de Bury was dean. Bury had been involved in the coup d'état of 1330 that resulted in the execution of Mortimer, and the de facto accession of Edward III to the throne. In 1333 de Bury was consecrated Bishop of Durham by the king, over-ruling the choice of the monks, who had elected and actually installed their sub-prior, Robert de Graynes. In February 1334 de Bury was made Lord Treasurer, an appointment he exchanged later in the year for that of Lord Chancellor. He gathered together a group of intellectuals including Thomas Fitzralph, Richard de Kilvington, Robert Holcott, Thomas Bradwardine and Burley himself. Walter may have been a relative of his younger contemporary Adam Burley. Philosophical work Burley was one of the first medieval logicians to recognize the priority of the propositional calculus over the term logic, despite the fact that the latter had been the main focus of logicians until then. Burley also seems to have been the only 14th-century logician to have taken the position that, in line with modern views on the material conditional, the principle that "from the impossible anything follows" ("ex impossibili sequitur quodlibet") is both a necessary and sufficient condition for explaining the logical relationship between antecedent and consequent. He was also known for his commentaries on Aristotle's Physics, which include the quodlibet De Primo et ultimo instanti (around 1320) and the longer work Expositio in libros octo de physico auditu. Burley wrote 39 Commentaries on Aristotle and 32 Treatises and Questions (many unedited). De Puritate Artis Logicae, in two versions: Tractatus brevior (before 1324) Tractatus longior (1325–28) This is Burley's main work, in which he covers such topics as the truth conditions for complex sentences, both truth-functional and modal, as well as providing rules of inferences for different types of inferences. This book is known to have been written after Ockham's Summa Logicae (c. 1323), possibly partly in response to it. Other works include: In Aristotelis Perihermenias (Questions on Aristotle's Perihermenias, 1301) De consequentiis (1302) De exclusivis (1302) De exceptivis (1302) De suppositions (1302) De obligationibus (1302) De ente (ca. 1310) De qualitatibus (ca. 1310) Expositio super libros De Anima (after 1310) Tractatus de formis (1324-1326) Tractatus de universalibus (after 1337) Bibliography De Puritate Artis Logicae Tractatus Longior, with a revised edition of the Tractatus Brevior, ed. P. Boehner, New York: 1955. On the Purity of the Art of Logic. The Shorter and