Spiritualism[51] rests on the conception that the mind can subsist and work in total independence of any tie to matter. It is true that, in details, spiritualists make some modification in this absolute principle in order to explain the perceptions of the senses and the execution of the orders of the will; but the duality, the independence, and the autonomy of the soul and the body remain, in any case, the peculiar dogma of the system. This dogma appears to me utterly false; the mind cannot exist without matter to which it is applied; and to the principle of heterogeneity, so often invoked to forbid all commerce between the two substances, I reply by appealing to intuition, which shows us the consciousness and its different forms, comparison, judgment, and reasoning, so closely connected with sensation that they cannot be imagined as existing with an isolated life. Materialism, we know, argues quite differently; it imagines that a particular state of the nerve centres has the virtue of generating a psychical phenomenon, which represents, according to various metaphors, property, function, effect, and even secretion. Critics have often asked how, with matter in motion, a phenomenon of thought could be explained or fabricated. It is very probable that those who admit this material genesis of thought, represent it to themselves under the form of something subtle, like an electric spark, a puff of wind, a will-of-the-wisp, or an alcoholic flame. Materialists are not alone responsible for these inadequate metaphors, which proceed from a metaphysics constructed of concepts. Let us recollect exactly what a psychical phenomenon is. Let us banish the will-o'-the-wisps, replace them by a precise instance, and return to the visual perception we took as an example a little while back: without intending a pun, "revenons a nos moutons." These sheep which I see in the plain are as material, as real, as the cerebral movement which accompanies my perception. How, then, is it possible that this cerebral movement, a primary material fact, should engender this secondary material fact, this collection of complicated beings which form a flock?