 In his analysis of propositions, Bolzano did not break through the traditional paradigms. In another respect, however, namely concerning the definition of basic semantic concepts, he opened wide the gates to modern logic. The main instrument to do so was the method of idea-variation that he invented. He himself took it to be his main contribution to logic that was for himself — who certainly did not suffer from arrogance — of “epoch making importance” (Bolzano 1838, 350).