 Although the idea of the social contract long antedates the modern era (Gough 1967), its full development occurred in the seventeenth century, when Thomas Hobbes and John Locke used the theory to rather different ends. Jean-Jacques Rousseau, Immanuel Kant, and other philosophers have also relied on social contract theory – in Kant’s case, in ways we will examine below (§1.5) – but the classic expressions of the contract theory of political obligation remain Hobbes’s Leviathan (1651) and Locke’s Second Treatise of Government (1690).