Francisco de Vitoria (c. 1485-1546) is well-known for his philosophical contributions to natural rights and international law. However, his extensive work on the conflict between civil authority and the authority of the Catholic Church has been largely neglected by political theorists and intellectual historians. While scholars have recently recognized the significant role played by natural law in the history of political secularism, they have focused almost exclusively on the “modern” natural law theories of Hobbes, Pufendorf, and Thomasius, as opposed to (...) the “scholastic” natural law of early modern Thomists like Vitoria. This essay undertakes an analysis of Vitoria’s use of natural law theory in his approach to civil-ecclesiastical conflict. Contrary to critiques from the “modern” natural lawyers, it argues that Vitoria’s idea of natural law spearheads a forceful defence of the autonomy of civil power from ecclesiastical power. Based on his sharp distinction between the natural and the supernatural spheres of human life, Vitoria argues for a “dualist” position in which civil and ecclesiastical powers are independent and equally binding on human consciences. The essay acknowledges that Vitoria’s dualism ultimately gives way to his endorsement of papal supremacy over all Christian princes. However, this papalist conclusion does not follow from Vitoria’s natural law theory but rather from an opposing political principle: the notion of the universal Christian commonwealth. (shrink)