All participants in late medieval debates recognized Holy Scripture as the principal authority in matters of Catholic doctrine. Popes, theologians, lawyers—all were bound by the divine truth it conveyed. Yet the church possessed no absolute means of determining the final authoritative meaning of the biblical text—hence the range of appeals to antiquity, to the papacy, and to councils, none of which were ultimately conclusive. Authority in the late medieval church was a vexing issue precisely because it was not resolved. Ian Christopher Levy’s book focuses on the quest for such...