But look at the world of nature a little more closely. It is one whole world with very many things in it. Why is this the case? Would it ever be so if our knowledge of the world was simply a reproduction of what the world presented to us? Of course not. There would be as many different worlds as there are human beings. The wholeness, the oneness of our world of many things to many individuals indicates not only that the understanding is the source of the laws of the world, but also that the faculties of understanding in all the millions of human beings have a transcendental unity. Knowledge has therefore a stronger proof of its validity, since what is knowledge for one human being is knowledge for all. Every individual man is conscious of the contrast between his own subjective world and the world of knowledge which he shares with other men. His own ideas have a movement of their own and have no validity beyond themselves; the ideas which he shares with others, however, are valid for all others because these ideas are beyond the control of any one man. Each individual man has to acknowledge this control of his knowledge as residing in something beyond himself. The categories of each man’s understanding coöperate exactly with those of every other man. The individual man is not actually conscious of this process of coöperation in experience, but he accepts the objective necessity of it. The individual consciousness is not therefore the creator of the objects of knowledge; rather consciousness in general――the consciousness of humanity――is the creator. Kant is not a solipsist, but an idealist. A higher consciousness, a super-conscious Self, must be assumed to explain the compactness of human knowledge. Kant does not call this super-conscious Self the “soul” or “spirit,” but the “I think” or the “transcendental ego,” or by the more clumsy phrase “the transcendental unity of apperception.” He contrasts it with what he calls the “empirical ego” on the ground that it is the ego always identical with itself, rather than the Self at this or that particular moment. It is the Self as thinker rather than the Self as thought about. The super-conscious Self is always self-active and never dependent upon empirical conditions. It must be accepted as the postulate of all knowledge. It is the universal Self, and through it the categories of the human understanding become universalized. Just as space and time are the unifying forms of synthetic consciousness on its lower level; just as the categories of the understanding are the unifying forms of the synthetic consciousness on a higher level; so the universal Self must be postulated to explain the universality of the categories. It is a postulate only because it, not known in experience, is necessary to explain the unity of knowledge. This theoretical conception of the Self by Kant is thus very different from the traditional notion of the soul.