born 1350, Compiègne, Fr.
died Aug. 9, 1420, Avignon
French theologian and cardinal.
D'Ailly worked to end the Western Schism. He advocated the doctrine of conciliarism (see Conciliar Movement ), which maintained that supreme authority in the church was held by a general council. He was active at the Council of Pisa (1409), which deposed both pope and antipope in favour of the new conciliar pope, Alexander V, but failed to end the schism. He was also involved in the Council of Constance (141418), which called for the abdication of the antipope John XXIII (r. 141015) and the election of another pope ( Martin V ) and ended the schism. His writings included a geographical treatise, Image of the World , used by Christopher Columbus .