How Tarski defined the undefinable CEZARY CIE Ś LI Ń SKI

Alfred Tarski, one of the greatest logicians of all time, was born as Alfred Tajtelbaum in 1901. He came from a Jewish family living in Warsaw. In 1918-24 he studied at the University of Warsaw, initially biology, and then mathematics. At this time Warsaw was becoming one of the world leading centers in the area of logic and mathematics. Tarski’s logic teachers were Jan Łukasiewicz and Stanisław Leśniewski, prominent members of the emerging Lvov-Warsaw school – a thriving community of researchers and students, which was to flourish in Poland until the beginning of World War II. 1 Tarski wrote his PhD dissertation “On the primitive term of logistic” under the supervision of Stanisław Leśniewski (the dissertation having to do with Prothotetics – a logical system devised by his supervisor). 2 In later years Leśniewski kept saying “All my PhD students are geniuses”. It was widely known however that Tarski was the only PhD student of Leśniewski. After completing the doctorate, Tarski became a docent at the University of Warsaw. He was at that time the youngest researcher working as a docent in Warsaw. Since his job was poorly paid, he also taught mathematics at a secondary school in Warsaw. In August 1939 Tarski left for the US to take part in the Unity of Science Congress in Harvard. The invitation to address the Congress probably saved his life – World War II broke out soon after his departure from Europe. He remained in America for the rest of his life, teaching in Harvard and Berkeley, where he created a prominent center of research in logic and foundations of mathematics. He died in Berkeley in 1983. 3