Comte's theory of the three stages through which human thought has passed is well known: the theological stage of primitive times, the metaphysical stage in the Middle Ages, the positive or scientific stage of modern times. If knowledge were the essence of religion, one could easily understand the logical course of this evolution, an inferior form of knowledge being condemned to disappear before a superior form. The proof that it is nothing of the kind is the fact that religion does not cease to reappear at all epochs and in the most widely different conditions of culture. The three stages are not successive but simultaneous; they do not correspond to three periods of history, but to three permanent needs of the human soul. You find them combined in various degrees in antiquity, in Socrates, Plato, and Aristotle; in modern times, in Descartes, Pascal, Leibniz, Kant, Claude Bernard, and Pasteur. The more science progresses and becomes conscious of its true method and of its limits, the more does it become distinguished from philosophy and religion. Scientific research, exclusively devoted to the determination of phenomena and of their conditions in time and space, is one thing; the philosophic need of comprehending the universe as an intelligible whole, and of explaining all that exists by a principle of sufficient reason, is another and a different thing; and, lastly, differing from both, is the religious need which, rightly understood, is but a manifestation, in the moral order, of the instinct of every being to persevere in being. Why may not these divers tendencies of soul, coexisting always and everywhere, manifest themselves simultaneously and on parallel lines?