In 1266, five English bishops were suspended from office for supporting Simon de Montfort, earl of Leicester, in rebellion against King Henry III. The action in which the bishops had conspired was highly controversial: the violent imposition of a conciliar government that ruled in the king's name. This article examines the justifications for this system of government produced by the Montfortian religious milieu, showing that the bishops' arguments were not part of a coherent philosophy on royal government but rather ad hoc responses shaped by the context of their production in the midst of dramatic political change.