A superficial apprehension of these Kantian principles might lead one to suppose that Kant’s criticism did not essentially go beyond the standpoint of Locke’s empiricism. But such a supposition disappears upon a careful scrutiny. Kant was obliged to recognize with Hume that the conceptions, cause and effect, substance and attribute, and the other conceptions which the human understanding sees itself necessitated to think in the phenomena, and in which every one of its thoughts must be found, do not arise from any experience of the sense. For instance, when we become affected through different senses, and perceive a white color, a sweet taste, a rough surface, &c., and predicate all these of one thing, as a piece of sugar, there come from without only the plurality of sensations, while the conception of unity cannot come through sensation, but is a category or conception borne over to the sensations from the mind itself. But instead of denying, for this reason, the reality of these conceptions of the understanding, Kant took a step in advance, assigning a peculiar province to this activity of the understanding, and showing that these forms of thought thus furnished to the matter of experience are immanent laws of the human faculty of knowledge, the peculiar laws of the understanding’s operations, which may be obtained by a perfect analysis of our thinking activity. (Of these laws or conceptions there are twelve, viz., unity, plurality, totality; reality, negation, limitation; substantiality, causality, reciprocal action; possibility, actuality, and necessity.)
From what has been said we can see the three chief principles of the Kantian theory of knowledge:
1. WE KNOW ONLY PHENOMENA AND NOT THINGS IN THEMSELVES.—The experience furnished us by the external world becomes so adjusted and altered in its relations (for we apprehend it at first in the subjective framework of space and time, and then in the equally subjective forms of our understanding’s conceptions), that it no longer represents the thing itself in its original condition, pure and unmixed.
2. NEVERTHELESS EXPERIENCE IS THE ONLY PROVINCE OF OUR KNOWLEDGE, AND THERE IS NO SCIENCE OF THE UNCONDITIONED.—This follows of course, for since every knowledge is the product of the matter of experience, and the form of the understanding, and depends thus upon the co-working of the sensory and the understanding, then no knowledge is possible of objects for which one of these factors, experience, fails us; a knowledge alone from the understanding’s conceptions of the unconditioned is illusory since the sensory can show no unconditioned object corresponding to the conception. Hence the questions which Kant places at the head of his whole Critick; how are synthetical judgments apriori possible? _i. e._ can we widen our knowledge apriori, by thought alone, beyond the sensuous experience? is a knowledge of the supersensible possible? must be answered with an unconditional negative.