|On Walter Dubislav
Preface and Acknowledgments
The task of this paper is to outline the scientific biography of Walter Dubislav. The paper was written together with another one, “Walter Dubislav’s Philosophy of Science and Mathematics”, that is more concentrated on Dubislav’s philosophy and says practically nothing about his biography. It is due to appear soon, and can be read together with the present paper.
The paper is greatly based on archival material collected by Eckart Menzler-Trott, to whom we would like to pronounce our warmest acknowledgements. We are also indebted to Christian Thiel who made steps in collecting archival material on Dubislav’s biography already in the late 1970s and in the 1980s. Prof. Thiel also greatly encouraged this work on Dubislav.
Dubislav (1895–1937) was a logician and formalist philosopher of mathematics and science, a core member of the Berlin Group organized around Hans Reichenbach and Kurt Grelling (Milkov 2013), and leading figure of the Society for Empirical/Scientific Philosophy in Berlin. He took part in the conference on Exact Theory of Knowledge in Prague (1929), where he spoke about Bolzano’s logic of probability,1 and at the succeeding conference in Königsberg (1930), where he delivered a talk on the subject-matter of the philosophy of mathematics, later published as Dubislav (1930a). Dubislav was also invited to deliver a presentation at the Erlangen Conference on Exact Philosophy in March 1923 and at the Paris Conference in 1935 and received an invitation to give talks at the Universities of Warsaw and Lemberg. Because of financial difficulties, however,2 he couldn’t visit these venues. After Reichenbach immigrated to Istanbul in the summer of 1933, Dubislav became the leader of the Berlin Society for Scientific Philosophy. In 1934 Carnap invited Dubislav to officially co-edit Erkenntnis with him. (RC )
Dubislav published works in the most prestigious journals and publishing houses of the time, including in Erkenntnis. When in 1930 Adolf Fraenkel edited an issue of the hewly founded journal Blätter für Deutsche Philosophie on the “Philosophical Foundation of Mathematics”, Dubislav was invited to contribute,3 together with five other leading figures of the Germanophone philosophy of mathematics of the time: Paul Bernays, Rudolf Carnap, Adolf Fraenkel, Karl Menger, and Heinrich Scholz. Immediately after the Second World War, Dubislav’s name was still not forgotten—in 1948 in Munich Wilhelm Britzelmayr4 delivered lectures on theory of definition following Dubislav’s ideas and made a colloquium on “scientific terminology” in Dubislav’s key.
Despite all this, in the last fifty years or so Dubislav’s name was practically forgotten.5 Even such meticulous studies on the philosophy of logic and mathematics of the first half of the twentieth century like Mancosu (2010), or on the logical empiricism like Uebel (2007), did not ever mention Dubislav once.6 One reason for this is that there is still no comprehensive study of Dubislav’s life and work also produced by German scholars based on archival material.7 The aim of this paper is to fill this gap, bringing to light the life and the ideas of this important logician, philosopher of mathematics and science. As we shall see in what follows, in many respects Dubislav is the missing puzzle element in the history of the logical empiricism, logic and philosophy of mathematics. In particular, the exposition of his philosophy clears up important points of Hans Reichenbach’s thought and throws light on aspects of Carnap’s ideas and also of that of Dubislav’s student Carl Hempel.
Peace and War
Walter Dubislav was born on September 20, 1895 in Berlin to the family of Gerorg and Olga Dubislav (née Buchholz). Georg Dubislav was a “high-school Professor” for English and French and sometime a principle of a “gymnasium” at which also the young Walter made his high-school diploma (Abitur). Georg Dubislav authored more than ten textbooks on English and French language learning (on historical syntax of the English language, in particular) which makes his name well-known in German libraries also today. Among other things, this point explains why Dubislav had no problem to read English or French (and also Italian) authors in the original.
In the Spring Term 1914 Walter Dubislav entered the University of Göttingen where he studied mathematics under David Hilbert and philosophy under Leonard Nelson. (Dubislav rented rooms in a house next to that of Nelson.) As we are going to see below, both thinkers played formative role in Dubislav’s intellectual development.8
Between January 1915 and March 1919 Dubislav was at the front, ending the Great War as lieutenant and Head of the signal cops in the Kerch fortress, East Ukraine. (The War lasted longer there than at the Western Front because of the Russian Revolution.) Between April and July 1919, he was P.O.W. in Thessaloniki, Greece.
In August 1919 Dubislav renewed his studies at the Friedrich Wilhelm (today Humboldt) University of Berlin. Only two years later, in December 1921, he submitted a Doctoral Thesis under the title “On the Axiomatic Method” (“Über die axiomatische Methode”) at the University of Hamburg. Unfortunately, this try failed. It is probable at that Ernst Cassirer, who was the Head of the Department of Philosophy in Hamburg at the time, was against it. In July 1922 Dubislav submitted another—related—Doctoral Thesis, this time at the University of Berlin, under the title “Contributions to the Theory of Definition and Proof from the Point of View of Mathematical Logic” (“Beiträge zur Lehre von der Definition und vom Beweise vom Standpunkt der mathematischen Logik aus”) of 53 pages. His doctoral supervisors were Heinrich Maier and Wolfgang Köhler.9 On August 24, 1922 Dubislav received his PhD with “laudabile” grade.
It is clear already from the very titles of his two Dissertations that the main subject of interest of Dubislav in the early 1920s was David Hilbert’s axiomatic method and its relevance for philosophy. More than this: Dubislav was more closely oriented to Hilbert as the two other core members of the Berlin Group, Hans Reichenbach and Kurt Grelling, were (despite the fact that Hilbert was Grelling’s Doktorvather). In fact, he was the only philosopher of the time to systematically and consistently defend formalism in philosophy of mathematics.
Dictionary of Philosophical Concepts
In his four years of studying in Berlin, between 1919 and 1922, Dubislav not only wrote two dissertations but also worked on the project for a Systematic Dictionary of Philosophy (Systematisches Wörterbuch der Philosophie) he authored together with Karl Clauberg, a medical PhD and friend of Dubislav (Clauberg and Dubislav 1923). This was a dictionary of concepts as they are used in philosophy, explained in terms of German ordinary language. Most importantly, it made use of Hilbert’s axiomatic method, logically connecting the philosophical termini technici in logical chains of definitions (in Kettendefinitionen) that do not produce a vicious circle (diallele).
It deserves notice that the conception of the dictionary was of Dubislav alone and has nothing to do with his collaborator. (p. v) The fact that Dubislav chose to work on it with a medical doctor, however, shows his inclination to connect philosophy with exact academic disciplines, as well as his penchant for interdisciplinary discussion of philosophical problems, later typical for the Berlin Group and the Society for Empirical / Scientific Philosophy.
Despite the fact that the authors insisted that it is a systematic (fixing logical connections between concepts) and not a philological–historical dictionary, the concepts explained in it are borrowed from the German philosophical tradition. Most often referred to are philosophical definitions given by Leibniz, Kant, Bolzano, Wilhelm Wundt and Leonard Nelson. Impressive is also the prominent place that concepts of philosophy of logic, mathematics and science have in it.
The dictionary made all philosophers in Germany, interested in exact (logical) treatment of their discipline, aware of a new colleague working in this direction. As we already have mentioned, in March 1923 Dubislav was invited at the famous Erlangen Workshop on exact philosophy. Almost ten years later, the book was also noticed in America. A review, published in International Journal of Ethics, finds that “thought this useful book is not recently published, it is not as widely known and used in America as its value suggests. In a single volume of easily manageable proportion, and at a modest price the student may get here what is not really available in English, a dictionary of philosophical terms.” (Smith 1932, 124)
Between 1928 and 1929 Dubislav worked on a second edition of the book: there are many corrections at the margins of his copy. Apparently, he considered the project both vital and deserving improvements. And Dubislav was not alone in this judgment. The Systematic Dictionary of Philosophy was rather popular in Germany for decades. In 1948 the “Office of Logical Research” (Büro für Logistische Forschung) of the already mentioned Wilhelm Britzelmayr started to work on its new edition. Soon, however, the project was abandoned because of “insurmountable difficulties”. (Schischkoff 1949, p. 549) Ten years later Albert Menne, a former student of Britzelmayr, wrote: “From a formal perspective, the excellence [of this book] remains unsurpassed till today.” (Menne 1958)
Dubislav as a Historian of Philosophy and Logic
At the very end of 1922 Dubislav married Gertrud Troitzsch. These were times of severe economic shortcomings in Germany that also affected Dubislav’s plans and projects. From the autumn of 1922 and till 1925 he was forced to work as a salesman. But he did not stop to be also active philosophically. Starting with the Winter Term 1922/23, Dubislav was a voluntary assistant of the mathematician Georg Hamel (a pupil of Hilbert and philosophically close to Leonard Nelson’s Group of neo-Frisians) at the Berlin Institute of Technology (Technische Hochschule in Berlin).10 Among other things, Dubislav strongly hoped that this work will help him to improve his knowledge of mathematics.
In 1924 Dubislav got acquainted with the historicist of logic and exact philosopher Heinrich Scholz, at that point in time an associate professor (Privatdozent) at the University of Kiel. Following Scholz’s advice, Dubislav wrote a MS on Fries’ theory of substantiation (Begründung) that was to serve as his habilitation thesis.11 Since he already knew well the philosophy of the neo-Friesian Leonard Nelson, Dubislav really enjoyed the work on the MS. In the summer of 1924 he submitted it at the University of Kiel. Facing a significant opposition to it from Prof. Johannes Wittmann, however, he dropped his thesis shortly afterwards. The MS was published two years later with a dedication to Heinrich Scholz. (Dubislav 1926a)
The upside of this story was that thanks to this work, Dubislav got well acquainted with Fries’ philosophy that was to become an important point of reference in his philosophy of mathematics, logic, and science. Three years later, in 1929, Dubislav published a brochure on Fries’ method. (Dubislav 1929a) In this way both sides of Fries’ critical philosophy—substantiation and method—were explored and assessed by Dubislav.
Especially prominent in Dubislav’s historical–philosophical investigations was the criticism of Kant’s concept of analyticity. Dubislav revealed seven “inconsistencies [in it], both in Kant’s explicit as well as in his implicit claims”. (1926c, p. 6) Here are two of them: (i) Kant’s division of propositions into analytic and synthetic was only valid for subject–predicate propositions. At the same time, however, Kant held that existential and hypothetic propositions are not subject–predicate. This means that his division of propositions into analytic and synthetic was not comprehensive. (ii) Kant claimed that definitions are analytic judgments, and also that mathematics has definitions. At the same time, however, he held that mathematics is synthetic, not analytic, discipline.
Dubislav further explored two successful attempts to improve Kant’s concept of analyticity: that of Bolzano, and that of Frege. (i) Bolzano claimed that analytic are sensu stricto those “judgments that have a variable” and to which we can ascribe the values “true” or “false”. All other judgments are synthetic. In other words, Bolzano defined as analytic the concept of propositional function. Above all, this conception of analyticity has the advantage to be objective, which cannot be said about Kant’s division of judgments in a priori and a posteriori that is epistemological and so “subjective”. (pp. 6, 19) But Bolzano’s definition of analyticity had its own problems. Above all, it didn’t confine the range of values—it is “all objects”. This position led to the paradoxes of classes. (ii) For Frege, analytic are those propositions that are derivable (ableitbar) from the axioms of logic. The problem with this conception is, so Dubislav, that logic can be derived from many alternative systems of axioms.
Importantly enough, Dubislav presented his formalist position as improvement and completion of the positions of Kant, Bolzano and Frege—not as their refutation. According to it, only those propositions are analytic, the truth or falsehood of which is derivable from a specific system of premises, with the help of specific valid forms of substantiation. (pp. 23 f.)
As a historian of philosophy, Dubislav is of importance mainly for three reasons:
(i) He was strongly interested in history of philosophy not only for itself. Rather, Dubislav considered it indispensable by discussing problems of the disciplines he was most interested in: philosophy of logic, of mathematics, and of science.12 For example, Dubislav’s analysis of the theory of definition in (1931c) started with Aristotle who set as its task to define the essence of objects. Kant and Fries, in contrast, explored definitions of concepts. The first logician who discussed definitions as setting the meaning of a newly introduced sign was Blaise Pascal. Another French logician, Joseph Gergonne, introduced the concept of “implicit definition”. Finally, Frege and Peano turn at the center of their logic the construction of concepts (Begriffsbildung). Unfortunately, the criteria for coordinating signs and objects remained unclear by them.
Dubislav also introduced a kind of “analytic” history of philosophy, later articulated with exemplary clarity in Peter Strawson’s The Bounds of Sense. (Strawson 1966) Its objective is to explicate the sound (“analytic”) elements of the past masters in philosophy, rejecting at the same time the false (“non-analytic”) ones. We find best case of this approach in Dubislav’s discussion of Bolzano’s criticism of Kant. In Dubislav’s interpretation, in his examinations of Kant’s philosophy, Bolzano didn’t simply assess Kant negatively; rather, he exercised a kind of “creative criticism” of Kant (1929e, 368), accepting and further developing some points of Kant, and rejecting others. Following Bolzano, Dubislav further maintained that the task of the historian of philosophy and logic is to clearly explicate the “sound ideas” that Kant only hinted at, and so expressed them in a rudimentary form, showing in this way their hidden fruitfulness.13 In this connection, Bolzano also held that “the more precise the perspective of the criticized philosopher is presented, the more useful will be the criticism of his teaching.” (p. 358)
Dubislav held that there are two grandfathers of exact philosophy: Fries and Bolzano. More than this: Dubislav underlined that their ideas “partly agree”. (p. 362) To this, we should like to add that there was an important difference between them, though. While Fries mainly prepared the rise of the upcoming philosophy of science, Bolzano, who introduced the concept of “propositions in itself”, was more of a predecessor of the analytic philosophy of language and of analytic metaphysics.14 In this connection it deserves notice that, in contrast to Bolzano, today Fries is practically forgotten as one of the ancestors of analytic philosophy. This makes Dubislav’s forays in history of his philosophy especially valuable.
By way of concluding this section, we are to say that Dubislav’s historical orientation was clearly related to that of his fellow member of the Berlin Group Hans Reichenbach, in particular, as it found expression in his The Rise of Scientific Philosophy. (In contrast, historical themes were clearly disregarded in the Vienna Circle.) Of course, there were two marked differences between Reichenbach’s and Dubislav’s historicism: (i) In contrast to Dubislav, Reichenbach’s history of philosophy was most closely connected with history of science. (ii) While Dubislav was conservative historian of philosophy, Reichenbach was a radical such. We mean with this that while Dubislav tried to preserve every idea of past masters in philosophy and logic that can be of interest for exact philosophy today and to develop it further, Reichenbach hold that history of philosophy is full of mistakes that can be only overcome through achievements of the exact science.
Theses On Definition
In 1925 Dubislav started to work more intensively in philosophy. Among other things, he wrote several reviews for Jahrbuch über die Fortschritte in der Mathematik. Only in the next years, however, he could exclusively devote himself to academic pursuits. His first task was to put his dissertation to print and to develop its ideas further. It was published in first edition in 1926 and in second in 1927, both under the title On Definition (Über die Definition). (Dubislav 1926b, 1927a)
In September 1927 Dubislav submitted his work “On the Theory of the so called Creative Definitions” (“Zur Lehre von den sogenannten schöpferischen Definitionen”) as habilitation thesis at the Berlin Institute of Technology. Joseph Petzoldt, Götz Brifs, Georg Hamel, Heinrich Scholz and Erich Becher wrote letters of assessment. The thesis itself was published in the next two years (1928/29) in which Dubislav worked on this topic further—a work that produced two more papers on definition: (1928), (1929b). In January 1928 Dubislav habilitated with the lecture “On Bolzano as a Critic of Kant”. (1929a)
The book that is most well-known of all works of Dubislav’s today, The Definition (Die Definition) (1931c), was a product of these continuing efforts. It was realized under an invitation of Reichenbach and Carnap to submit a manuscript that was to be published in a supplementary series of Erkenntnis. (Unfortunately, Dubislav’s book was the only volume published in the series.) Technically, it was a third edition of On Definition.15 In fact, however, it was radically rewritten and more than two times ticker, including material based on the papers he published on this subject between 1927 and 1930. In comparison with the first two editions of the book, it showed an increased attention to problems of philosophy of science that reflects Dubislav’s collaboration with Reichenbach and Grelling on this subject between 1928 and 1931. As one of its reviewers has noted at the time, the book “is quite as important a contribution to science—and is, naturally, broader in scope, as the definition of definition is not an affair of mathematics exclusively.” (Allen 1933, p. 331)
Dubislav’s putting definitions at the center of his interest was, in fact, a consequence of the fact that he proceeded as a radical formalist in philosophy of mathematics and science who followed Hilbert’s axiomatic method. Indeed, abstract axiomatic systems are nothing but implicit definitions. (Gorskij 1981, p. 40) Also Dubislav’s formalistic theory of science can be seen as part of the theory of definitions. Indeed, instead of replacing signs with signs, it treats replacement (definition) of “objects” (i.e. of facts), of the external world with system of signs, or theories.
Dubislav Working in Philosophical Tandem with Reichenbach
After his habilitation in 1928 and till 1931 Dubislav was an Associate Professor (Privat-Dozent) in philosophy at the Berlin Institute of Technology with financial support from the “Emergency Association of German Science” (Notgemeinschaft der deutschen Wissenschaft), a predecessor of the “German Research Foundation” (Deusche Forschungsgemeinschaft).16 In 1930 Dubislav received a venia legendi—license to teach “Philosophy with Emphasis on the Natural Sciences and on Technology”—at that Institute. At the same year he made efforts to start teaching at the College of Education (Berufspädagogisches Institut) in Frankfurt am Main. (Tilitzki 2002, p. 232) For unclear reasons, this project failed.
At least till January 1928 Dubislav was not in close terms with Reichenbach:17 in than month he wrote Reichenbach a letter—despite the fact that both lived in (different parts of) Berlin (a city of 4.3 million at the time)—with which he also sent a copy of the paper later printed as “Elementarer Nachweis der Widerspruchslosigkeit des Logik-Kalküls.” (1929c). Reichenbach, on his side, promised to write to the publisher of his Philosophie der Raum-Zeit-Lehre (Reichenbach 1928) to make it possible for Dubislav to buy it on reduced (on author’s) price.
Soon the situation changed dramatically. Apparently, the paper Reichenbach received from Dubislav was a kind of revelation to him. Appearing in the Crelles Journal, this essay featured Dubislav’s “quasi truth-tables” that helped Reichenbach to develop an original logic of probability according to which propositions have three values: true, false, and their weight. Through Dubislav, Reichenbach also rediscovered the probability implication as generalization of the conventional implication, an idea introduced by Bolzano.18 Reichenbach used it ever since in his writings on logic of probability, including in his Symbolic Logic. ( ) Dubislav, in turn, started to use Reichenbach’s argument that Einstein’s theory of relativity made Kant’s philosophy of geometry false. (1930a, p. 31)
In more general terms, Dubislav showed Reichenbach the importance of logic for his studies. Indeed, before Reichenbach met Dubislav, he displayed scarcely any interest in logic proper. Of course, starting with (1920) he spoke on “logical analysis” of science. He meant under this, however, axiomathization of science, in particular, of theory of relativity, not logic of science. Finally, Dubislav’s work on definitions helped Reichenbach to clarify his position on “coordinate definitions”. The formalist philosopher of science unequivocally attaches, and so co-ordinates objects and concepts of science with calculi, complementing this procedure with instructions for interpretation. (1930a, p. 47)
Dubislav and Reichenbach also shared a joint position in ethics, one that opposed the Vienna Circle’s doctrine on the subject. Although both groups took anti-cognitivist stand, the Vienna exact philosophers championed a form of emotivism: they maintained that value judgments are expressions of emotions. This position distinguished two forms of understanding, knowledge and emotions, a position that, by the way, was also embraced by Wilhelm Dilthey and his acolytes. In contrast, Dubislav maintained that propositions of ethics are not a product of human understanding—they are implicit commands.19 Reichenbach followed his in this matter.20 Thus as with scientific propositions, which are posits, the propositions of ethics are, according to Reichenbach and Dubislav, products of the free will. The two philosophers saw this position as a triumph of the radical empiricism. In short, we can say that Reichenbach and Dubislav build up the tandem around which the berlin Group functioned.
A Member of the Berlin Group and the Society for Empirical / Scientific Philosophy
The Berlin Group and the Society for Empirical / Scientific Philosophy were two different entities. The Group developed around Reichenbach’s seminars at the University of Berlin after 1926. Later Reichenbach and Dubislav hold joint seminars. Its core members were Reichenbach, Dubislav, Kurt Grelling and Alexander Herzberg. (Reichenbach 1936, p. 143)
The Society for Empirical Philosophy was founded on February 27, 1927, by Josef Petzoldt as a Berlin Branch of the Society of Empirical Philosophy, established in 1925 in Frankfurt am Main. (cf. Milkov 2013) Dubislav joined it shortly afterwards, in May the same year. On December 12, he read his first paper at it: “On Conventional and Modern Logic”. The immediate occasion for applying to read it was his looming habilitation—Dubislav’s “Habilitation father”, Georg Hamel, advised him to approbate his ideas at some forum of academic importance.21
The situation changed after October 1928, when Dubislav persuaded Reichenbach to join the Society. It so happened that some months later Petzoldt fell ill. In May 1929 he resigned, while Reichenbach, Dubislav and Alexander Herzberg were elected to the Board of the Society. From now on, Reichenbach and Dubislav had the real power in it. They used in order it to reorganize the society which found expression in the change of its new name to “Society for Scientific Philosophy”. The Society attracted the scientific elite of Berlin and, in fact, of the whole Germanophone world. Discussed were interdisciplinary themes whith clear philosophical spin. Apparently, Dubislav was its most active member, which is shown in the fact that he delivered nine lectures at the Society (Reichenbach’s record was “only” six lectures).
After Reichenbach left Germany in the summer of 1933, Dubislav became the Head of the Society that had another seven meetings in 1934. In a letter to Reichenbach from December 1933 Carl Hempel wrote: “The meeting … was less attended than on earlier occasions, but the level of the discussion was still good.” (Hempel 1991, p. 9) On Dubislav’s colloquium, around which the “Berlin Group” was now organized and continued to exist, Hempel noted: “Dubislav’s colloquium was very exiting again. Helmer thought over something about the paradoxes and presented it there, Dubislav himself spoke about the thesis of extensionality, and now, at the end of the term, we had a last session in his apartment at which Miss Dr. Herrmann, the [former] student of [Leonard] Nelson, discussed on apriorism.”22
The things changed at the beginning of 1935 when Dubislav faced legal problems (cf. § 11): the Group and the Society practically stopped functioning—which shows the importance of Dubislav’s person for them, especially after Reichenbach’s immigration. Grelling tried to revive the Group in 1936, but soon he, too, was to left Berlin.
Exchange with Carnap
The philosopher who first recognized the originality and the power of Dubislav’s thinking earlier than anybody else was, however, not Reichenbach but Rudolf Carnap. In Aufbau Carnap referred to Dubislav’s Systematic Dictionary of Philosophy as the only form of a “constitution system” ever published. (Carnap 1928, p. 4) Indeed, Dubislav’s insistance insistence that the philosophical termini are to be strictly connected logical chains of definitions was closely related to Carnap’s project. It is no surprise, then, that it was Carnap, not Reichenbach, who invited Dubislav to take part at the 1923 Erlangen conference on exact philosophy.23
Three years later, in the spring of 1926, Dubislav sent a copy of the first edition of On Definition to Carnap who read it “with great interest”. Carnap, in turn, sent to Dubislav excerpts of the Aufbau and cordially invited him to make his comments on the nature of definition and concept formation as expressed in it.24 Next Dubislav sent Carnap his paper “On the Relation Between Logic and mathematics” (“Über das Verhältnis der Logik zur Mathematik”) (1925/26) and On the So-called Analytic and synthetic Judgments (Über die sogenannten analytischen und synthetischen Urteile) (1926c).25 Carnap showed himself very enthusiastic and on June 20, 1926, mailed Dubislav an extensive, 808 words letter (RC 028-13-08) which underlined his “extraordinary interested [especially] in” the paper on analytic and synthetic judgment: a problem that would interest Carnap till the end of his days. Carnap also found Dubislav’s idea of mirroring the logical axioms by the arithmetical “very interesting”. It deserves notice that a few years later, this idea will be developed more extensively and with much greater precision by Carnap’s student Kurt Gödel.
Of course, there were also points of disagreement between the two thinkers. Above all, while Carnap followed Russell in the assumption that mathematics is reducible to logic, Dubislav in 1926 maintained that mathematic is more fundamental than logic and that it, of course, is not reducible to it.26 Typically, Carnap tried to play this difference down, stating that “in principle, this is nothing but a terminological question”.
Carnap ended his letter to Dubislav with the words: “despite all my critical remarks, you see that I agree on many points with you and that I learned much from your presentations” (my italics—N. M.). These lines give good reasons to assume that Dubislav exerted perceptive influence on Carnap. This is especially well 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 to the problem of axiomatic (Carnap 1930) and his general turn in direction formalism.27
The two philosophers stayed in contact till Dubislav’s tragic death in 1937. (cf. § 11) In February 1931, under request from the Prussian ministry of education, Carnap wrote a letter of recommendation for an extraordinary professorship at the Berlin Institute of Technology on Dubislav’s behalf. The recommendation proved helpful: in Mai 1931 Dubislav was already a Professor. Also in 1931, Carnap recommended Dubislav to the editors of the French journal Recherches philosophiques as an author of an article on the Germanophone philosophy of mathematics of the time. Dubislav wrote the paper in German, while the young Emmanuel Lévinas translated it into French. (Dubislav 1931/32)28 Finally, Carnap wrote clearly positive reviews of Dubislav’s The Philosophy of Mathematics Today and Philosophy of Nature. Carnap (1934), (1935) A short reference to the bibliography of Carnap’s works shows that Dubislav was the only author to which Carnap wrote reviews of two different books—which evidences his affection for Dubislav.
Dubislav, in turn, was very enthusiastic with Carnap’s Logical Syntax of Language. In an extensive review of the book he wrote: “The author understands under logical syntax of language the formal theory constructed by him, partly absolutely new, and with thorough success. … This is an epoch-making work.” (Dubislav 1934)
General Philosophy of Natural Science: Influences on Carl Hempel
Under the continuing influence of his discussions with Reichenbach, Dubislav’s interest gradually moved into the direction of the relation between mathematics and science. On this topic he first published the papers (1929d) and (1930b). As we already have seen in § 6, it also played an important role in The Definition. Most importantly, in that same book Dubislav also started to discuss themes of general philosophy of science. His explorations on this subject found a full-fledged expression in Philosophy of Nature. (Dubislav 1933) Dubislav’s student Carl Hempel wrote it two enthusiastic reviews, presenting the book as “extremely stimulating, concise and clearly written.” (Hempel 1933, 56) What made Dubislav’s book different from the Philosophy of Nature works of some members of the Vienna Circle, Schlick and Zilsel,29 for example, was that it didn’t primary discuss specific problems of science, for example, the problem of biological life but systematically explores the logical and methodological problems of scientific knowledge. (Hempel 1934, column 760) Importantly enough, this was a program Hempel also followed in his Philosophy of Natural Science (Hempel 1966) that today is considered standard work in philosophy.30 Dubislav’s book can be thus seen as perhaps the first work in philosophy of science as we understand this discipline today.
Hempel also borrowed some specific conceptions and concepts from Dubislav. Two examples: (i) He conceded with Dubislav’s criticism of the experimentum crucis and 33 years later repeated it in Hempel (1966, 25–82); (ii) Dubislav also coined the term “logical behaviorism” (Dubislav 1933, 69–74) that today is often credited to Hempel. Hempel adopted it first in his paper “The Logical Analysis of Psychology” exactly in the same sense in which Dubislav used it: as “physicalistic interpretation of psychology” (1935, p. 381).
Leading problems in Dubislav’s philosophy of science were that of substantiation, concept formation and theories formation in science. He defended a form of “critical empiricism”31 (he didn’t spoke about “logical empiricism”) that grew on the soil of formalism in philosophy of mathematics and logic. (Dubislav 1933, p. 33) In this connection Dubislav criticized the “old empiricism and positivism” which holds that propositions of science are to be verified by “pure observatory statements”. In fact, the process of verification is much more complex. (Cf. Milkov 2014) It deserves notice that while, officially, Dubislav criticized the old empiricist and positivist authors like J. S. Mill, his arguments were also valid against the logical positivism of the Vienna Circle. But Dubislav was never directly critical to the Vienna Circle neo-positivism in the way Hans Reichenbach was (in particular, in Reichenbach 1936, 1938).
After Hitler came to power and Reichenbach left Berlin Dubislav’s situation worsened dramatically. Here is, for example, a report on how he spent the Christmas night of 1933 we have by good fortune: “By my brother in law [Walter Dubislav], where we spent the Christmas night there was nothing Christmassy beside the food and the punch. We, i.e. the man, drank till 3 a.m., there was a Gramophone music (Dreigroscheoper) that dignified the night with the American song “Sing the chorus together, bali bali bambam”. … We were in markedly gallows humor spirit.” (Stresau 1948, p. 78)
In December 1934 died Dubislav’s wife Gertrud. This tragic event outpoured a series of misfortunes that eventually led to Dubislav’s demise. In the spring of 1935 Dubislav severely wounded a girlfriend in the eye. He was taken in custody and as consequence lost his right to teach (his Lehrauftrag) at the Berlin Institute of Technology. Between August 1935 and May 1936 Dubislav was detained in Moabite prison, Berlin.32 For some months he was also under psychiatric observation.
Meanwhile, the victim dropped her lawsuit against Dubislav so that in May 1936 the public prosecutor closed the case. Dubislav’s first reaction was to try to receive a teaching position at the University of Berlin, in particular, with the help of Heinrich Scholz. To this purpose, Dubislav was not shy to also contact Ludwig Bieberbach, one of the supporters of the movement “German Mathematics” that fought the “Jewish influence” in this discipline. As it could be expected, this try failed.
In order to better to understand this step of Dubislav, as well the psychology of the situation in which he was, it is enlightening to read Carl Hempel’s memoir about these dark times (in his case, 1933/34):
I recall having worked at writing reviews for the Deutsche Literaturzeitung, which was a review published by the Prussian Academy of Sciences. One day there was change in directors and the new young director called me into his office and suggested that it would be a good idea for me to join the party. He pointed to “Unter den Linden” where his office was. There were as a matter of fact a group of Brown Shirts walking around outside; those of course were boors, but we must reform the party from the inside and therefore it would be good if I joined. Well, I resisted this suggestion. I sometimes ask myself if I could have been able to resist all such suggestions if I had stayed in Germany. (Hempel 2000, p. 8)
Soon, however, the public prosecutor resumed the process against Dubislav with clear purpose to eventually intern him. Dubislav and his attorneys at law strongly suspected that the case against him goes in political direction. As a result, he decided to immigrate. In September 1936 he was already in Prague. (Adorno and Horkheimer 2003, p. 88) Dubislav’s motives for emigrating were best formulated by one of the Prague newspapers wrote a year later: “Dubislav left Germany at the end of 1936, partly for political reasons, partly because of a case in which this, in his passion indomitable man was mixed up.”33
In Prague, Dubislav started efforts to receive a teaching position at the German University there. In particular, he hoped to get the chair of Carnap who just moved to Chicago. To this purpose, Dubislav handed over a positive report from the Head of psychiatric clinic at the Berlin University, Prof. Karl Bonhoeffer.
Unexpectedly, in September 1937 the Berlin Institute of Technology reactivated Dubislav’s permission to teach (his Lehrauftrag). Dubislav decided to return, but not without his new girlfriend, Gertrude Landberger, 23 years old student of graphic design from Breslau who already have some reputation as an independent artist. Apparently, she refused to follow him. On September 17, three days before his 42 birthday, Dubislav killed her and then also himself, presumably in a fit of jealousy. (A short remark he left said that he killed his girlfriend on her request.) The next day Dubislav was buried in a mass grave. The story occupied central place in the Germanophone Prague’s newspapers.
Two days later, the unsuspected Otto Neurath wrote Dubislav a letter which came to invite him to write a chapter for the Encyclopedia of Unified Sciences. Unfortunately, it was never written.
Concluding Remarks on Dubislav’s Life and Work
Dubislav led an unusually hard life, even when compared with the life of other exact philosophers of the time. First of all, in contrast to Reichenbach and Carnap, who were four years older, or to Carl Hempel, who as ten years younger, Dubislav cannot finish his training in exact sciences in his youth—he studied with Hilbert just one semester and had to go to the front only 19 years old. His endeavor to catch up for the lost time after the Great War can’t fully compensate the lost years. This partly explains why his ideas in logic—in contrast to these of Gödel, for example—lack in precision, despite the fact that they were very resourceful and at the time also influential.
Another point of difference between Dubislav and the other exact philosophers of the time is the very difficult path he went in the War: he was on the Eastern Front from the very beginning of 1915 and till April 1919. Dubislav ended the War highly decorated with military honors, among others with the “Knight’s Cross of the Albert Order with Swords”, which evidences that he was repeatedly engaged in combat scenes.
Decades later, Olaf Helmer remembered Dubislav as “a brilliant logician and teacher [who, unfortunately …] began to exhibit what were then considered to be paranoid tendencies, abetted no doubt by the political circumstances of the time” (quoted in Luchins 2000, 238). The turn clearly coincided with the political changes in Germany after January 1933. It also found expression in the fact that when Reichenbach invited Dubislav, after the former moved to Istanbul, to formally co-edit Erkenntnis together with Carnap, Dubislav asked for veto rights.nd He was simply afraid that some publications can badly discredit him before the new authorities in Berlin. Both Reichenbach and Felix Meiner, the owner of the publishing house, however, refused to grant him such rights. Apparently, the reason was that Dubislav, who unlike Reichenbach and Grelling was not Jewish “believed that his connection with [the journal Erkenntnis] would be harmful for his career.”34
Of course, there were earlier signs that Dubislav had psychological instability before 1933. Carl Hempel recalled, for example, Dubislav as a person, who at meetings of the Society for Scientific Philosophy, “could be quite brusque, scurrying about and urging the persons sitting on the steps between the aisles to leave voluntary in conformance with fire-safety regulations: or they rather have him call in the police?” (Hempel 1991, 7) The things went worse after Hitler came to power, however.
By way of conclusion, we would like to suggest as highly probable that Dubislav’s prolonged War experience contributed to some psychological problems he developed in the early 1930s and especially after 1933. Of course, nobody in the 1930s paid attention to psychological traumata after war…
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