To summarise before proceeding. We have obtained two important conclusions: first, that all consciousness involves self-consciousness; and secondly, that self-consciousness is a mere form, in terms of which contents that do not constitute the self are apprehended as existing for the self. The first leads up to the second, and the second is equivalent to the assertion that there can be no such thing as a pure self-consciousness, _i.e._ a consciousness in which the self is aware of itself and of nothing but itself. Self-consciousness, to be possible at all, must at the same time be a consciousness of something that is not-self. Only one further step is now required for the completion of the deduction, namely, proof that this not-self, consciousness of which is necessary to the possibility of self-consciousness, must consist in empirical objects apprehended in terms of the categories. For proof Kant again appeals to the indispensableness of apperception. As no intuitions can enter consciousness which are not capable of being related to the self, they must be so related to one another that, notwithstanding their variety and diversity, the self can still be conscious of itself as identical throughout them all. In other words, no intuition can be related to the self that is incapable of being combined together with all the other intuitions to form a unitary consciousness. I may here quote from the text of the second edition:[893] “...only in so far as I can grasp the manifold of the representations in one consciousness, do I call them one and all mine. For otherwise I should have as many-coloured and diverse a self as I have representations of which I am conscious to myself.” Or as it is stated in the first edition:[894] “We are _a priori_ aware of the complete identity of the self in respect of all representations which belong to our knowledge ... as a necessary condition of the possibility of all representations.” These are the considerations which lead Kant to entitle the unity of apperception _transcendental_. He so names it for the reason that, though it is not itself _a priori_ in the manner of the categories, we are yet enabled by its means to demonstrate that the unity which is necessary for possible experience can be securely counted upon in the manifold of all possible representations, and because (as he believed) it also enables us to prove that the forms of such unity are the categories of the understanding.