'Since the given manifold of sense consists of isolated elements, this manifold, in order to enter into knowledge, must be combined into an image. This combination is effected by the imagination, which however must first apprehend the elements one by one.'
'But this apprehension of the manifold by the imagination could produce no image, unless the imagination also possessed the power of reproducing past elements of the manifold, and, if knowledge is to arise, of reproducing them according to rules. This faculty of reproduction by which, on perceiving the element A, we are led to think of or reproduce a past element B--B being reproduced according to some rule--rather than C or D is called the faculty of association; and since the rules according to which it works depend on empirical conditions, and therefore cannot be anticipated _a priori_, it may be called the subjective ground of reproduction.'
'But if the image produced by association is to play a part in knowledge, the empirical faculty of reproduction is not a sufficient condition or ground of it. A further condition is implied, which may be called objective in the sense that it is _a priori_ and prior to all empirical laws of imagination. This condition is that the act by which the data of sense enter the mind or are apprehended, i. e. the act by which the imagination _apprehends and combines_ the data of sense into a sensuous image, must _make_ the elements such that they have affinity, and therefore such that they can subsequently be recognized as parts of a necessarily related whole.[17] Unless this condition is satisfied, even if we possessed the faculty of association, our experience would be a chaos of disconnected elements, and we could not be self-conscious, which is impossible. Starting, therefore, with the principle that we must be capable of being self-conscious with respect to all the elements of the manifold, we can lay down _a priori_ that this condition is a fact.'
[17] On this interpretation 'entering the mind' or 'being apprehended' in the fourth paragraph does not refer merely to the apprehension of elements one by one, which is preliminary to the act of combining them, but includes the act by which they are combined. If so, Kant's argument formally involves a circle. For in the second and third paragraphs he argues that the synthesis of perceptions involves reproduction according to rules, and then, in the fourth paragraph, he argues that this reproduction presupposes a synthesis of perceptions. We may, however, perhaps regard his argument as being in substance that knowledge involves _re_production by the imagination of elements capable of connexion, and that this reproduction involves _pro_duction by the imagination of the data of sense, which are to be reproduced, into an image.