AILLY, PIERRE D', (Lat. Petrus de Alliaco): Chancellor of the University of Paris, later bishop of Cambrai and cardinal, one of the distinguished churchmen who sought to restore unity to the divided Church during the great papal schism (1378-1429; see SCHISM) by means of a general council; b., probably at Ailly-le-haut-clocher (20 m. n.w. of Amiens), in the present department of Somme,1350; d. at Avignon Aug. 9, 1420. He was brought up in Compiègne in the midst of the desolation caused by the war with England and an insurrection of the peasants (the Jacquerie); to this was no doubt in part due the strong national feeling and the prejudice against England which he showed later. He entered the University of Paris as a student of theology in the College of Navarre in 1372, and began to lecture on Peter Lombard in 1375. His lectures printed as Quaestiones super libros sententiarum, Strasburg, 1490), gained for him the reputation of a clear thinker, and helped to make the nominalisin of Occam predominant in the university. He also distinguished himself as a preacher.

On Apr. 11, 1380, Ailly was made doctor of theology and professor. His treatise on this occasion, and other essays written about the same time published as appendix to the Quaestiones; also in Gersonii opera, ed. Du Pin, i. 603 sqq., Antwerp, 1706), show his position concerning the doctrine of the Church, which was brought to the front by the schism. The Christian Church, he said, is founded on the living Christ, not on the erring Peter, on the Bible, not on the canon law. The existing evils can be cured by a general council. Against those who opposed this idea of a council he wrote in 1381 a satirical epistle "from the devil to his prelates" (text in Tschackert, Appendix, pp.15 sqq.). In 1384 he became director of the College of Navarre, where he had among life pupils Jean Gerson, who became his faithful friend. In 1389 Ailly was made chancellor of the university and almoner of Charles VI. of France, a position which brought him in close relation with the court at Paris. When the Avignonese pope, Clement VII., died (1394), Ailly's influence secured the recognition by France of his successor, the Spaniard Peter de Luna (Benedict XIII.). As a reward Benedict made Ailly bishop of Puy (1395), and two years later bishop of Cambrai. In 1398 Charles VI. of France and Wenceslaus of Germany sent him upon unsuccessful missions to both Boniface IX. and Benedict, to try to induce them to resign their office. Benedict was then kept a prisoner in Avignon by French troops till he escaped to Spain (1403). In 1398 and again in 1408 France withdrew its obedience from Benedict, without, however, declaring for his rival. The attempt to nationalize the French Church failed because the civil authorities of the time conducted Church affairs worse than the pope. In 1408 Ailly finally abandoned the cause of Benedict. The addition of a new element of discord by the choice of a third pope at the Council of Pisa (q.v.) in June, 1409, was not in accord with Ailly's wishes; but in the main he stood by the council (cf. his Apologia concilii Pisani, in Tschackert, pp.31 sqq.), though he continued to write in favor of reform by another council. John XXIII. (the Roman pope) sought to conciliate him by an appointment (June 7, 1411) as cardinal, with the title Cardinalis Sancti Chrysogoni, though he himself preferred to be called "the Cardinal of Cambrai." He attended the council called in Rome by John in 1412, where he interested himself in a reform of the calendar. In 1413 he traveled through Germany and the Netherlands as papal legate, and at the same time was active as a writer.

Ailly’s most important services in church history, however, were rendered at the Council of Constance (met Nov. 5, 1414; see CONSTANCE, COUNCIL OF). Here he maintained the superiority of a general council over the pope, but at the same time defended the privileges of the college of cardinals against the council. It was due to Gerson and Ailly that after the flight of John XXIII. from Constance (Mar. 20, 1415), the council was not adjourned. He had the courage to preside over the first popeless session (Mar. 26, 1415), and to carry out the order of business of that important gathering. The council had to decide three points: (1) The causa unionis. (abolition of the schism); (2) the causa reformationis (reformation of the Church in capite et in membris); and (3) causa fidei (the case of John Huss). Ailly was very active in the last two. As president of the commission on faith, he examined Huss (June 7 and 8, 1415; Documenta J. Hus., ed. F. Palacky, Prague, 1869, pp. 273 sqq.), and was present at his condemnation (July 6). He expressed his ideas on reform, as deputy of the college of cardinals, in the commission on reform and in a writing of Nov., 1416, De reformatione ecclesiæ (in H. von der Hardt, Magnum œcumenicum Constantiense Concilium, i., part viii., Frankfort, 1700). His views on the power of the Church he had already published (October) in his De potestate ecclesiæ. When, in November, the council proceeded to the choice of a new pope, Ailly was a candidate; but the opposition of the English prevented his election. He lived on good terms with his successful competitor, Otto di Colonna, and as his legate at Avignon continued influential in the French Church till his death. Ailly was always faithful to the interests of his country, although he was more churchman than Frenchman. He influenced the young Luther by his doubts concerning the doctrine of transubstantiation (cf. Luther's De captivitate Babylonica, Erlangen ed., var. arg., v. 29). In 1410 he wrote a geographical work Imago mundi (n.p., n.d.), which has interest as having been one of the sources from which Columbus drew his belief in the possibility of a western passage to India (cf. Tschackert, 334 sqq.).