Peter Abelard (1079–1142) came from a Breton knightly family and chose logic over the sword. In Paris he became the most brilliant and most controversial teacher of his time. His forbidden affair with Heloise of Argenteuil upended his career and his life — his famous letters became part of European philosophy alongside his logical works.

One of his core contributions to logic is the middle position in the debate over universals: universals are neither mere names (nominalism) nor independent entities (Platonic realism), but mental concepts the mind extracts from real particulars ('conceptualism'). That framing shaped centuries of subsequent debate, from Aquinas through Locke.

His most lasting methodological contribution is the Sic et Non ('Yes and No'), compiled around 1120. Abelard sets out 158 theological questions and, under each, juxtaposes openly contradictory citations from the church fathers (Augustine, Jerome, Gregory): on one side, 'yes, it is so'; on the other, 'no, it is not'. He offers no resolution himself — he offers a method: careful reading, distinguishing senses of terms, attending to linguistic and historical context. Within a generation this method had crystallised at the University of Paris as the standard pedagogical form, the quaestio disputata. Every article of Aquinas' Summa Theologica — 'Is it so? Objections. I answer. Replies to the objections.' — inherits the path Abelard cleared.