The act of association is a reciprocal commitment of public and private individuals, and each individual, contracting with himself, is under a twofold commitment, as a member of the sovereign to individuals, and as a member of the state to the sovereign.
Gist of Idea
The act of association commits citizens to the state, and the state to its citizens
Jean-Jacques Rousseau (The Social Contract (tr Cress) , I.7)
This seems to be expressed in modern terms as a mutual entailment of rights and duties. Where the traditional social contract is just between individuals, this seems to be a contract with a unified abstraction, of state commitment to citizens.
Rousseau,Jean-Jacques: 'The Basic Political Writings', ed/tr. Cress,Donald A. [Hackett 1987], p.149