Social contract theory says that people live together in society in accordance with an agreement that establishes moral and political rules of behavior. Some people believe that if we live according to a social contract, we can live morally by our own choice and not because a divine being requires it. Over the centuries, philosophers as far back as Socrates have tried to describe the ideal social contract, and to explain how existing social contracts have evolved. Philosopher Stuart Rachels suggests that morality is the set of rules governing behavior that rational people accept, on the condition that others accept them too. Social contracts can be explicit, such as laws, or implicit, such as raising one’s hand in class to speak. The U.S. Constitution is often cited as an explicit example of part of America’s social contract. It sets out what the government can and cannot do. People who choose to live in America agree to be governed by the moral and political obligations outlined in the Constitution’s social contract. Indeed, regardless of whether social contracts are explicit or implicit, they provide a valuable framework for harmony in society.