  The development of logic in Warsaw had two subperiods in 1918–1939, namely 1918–1929 and 1929–1939. The first decade consisted in intensive teaching and scientific work at the seminars of Leśniewski and Łukasiewicz. Not many results were published at that time. The explosion of publications took place in 1929 and later. There are several factors which caused the development of mathematical logic in Poland. The Warsaw school of logic appears to be model case, but the power of this circle influenced other places where the general environment was not so favourable to logic. The fruitful co-operation of mathematicians and philosophers in Warszawa had the utmost significance. The founders of the Polish mathematical school made a brave experiment consisting in inviting two philosophers with a modest mathematical background as professors at the Faculty of Mathematics and Natural Sciences; this did not happen in any other country. The gifts of Leśniewski and Łukasiewicz as teachers and the abilities of the latter as an organizer attracted young mathematicians. In Poland mathematical logic was considered to be an autonomous science, not a part of mathematics or philosophy. From the present-day point of view this might seem as an exaggeration, but this ideology contributed essentially to the strength of Polish logic. Their representatives were fairly conscious of the fact that the propagation and defence of the autonomy of this field had to be confirmed by important scientific results and international recognition. Moreover, this view about logic motivated various purely theoretical investigations on formal systems. On the other hand, Polish logicians strongly insisted that logic should not be restricted only to mathematics and required the co-operation of representatives of all field in which logic might be used. Still another factor played an important role, namely the conviction about the social significance of logic as a weapon against all kinds of irrationalism. Tarski once said “Religion [you can also say ‘ideology’ — JW] divides people, logic brings them together.” According to Łukasiewicz, “Logic is morality of thought and speech”. Thus, Polish logicians doing logic and teaching it were convinced that they were performing an important social service.