Alfred Tarski 1901 – 1983

Alfred Tarski was a Polish-American logician, mathematician, and philosopher and one of the founders of modern mathematical logic and model theory. After his early career in the Lwow-Warsaw school of analytic philosophy, he was stranded in the United States by the German invasion of Poland in 1939 and spent the rest of his life at the University of California, Berkeley, where he trained generations of logicians. His Concept of Truth in Formalized Languages set out the celebrated semantic conception of truth, while his Decision Method for Elementary Algebra and Geometry and his extensive work in set theory and metamathematics shaped the discipline.

Alfred Tajtelbaum, who from 1923 used the name Tarski, was born at Warsaw in January 1901 into an assimilated Jewish family of merchants. He studied at the University of Warsaw and took his doctorate in 1924 under Stanisław Leśniewski with a thesis on the primitive notions of the Principia Mathematica. He taught logic at Warsaw and at the Stefan Żeromski gymnasium throughout the 1930s; in August 1939 he sailed to a conference in the United States and was prevented by the German invasion from returning. After uncertain years at Harvard and the Institute for Advanced Study he was appointed in 1942 to the University of California, Berkeley, where he founded the leading American school of mathematical logic and remained until his death.

His seminal papers include 'On the Concept of Truth in Formalised Languages' (1933), 'On the Concept of Logical Consequence' (1936), 'A Decision Method for Elementary Algebra and Geometry' (1948), and the posthumous 'What Are Logical Notions?' His books include the textbook Introduction to Logic (1941), the great collection Logic, Semantics, Metamathematics (1956), and Cylindric Algebras (with Henkin and Monk, 1971–1985).

Tarski gave the canonical definition of truth for formalised languages by way of his T-schema and the concept of satisfaction, founded model theory as an independent discipline, proved the undefinability of truth within sufficiently strong formalised languages, and gave decision procedures for the elementary theories of real algebra and geometry. He stands with Kurt Gödel as one of the two principal logicians of the twentieth century. He died at Berkeley in October 1983.