This chapter explores Gottlob Frege's contribution to logic. Frege has been called the greatest logician since Aristotle, but he failed to gain influence on the mathematical community of his time and the depth and pioneering character of his work was acknowledged only after the collapse of his logicist program due to the Zermelo–Russell antinomy in 1902. Frege, by proving his theorem χ without recourse to Wertverläufe, exhibited an inconsistency in the traditional notion of the extension of a concept. He prompted (...) our awareness of a situation the future analyses of which will hopefully not only deepen our systematic control of the interplay of concepts and their extensions but also improve our understanding of the historical development of the notion of “extension of a concept” and its historiographical assessment. (shrink)

Friedrich Albert Lange (1828-1875) author of a famous History of Materialism and Critique of Its Present Significance (1866, English transI. 1877-79, repr. 1925 with introduction by Bertrand Russell), was also interested in the epistemological foundations of formal logic. Part I of his intended two-volume Logische Studien was published posthumously in 1877 by Hermann Cohen, head of the Marburg school of neo-Kantianism. Lange, departing from Kant, claims that spatial intuition is the source of the apodeictic character not only of the truths (...) of mathematics, but also of the truths of logic. He aims at showing this by basing validity and invalidity of syllogistic inferences on an interpretation of the standard forms (of proposition in assertoric syllogistic) with the help of the five kinds of possible relations (in fact what is known today as the Gergonne-Euler relations) between extensions of concepts given to us as areas in a plane, i.e.in space. Generality is achieved by considering all possible variations within each type of spatial relation, exhibiting a connection between concept and intuition reminding Lange of the Kantian "schema". Lange is well aware of the contemporary English "algebraic" logic, but he considers its approach as the appropriate one for a logic of content (Inhaltslogik) and not for a logic of extension (Umfangslogik). Lange did not live to enjoy the recognition by some leading logicians (amongst them John Venn, to whose reference in 1881 to Lange's "admirable Logische Studien" the present paper owes it title), nor could he respond to the many critics of his proposed foundation of logic. Its radicality as well as its broad reception (and discussion up to at least 1959) seem to entitle Lange's Logische Studien to an, if modest, place in the history of logic in the 19th century. (shrink)

The paper begins by delimiting the scope of ‘logic’ and ‘philosophy of science’ and goes on to present the biographies and select bibliographies of 36 émigré scholars from Germany and Austria working in these fields. An evaluation of this material, and of data on societies, congresses, lecture series, books and periodicals on logic and philosophy of science, is then undertaken. Against the rich background of activity in the 20s and 30s of our century, there is manifest a rapid decline of (...) high-ranking research in the philosophy of science and in logic in Germany and Austria. Since, with one exception, émigré logicians and philosophers of science did not return after the breakdown of the Third Reich, recovery in these fields has been extremely slow. Pertinent knowledge had to be re-imported, and a satisfactory level has been reached only with the coming of a new generation. (shrink)

Brouwer's criticism of mathematical proofs making essential use of the tertium non datur had a surprisingly late response in logical circles. Among the diverse reactions in the mid 1920s and early 1930s, it is possible to delimit a coherent body of opinions on these questions: (1) whether Brouwer's denial of the tertium non datur meant only the abandonment of this classical law or, beyond that, the affirmation of its negation; (2) whether one or both of these alternatives were logically inconsistent; (...) and (3) whether Brouwer's line of argument was forced to take resort to the very law it was designed to refute. The controversy centred around a series of articles by Marcel Barzin and Alfred Errera who fought against the intuitionistic critique, missed their victory because of conceptual confusions and fallacious reasoning, but emerged unconvinced from the debate in the late 1930s. The controversy is of interest to the historiography of formal logic since it stimulated the clarification not only of the concepts of formal validity, decidability, many-valued systems of logic and non-classical systems generally, but also of the distinction between object and meta-level, and between a formal system and its semantics. Most important, the debate, by putting pressure on the intuitionistic camp to make their ideas more precise, seems to have given the decisive motivation towards Heyting's answer to this demand by his axiomatization of intuitionistic logic in 1930. (shrink)

On 5 May 1957, Leopold Löwenheim passed away in a Berlin hospital following a short but severe illness, unnoticed by the community of mathematical logicians who believed that he had perished in a Nazi concentration camp in or shortly after 1940 (the year of publication in the Journal of Symbolic Logic of his last paper before the end of World War II). The 50th anniversary of his death seems an appropriate date for the posthumous publication of a paper that was (...) supposed to appear in Fundamenta Mathematicae in 1939, the galley proofs of which Löwenheim had already seen and corrected when German troops invaded Poland on 1 September 1939. Löwenheim managed to save the proofs through the War, despite the loss of most of his possessions during the bombing of Berlin in 1943 and 1944. By another lucky chance, a copy of the proofs survived in the present author's possession, when the originals were lost during a flat clearing in Berlin as part of the estate of Johannes Teichert (1904?1994), Löwenheim's step-son, when his widow moved into a nursing-home in May 1999. Later, I will expand these short remarks slightly but seize the present opportunity to resume (and in some places add to) the extant data on Löwenheim's life and writings. (shrink)