The contract is the central notion of the theories of the modern natural right, to which Hobbes gave a canonical form. Sovereignty is legitimate only if it draws its origin from the individual wills of those which are subjected to him. It is thus necessary to go back to an originating contract where each one gave up its rights to transmit them to the Sovereign or to let this one exert the plenitude as of his.
This renunciation is not free: each one agrees to it in order to protect its life (Hobbes) or its goods (Locke). It is not necessary that this pact truly took place: its statement indicates only the logical base of the civil society. Rousseau introduces into the second part of speech on the origin of the inequality a bad contract, where the rich person deceives his neighbors in their proposer as their safety the political union which will devote its power and will complete to ruin their freedom.
In the social Contract, on the contrary, it describes the contract which founds a really free company; in such a pact, each one contracts with the sovereign who is not other than the people consisted the pact itself; thus each associate alienates himself completely at the community: the condition is thus equal for all and cannot generate of new oppression.
As there does not remain any right apart from association, no private individual can reserve a piece of being able which would restore the state of nature; finally, “each one being given to all is not given to anybody”. Each citizen thus is at the same time submitted to the sovereign and member of this same sovereign, natural freedom was replaced by the civil liberty.