Kazimierz Ajudkiewicz (1890–1963) is rightly regarded as one of the most distinguished Polish philosophers. He was a member of the Lvov-Warsaw School and a close collaborator of Kazimierz Twardowski, the founder and main organizer of the School. Like Twardowski, Ajdukiewicz was a great pedagogue and devoted much of his time and effort to organizing philosophical and scientific life; in 1953 he founded one of the most prestigious, and still extant, Polish logical journals, Studia Logica. In addition, he contributed regularly to another famous journal, Erkenntnis. Before the World War II, he was professor at the Jan Kazimierz University in Lvov. After the war, Ajdukiewicz moved to Poznań, where he was professor at the Adam Mickiewicz University as well as the President of the university for a term. Later he was nominated professor at Warsaw University, where he remained until he retired in 1961. Regarding his private life and connections with Twardowski, it is worth mentioning that Ajdukiewicz married one of Twardowski’s daughters. During the Soviet invasion of Poland in 1920, he fought as a soldier under Józef Piłsudski’s command.

Perhaps the most representative for his intellectual career and scientific achievements is a two-volume collection of essays and articles, Język i poznanie (Language and cognition), first published in 1960. The papers in that collection are characterized not only by a very precise style of argumentation, but also by originality, intellectual courage, and depth in discussing the fundamental philosophical problems, and in proposing new solutions. Ajdukiewicz authored as well some introductory books and textbooks, such as Problems and Theories of Philosophy and An Outline of Logic and Pragmatic Logic (the latter was published posthumously), which for many generations of Polish philosophers provided an unequalled ideal of clarity and precision in discussing philosophical problems.

What was of particular significance for Ajdukiewicz was logic and “logical culture”. He was a dedicated and enthusiastic teacher of logic, at all levels of education, and wrote some textbooks of logic which have been used by generations of teachers and students. He regarded logic not only as a indispensable tool of philosophising, but also as a salient condition for individual human development and for humankind as a whole. As he wrote, “logical anti-irrationalism” could prevent societies from falling into “falsehood and absurdity” and protect them against “a madman advertising the products of his sick imagination, or a fraud who wants to convert others to his views for the sake of his egoistic and mean purposes”. Bearing in mind the war experiences of Ajdukiewicz’s generation these optimistic views on the prospects of logical culture are remarkable.

Ajdukiewicz contributed to many fields of philosophy and his achievements are still inspiring and deserve thorough study. His terminology, conceptual distinctions, classifications, and many philosophical ideas are still in use among contemporary Polish philosophers. Ajdukiewicz’s method of paraphrasing became an original and stimulating way of philosophising, which still has its defenders and practitioners in Poland. He was always faithful to the principle, saying that only sufficiently justified beliefs can be accepted. A critical attitude has to navigate between the Scylla of scepticism and the Charybdis of dogmatism. Such an attitude saves us from holding unjustified, or not sufficiently justified, beliefs, and from dogmatism. It is worthy of note that Ajdukiewicz saw more doctrinarism in political ideologies, such as Marxism, than in religion, whose dogmas have some kind of emotional and moral justification.

He exhibited a critical attitude as well to his own views and conceptions. In the 1930s, Ajdukiewicz formulated and defended radical conventionalism, a view which anticipated many theses advanced by Kuhn, Feyerabend, and other philosophers of science. The heart of the view was the idea that none of our judgements about the world (our world-picture or ‘world perspective’) is determined by experiential data, but each depends on the conceptual apparatus we choose to use when representing experiential data. However, already before 1939 Ajdukiewicz came to the conclusion that his conception faced serious difficulties, such that, finally, after 1945, he abandoned radical conventionalism, though without giving up his belief that language plays an important role in cognition. After the war Ajdukiewicz adopted radical empiricism, i.e., a view quite opposite to radical conventionalism according to which every statement, the laws of logic included, is based on experience.

Among the important reasons why he changed his views regarding radical conventionalism was the development of semantics, in which Alfred Tarski’s semantic theory of truth played a decisive role. Already prior to 1939 Ajdukiewicz started to apply the results of semantics to the analysis and criticism of Heinrich Rickert’s transcendental idealism and later, after the war, to that of Berkeley. The criticism of subjective and objective idealism was conducted by Ajdukiewicz with the help of the method of semantic paraphrasing; the application of semantics to epistemology resulted in the defence of ontological realism. The main idea of Ajdukiewicz’s semantic paraphrase of transcendental idealism was that a transcendental subject of cognition can be identified with the set of true propositions regardless of whether any of those propositions happens to be stated or thought by a real cognizing subject. In spite of some criticism and doubts, Ajdukiewicz’s refutation of idealism is still regarded as the most original and powerful argument against idealism.

Regarding his contribution to logic and semiotics, his pioneering investigations in the logic of questions (erotetic logic) and categorical grammar are highly valued by both logicians and linguists. Moreover, he contributed significantly to the discussion about reasoning by introducing statistical reasoning, that Jan Łukasiewicz and Tadeusz Czeżowski, two other eminent logicians and philosophers, had overlooked, and by laying more stress on the pragmatic element (the assertion of a sentence) than on the logical one (the correctness of inference).

Ajdukiewicz was interested not only in logic, semiotics, and metaphysics, i.e., theoretical philosophy, but in practical philosophy as well, ethics in particular. He was quite explicit that ethics should not be based on metaphysical premises such as God, the freedom of the will, and immortality of the soul. A normative ethics which does not derive its norms and principles from metaphysics is called “independent ethics”, and, in his view, such an ethics is to be built solely on the moral experience which is common to people of any time and culture. In addition, he defended an egalitarian theory of justice advanced under the banner of “equal measure”.

The present special issue of Studies in East European Thought includes texts originally presented (except that by Dariusz Łukasiewicz) at a symposium organized in October 2013 by the Institute of Philosophy of Casimir the Great University, Bydgoszcz, Poland, on the occasion of the 50th anniversary of Ajudkiewicz’s death. Taken together, these contributions show how Ajdukiewicz’s thinking is received today, some 50 years after his death. We would like to express our appreciation and thanks to all the authors whose papers have contributed to the present volume. Gratitude is due to the editor of Studies in East European Thought for his help and assistance in the preparation of the texts.