Before Kant it was known well enough that "matter," however we must all accept it with our hands and eyes, has no standing, under the analysis of thought, except as a system of effects on ourselves. Hume, we remember, saw all this so clearly that he pronounced the very organs of sense, "our limbs and members," to be "not our body," but "certain impressions" to which the mind ascribes "a corporeal existence." Our limbs and members certainly _are_ our body--the only body we have--but Hume was right in his meaning that our body is a phenomenon which has no existence but as a plexus of impressions on a principle of intelligence, possessing various modes of reception, named senses. But this _principle_ of _intelligence_ itself was, to Hume, not a fact to be grasped by "reason," not a principle to be known and described, but was to be taken as a "force and vivacity" unknowable beyond an _instinct_ of it. Hume's unknowable "force and vivacity"--an improved form of Locke's "blank-tablet"--Kant _analyzed_ in the light of its products; namely, those conjuncts of sense-effects called objects; those conjuncts of objects called species, genera, and categories; and finally those conjuncts of all things and all conditions of things, called transcendental ideas. Now, such conjuncts of various "manifolds" actually exist. They are man's percepts and concepts; they are his facts, his environment. But _as_ percepts and concepts, and always conjuncts of "the manifold," they are formed, organized, totalized, through a _principle_--the principle of perception and conception itself. This is Kant's _a-priori_ synthetical unit, common and necessary to all "things" and to all "experience." The last word of any weight, against this reduction of matter to mind, was said a few years ago by that exceptionally acute thinker, Professor Huxley, in his summary of Hume. Too able and learned, both as philosopher and scientist, to question idealism, Huxley admitted it unqualifiedly. But, not having gone beyond the British proofs of it, he defended what is commonly called "materialism" in this way: "If we analyze the proposition that all mental phenomena are the effects or products of material phenomena, all that it means amounts to this: that whenever those states of consciousness which we call sensation, or emotion, or thought, come into existence, complete investigation will show good reason for the belief that they are preceded by those other phenomena of consciousness to which we give the names of matter and motion. All material changes appear, in the long run, to be modes of motion; but our knowledge of motion is nothing but that of a change in the place and order of our sensations; just as our knowledge of matter is restricted to those feelings of which we assume it to be the cause."