These categories, then, are the fundamental, primary, or native conceptions of the understanding, which flow from, or constitute the mechanism of, its nature, are inseparable from its activity, and are therefore, for human thought, universal and necessary, or a priori. They are not contingent states or images of sensuous consciousness, and hence not to be thence derived. But they are not known to us independently of such consciousness or of sensible experience. On the one hand, they are exclusively involved in, and hence come to our knowledge exclusively through, the spontaneous activity of the understanding. But, on the other hand, the understanding is never active, until sensible data are furnished as material for it to act upon, and so it may truly be said that they become known to us "only on the occasion of sensible experience." For Kant, in opposition to Wolff and Hobbes, the categories exist only in the mind.[27]
These categories are "pure" conceptions of the understanding, in as much as they are independent of all that is contingent in sense. They are not derived from what is called the matter of sense, or from particular, variable sensations. But they are not independent of the universal and necessary form of sense. Again, Kant, in the "Transcendental Logic," is professedly engaged with the search for an answer to the second main question of the Critique, How is pure physical science, or sensible knowledge, possible? Kant, now, has said, and, with reference to the kind of knowledge mentioned in the foregoing question, has said truly, that thoughts, without the content which perception supplies, are empty. This is not less true of pure thoughts, than of any others. The content which the pure conceptions, as categories of pure physical science or sensible knowledge, cannot derive from the matter of sense, they must and do derive from its pure form. And in this relation between the pure conceptions of the understanding and their pure content there is involved, as we shall see, the most intimate community of nature and origin between sense, on its formal side (space and time), and the understanding itself. For Kant, space and time are a priori intuitions. Out of a total of six arguments in favor of space as a priori intuition, Kant presents four of them in the Metaphysical Exposition of space: two argue for space a priori and two for space as intuition.[28]

the number one has no complexity , it can't sustain , anything