There reaches a point in the state of nature, Rousseau suggests, when people need to combine forces in order to survive. The problem resolved by the social contract is how people can bind themselves to one another and still preserve their freedom. The social contract essentially states that each individual must surrender himself unconditionally to the community as a whole. Rousseau draws three implications from this definition: (1) Because the conditions of the social contract are the same for everyone, everyone will want to make the social contract as easy as possible for all. (2) Because people surrender themselves unconditionally, the individual has no rights that can stand in opposition to the state. (3) Because no one is set above anyone else, people don't lose their natural freedom by entering into the social contract.
The community that is formed by this social contract is not simply the sum total of the lives and wills of its members: it is a distinct and unified entity with a life and a will of its own. This entity, called a "city" or "polis" in ancient times, is now called a "republic" or a "body politic." Some further definitions: in its passive role it is a "state," in its active role a "sovereign," and in relation to other states a "power"; the community that forms it is "a people," and individually they are "citizens"; they are "subjects" insofar as they submit themselves to the sovereign.
Because the sovereign is a distinct and unified whole, Rousseau treats it in many respects as if it were an individual. Since no individual can be bound by a contract made with himself, the social contract cannot impose any binding regulations on the sovereign. By contrast, subjects of the sovereign are doubly bound: as individuals they are bound to the sovereign, and as members of the sovereign they are bound to other individuals. Though the sovereign is not bound by the social contract, it cannot do anything that would violate the social contract since it owes its existence to that contract. Further, in hurting its subjects it would be hurting itself, so the sovereign will act in the best interests of its subjects without any binding commitment to do so.
Individuals, on the other hand, need the incentive of law to remain loyal to the sovereign. Self-interested individuals might try to enjoy all the benefits of citizenship without obeying any of the duties of a subject. Thus, Rousseau suggests that unwilling subjects will be forced to obey the general will: they will be "forced to be free."
In contrast to the Discourse on Inequality, Rousseau here draws a distinction between nature and civil society that heavily favors the latter. While we lose the physical liberty of being able to follow our instincts freely and do whatever we please, we gain the civil liberty that places the limits of reason and the general will on our behavior, thereby rendering us moral. In civil society, we take responsibility for our actions, and become nobler as a result.
Rousseau concludes Book I with a discussion of property. He suggests that ownership of land is only legitimate if no one else claims that land, if the owner occupies no more land than he needs, and if he cultivates that land for his subsistence. In the social contract, each individual surrenders all his property along with himself to the sovereign and the general will. In doing so, he does not give up his property since he is also a subject of the sovereign.