Although it has become commonplace to regard Marsiglio of Padua's Defensor Pacis (completed in 1324) as a quintessential work of medieval Aristotelian political theory, this view has been challenged for various reasons in recent years. Some scholarship has pointed to the superficial quality of Marsiglio's appeal to Aristotle's ‘authority’. Others have emphasized Marsiglio's decisive reliance on sources and doctrines which were quite at odds with his overtly Aristotelian commitments. A revealing measure of the depth of his Aristotelianism is perhaps his failure to cite Aristotle's authority at all in the Defensor Minor, an abbreviated version of the Defensor Pacis composed about 1340.4 At minimum, it seems necessary to reconsider the claim (pioneered already by Albertus Pighius in the sixteenth century) that Marsiglio was ‘homo magis aristotelicus quam christianus’.5 Indeed, it may be true to say that the assumption of Marsiglio's fidelity to Aristotle has acted as a filter, screening out interesting or original features of his thought because they are cloaked in outwardly Aristotelian language. In this paper, I would like to test this hypothesis with reference to Marsiglio's alleged application of the basic principles of Aristotelian moral psychology (in particular, Aristotle's doctrine of hexis) within the Defensor's account of the constituent parts of the political community. In both his Ethics and his Politics, Aristotle had employed the idea of hexis (often translated as ‘habit’, but more properly denoting ‘state’ or ‘firm disposition’) to explain the way in which moral and civil virtues come to be instilled in persons. Thus, hexis served as the foundation for his conception of ethical and political education. Marsiglio seems to use the Latin rendering of hexis, habitus, in a very similar manner. He argues that the different parts of the community, ranging from the rulers and priests to the warriors and farmers, each have a set of characteristics unique to their function. These functional properties are, he says, a result of the differing kinds of habitus which typify each part of the community.