Social contract theory explains political authority as arising from an agreement among the governed. Legitimacy comes from consent rather than from divine appointment, conquest or tradition.

Three versions

Thomas Hobbes argued in Leviathan (1651) that life without a common power is a war of all against all, and that rational people would transfer their rights to a sovereign able to enforce peace. The surrender is near-total, because a sovereign that can be resisted cannot do the one job it exists for.

John Locke disagreed in the Second Treatise (1689). The state of nature is governed by a law of nature, and people have rights to life, liberty and property before any government exists. Government is established as a trustee to protect those rights, its powers are limited to that purpose, and a government that violates the trust may be replaced. This argument shaped the American founding documents directly.

Jean-Jacques Rousseau argued in 1762 that legitimate authority comes from the general will — what citizens will as members of the body politic rather than as private individuals. Obeying that will is obeying yourself, which is how he reconciles authority with liberty. Critics have noted how easily the general will can be claimed on a population's behalf.

The obvious objection

No such contract was ever signed. Defenders answer that the contract is a test rather than a historical event: it asks which arrangements could be justified to those living under them.

John Rawls rebuilt the tradition on that basis in 1971. Principles of justice are fair if they would be chosen behind a veil of ignorance, by people who do not know their own position. The device keeps the contract's justificatory force while dropping the claim that anyone agreed to anything.