The language of life as well as of science in attributing a memory to the mind attempts to point out the facts and their interpretation somewhat as follows:
Mental states of every kind, -- sensations, feelings, ideas, -- which were at one time present in consciousness and then have disappeared from it, have not with their disappearance absolutely ceased to exist. Although the inwardly-turned look may no longer be able to find them, nevertheless they have not been utterly destroyed and annulled, but in a certain manner they continue to exist, stored up, so to speak, in the memory. We cannot, of course, directly observe their present existence, but it is revealed by the effects which come to our knowledge with a certainty like that with which we infer the existence of the stars below the horizon. These effects are of different kinds.
In a first group of cases we can call back into consciousness by an exertion of the will directed to this purpose the seemingly lost states (or, indeed, in case these consisted in immediate sense-perceptions, we can recall their true memory images) that is, we can reproduce them voluntarily. During attempts of this sort, -- that is, attempts to recollect -- all sorts of images toward which our aim was not directed, accompany the desired images to the light of consciousness. Often, indeed, the latter entirely miss the goal, but as a general thing among the representations is found the one which we sought, and it is immediately recognised as something formerly experienced. It wou1d be absurd to suppose that our will has created it anew and, as it were, out of nothing; it must have been present somehow or somewhere. The will, so to speak, has only discovered it and brought it to us again.
In a second group of cases this survival is even more striking. Often, even after years, mental states once present in consciousness return to it with apparent spontaneity and without any act of the will; that is, they are reproduced involuntarily. Here, also, in the majority of cases we at once recognise the returned mental state as one that has already been experienced; that is, we remember it. Under certain conditions, however, this accompanying consciousness is lacking, and we know only indirectly that the "now" must be identical with the "then"; yet we receive in this way a no less valid proof for its existence during the intervening time. As more exact observation teaches us, the occurrence of these involuntary reproductions is not an entirely random and accidental one. On the contrary they are brought about through the instrumentality of other immediately present mental images. Moreover they occur in certain regular ways which in general terms are described under the so-called 'laws of association.'
Finally there is a third and large group to be reckoned with here. The vanished mental states give indubitable proof of their continuing existence even if they themselves do not return to consciousness at all, or at least not exactly at the given time. Employment of a certain range of thought facilitates under certain conditions the employment of a similar range of thought, even if the former does not come before the mind directly either in its methods or in its results. The boundless domain of the effect of accumulated experience belongs here. This effect results from the frequent conscious occurrence of any condition or process, and consists in facilitating the occurrence and progress of similar processes. This effect is not fettered by the condition that the factors constituting the experience shall return in toto to consciousness. This may incidentally be the case with a part of them; it must not happen to a too great extent and with too great clearness, otherwise the course of the present process will immediately be disturbed. Most of these experiences remain concealed from consciousness and yet produce an effect which is significant and which authenticates their previous existence.
Section 2. Memory in its Dependence
Along with this bare knowledge of the existence of memory and its effects, there is abundant knowledge concerning the conditions upon which depend the vitality of that inner survival as well as the fidelity and promptness of the reproduction.
How differently do different individuals behave in this respect! One retains and reproduces well; another, poorly. And not only does this comparison hold good when different individuals are compared with each other, but also when different phases of the existence of the same individual are compared: morning and evening, youth and old age, find him different in this respect.
Differences in the content of the thing to be reproduced are of great influence. Melodies may become a source of torment by the undesired persistency...