The Social Contract theory is as old as the sophists of Greece (see Plato, Republic , Book II and the Gorgias ), and as 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 medieval 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