At Avignon, Pierre d'Ailly was entrusted by the king with a mission of congratulation to the new pontiff.
Pierre d'Ailly himself had not long before taken part in the drawing up of a letter to the king in which the advantages of this double abdication were set forth, but since then his zeal had seemed to cool a little.
Some time afterwards Pierre d'Ailly became bishop of Cambrai (March 1 9, 1 397) by the favour of the pope, who had yielded no whit, and, by virtue of this position, became also a prince of the empire.
The latter, though a partisan of the pope of Rome, took the opportunity of enjoining on Pierre d'Ailly to go in his name and argue with the pope of Avignon, a move which had as its object to persuade Benedict XIII.
Pierre d'Ailly, who, in spite of his attachment to the pope, had been carried away by the example of the kingdom, was among the first who, in 1403, after experience of what had happened, counselled and celebrated the restoration of obedience.
At the ecclesiastical council which took place at Paris in 1406 Pierre d'Ailly made every effort to avert a new withdrawal from the obedience and, by order of the king, took the part of defender of Benedict XIII., a course which yet again exposed him to attacks from the university party.
It was not till after the cardinals of the two colleges had led to the convocation of the general council of Pisa that Pierre d'Ailly renounced the support of Benedict XIII., and, for want of a better policy, again allied himself with the cause which he had championed in his youth.
This was, in fact, the procedure of the council of Pisa, in which Pierre d'Ailly took part.
This pope reigned only ten months; his successor, John XXIII., raised Pierre d'Ailly to the rank of cardinal (June 6, 1411), and further, to indemnify him for the loss of the bishopric of Cambrai, conferred upon him the administration of that of Limoges (November 3, 1412), which was shortly after exchanged for the bishopric of Orange.
He also nominated Pierre d'Ailly as his legate in Germany (March 18, 1413).
From this point of view Pierre d'Ailly, together with his compatriot Cardinal Fillastre, took the preponderating part during the first.
When at last the question arose of giving the Christian world a new pope, this time sole and uncontested, Pierre d'Ailly defended the right of the cardinals, if not to keep the election entirely in their own hands, at any rate to share in the election, and he brought forward an ingenious system for reconciling the pretensions of the council with the rights of the Sacred College.
(November 11, 1417), and the task of Pierre d'Ailly was at last finished.
Whatever reservations may be made as to a certain interested or ambitious side of his character, Pierre d'Ailly, whose devotion to the cause of union and reform is incontestable, remains one of the leading spirits of the end of the 14th and beginning of the 15th centuries.
Fully a century later, when the system of scholasticism was gradually breaking up under the predominance of Occam's nominalism, Pierre d'Ailly (1350-1425), and his more famous scholar John Gerson (1363-1429), chancellor of the university of Paris, are found endeavouring to combine the doctrines of the Victorines and Bonaventura with a nominalistic philosophy.
The question, for all that, was not finally settled until the council of Constance (1414), when their cause was triumphantly defended by Pierre d'Ailly and Gerson.
So urgent was the need of restoring union at any cost that even prelates who had taken an active part in the work of the council of Pisa, such as Pierre d'Ailly, cardinal bishop of Cambrai, were forced to admit, in view of the fact that the decisions of that council had been and were still contested, that the only possible course was to reconsider the question of the union de novo, entirely disregarding all previous deliberations on the subject, and treating the claims of John and his two competitors with the strictest impartiality.
The arrival of the Spaniards at Constance necessitating the formation of a fifth nation, Pierre d'Ailly availed himself of the opportunity to ask either that the English nation might be merged in the German, or that each great nation might be allowed to divide itself into little groups each equivalent to the English nation.
Pierre d'Ailly (1350-1425) and John Gerson (Jean Charlier de Gerson, 1363-1429), both chancellors of the university of Paris, and the former a cardinal of the church, are the chief figures among the later Nominalists.
The council, however, showed itself inaccessible to all his arguments and explanations, and its final resolution, as announced by Pierre d'Ailly, was threefold: first, that Huss should humbly declare that he had erred in all the articles cited against him; secondly, that he should promise on oath neither to hold nor teach them in the future; thirdly, that he should publicly recant them.
He had three sons: Charles (1578-1621), first duke of Luynes, and favourite of Louis XIII.; Honore (1581-1649), seigneur de Cadenet, who married Charlotte Eugenie d'Ailly, countess of Chaulnes, in 1619, and was created duke of Chaulnes in 1621; and Leon, seigneur de Brantes, who became duke of Luxemburg-Piney by his marriage in 1620 with Margaret Charlotte of Luxemburg.
Louis Auguste d'Albert d'Ailly (1676-1744), duke of Chaulnes, also became marshal of France (1741).
Louis Charles d'Albert (1620-1690), duke of Luynes, son of the constable, was an ascetic writer and friend of the Jansenists; Paul d'Albert de Luynes (1703-1788), cardinal and archbishop of Sens, an astronomer; Michel Ferdinand d'Albert d'Ailly (1714-1769), duke of Chaulnes, a writer on mathematical instruments, and his son Marie Joseph Louis (1741-1793), a chemist; and Honore Theodore Paul Joseph (1802-1867), duke of Luynes, a writer on archaeology.
But these declarations as to the superiority of an ecumenical council never attained legal validity, in spite of their defence by Pierre d'Ailly and Gerson.
Cardinal Pierre d'Ailly pleaded before the council of Constance in 1415 for the reform of "that most scandalous custom, or rather abuse, whereby many [clergy] fear not to keep concubines in public."