Introduction

Walter Burley was born around 1275, probably in Yorkshire, England. He was a master of arts by 1301/2, and a fellow of Merton College, Oxford, by 1305. By 1310 he was in Paris studying theology, and in 1327 Edward III appointed him an envoy to the papal court. The remainder of his career was devoted to diplomatic service as well as philosophical writing. He died soon after 1344.

Burley was a prolific writer. He wrote commentaries on most of Aristotle's works on natural philosophy, sometimes more than one commentary on the same work, and he also composed some influential treatises on philosophical considerations growing out of the intensification and diminution of qualities (the intension and remission of forms) and out of the assignment of first or last instants to a thing's or an event's duration. His work on the lives of the philosophers, written in the early 1340s, was very popular. Around the same time he finished his commentary on Aristotle's Politics. His commentary on the Ethics had been completed earlier, in 1333–4. He also commented on all of Aristotle's logical works and wrote several logic treatises of his own. His best-known work of this sort, The Purity of the Art of Logic (De puritate artis logicae), was published in two versions. The earlier, shorter version was written before the appearance of Ockham's Summa logicae in 1324. The second version, dating from 1325–8, is in many ways a response to Ockham's logic.