Kazimierz Ajdukiewicz 1890 – 1963

Kazimierz Ajdukiewicz was a Polish philosopher and logician of the Lwow-Warsaw school and one of the leading philosophers of language and theory of knowledge of the interwar period. A pupil of Twardowski and a colleague of Lesniewski and Tarski, he held chairs at Warsaw, Lwow, and Poznan and developed the position he called radical conventionalism, according to which the meaning of expressions depends on the rules of an entire conceptual scheme that we have a limited but real freedom to choose. His Pragmatic Logic, Categorial Grammar, and the many essays later gathered in The Scientific World-Perspective shaped subsequent work on formal semantics and the philosophy of science.

Kazimierz Ajdukiewicz was born at Tarnopol in eastern Galicia in December 1890. He studied philosophy and mathematics at Lwów under Kazimierz Twardowski, took his doctorate in 1912 with a thesis on Kant's philosophy of space, and after service in the Polish army during the First World War habilitated at Lwów in 1921. He held chairs at Warsaw, Lwów (until the Soviet annexation), and Poznań, and after the Second World War rebuilt the Poznań department before returning to Warsaw, where he served from 1955 as professor of logic and editor of Studia Logica.

His works include the early Z metodologii nauk dedukcyjnych (1921), Główne zasady metodologii nauk i logiki formalnej (1928), the celebrated paper 'O znaczeniu wyrażeń' (On the Meaning of Expressions, 1931) and 'Sprache und Sinn' (1934), the textbook Logiczne podstawy nauczania (1938), the late Język i poznanie (Language and Cognition, 1960–1965), and the posthumously translated Pragmatic Logic (1965).

Ajdukiewicz was a leading member of the Lwów-Warsaw School and developed the categorial grammar with index notation that bears his name and still underlies modern type-logical syntax. His radical conventionalism on meaning treated languages as systems of meaning-rules wholly chosen by their users, while his later work in the methodology of the empirical sciences placed him among the foremost Polish epistemologists. He died in Warsaw in April 1963.