William of Ockham was a leading English philosopher and theologian in the fourteenth century who came into controversy with Pope John XXII. His Dialogus is a survey of a wide range of matters controversial in the Catholic Church in the early fourteenth century. Topics discussed include the concepts of orthodoxy and heresy and the procedures for deciding whether a person is a heretic, the power of the pope within the Church, the power of the Church in relation to secular government, the constitution of the Church, and the constitution of secular government. The Dialogus is an important source of ideas on ecclesiology and political philosophy in the late middle ages. The present volume is concerned with heresy and heretics. Preface Introduction Apparatus and notes 1 DIALOGUS 1-5 Prologus 1. Ad quos, theologos videlicet vel canonistas, pertinet principaliter diffinire que assertiones catholice, que heretice, qui heretici et qui catholici, debeant reputari 2. Que assertiones heretice, que catholice, sunt censende 3. Quis errans est inter hereticos computandus 4. Quomodo de pertinacia et pravitate heretica debeat quis convinci 5. Qui possunt pravitate heretica maculari Manuscripts and early editions Publications referred to Index John Kilcullen now retired, taught English Literature in the University of Queensland, Philosophy in the University of Toronto, and Politics and Philosophy in Macquarie University. Publications include Philosophy and Politics and early modern and medieval intellectual history. John Scott worked at the University of Tasmania, Macquarie University, and the University of Sydney. Publications and translations of works include William of Malmesbury, Hugh of Poitiers, Robert Kilwardby, and William of Alnwick, and with John Kilcullen, the translation of William of Ockham's Work of Ninety Days and William of Ockham's Dialogus Parts 2 and 3.1.