In order to solve the problem of a perfect social organisation, or what comes to the same thing, of the best of all possible legislation, we must eventually have some criterion by the help of which we may compare the various "legislations" one with the other. And the criterion must have a special attribute. In fact, there is no question of a "legislation" _relatively_ the best, _i.e._, _the best legislation under given conditions_. No, indeed! We have to find a _perfect_ legislation, a legislation whose perfection should have nothing relative about it, should be entirely independent of time and place, should be, in a word, absolute. We are therefore driven to make abstraction from history, since everything in history is relative, everything depends upon circumstance, time, and place. But abstraction made of the history of humanity, what is there left to guide us in our "legislative" investigations? Humanity is left us, man in general, human nature--of which history is but the manifestation. Here then we have our criterion definitely settled, a perfect legislation. The best of all possible legislation is that which best harmonises with human nature. It may be, of course, that even when we have such a criterion we may, for want of "light" or of logic, fail to solve this problem of the best legislation. _Errare humanum est_, but it seems incontrovertible that this problem _can_ be solved, that we can, by taking our stand upon an exact knowledge of human nature, find a perfect legislation, a perfect organisation. Such was, in the domain of social science, the point of view of the French Materialists. Man is a sentient and reasonable being, they said; he avoids painful sensations and seeks pleasurable ones. He has sufficient intelligence to recognise what is useful to him as well as what is harmful to him. Once you admit these axioms, and you can in your investigations into the best legislation, arrive, with the help of reflection and good intentions, at conclusions as well founded, as exact, as incontrovertible as those derived from a mathematical demonstration. Thus Condorcet undertook to construct deductively all precepts of healthy morality by starting from the truth that man is a sentient and reasonable being.