On Walter Dubislav

Nikolay Milkov

University of Paderborn, Germany

Walter Dubislav (1895–1937) was, together with Hans Reichenbach, a leading member of the Berlin Group of scientific philosophy (not to be confused with the Berlin Society for Empirical / Scientific Philosophy that was organized and led by the Group), the “sister group” of the Vienna Circle. Dubislav was a radical formalist in philosophy of mathematics who followed Hilbert’s axiomatic method. A product of this orientation was putting definitions at the center of his explorations. (He maintained that abstract axiomatic systems are nothing but implicit definitions.) Also Dubislav’s formalistic theory of science can be seen as part of the theory of definitions: instead of replacing signs with signs, it treats replacement (definition) of facts of the external world with system of signs, or “theories”. Dubislav’s partnership with Reichenbach between 1928 and 1933 brought out important results. Some examples: (i) the “quasi truth-tables” Dubislav introduced in 1928 helped Reichenbach to develop an original logic of probability according to which propositions have three values: true, false, and weight. (ii) Through Dubislav, Reichenbach also rediscovered the probability implication as generalization of the conventional implication (an idea introduced by Bolzano). (iii) Dubislav’s work on definitions helped Reichenbach to clarify his position on “coordinative definitions”. (iv) Through his discussions with Reichenbach Dubislav, in turn, became increasingly interested in philosophy of science. In more general terms, Dubislav showed Reichenbach the importance of logic for his studies. Indeed, before Reichenbach met Dubislav, he displayed no interest in logic proper. Of course, he spoke about “logical analysis” of science already in 1920. He meant with this, however, axiomathization of science, in particular, of theory of relativity, not logic of science. The philosopher who first recognized the originality and the power of Dubislav’s thinking earlier than anybody else was, however, not Reichenbach but Carnap. In Aufbau (p. 4) Carnap referred to Dubislav’s Systematic Dictionary of Philosophy as the only case of “constitution system” ever published. In a letter to Dubislav from 1926 Carnap wrote: “You see that I agree on many points with you and that I learned much from your presentations”. Dubislav influence on Carnap is especially pronounced in Carnap’s paper “Proper and Improper Concepts” (1927)—a paper that treated Dibislav’s problem of definition; but also in the whole reorientation of Carnap attention from Russell’s logicism to the Hilbert’s problem of axiomatic around 1930 and in his general turn in direction formalism. Dubislav also deeply influenced his student Carl Hempel, especially with his book Philosophy of Nature (1933). In his review of the book of 1934 Hempel noted that what made Dubislav’s book different from the Philosophy of Nature works of some members of the Vienna Circle, Schlick and Zilsel, in particular, was that it didn’t primary discuss specific problems of science but systematically explores the logical and methodological problems of scientific knowledge. This was a program Hempel also followed in his influential Philosophy of Natural Science (Hempel 1966).