Hume, by Huxley

Chapter 4.

The Classification and the Nomenclature of Mental Operations.

If, as has been set forth in the preceding chapter, all mental states are effects of physical causes, it follows that what are called mental faculties and operations are, properly speaking, cerebral functions, allotted to definite, though not yet precisely assignable, parts of the brain.

These functions appear to be reducible to three groups, namely: Sensation, Correlation, and Ideation.

The organs of the functions of sensation and correlation are those portions of the cerebral substance, the molecular changes of which give rise to impressions of sensation and impressions of relation.

The changes in the nervous matter which bring about the effects which we call its functions, follow upon some kind of stimulus, and rapidly reaching their maximum, as rapidly die away. The effect of the irritation of a nerve-fibre on the cerebral substance with which it is connected may be compared to the pulling of a long bell-wire. The impulse takes a little time to reach the bell; the bell rings and then becomes quiescent, until another pull is given. So, in the brain, every sensation is the ring of a cerebral particle, the effect of a momentary impulse sent along a nerve-fibre.

If there were a complete likeness between the two terms of this very rough and ready comparison, it is obvious that there could be no such thing as memory. A bell records no audible sign of having been rung five minutes ago, and the activity of a sensigenous cerebral particle might similarly leave no trace. Under these circumstances, again, it would seem that the only impressions of relation which could arise would be those of coexistence and of similarity. For succession implies memory of an antecedent state.24

But the special peculiarity of the cerebral apparatus is, that any given function which has once been performed is very easily set a-going again, by causes more or less different from those to which it owed its origin. Of the mechanism of this generation of images of impressions or ideas (in Hume’s sense), which may be termed Ideation, we know nothing at present, though the fact and its results are familiar enough.

During our waking, and many of our sleeping, hours, in fact, the function of ideation is in continual, if not continuous, activity. Trains of thought, as we call them, succeed one another without intermission, even when the starting of new trains by fresh sense-impressions is as far as possible prevented. The rapidity and the intensity of this ideational process are obviously dependent upon physiological conditions. The widest differences in these respects are constitutional in men of different temperaments; and are observable in oneself, under varying conditions of hunger and repletion, fatigue and freshness, calmness and emotional excitement. The influence of diet on dreams; of stimulants upon the fulness and the velocity of the stream of thought; the delirious phantasms generated by disease, by hashish, or by alcohol; will occur to every one as examples of the marvellous sensitiveness of the apparatus of ideation to purely physical influences.

The succession of mental states in ideation is not fortuitous, but follows the law of association, which may be stated thus: that every idea tends to be followed by some other idea which is associated with the first, or its impression, by a relation of succession, of contiguity, or of likeness.

Thus the idea of the word horse just now presented itself to my mind, and was followed in quick succession by the ideas of four legs, hoofs, teeth, rider, saddle, racing, cheating; all of which ideas are connected in my experience with the impression, or the idea, of a horse and with one another, by the relations of contiguity and succession. No great attention to what passes in the mind is needful to prove that our trains of thought are neither to be arrested, nor even permanently controlled, by our desires or emotions. Nevertheless they are largely influenced by them. In the presence of a strong desire, or emotion, the stream of thought no longer flows on in a straight course, but seems, as it were, to eddy round the idea of that which is the object of the emotion. Every one who has “eaten his bread in sorrow” knows how strangely the current of ideas whirls about the conception of the object of regret or remorse as a centre; every now and then, indeed, breaking away into the new tracks suggested by passing associations, but still returning to the central thought. Few can have been so happy as to have escaped the social bore, whose pet notion is certain to crop up whatever topic is started; while the fixed idea of the monomaniac is but the extreme form of the same phenomenon.

And as, on the one hand, it is so hard to drive away the thought we would fain be rid of; so, upon the other, the pleasant imaginations which we would so gladly retain are, sooner or later, jostled away by the crowd of claimants for birth into the world of consciousness; which hover as a sort of psychical possibilities, or inverse ghosts, the bodily presentments of spiritual phenomena to be, in the limbo of the brain. In that form of desire which is called “attention,” the train of thought, held fast, for a time, in the desired direction, seems ever striving to get on to another line — and the junctions and sidings are so multitudinous!

The constituents of trains of ideas may be grouped in various ways.

Hume says:—

“We find, by experience, that when any impression has been present in the mind, it again makes its appearance there as an idea, and this it may do in two different ways: either when, on its new appearance, it retains a considerable degree of its first vivacity, and is somewhat intermediate between an impression and an idea; or when it entirely loses that vivacity, and is a perfect idea. The faculty by which we repeat our impressions in the first manner, is called the memory, and the other the imagination.”—(I. pp. 23, 24.)

And he considers that the only difference between ideas of imagination and those of memory, except the superior vivacity of the latter, lies in the fact that those of memory preserve the original order of the impressions from which they are derived, while the imagination “is free to transpose and change its ideas.”

The latter statement of the difference between memory and imagination is less open to cavil than the former, though by no means unassailable.

The special characteristic of a memory surely is not its vividness; but that it is a complex idea, in which the idea of that which is remembered is related by coexistence with other ideas, and by antecedence with present impressions.

If I say I remember A. B., the chance acquaintance of ten years ago, it is not because my idea of A. B. is very vivid — on the contrary, it is extremely faint — but because that idea is associated with ideas of impressions coexistent with those which I call A. B.; and that all these are at the end of the long series of ideas, which represent that much past time. In truth I have a much more vivid idea of Mr. Pickwick, or of Colonel Newcome, than I have of A. B.; but, associated with the ideas of these persons, I have no idea of their having ever been derived from the world of impressions; and so they are relegated to the world of imagination. On the other hand, the characteristic of an imagination may properly be said to lie not in its intensity, but in the fact that, as Hume puts it, “the arrangement,” or the relations, of the ideas are different from those in which the impressions, whence these ideas are derived, occurred; or in other words, that the thing imagined has not happened. In popular usage, however, imagination is frequently employed for simple memory —“In imagination I was back in the old times.”

It is a curious omission on Hume’s part that, while thus dwelling on two classes of ideas, Memories and Imaginations, he has not, at the same time, taken notice of a third group, of no small importance, which are as different from imaginations as memories are; though, like the latter, they are often confounded with pure imaginations in general speech. These are the ideas of expectation, or as they may be called for the sake of brevity, Expectations; which differ from simple imaginations in being associated with the idea of the existence of corresponding impressions, in the future, just as memories contain the idea of the existence of the corresponding impressions in the past.

The ideas belonging to two of the three groups enumerated: namely, memories and expectations, present some features, of particular interest. And first, with respect to memories.

In Hume’s words, all simple ideas are copies of simple impressions. The idea of a single sensation is a faint, but accurate, image of that sensation; the idea of a relation is a reproduction of the feeling of coexistence, of succession, or of similarity. But, when complex impressions or complex ideas are reproduced as memories, it is probable that the copies never give all the details of the originals with perfect accuracy, and it is certain that they rarely do so. No one possesses a memory so good, that if he has only once observed a natural object, a second inspection does not show him something that he has forgotten. Almost all, if not all, our memories are therefore sketches, rather than portraits, of the originals — the salient features are obvious, while the subordinate characters are obscure or unrepresented.

Now, when several complex impressions which are more or less different from one another — let us say that out of ten impressions in each, six are the same in all, and four are different from all the rest — are successively presented to the mind, it is easy to see what must be the nature of the result. The repetition of the six similar impressions will strengthen the six corresponding elements of the complex idea, which will therefore acquire greater vividness; while the four differing impressions of each will not only acquire no greater strength than they had at first, but, in accordance with the law of association, they will all tend to appear at once, and will thus neutralise one another.

This mental operation may be rendered comprehensible by considering what takes place in the formation of compound photographs — when the images of the faces of six sitters, for example, are each received on the same photographic plate, for a sixth of the time requisite to take one portrait. The final result is that all those points in which the six faces agree are brought out strongly, while all those in which they differ are left vague; and thus what may be termed a generic portrait of the six, in contradistinction to a specific portrait of any one, is produced.

Thus our ideas of single complex impressions are incomplete in one way, and those of numerous, more or less similar, complex impressions are incomplete in another way; that is to say, they are generic, not specific. And hence it follows, that our ideas of the impressions in question are not, in the strict sense of the word, copies of those impressions; while, at the same time, they may exist in the mind independently of language.

The generic ideas which are formed from several similar, but not identical, complex experiences are what are commonly called abstract or general ideas; and Berkeley endeavoured to prove that all general ideas are nothing but particular ideas annexed to a certain term, which gives them a more extensive signification, and makes them recall, upon occasion, other individuals which are similar to them. Hume says that he regards this as “one of the greatest and the most valuable discoveries that has been made of late years in the republic of letters,” and endeavours to confirm it in such a manner that it shall be “put beyond all doubt and controversy.”

I may venture to express a doubt whether he has succeeded in his object; but the subject is an abstruse one; and I must content myself with the remark, that though Berkeley’s view appears to be largely applicable to such general ideas as are formed after language has been acquired, and to all the more abstract sort of conceptions, yet that general ideas of sensible objects may nevertheless be produced in the way indicated, and may exist independently of language. In dreams, one sees houses, trees and other objects, which are perfectly recognisable as such, but which remind one of the actual objects as seen “out of the corner of the eye,” or of the pictures thrown by a badly-focussed magic lantern. A man addresses us who is like a figure seen by twilight; or we travel through countries where every feature of the scenery is vague; the outlines of the hills are ill-marked, and the rivers have no defined banks. They are, in short, generic ideas of many past impressions of men, hills, and rivers. An anatomist who occupies himself intently with the examination of several specimens of some new kind of animal, in course of time acquires so vivid a conception of its form and structure, that the idea may take visible shape and become a sort of waking dream. But the figure which thus presents itself is generic, not specific. It is no copy of any one specimen, but, more or less, a mean of the series; and there seems no reason to doubt that the minds of children before they learn to speak, and of deaf mutes, are peopled with similarly generated generic ideas of sensible objects.

It has been seen that a memory is a complex idea made up of at least two constituents. In the first place there is the idea of an object; and secondly, there is the idea of the relation of antecedence between that object and some present objects.

To say that one has a recollection of a given event and to express the belief that it happened, are two ways of giving an account of one and the same mental fact. But the former mode of stating the fact of memory is preferable, at present, because it certainly does not presuppose the existence of language in the mind of the rememberer; while it may be said that the latter does. It is perfectly possible to have the idea of an event A, and of the events B, C, D, which came between it and the present state E, as mere mental pictures. It is hardly to be doubted that children have very distinct memories long before they can speak; and we believe that such is the case because they act upon their memories. But, if they act upon their memories, they to all intents and purposes believe their memories. In other words, though, being devoid of language, the child cannot frame a proposition expressive of belief; cannot say “sugar-plum was sweet;” yet the psychical operation of which that proposition is merely the verbal expression, is perfectly effected. The experience of the coexistence of sweetness with sugar has produced a state of mind which bears the same relation to a verbal proposition, as the natural disposition to produce a given idea, assumed to exist by Descartes as an “innate idea” would bear to that idea put into words.

The fact that the beliefs of memory precede the use of language, and therefore are originally purely instinctive, and independent of any rational justification, should have been of great importance to Hume, from its bearing upon his theory of causation; and it is curious that he has not adverted to it, but always takes the trustworthiness of memories for granted. It may be worth while briefly to make good the omission.

That I was in pain, yesterday, is as certain to me as any matter of fact can be; by no effort of the imagination is it possible for me really to entertain the contrary belief. At the same time, I am bound to admit, that the whole foundation for my belief is the fact, that the idea of pain is indissolubly associated in my mind with the idea of that much past time. Any one who will be at the trouble may provide himself with hundreds of examples to the same effect.

This and similar observations are important under another aspect. They prove that the idea of even a single strong impression may be so powerfully associated with that of a certain time, as to originate a belief of which the contrary is inconceivable, and which may therefore be properly said to be necessary. A single weak, or moderately strong, impression may not be represented by any memory. But this defect of weak experiences may be compensated by their repetition; and what Hume means by “custom” or “habit” is simply the repetition of experiences.

“wherever the repetition of any particular act or operation produces a propensity to renew the same act or operation, without being impelled by any reasoning or process of the understanding, we always say that this propensity is the effect of Custom. By employing that word, we pretend not to have given the ultimate reason of such a propensity. We only point out a principle of human nature which is universally acknowledged, and which is well known by its effects.”—(IV. p. 52.)

It has been shown that an expectation is a complex idea which, like a memory, is made up of two constituents. The one is the idea of an object, the other is the idea of a relation of sequence between that object and some present object; and the reasoning which applied to memories applies to expectations. To have an expectation25 of a given event, and to believe that it will happen, are only two modes of stating the same fact. Again, just in the same way as we call a memory, put into words, a belief, so we give the same name to an expectation in like clothing. And the fact already cited, that a child before it can speak acts upon its memories, is good evidence that it forms expectations. The infant who knows the meaning neither of “sugar-plum” nor of “sweet,” nevertheless is in full possession of that complex idea, which, when he has learned to employ language, will take the form of the verbal proposition, “A sugar-plum will be sweet.”

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 coexistence and succession. But, memories of the coexistence 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 today 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.

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.”

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