1350-1420. French cardinal and theologian. Born in Compiègne, he entered the College of Navarre, Paris, in 1363, graduating in arts in 1368 and becoming doctor of theology in 1381. He had many interests and wrote on scientific, philosophical, geographical, and astronomical, as well as theological, subjects. His work shows the influence of Bacon and William of Ockham.* He was made canon at Noyon in 1318, rector of his college in 1384, and chancellor of the University of Paris in 1389. He had close contact with the French court, as confessor and almoner to Charles VI. Among the many benefices he held in plurality was the archdeaconry of Cambrai, and on the accession of Benedict XIII (1395) he was appointed bishop of Puy, which office he never fulfilled, for in 1397 he was translated to the see of Cambrai. Deeply concerned to end the Western Schism which had divided Western Christendom since 1378, he supported the Council of Pisa* which had been convoked by the cardinals in 1409. This ended in the existence of three popes, with d'Ailly supporting the third, Alexander V. On the accession of John XXIII, d'Ailly was created cardinal in the hope that his support would be given to Rome. At the Council of Constance* (1414) he supported the theory of the supremacy of the general council over the pope. In 1416 he published his Tractatus super Reformatione Ecclesia, which was the third part of a much larger work, De Materia Concilii Generalis. Some of his suggested reforms were adopted by the Council of Trent,* and the Tractatus was well received in England and Germany. His theology was greatly influenced by that of Ockham, as seen in his belief that God could not be proved by reason, only faith; he argued also that the pope was not essential to the church. It is not surprising that these views found acceptance with Luther and other Reformers.
See J. McGowan, Pierre d'Ailly (1936).