Abstract

BEFORE Frege’s Begriffsschrift, propositional logic was submerged in the often murky theory of the "hypothetical syllogism." With the exception of the Stoa, a handful of astute mediaeval logicians, Leibniz, and Bolzano, one might well obtain the impression from studying the history of logic that Frege created his theory ex nihilo—which is substantially true, since Frege was apparently little influenced by previous work. One might also obtain the impression, especially by reading Frege himself, that very little was being done on propositional logic in the 19th century. This claim would be false. As one might expect from a philosopher who is sometimes grouped with Frege and De Morgan as one of the greatest nineteenth century logicians, Charles S. Peirce dealt extensively with propositional logic, or as he would have called it, with the theory of the hypothetical syllogism.