[66] I understand this to mean 'This through and through identical consciousness of myself as the identical subject of a manifold given in perception involves a synthesis of representations'.
[67] The drift of the passage as a whole (cf. especially § 16) seems to show that here 'the synthesis of representations' means 'their connectedness' and not 'the act of connecting them'.
[13.] "Now this principle of the necessary unity of apperception is indeed an identical, and therefore an analytical, proposition, but nevertheless it declares a synthesis of the manifold given in a perception to be necessary, without which the thorough-going identity of self-consciousness cannot be thought. [14.] For through the Ego, as a simple representation, is given no manifold content; in perception, which is different from it, a manifold can only be given, and through _connexion_ in one consciousness it can be thought. An understanding, through whose self-consciousness all the manifold would _eo ipso_ be given, would _perceive_; our understanding can only _think_ and must seek its perception in the senses. [15.] I am, therefore, conscious of the identical self, in relation to the manifold of representations given to me in a perception, because I call all those representations _mine_, which constitute _one_. [16.] But this is the same as to say that I am conscious _a priori_ of a necessary synthesis of them, which is called the original synthetic unity of apperception, under which all representations given to me stand, but also under which they must be brought through a synthesis."[68]
Though this passage involves many difficulties, the main drift of it is clear. Kant is anxious to establish the fact that the manifold of sense must be capable of being combined on principles, which afterwards turn out to be the categories, by showing this to be involved in the fact that we must be capable of being conscious of ourselves as the identical subject of all our representations. To do this, he seeks to prove in the first paragraph that self-consciousness in this sense must be possible, and in the second that this self-consciousness presupposes the synthesis of the manifold.
Examination of the argument, however, shows that the view that self-consciousness must be possible is, so far as Kant is concerned,[69] an assumption for which Kant succeeds in giving no reason at all, and that even if it be true, it cannot form a basis from which to deduce the possibility of the synthesis.