Zygmunt Zawirski: The forgotten forefather of quantum logic.

This paper reconstructs a forgotten episode in the early history of quantum logic by examining the work of Polish philosopher Zygmunt Zawirski. In the early 1930s, Zawirski developed an original system of many-valued logic explicitly designed to interpret quantum mechanics. Anticipating later views by Reichenbach and Putnam, Zawirski argued that the indeterminacy and probabilistic structure of quantum theory required a departure from classical two-valued logic. Drawing on Łukasiewicz's many-valued logic and Post's formal constructions, he built a system of truth-functional operators capable of representing probabilistic conjunction and disjunction. This article offers a technical and conceptual reconstruction of Zawirski's logic, based on his 1934 monograph and recent interpretations by Garbacz. While the system's practical limitations have been noted, its philosophical ambition and originality remain significant. Zawirski's logic not only constitutes the first formal system of quantum logic but also anticipates contemporary debates on the empirical foundations of logic and the relation between logic and probability. By recovering his overlooked contribution, this paper broadens our understanding of early responses to quantum theory and highlights the role of Polish logicians in shaping 20th-century philosophy of science.