"The _a priori_ conditions of any possible experience whatever are at the same time conditions of the possibility of the objects of experience. Now I assert that the above mentioned _categories_ are nothing but _the conditions of thinking in any possible experience_, just as _space and time_ are the _conditions of perception_ requisite for the same. The former therefore are also fundamental conceptions by which we think objects in general for phenomena, and are therefore objectively valid _a priori_--which is exactly what we wished to know."
The next sentence, however, bases the necessity of the categories on the possibility of self-consciousness, without giving any indication that a change of standpoint is involved.
"But the possibility, nay, even the necessity, of these categories rests on the relation which the whole sensibility, and with it also all possible phenomena, have to original apperception, a relation which forces everything to conform to the conditions of the thoroughgoing unity of self-consciousness, i. e. to stand under universal functions of synthesis, i. e. of synthesis according to conceptions, as that wherein alone apperception can prove _a priori_ its thorough-going and necessary identity."
Finally, the conclusion of the paragraph seems definitely to treat both starting-points as really the same.[60] "Thus the conception of a cause is nothing but a synthesis (of the consequent in the time series with other phenomena) _according to conceptions_; and without such a unity, which has its _a priori_ rule and subjects phenomena to itself, thorough-going and universal and therefore necessary unity of consciousness in the manifold of sense-perceptions would not be met with. But then also these perceptions would belong to no experience, consequently they would have no object, and would be nothing but a blind play of representations, less than a dream."
[60] Cf. A. 113, Mah. 205-6 and A. 108-10, Mah. 202-3.
The fact is that since for Kant the synthesis of representations in accordance with the categories, accompanied by the consciousness of it, is at once the necessary and sufficient condition of the relatedness of representations to an object and of the consciousness of our identity with respect to them, it seems to him to be one and the same thing whether, in vindicating the synthesis, we appeal to the possibility of knowledge or to the possibility of self-consciousness, and it even seems possible to argue, _via_ the synthesis, from knowledge to self-consciousness and vice versa.