 John Buridan (c. 1300–1361) was the foremost logician of the later Middle Ages and in his hands the theory of the syllogism was reworked and developed well beyond anything seen before in the history of logic. His two most important logical works are the Treatise on Consequence and the Summulae de Dialectica. The presentation here is primarily based on the Treatise (for further discussion, see Lagerlund 2000, Chapter 5, and Zupko 2003, Chapters 5–6). 