Life and career
He was born in 1906 in Warsaw to father Feliks Jaśkowski and mother Kazimiera (née Dzierzbicka). In 1924, he graduated from high school in Zakopane and enrolled at the University of Warsaw to study mathematics. He was taught mathematical logic under Jan Łukasiewicz and participated in the Polish Mathematicians' Congresses in Lviv (1927) and Vilnius (1931). In 1932, Jaśkowski earned his doctorate on the basis of his thesis Reguły wnioskowania za pomocą założeń (Rules of Inference by Means of Assumptions) written under the supervision of Łukasiewicz.
After the outbreak of World War II, he participated in the September Campaign as a volunteer. In 1942, he was briefly imprisoned by the Germans. In 1945, he continued his scientific career at the University of Toruń where co-organized the Departments of Mathematics, Physics and Chemistry. In 1946, he defended his habilitation at the Jagiellonian University and subsequently assumed the post of the head of the Faculty of Mathematical Logic at the University of Toruń.
Since 1950, he collaborated with the State Institute of Mathematics of the Polish Academy of Sciences (PAN). Between 1959–1962, he served as the Rector of the University. He was among the founders and served as the first President of the Polish Mathematical Society's branch in Toruń.
Jaśkowski is considered to be one of the founders of natural deduction, which he discovered independently of Gerhard Gentzen in the 1930s. Gentzen's approach initially became more popular with logicians because it could be used to prove the cut-elimination theorem. However, Jaśkowski's is closer to the way that proofs are done in practice. He was also one of the first to propose a formal calculus of inconsistency-tolerant (or paraconsistent) logic. Furthermore, Jaśkowski was a pioneer in the investigation of both intuitionistic logic and free logic.
He died in 1965 in Warsaw and was buried at the Powązki Cemetery.
