Although Locke and Rousseau wrote prominent treatises on the social contract, Thomas Hobbes introduced the idea of it. He argued that human beings were evil in nature, and thus needed to enter a contract in which everyone basically agreed not to kill each other (i.e. in his natural state, although completely free, man would always be wary of subjected to another man's brutishness. Whereas in society we are all supposedly better off-even if there are sacrifices involved-because there is an agreement binding each man into behavior that's meant to contain man's evil nature).