He will do well to begin by persuading himself, with Montaigne, that the “hinges of custom” are not always the “hinges of reason,” and still less those of reality in all times and places. He will do better still to steep himself in the spirit of scientific evolution, and to bear in mind that incessant change is the law of the social, quite as much as of the physical and organic world, and that the most splendid blossoms have sprung from very humble germs. This is the supreme truth of science, and it is only when such a point of view has become quite familiar to us that we shall be neither troubled nor disconcerted by the sociological history of humanity; and however shocking or unnatural certain customs may appear, we shall guard ourselves against any feeling of indignation at them, and more especially against a thoughtless refusal to give credence to them, simply because they run counter to our own usages and morality. All that social science has a right to ask of the facts which it registers is that they should be authentic; this duly proved, it only remains to accept, classify, and interpret them. Faithful to this method, without which there could be no science of sociology, I have here gathered together as proofs a number of singular facts, which, improbable as they may appear according to our pre-conceived notions, and criminal according to our moral sense, are nevertheless most instructive. Although in a former work I have taken care to establish the relativity of morality, the explanations that I am about to make are not out of season; for the subject of this book is closely connected with what, _par excellence_, we call “morals.” On this point I must permit myself a short digression.