Furthermore, this defence gives Kant's real attitude on the subject of experience. Kant touched experience at all only to explain a priori knowledge, which was the supreme and all-engrossing subject of his interest. And, accordingly, he never got beneath the formal side of experience, those a priori conditions which the mind puts into things. For since what we know a priori is what we put into objects, we need not trouble ourselves, in the explanation of mathematics and physics, with the other constituents of the object. These Kant massed together as "matter," and considered as "given a posteriori," and as forming a kind of experience like that of the animals. But for us whom Darwin has taught to respect the brutes, and who do not believe in an a priori knowledge, or in a universal and necessary part of experience, this a posteriori sense-given matter, which was below the plane of Kant's contemplation, is precisely what stands in need of examination. And so far as our philosophy and physiological psychology can to-day make out, Kant was under an illusion in supposing the senses "gave" us something on which the understanding had only to impose its a priori apparatus to turn it into an object. What is "given" is the physical stimulus accompanying sensation. This serves, we know not how, like the movement of a trigger, to occasion (we need not say "cause") the production of (let us say) a sensation of color, which sensation is as much mind-produced as the category of substance in virtue of which it is referred to an objective ink-bottle. Color, substance, cause, are all elements of knowledge, all phenomena of the mind, yet all original on the occasion of specific, nervous stimulation. None of them is "given," all are produced by the mind. The distinction between a priori and a posteriori thus vanishes even for experience, when experience is analyzed more exhaustively than it was by Kant. If by the a priori elements or factors of knowledge or experience you mean what has been mind-originated (not sense-given), there is nothing in experience that is not a priori, for colors, sounds, smells, and tastes are no more "given" to us than the notion of causality or the idea of space. It is because Kant, in common with Locke,
