 Historically, medieval logic is divided into the old logic (logica vetus), the tradition stretching from Boethius (c. 480–525) until Abelard (1079–1142), and the new logic (logica nova), from the late twelfth century until the Renaissance. The division reflects the availability of ancient logical texts. Before Abelard, medieval logicians were only familiar with Aristotle’s Categories and On Interpretation and Porphyry’s Isagoge or Introduction to the Categories and not the Prior Analytics, where Aristotle develops the theory of the syllogism — though they did know something of his theory through secondary sources. Once the Prior Analytics reappeared in the West in the middle of the twelfth century, commentaries on it began appearing in the late twelfth and early thirteenth centuries.