Book 3, Chapter 2 — The Constituent Principle in the Various Forms of Government

The body of the magistrate can be composed of any number of members, and the relation of government to its own magistrates parallels the relation of Sovereign to subjects. The critical variable is force: the total force of the government is fixed (it is the State's force), and the more members the government has, the more of that force is consumed internally. A government of many magistrates is weaker in relation to the people than a government of few, because more of its force is spent maintaining internal coherence.

In every magistrate, Rousseau identifies three distinct wills. The private will aims at personal advantage — this is the will closest to the person and naturally the strongest. The corporate will aims at the advantage of the government as a body — it is general with respect to the government but particular with respect to the State. The sovereign will aims at the common good of the whole — general in every respect. In a perfect system, the private will would be zero, the corporate will subordinate, and the sovereign will dominant. In practice, these rank in the opposite order: private will strongest, corporate will next, sovereign will weakest.

This inversion is the structural problem of all government. A magistrate is always more strongly pulled toward his private advantage than toward the common good, however virtuous he may be. Institutional design can work against this tendency — selection mechanisms, term limits, accountability structures — but cannot overcome it entirely. The corporate interest of the governing body will always, given enough time, assert itself against the sovereign interest of the people as a whole. This is why Rousseau will argue later that governments inevitably degenerate, and why frequent reassembly of the sovereign people is the only real check on this tendency.