A Neo-Kantian reading of the Aufbau: Rudolf Carnap and the Marburg School

Lois Marie Rendl
University of Vienna
According to Richard Rorty the “difference between the ‘mainstream’ Anglo-Saxon tradition and the ‘mainstream’ German tradition in twentieth-century philosophy is the expression of two opposed stances toward Kant.” But although the analytic tradition following Russell dismissed the conception of a “synthetic a priori” while most German philosophers insisted on a “transcendental” foundation of knowledge, most philosophers – Dewey, Wittgenstein, and Heidegger being the great exceptions – on both sides adhered to what Rorty calls a “neo-Kantian consensus”: “Even when they claim to have ‘gone beyond’ epistemology, they have agreed that philosophy is a discipline which takes as its study the ‘formal’ or ‘structural’ aspects of our beliefs, and that by examining these the philosopher serves the cultural function of keeping other disciplines honest, limiting their claims to what can be properly ‘grounded’.” Agreeing with Rorty’s analysis Kurt Walter Zeidler speaks of “the analytical heirs of Neo-Kantianism”, who had taken over “with its Anti-psychologism, its criticism of metaphysics and its orientation of epistemology on the ‘fact of science’ three columns of the neo-Kantian program”. The consensus between all schools of Neo-Kantianism was according to Zeidler, “that it was Kant’s main achievement to have referred philosophy to the ‘facts of exact science’ and thereby to have secured her her own ‘object’ as well as her claim to be a science.” Michael Friedman argues for an even stronger connection between Neo-Kantianism and analytic philosophy. According to him the logical positivists, reacting to revolutions in mathematics and mathematical physics, did not simply dismiss but rather ventured “a profound transformation of the Kantian conception of synthetic a priori principles”. They attempted to articulate what Friedman calls “relativized a priori principles”, i.e. “nonempirical principles, which, despite their tendency to be revised in periods of deep conceptual revolution, are nonetheless constitutive of the framework for natural scientific investigation […] at a given time.” This transformation was according to Friedman first conceived by Reichenbach in his book Relativitätstheorie und Erkenntnis apriori (1920), where Reichenbach distinguishes two meanings of “the Kantian notion of the a priori”, the first is “necessarily and unrevisably true”, the second is “constitutive of the concept of the object of knowledge”. “What the development of modern geometry and relativity theory really shows is that these two meanings must be separated.” Even though no physical theory is “true for all time”, there are principles which are relative to a particular theory “constitutively a priori”, i.e. “they are not themselves subject to straightforward empirical confirmation or disconfirmation”. In Carnap’s Logical Syntax of Language (1934) Friedman finds “a revival of the relativized a priori in something very like Reichenbach’s original sense.” By contrast “the Aufbau construction suffers from serious technical problems – problems that, in fact, undermine Carnap’s attempt to distinguish himself from the Marburg School with respect to the never completed ‘X’ of empirical cognition and the synthetic a priori.” According to Friedman’s reading of the Aufbau “the entire constitution of the external world is determined from sensory data on the basis of a complicated system of physical and methodological conventions or stipulations”. Because the epistemological “status of these methodological principles remains […] fundamentally unclear” according to Friedman, “Carnap ends up with no objection, in particular, to the synthetic a priori.” When Carnap speaks of the Marburg School of Neo-Kantianism he primarily refers to Natorp and Cassirer. But it was the founder of this school Hermann Cohen who programmatically referred philosophy to the “fact of science” and consequently identified the synthetic a priori with the methodological principles of science. But Cohen does not conceive these a priori principles to be “necessarily and unrevisably true” in the sense that Kant did. “New problems will necessitate new presuppositions. The necessary idea of the progress of science necessarily not only is accompanied by but presupposes the idea of the progress of pure knowledge.” “New problems will bring new categories; will necessitate new presuppositions.” Thus already Cohen argues for a historically relativized a priori. As Carnap was certainly influenced by the ideas of Cohen trough Cassirer and Natorp this raises several questions with regard to the relation of Carnap to the Marburg School and Friedman’s account of it. Carnap rejects the synthetic a priori because according to the conception of the constitutional theory of the Aufbau “there are no other components in cognition than these two – the conventional and the empirical”. But this rejection fails according to Friedman, because the methodological principles cannot be viewed “as simple definitional conventions”. This is indirectly supported by Friedman’s claim, that what he calls Reichenbach’s relativized conception of a synthetic a priori is not to be identified with Schlick’s characterization of constitutive principles as conventions. But if the relativized a priori is neither to be viewed as a convention nor as an a priori knowledge in the Kantian sense what exactly is its epistemological status and in what way is it distinguished from the historically relativized a priori of the Marburg School? This question shall be addressed by a comparison of the conceptions of the methodological principles of science as stated by Cohen in his Logik der reinen Erkenntnis and by Carnap in his Aufbau.
Keywords Rudolf Carnap  Hermann Cohen  Paul Natorp  Ernst Cassirer
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