The ambiguity in Kant’s doctrine makes him a confusing representative of that criticism of perception which malicious psychology has to offer. When the mind has made its great discovery; when it has recognised independent objects, and thus taken a first step in its rational life, we need to know unequivocally whether this step is a false or a true one. If it be false, reason is itself misleading, since a hypothesis indispensable in the intellectual mastery of experience is a false hypothesis and the detail of experience has no substructure. Now Kant’s answer was that the discovery of objects was a true and valid discovery in the field of experience; there were, scientifically speaking, causes for perception which could be inferred from perception by thought. But this inference was not true absolutely or metaphysically because there was a real world beyond possible experience, and there were oracles, not intellectual, by which knowledge of that unrealisable world might be obtained. This mysticism undid the intellectualism which characterised Kant’s system in its scientific and empirical application; so that the justification for the use of such categories as that of cause and substance (categories by which the idea of reality is constituted) was invalidated by the counter-assertion that empirical reality was not true reality but, being an object reached by inferential thought, was merely an idea. Nor was the true reality appearance itself in its crude immediacy, as sceptics would think; it was a realm of objects present to a supposed intuitive thought, that is, to a non-inferential inference or non-discursive discourse. So that while Kant insisted on the point, which hardly needed pressing, that it is mind that discovers empirical reality by making inferences from the data of sense, he admitted at the same time that such use of understanding is legitimate and even necessary, and that the idea of nature so framed his empirical truth. There remained, however, a sense that this empirical truth was somehow insufficient and illusory. Understanding was a superficial faculty, and we might by other and oracular methods arrive at a reality that was not empirical. Why any reality—such as God, for instance—should not be just as empirical as the other side of the moon, if experience suggested it and reason discovered it, or why, if not suggested by experience and discovered by reason, anything should be called a reality at all or should hold for a moment a man’s waking attention—that is what Kant never tells us and never himself knew. Clearer upon this question of perception is the position of Berkeley; we may therefore take him as a fair representative of those critics who seek to invalidate the discovery of material objects. [Sidenote: Berkeley’s algebra of perception.]