Bolzano e la logica

Bolzano’s Wissenschaftslehre (1837) is one of the two most important works in logic between Leibniz and Frege. In it, Bolzano revolutionised logic by placing it for the first time on a firm semantic footing, employing the concepts of objective, abstract propositions and ideas. The chief instrument in his account of logic is the variation of ideas, which enabled him to define a wide range of logical concepts, and further allowed him to merge deductive logic with a logical conception of probability. This article summarizes the main points of Bolzano’s logic and indicates ways in which they relate to post-Fregean logic.