This paper argues that throughout his intellectual career, Hobbes remains unsatisfied with his own attempts at proving the invariant advisability of contract-keeping. Not only does he see himself forced to abandon his early idea that contractual obligation is a matter of physical laws. He also develops and retains doubts concerning its theoretical successor, the doctrine that the obligatoriness characteristic of contracts is the interest in self-preservation in alliance with instrumental reason – i.e. prudence. In fact, it is during his work on Leviathan that Hobbes notes the doctrine's main shortcoming, namely the limitation of its dialectical potential to cases in which contract-breakers are publicly identifiable. This essay shows Hobbes's doubts about his Leviathan's treatment of contractual obligation by way of a close reading of its central 15 th chapter and an analysis of some revealing shifts between the English Leviathan and the (later) Latin edition. The paper ends by suggesting that Hobbes's awareness of the flaws at the heart of his political philosophy helps account for some striking changes in his latest writings.