What is “conciliarism” in late medieval church politics?

The story behind the answer

Conciliarism argued that in extraordinary circumstances the Church as a whole, expressed through a universal council, could exercise supreme jurisdiction—even over a reigning pope. It arose amid the Western Schism (1378–1417), when multiple claimants divided Christendom. At the Council of Constance (1414–1418), decrees like Haec Sancta asserted council supremacy and the assembly deposed or accepted the resignation of rival popes before electing Martin V, restoring unity.

Its roots lay in canon law and university theology (e.g., Jean Gerson, Pierre d’Ailly). Though the Council of Basel later pushed the idea, papalist reactions at the Fifth Lateran Council and, much later, Vatican I reasserted papal primacy and infallibility, curbing the conciliar program. The debate left a lasting mark on ideas of corporate governance and constitutional limits, influencing currents such as Gallicanism and shaping how Europeans thought about balancing authority and accountability.