Pierre d'Ailly, the Ockhamist philosopher, was born at Compiègne in France. He studied at the Navarre College in Paris in 1372, receiving his doctoral degree in 1380 and becoming chancellor of the university in 1389. He was made bishop of Puy in 1395 and bishop of Cambrai in 1396 and cardinal in 1411. He took a leading part in the Council of Constance (1414–1418), where he asserted the superiority of a general council of the church over the pope. He died as papal legate at Avignon.

D'Ailly's literary output was vast and wide-ranging. It comprehended philosophy, theology, scientific theory, political theory, canon law, and ecclesiastical politics and touched on mysticism. Among his more important writings were the treatise De Anima, commentaries on Boethius's Consolation of Philosophy and the four books of the Sentences, two studies of mysticism and asceticism, three works on different aspects of church...