Without memory no intellect is possible. The only material at the disposal of the intellect is received from the senses. It has been provided solely out of sensations. Now a sensation in itself alone, as a simple fundamental experience affecting primarily the one who has the sensation, can not be the object of any intellectual operation whatever. In order to make such activity possible there must be several sensations: two of different kinds, of unequal strength; or two of different kinds, of the same strength; or two of the same kind unequally strong; in any case, two unlike sensations (cf. my treatise "Elemente der reinen Empfindungslehre," Jena, 1876), if the lowest activity of the intellect, _comparison_, is to operate. But because the sensations that are to be compared can not all exist together, recollection of the earlier ones is necessary (for the comparison); that is, individual or personal memory. This name I give to the memory formed by means of individual impressions (occurrences, experiences) in contrast with the _phyletic_ memory, or instinct, the memory of the race, which results from the inheritance of the traces of individual experiences of ancestors; of this I do not here speak. All sensations leave traces behind in the brain; weak ones leave such as are easy to be obliterated by others; strong ones, traces more enduring. At the beginning of life it seems to be the department of taste (sweet) and of smell (smell of milk) in which memory is first operative (Vol. I, p. 124). Then comes the sense of touch (in nursing). Next in order the sense of sight chiefly asserts itself as an early promoter of memory. Hearing does not come till later. If the infant, in the period from three to six months of age, is brought into a room he has not before seen, his expression changes; he is astonished. The new sensations of light, the different apportionment of light and dark, arouse his attention; and when he comes back to his former surroundings he is not astonished. These have lost the _stimulus of novelty_--i. e., a certain _reminiscence_ of them has remained with the child, they have _impressed_ themselves upon him.