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On the occasion of the Third World Logic Day Adam Mickiewicz University and University of Lodz organizes a two-day online conference, 14-15.01.2021. On the first day, 14th of January, we would like to honour Roman Suszko. The second day, 15th of January, will be devoted to the memory of Jan Gregorowicz.

Roman Suszko (1919-1979) was a Polish logician and philosopher. In the years from 1937 to 1939 he studied physics, mathematics and chemistry at Poznań University. During the occupation of Poland, he was working in Cracow while studying physics, mathematics and philosophy at underground Jagiellonian University where he was also teaching clandestine classes on logic and methodology of science. After the Second World War he moved to Poznań, where he defended his PhD thesis under Kazimierz Ajdukiewicz. In 1951 he completed his habilitation (“Canonic axiomatic systems”). In 1952 he moved to Warsaw, where he worked at Warsaw University and Polish Academy of Sciences. In the years 1955-1956 he was a deputy dean at the Faculty of Philosophy of the Warsaw University and served as a dean there in the years 1960-1963. In the meantime, he defended his second PhD thesis on philosophy (“Logika formalna a niektóre zagadnienia teorii poznania. Diachroniczna logika formalna” [Formal logic and some problems of the theory of knowledge. Diachronic formal logic], 1957). In the years 1967-1969 and 1970-1973 he worked at Stevens Institute of Technology in Hoboken, New Jersey.

His research interests included a variety of topics related to mathematical logic and philosophy. Let us name only a few: the liar’s paradox, theory of definitions, semantics and model theory, many-valued logics, theory of consequence operations, formal ontology. His habilitation thesis concerns set theory and Skolem paradox. But Suszko is perhaps best known from his work on sentential logics. In 1958 he published (together with Jerzy Łoś) a very influential paper “Remarks on sentential logics”. In the 1960s, inspired by the monograph by Bogusław Wolniewicz about ontology in Wittgenstein’s “Tractatus Logico-Philosophicus”, he introduced a class of non-Fregean logics — Sentential Calculus with Identity (SCI) being the simplest one. He devoted several dozen papers to this topic. The main idea of non-Fregean logic lies in the abolition of the Fregean axiom which states that two sentences having the same logical value also have the same semantic referent and thus there are no more than two objects described by sentences: Truth and Falsity. In non-Fregean logics, as in Wittgenstein’s Tractatus, sentences are not names of the aforementioned objects, but denote situations. Suszko was convinced of the importance of the non-Fregean paradigm. He wrote in “Abolition of the Fregean axiom”:

If one accepts the Fregean axiom and follows Frege in constructing pure logic then one will arrive at FL, the Fregean logic. We will continue Frege’s program without his axiom. It is like realising Euclid’s program without his fifth postulate. In that case, one arrives at so called absolute geometry and there are just two possibilities: the way of Euclid or that of Lobachevski and Bolyai. Here, we get NFL, that is, the absolute non-Fregean logic.

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