If philosophers of the Cartesian school had taken to heart, as the German transcendentalists did, the _cogito ergo sum_ of their master, and had considered that a physical world is, for knowledge, nothing but an instrument to explain sensations and their order, they might have expected this collapse of half their metaphysics at the approach of their positive science: for if mental existence was to be kept standing only by its supposed causal efficacy nothing could prevent the whole world from becoming presently a _bête-machine._ Psychic events have no links save through their organs and their objects; the function of the material world is, indeed, precisely to supply their linkage. The internal relations of ideas, on the other hand, are dialectical; their realm is eternal and absolutely irrelevant to the march of events. If we must speak, therefore, of causal relations between mind and body, we should say that matter is the pervasive cause of mind’s distribution, and mind the pervasive cause of matter’s discovery and value. To ask for an efficient cause, to trace back a force or investigate origins, is to have already turned one’s face in the direction of matter and mechanical laws: no success in that undertaking can fail to be a triumph for materialism. To ask for a justification, on the other hand, is to turn no less resolutely in the direction of ideal results and actualities from which instrumentality and further use have been eliminated. Spirit is useless, being the end of things: but it is not vain, since it alone rescues all else from vanity. It is called practical when it is prophetic of its own better fulfilments, which is the case whenever forces are being turned to good uses, whenever an organism is exploring its relations and putting forth new tentacles with which to grasp the world. [Sidenote: Consciousness expresses vital equilibrium and docility.]