The Social Contract theory is as old as the sophists of Greece (see Plato, _Republic_, Book II and the _Gorgias_), and as I elusive. It has been adapted to the most opposite points of view, and used, in different forms, on both sides of every question to which it could conceivably be applied. It is frequent in mediæval writers, a commonplace with the theorists of the Renaissance, and in the eighteenth century already nearing its fall before a wider conception. It would be a long, as well as a thankless, task to trace its history over again: it may be followed best in D. G. Ritchie's admirable essay on it in _Darwin and Hegel and Other Studies_. For us, it is important only to regard it in its most general aspect, before studying the special use made of it by Rousseau. Obviously, in one form or another, it is a theory very easily arrived at. Wherever any form of government apart from the merest tyranny exists, reflection on the basis of the State cannot but lead to the notion that, in one sense or another, it is based on the consent, tacit or expressed, past or present, of its members. In this alone, the greater part of the Social Contract theory is already latent. Add the desire to find actual justification for a theory in facts, and, especially in an age possessed only of the haziest historical sense, this doctrine of consent will inevitably be given a historical setting. If in addition there is a tendency to regard society as something unnatural to humanity, the tendency will become irresistible. By writers of almost all schools, the State will be represented as having arisen, in some remote age, out of a compact or, in more legal phrase, contract between two or more parties. The only class that will be able to resist the doctrine is that which maintains the divine right of kings, and holds that all existing governments were were imposed on the people by the direct interposition of God. All who are not prepared to maintain that will be partisans of some form or other of the Social Contract theory. It is, therefore, not surprising that we find among its advocates writers of the most opposite points of view. Barely stated, it is a mere formula, which may be filled in with any content from absolutism to pure republicanism. And, in the hands of some at least of its supporters, it turns out to be a weapon that cuts both ways. We shall be in a better position to judge of its usefulness when we have seen its chief varieties at work. All Social Contract theories that are at all definite fall under one or other of two heads. They represent society as based on an original contract either between the people and the government, or between all the individuals composing the State. Historically, modern theory passes from the first to the second of these forms.