Systematic analysis shows the psychological premises of Machiavelli's political theory to be fairly consistent and to transcend historical circumstance. Above all, the apparent contradiction between its rapacious and consensual sides can be resolved by unearthing his distinction between necessary properties and contingent attributes qua habits. Following medieval medical theory, necessary properties include: spirit that animates the body; mind with faculties of ingenuity, imagination, and memory; desires for preservation, glory, power, freedom, wealth, and sexual pleasure; and four humors received from the stars. While serving the desires, mind stimulates them to expand into the limitless ambition characteristic of Machiavellian individuals. Habituation to laws and gods makes possible the institutional life of republics, in that cooperative habits solve the collective-action problem faced by a multitude of self-ruling citizens. However, such republics are ultimately alliances for joint gain rather than structures of virtue—challenging the ascendant view of Machiavelli as a “civic humanist” and Aristotelian.