But space and number are the two forms of immobility, the two schemes of analysis, by which we must not let ourselves be obsessed. I do not say that there is no place to give them, even in the internal world. But the more deeply we enter into the heart of psychological life, the less they are in place. The fact is, there are several planes of consciousness, situated at different depths, marking all the intervening degrees between pure thought and bodily action, and each mental phenomenon interests all these planes simultaneously, and is thus repeated in a thousand higher tones, like the harmonies of one and the same note. Or, if you prefer it, the life of the spirit is not the uniform transparent surface of a mere; rather it is a gushing spring which, at first pent in, spreads upwards and outwards, like a sheaf of corn, passing through many different states, from the dark and concentrated welling of the source to the gleam of the scattered tumbling spray; and each of its moods presents in its turn a similar character, being itself only a thread within the whole. Such without doubt is the central and activating idea of the admirable book entitled "Matter and Memory". I cannot possibly condense its substance here, or convey its astonishing synthetic power, which succeeds in contracting a complete metaphysic, and in gripping it so firmly that the examination ends by passing to the discussion of a few humble facts relative to the philosophy of the brain! But its technical severity and its very conciseness, combined with the wealth it contains, render it irresumable; and I can only in a few words indicate its conclusions. First of all, however little we pride ourselves on positive method, we must admit the existence of an internal world, of a spiritual activity distinct from matter and its mechanism. No chemistry of the brain, no dance of atoms, is equivalent to the least thought, or indeed to the least sensation. Some, it is true, have brought forward a thesis of parallelism, according to which each mental phenomenon corresponds point by point to a phenomenon in the brain, without adding anything to it, without influencing its course, merely translating it into another tongue, so that a glance sufficiently penetrating to follow the molecular revolutions and the fluxes of nervous production in their least episodes would immediately read the inmost secrets of the associated consciousness. But no one will deny that a thesis of this kind is only in reality a hypothesis, that it goes enormously beyond the certain data of current biology, and that it can only be formulated by anticipating future discoveries in a preconceived direction. Let us be candid: it is not really a thesis of positive science, but a metaphysical thesis in the unpleasant meaning of the term. Taking it at its best, its worth today could only be one of intelligibleness. And intelligible it is not.