Introduction

After teaching at the Dominican school in Naples from around 1300, John of Naples was sent to Paris in 1310 for further theological study. He was a strict adherent of Thomas Aquinas and was commissioned in 1313 (together with Pierre de la Palu) to examine the teachings of their fellow Dominican, Durand of St. Pourcain. In 1315 John became a regent master at Paris, where he taught until returning to Naples in 1317 as Dominican lector. His work survives in the form of forty-two Disputed Questions, thirteen Quodlibets, and a series of sermons. He died around 1350.

John's discussion of just war provides further illustration of the close connection between teaching within the Faculty of Theology at Paris and issues of pressing political and ecclesiological concern in western Europe. In discussing whether evil can be used for a good end, in exploring the parallel drawn by Augustine between military and legal contexts, and in expounding Aquinas's reflections on the justification of war and the legitimacy of non-Christian lordship, John makes detailed use of Scripture and of the law – canon, Roman, and customary. His conclusion is nothing if not bold: It is indeed permissible for a Christian ruler to use non-Christian mercenaries to defend a Christian commonwealth. Basing his argument on the distinction between what is true without qualification (simpliciter, per se) and what is true in certain circumstances (secundum quid), John is careful to add important practical reservations.