Thus, beliefs of expectation, or at any rate their potentialities, are, as much as those of memory, antecedent to speech, and are as incapable of justification by any logical process. In fact, expectations are but memories inverted. The association which is the foundation of expectation must exist as a memory before it can play its part. As Hume says,—
" ... it is certain we here advance a very intelligible proposition at least, if not a true one, when we assert that after the constant conjunction of two objects, heat and flame, for instance, weight and solidity, we are determined by custom alone to expect the one from the appearance of the other. This hypothesis seems even the only one which explains the difficulty why we draw from a thousand instances, an inference which we are not able to draw from one instance, that is in no respect different from them." ...
"Custom, then, is the great guide of human life. It is that principle alone which renders our experience useful to us, and makes us expect, for the future, a similar train of events with those which have appeared in the past." ...
"All belief of matter-of-fact or real existence is derived merely from some object present to the memory or senses, and a customary conjunction between that and some other object; or in other words, having found, in many instances, that any two kinds of objects, flame and heat, snow and cold, have always been conjoined together: if flame or snow be presented anew to the senses, the mind is carried by custom to expect heat or cold, and to believe that such a quality does exist, and will discover itself upon a nearer approach. This belief is the necessary result of placing the mind in such circumstances. It is an operation of the soul, when we are so situated, as unavoidable as to feel the passion of love, when we receive benefits, or hatred, when we meet with injuries. All these operations are a species of natural instincts, which no reasoning or process of the thought and understanding is able either to produce or to prevent."—(IV. pp. 52-56.)
The only comment that appears needful here is, that Hume has attached somewhat too exclusive a weight to that repetition of experiences to which alone the term "custom" can be properly applied. The proverb says that "a burnt child dreads the fire"; and any one who will make the experiment will find, that one burning is quite sufficient to establish an indissoluble belief that contact with fire and pain go together.
As a sort of inverted memory, expectation follows the same laws; hence, while a belief of expectation is, in most cases, as Hume truly says, established by custom, or the repetition of weak impressions, it may quite well be based upon a single strong experience. In the absence of language, a specific memory cannot be strengthened by repetition. It is obvious that that which has happened cannot happen again, with the same collateral associations of co-existence and succession. But, memories of the co-existence and succession of impressions are capable of being indefinitely strengthened by the recurrence of similar impressions, in the same order, even though the collateral associations are totally different; in fact, the ideas of these impressions become generic.
If I recollect that a piece of ice was cold yesterday, nothing can strengthen the recollection of that particular fact; on the contrary, it may grow weaker, in the absence of any record of it. But if I touch ice to-day and again find it cold, the association is repeated, and the memory of it becomes stronger. And, by this very simple process of repetition of experience, it has become utterly impossible for us to think of having handled ice without thinking of its coldness. But, that which is, under the one aspect, the strengthening of a memory, is, under the other, the intensification of an expectation. Not only can we not think of having touched ice, without feeling cold, but we cannot think of touching ice, in the future, without expecting to feel cold. An expectation so strong that it cannot be changed, or abolished, may thus be generated out of repeated experiences. And it is important to note that such expectations may be formed quite unconsciously. In my dressing room, a certain can is usually kept full of water, and I am in the habit of lifting it to pour out water for washing. Sometimes the servant has forgotten to fill it, and then I find that, when I take hold of the handle, the can goes up with a jerk. Long association has, in fact, led me to expect the can to have a considerable weight; and, quite unawares, my muscular effort is adjusted to the expectation.
The process of strengthening generic memories of succession, and, at the same time, intensifying expectations of succession, is what is commonly called verification. The impression B has frequently been observed to follow the impression A. The association thus produced is represented as the memory, A → B. When the impression A appears again, the idea of B follows, associated with that of the immediate appearance of the impression B. If the impression B does appear, the expectation is said to be verified; while the memory A → B is strengthened, and gives rise in turn to a stronger expectation. And repeated verification may render that expectation so strong that its non-verification is inconceivable.
FOOTNOTES:
[24] It is not worth while, for the present purpose, to consider whether, as all nervous action occupies a sensible time, the duration of one impression might not overlap that of the impression which follows it, in the case supposed.
[25] We give no name to faint memories; but expectations of like character play so large a part in human affairs that they, together with the associated emotions of pleasure and pain, are distinguished as "hopes" or "fears."