theory of a scientific research.
What we wish to point out with our theory of induction is the logical relation
of the new theory to the known facts. We do not insist that the discovery of our
new theory is performed by the reflection of a kind similar to our expositions;
we do not maintain anything about the question of how it is performed—what
we maintain is nothing but a relation of a theory to facts, independent of the man
who found the theory. There must be some definite relation of this kind, or there
would be nothing to be discovered by the man of science (1938, p. 382).
Reichenbach then asks the following question: why was Einstein’s theory of gravitation a great discovery, even before it was confirmed by astronomical observations?
His answer is that:
[B]ecause Einstein saw –as his predecessors had not seen- that the known facts
indicate such a theory; i.e., that an inductive expansion of the known facts leads
to the new theory. This just what distinguishes the great scientific discoverer
from a clairvoyant. The latter wants to foresee the future without making use
of induction; his forecast is a construction in open space, without any bridge
to the solid domain of observation, and it is a mere matter of chance whether
his prediction will or will not be confirmed. The man of science constructs his
forecast in such a way that known facts support it by inductive relations; that
is why we must trust his prediction. What makes the greatness of his work is
that he sees the inductive relations between different elements in the system of
knowledge where other people did not see them; but it is not true that he predicts
phenomena which have no inductive relations at all to known facts. Scientific
genius does not manifest itself in contemptuously neglecting inductive methods;
on the contrary, it shows its supremacy over inferior ways of thought by better
handling, by more clearly using the methods of induction, which always will
remain the genuine methods of scientific discovery” (1938, pp. 382–383).
One may find this passage a bit confusing; for Reichenbach, on the one hand, asserts
that the context of discovery is not the proper domain of epistemology, and on the
other hand, claims that methods of inductive reasoning is and will always remain the
genuine methods of scientific discovery. However, there is not anything confusing
here. This is because Reichenbach rejects the context of discovery as the actual process of discovery being a proper domain of epistemology; but he does not reject the
formal or normative aspects of discovery which is basically directed at finding the
objective inductive relations of the known facts to the theory. Gathering the objective
inductive relations between the known facts to the theory is a part of justification,
and is independent of how the discoverer actually got them or of the psychological,
social and cultural basis of this process of discovery. Reichenbach maintains that such
relations should exist physically between the known facts and the theory. Otherwise

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“there would be nothing to be discovered by the man of science”. He also iterates
this point by saying that “the inductive connections of modern physics are constructed
analytically…” (1938, p. 385). We can and should be interested in providing a rational
account of how these relations, which are supposedly exist between the facts and the
theory or that particular new piece of knowledge, are obtained.
Reichenbach also adds the remark that the difference of the context of justification
from the context of discovery is not restricted only to inductive thinking alone. The
same distinction can also be made with respect to deductive operations of thought (see
1938, p. 383). He states a particular example in geometry, “the construction of a triangle from three given parameters”. He maintains that “the objective relations from the
given entities to the solution and the subjective way of finding it are clearly separated
for problems of a deductive character; we must learn to make the same distinction for
the problem of the inductive relation from facts to the theories” (1938, p. 384).
Reichenbach stresses the difference between the logical relations existing between
the set of the givens and the conclusion and the way one sees or discovers those
relations in the problems of deductive character. Although, as it is pointed out, the
discovery/justification distinction seems to have been present before Reichenbach
reintroduced in his E&P,3 it seems that Reichenbach takes his cue for the context
distinction from this difference in deduction. This characterisation thereby makes the
distinction as the one between factual and formal/normative.
Reichenbach by this distinction basically intended to show that the psychological,
sociological, cultural origins of statements, theories have nothing to do with the way of
determining their truth values, and thereby having no epistemological concern. What
is relevant epistemologically is the possibility of confirming statements.
Giere argues that this distinction is a matter as deeply personal as it was philosophical. He thinks that “there may well exist additional documentary evidence regarding
Reichenbach’s personal motivations for insisting on a distinction between discovery
and justification around 1935” (1999, p. 230). So, Reichenbach wanted to have a scientific epistemology dictating as a precondition that rules out the possibility of Jewish
or any national or culturally identifiable science. Giere also thinks that “that had to be
a very useful stance for anyone in his position”, given the historical evidence such as
he was called back to Berlin prior to 1938 and he was looking for safe heaven in the
States, as well as completed the book in English in 1934–1937 (see 1999, pp. 13–15
and 227–230).
There is one more role for this distinction to play: Reichenbach criticises in E&P a
doctrine to which a number of early positivists had been committed: phenomenalism.
The roots of Reichenbach’s rejection of phenomenalism go back to his alliance with
Kantianism: in TRAK, he rejects the synthetic a priori status of Euclidean geometry
and of causality, but he retains the idea of a priori to play an essential role in constituting objects of knowledge. From this, one can safely say that he did not hold the
view that ordinary physical objects could be constructed solely out of sense data or
that statements about such objects are logically equivalent to a finite set of “protocol” statements; instead, he holds that to do so, some sort of constitutive principle
3 Reichenbach earlier had given a clearly obvious statement of this anti-Machian view in his paper of 1929.
See also Salmon (1979), pp. 43–44.

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was also required. Since his theory of empirical confirmation is probabilistic, then he
thinks, it is easy to adopt a kind of empiricism and to maintain a consistent empiricist
epistemology without appealing to any form of phenomenalism.4
However the distinction is introduced by Reichenbach not as a logical conclusion
of any series of arguments. This is also the case with the first distinction as well. It
is introduced as a precondition for doing a normative epistemology which deals with
the “three predicates of propositions”, meaning, truth-value, and weight (probability).
It is clear that none of these predicates has anything to do with questions concerning
the psychological, sociological, cultural origins of propositions or theories. Put it in
another way, the way a particular theory is discovered or constructed has no bearing
upon the way it is to be justified. So the legitimate domain of any epistemology that
aims at providing a scientifically articulated account of human knowledge is not the
context of discovery, but that of justification.

4 The relationship between Reichenbach’s two sets of distinctions
Let me begin by asking the following question: Is there any relation between these
two sets of distinctions Reichenbach introduces? There does not appear to be so. Reichenbach never states that these two distinctions are in one way or other related to
each other. But can they be related by asking the question of justification concerning
the definitions (earlier axioms) of coordination, or conventions?
One may think that this is a legitimate question given Reichenbach’s original definitions of the descriptive and critical task of epistemology. However, one can immediately raise an objection here: their justification cannot arise given the fact that they are
the ones that facilitate the normative justification procedure. Prior to this distinction
no question of justification can meaningfully be asked. So they cannot be subjected
to any procedure of justification. But let’s assume that a permission be granted to ask
the aforementioned question just to see what Reichenbach can say on the issue.
With respect to this issue, the justification of the axioms or definitions of coordination, Reichenbach in his earlier epistemology says almost nothing except that “… the
principles of coordination are determined by the nature of reason; experience merely
selects from among all possible principles” (1920, p. 87). And he also adds that “the
contribution of reason is not expressed by the fact that the system of coordination

4 Moreover, Reichenbach assumes a certain link between the definitions (earlier the axioms) of coordination in each of Newtonian physics, STR and GTR, and thereby the mathematical structures associated
with each theory and the empirical findings or experience. However, the link between these definitions and
the invariance groups is not something to be assumed, but something to be demonstrated (see Friedman
(1999), p. 70). Hence, here a series of independent arguments is required. However such an argument is not
forthcoming in Reichenbach. A similar assumption is made by Kant concerning an a priori link between
the appearances and the a priori forms of intuition. However, this link is not there to suppose, but to be
demonstrated. Kant tried to provide such arguments in order to justify such a link in the Transcendental
Aesthetic of the first Critique (1787/1987). However, he failed to demonstrate this a priori link between
the appearances and the a priori forms of intuition. The absence of such a demonstration is one of the
reasons that Kant’s a priorist project in epistemology fails. Furthermore, Torretti claims that coordination
as described by Reichenbach can hardly be said to define the individual elements of reality (1983, p. 235).

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contains unchanging elements, but in the fact that arbitrary elements occur in the
system” (1920, pp. 88–89).
In his later epistemology, there seems to be one more thing Reichenbach could say:
these definitions of coordination or conventions, say, in the case of GTR, are chosen simply because they have produced a system which contains no universal forces,
i.e. normal system. Although his theory of probability is defective, especially with
respect to the distributing the prior probabilities, he could still argue for the claim
that by appealing to the idea of induction and descriptive simplicity, we can justify
our choice of these conventions over others as the best posits exhibiting the objective
inductive relation from the known facts to the theory.
But in this case Reichenbach would face some serious difficulties. The first one
is that one cannot guarantee that the so called objective relations between the known
facts and the theory can only accounted for and discovered simply by the application
of inductive methods. There are other formal methods, such as group theory, deductive
quasi-empirical methods, that might be at work in establishing the link.
The second one is that Reichenbach’s account of induction cannot be powerful
enough to lead us necessarily to one unique scientific theory. It is perfectly possible
the same objective relations can also be captured by more than one scientific theory.
After all, there are in principle infinitely many ways to generalise on the basis of the
given empirical data.
This is a possibility that Reichenbach himself does not rule out, and because of this
fact, Reichenbach introduces his definition of equivalent descriptions and of synonymy. According to Reichenbach, all these equivalent descriptions express the same
physical content, but in different languages. The question here is not which of the
equivalent descriptions is the true one; for that question is ill-formed: they all are
either true or false. If one of these equivalent descriptions contains no universal force,
(or, say, it involves a normal system), according to Reichenbach, it is the one that we
should choose. Justification of choosing the normal system as the preferred description
is given by means of the principle of descriptive simplicity.
But this is the point where Reichenbach goes wrong when he says that the objective
relations can only be discovered by the application of inductive methods. One of the
equivalent systems is denying the existence of some universal forces, and the other one
positing their existence. Since one cannot empirically confirm or falsify such claims,
we cannot maintain that one has obtained such objective relations by means of the
theory. The only way one can argue for the objectiveness of such claims is through
justifying the theory altogether in question, that is, the one that denies the existence
of such forces.5
This means that one has to have constructed the theory beforehand in order to argue
for the objective character of the relations between the theory and the known facts.
Otherwise it would be an impossible task to achieve. In other words, in Reichenbach’s
case, he should have committed to the truth of the relativity theory; he could then argue
that those objective relations between the known facts and the theory could be obtainable by induction alone. It is clear that Reichenbach was only interested in justifying

5 For more on these issues, see Peckhaus (2006) and Floridi (1996).

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the choice of certain conventions lying at the very basis of the relativity theory. Put it
in other way, Reichenbach’s account of knowledge outlined in his E&P is supposed
to yield a justification for scientific knowledge exemplified by the relativity theory.
This is exactly the primary reason for Reichenbach to introduce the context diction:
to safeguard those coordinative definitions or conventions upon which the theory was
erected so that they could not be subjected to a further justification. This is the point
where the relationship between these two sets of distinction seems to arise. Because
of this, Reichenbach seems to have introduced separately these two different sets of
the distinctions.
The justification of the relativity theory is an empirical matter, and depends upon
the number of the correct predictions it makes. The relativity theory had made some
correct predictions by the time Reichenbach got interested in the theory. There is no
question that Reichenbach’s trust in the theory must have been affected by these predictions. However, these correct predictions cannot be the only reason for his trust
in the success and truth of the theory. Howard outlines other important factors in the
following way:
It is, of course, not surprising that three [Schlick, Reichenbach and Carnap]
bright, technically sophisticated, young philosophers would be excited by the
relativity, especially in the wake of the wave of public interest after Eddington’s
1919 eclipse expedition yielded confirmation of the predicted bending of the
light near the sun. With its radical challenge to received views about the nature
of space and time, and gravitation, with its implicit challenge even to the method
whereby physics had earlier been done, general relativity suited the rebellious
temperaments of young thinkers who were coming of age at a time of political
and cultural upheaval and eager to lead a revolt against the philosophy of their
elders similar to the revolt then underway against the politics of their elders [...].
Certainly Schlick and Reichenbach were also attracted not only to the theory,
but to its author. Einstein was more than just a world-famous scientific genius.
He was a pacifist who was notorious in Germany for his early expression of
doubts about German war aims. He was a socialist who was sympathetic to the
aims of young Berlin student radicals, like Reichenbach [...]. He was a Jew in
a Germany already showing the first signs of a vindictive anti-Semitism. How
could one not be drawn to such a man and his science? How could one not seek
to develop a philosophy of science that would legitimate the relativity theory’s
claims to superiority over its predecessors, a philosophy of science that would
be legitimated in turn by its success in thus rationalizing the achievements of
relativity? (1994, p. 46).
As Howard points out, these additional factors must have played some considerable
role in Reichenbach’s belief in the achievement of the theory. These factors are not
something that can be inferred by the logical analysis and justification of the theory.
They are the so called “social” elements that have contributed to his belief in the
theory. Thus, the context distinction is already blurred.
The path Reichenbach followed in introducing these distinctions separately is the
path followed by Kant in articulating his theory of knowledge. By the transcendental
method of his first Critique Kant intended to provide a justification of scientific knowl-

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edge exemplified by Newtonian physics as well as Euclid’s geometry. As pointed out
by Reichenbach himself, Kant’s theory of knowledge was historical. In other words,
it was with respect to these particular theories at his period. He wanted to provide an
indisputable epistemological basis for the aforementioned theories so that no form of
scepticism could arise. There was only one way to do so and this move to suppress any
scepticism should be made right at the beginning, that is, by providing such an a priori
basis for these theories which could immunise them for further justification. By this
move, Kant was able to put some restriction on what aspects of the nature were knowable and to legitimise what kinds of questions were epistemologically permissible.
This is exactly the job for Reichenbach that was intended to be done by the introduction of the context distinction so that no possible form of scepticism and any question
of the origin and justification could arise concerning the coordinative definitions in
the case of the general theory of relativity. Thus, his account of knowledge is too
historical, with respect to a particular scientific theory, the general theory of relativity.
Reichenbach, like Kant, was introducing certain restrictions to determine the domain
of epistemological activity. Reichenbach’s account of knowledge becomes susceptible
to the same pitfalls Kant had.
Moreover, after Kant there was a discussion about the problem of the foundation of
epistemology raised by K. L. Reinhold concerning the first Critique. This problem later
was formulated as a trilemma by Jakop Friederich Fries—dogmatism, infinite regress,
and psychological basis. Later on with the revival of Fries’s philosophy through the
works of Leonard Nelson, the foundational problem was discussed as the distinction
between genesis and validity in epistemology. Reichenbach must have been aware of
these discussions. So, one reason for him to introduce the context distinction might
be to provide a solution to the foundation problem then.6
To conclude: Reichenbach was not interested in how to account for the role of human
creativity in providing genuine scientific knowledge; but interested in accounting for
a kind of knowledge provided by a specific scientific theory. Since he was primarily
interested in justifying the relativity theory, he introduced the context distinction. He
was still Kantian in E&P too, though much he wanted to disassociate himself from it,
and the reason why Kant failed are the reasons why Reichenbach fails.
The so called personal or social or conventional elements play important roles in
producing scientific knowledge. These are exactly the elements for Reichenbach that
need to be pointed to and accounted of. This was the gist of his general epistemological
programme. To map out what kinds of roles and how conventional, subjective or social
elements in human knowledge play in constructing certain structures yielding scientific
knowledge is certainly a proper job for epistemology. However, introducing certain
restrictions on what aspect of nature one can know and what kinds of epistemological
questions are allowable to ask is certainly not a step in the right direction in dealing
with fundamental epistemological questions. By doing so, one would definitely lead
to an epistemological impoverishment.

6 This is what I suspect what he means by saying that the relation between philosophy and science should

not be considered as an absolute but as an historical category.

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This is what writes in the Preface to E&P and later forgets all about it:
The idea that knowledge is an approximate system which will never become
“true” has been acknowledged by almost all writers of the empiricist group; but
never have the logical consequences of this idea been sufficiently realized. The
approximate character of science has been considered as evil, unavoidable for
all practical knowledge, but not to be counted among the essential features of
knowledge; the probability element in science was taken as provisional feature,
appearing in scientific investigation as long as it is on the path of discovery but
disappearing in knowledge as a definite system. Thus a fictive definite system
of knowledge was made the basis of epistemological inquiry, with the result
that the schematized character of this basis was soon forgotten, and the fictive
construction was identified with the actual system. It is one of the elementary
laws of approximative procedure that the consequences drawn from schematized
conception do not hold outside the limits of the approximation; that in particular
no consequences may be drawn from features belonging to the nature of the
schematization only and not to the co-ordinated object (1938, p. vi).
Acknowledgements I wish to thank Alan Richardson for instructive remarks on the topic of this paper;
Stathis Psillos for enlightening talks and comments on an earlier draft; and Thomas Uebel for valuable
discussions and observations while formulating the problem of this paper.

References
Floridi, L. (1996). Scepticism and the foundation of epistemology: A study in the metalogical fallacies. Leiden: Brill..