 Contracts lie at the very core of economic thought. A simple purchase is a type of contract, the use of money another. Property rights are also grounded in the idea of a contract, at least since the early modern period. Aristotle had argued in favor of private property, primarily with appeals to security and superior stewardship. Aquinas reinforced these claims but also argued that in the case of a famine or siege, one might appropriate available foods to fulfil the Christian dictate of self-preservation. In the early modern period, Bodin, Grotius, and Pufendorf reflected at length on the question of property rights, prompted by the breakdown of feudal land tenure and ever-expanding overseas trade. Grotius’s De Mare Liberum (1609) addressed the possibility of unregulated naval and fishing rights. Hobbes (1651) and Locke (1689), with their respective appeals to the state of nature, motivated the formation of property rights and hence the government. Sovereign rule would alleviate penury, facilitate the spread of trade and commerce and, above all, foster population growth, or so it was widely believed.