This was the problem which sorely tried the genius of Leibniz. Descartes, in earlier days, attacked it vigorously, like an Alexander cutting the Gordian knot. He separated the soul from the body, and made of the latter a pure machine in the government of which the soul had no part. He attributed all the known manifestations of vital activity to inanimate forces. Leibniz, also, was compelled to reject all action, all contact, all direct relation, every real bond between soul and body, and to imagine between them a purely metaphysical relation—pre-established harmony:—“Soul and body agree in virtue of this harmony, the harmony pre-established since the creation, and in no way by a mutual, actual, physical influence. Everything that takes place in the soul takes place as if there were no body, and so everything takes place in the body as if there were no soul.” At this point we almost reach a scientific materialism. It is easy for the materialist to break this frail tie of pre-established harmony which so loosely unites body and soul, and to exhibit the organism as under the sole control of universal mechanics and physics. Thus the weak point of Stahl’s animism was the supposition of a direct action exercised on the organism by a distinct, heterogeneous, spiritual principle. Chauffard has endeavoured to avoid this pitfall. In conformity with modern ideas, he has brought together what the ancient philosophers and Stahl himself separated—the activity of matter and the activity of the soul. “Thought, action, function, are embraced in an indissoluble union.” This is the classical but not very lucid theory which has been so often reproduced—_Homo factus est anima vivens_—which Bossuet has expressed in the celebrated formula: “Soul and body form a natural whole.”