Finally, the origin of knowledge was sought within this pure sequence of representations a sequence so perfect and so linear that the second had replaced the first without one's becoming conscious of the fact, since they were not simultaneous, since it was not possible to establish any difference between them, and since one could not experience the second as other than 'like' the first; and it was only when a sensation appeared to be more 'like' a previous one than all the others that reminiscence could come into play, that imagination could represent a representation afresh, and that knowledge could gain a foothold in this duplication.