The Social Contract opens with a challenge: political authority, as Rousseau finds it in his world, rests on force and habit, not on right. His task is to discover whether any legitimate rule of administration exists, men being taken as they are and laws as they might be. Book I dismantles the competing foundations: the family produces only a natural attachment that dissolves when children grow up; conquest produces subjection but not obligation; and the right of the strongest is no right at all, since it evaporates the moment greater force appears.
The solution is the social compact. When individuals in the state of nature can no longer preserve themselves alone, they pool their forces by forming an association in which each gives themselves wholly to all under a single general will. Because the total alienation is equal for everyone, no associate gains a special advantage over another, and each gains the protection of the whole body. Rousseau summarizes the compact in a single formula: each member puts their person and power under the supreme direction of the general will and receives each other member as an indivisible part of the whole.
Book II works out the theory of sovereignty. The sovereign, the assembled people acting through its general will, is inalienable, because the will cannot be transmitted even when power can, and indivisible, because a will is either general or it is not. The general will is always right and tends to the public advantage, yet the people can be deceived; there is a critical difference between the general will (which considers only the common interest) and the will of all (which is a sum of private interests). Law is defined as an act of the general will, and the legislator is a rare figure who frames fundamental institutions without possessing any governing authority.
Book III turns to government, the executive body charged with carrying out law. Rousseau distinguishes sharply between sovereignty, which belongs to the people alone and is legislative, and government, which is only a commissioned agent. The size and form of government should vary with the size and character of the state: democracy suits small and simple republics, elective aristocracy suits mid-size states with moderate inequality, and monarchy concentrates force at the cost of the particular will overriding the general one. Whatever the form, government always tends to usurp sovereignty, and the people must retain the power to convene, constrain, and if necessary replace its governors.
Book IV examines voting, assemblies, dictatorship, and the civil religion. As long as citizens deliberate as a single body on common affairs, the general will is vigorous and clear. When faction, private interest, and corruption encroach, the general will becomes mute without ceasing to exist. The book ends with Rousseau's contention that a civil profession of faith (a set of positive and negative dogmas consistent with good citizenship) must accompany any sound republic, and that purely antisocial conduct, not impiety itself, is what the sovereign may rightly punish.