CHAPTER IV.

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 co-existence 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 co-existence 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 co-existent 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 co-existence, 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 co-existence 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 expectation[25] 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 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.

CHAPTER V.

But, if we accept it, we must extend it to a much wider assemblage of living beings. Whatever cogency is attached to the arguments in favour of the occurrence of all the fundamental phenomena of mind in young children and deaf mutes, an equal force must be allowed to appertain to those which may be adduced to prove that the higher animals have minds. We must admit that Hume does not express himself too strongly when he says—

"no truth appears to me more evident, than that the beasts are endowed with thought and reason as well as men. The arguments are in this case so obvious, that they never escape the most stupid and ignorant."—(I. p. 232.)

In fact, this is one of the few cases in which the conviction which forces itself upon the stupid and the ignorant, is fortified by the reasonings of the intelligent, and has its foundation deepened by every increase of knowledge. It is not merely that the observation of the actions of animals almost irresistibly suggests the attribution to them of mental states, such as those which accompany corresponding actions in men. The minute comparison which has been instituted by anatomists and physiologists between the organs which we know to constitute the apparatus of thought in man, and the corresponding organs in brutes, has demonstrated the existence of the closest similarity between the two, not only in structure, as far as the microscope will carry us, but in function, as far as functions are determinable by experiment. There is no question in the mind of any one acquainted with the facts that, so far as observation and experiment can take us, the structure and the functions of the nervous system are fundamentally the same in an ape, or in a dog, and in a man. And the suggestion that we must stop at the exact point at which direct proof fails us; and refuse to believe that the similarity which extends so far stretches yet further, is no better than a quibble. Robinson Crusoe did not feel bound to conclude, from the single human footprint which he saw in the sand, that the maker of the impression had only one leg.

Structure for structure, down to the minutest microscopical details, the eye, the ear, the olfactory organs, the nerves, the spinal cord, the brain of an ape, or of a dog, correspond with the same organs in the human subject. Cut a nerve, and the evidence of paralysis, or of insensibility, is the same in the two cases; apply pressure to the brain, or administer a narcotic, and the signs of intelligence disappear in the one as in the other. Whatever reason we have for believing that the changes which take place in the normal cerebral substance of man give rise to states of consciousness, the same reason exists for the belief that the modes of motion of the cerebral substance of an ape, or of a dog, produce like effects.

A dog acts as if he had all the different kinds of impressions of sensation of which each of us is cognisant. Moreover, he governs his movements exactly as if he had the feelings of distance, form, succession, likeness, and unlikeness, with which we are familiar, or as if the impressions of relation were generated in his mind as they are in our own. Sleeping dogs frequently appear to dream. If they do, it must be admitted that ideation goes on in them while they are asleep; and, in that case, there is no reason to doubt that they are conscious of trains of ideas in their waking state. Further, that dogs, if they possess ideas at all, have memories and expectations, and those potential beliefs of which these states are the foundation, can hardly be doubted by any one who is conversant with their ways. Finally, there would appear to be no valid argument against the supposition that dogs form generic ideas of sensible objects. One of the most curious peculiarities of the dog mind is its inherent snobbishness, shown by the regard paid to external respectability. The dog who barks furiously at a beggar will let a well-dressed man pass him without opposition. Has he not then a "generic idea" of rags and dirt associated with the idea of aversion, and that of sleek broadcloth associated with the idea of liking?

In short, it seems hard to assign any good reason for denying to the higher animals any mental state, or process, in which the employment of the vocal or visual symbols of which language is composed is not involved; and comparative psychology confirms the position in relation to the rest of the animal world assigned to man by comparative anatomy. As comparative anatomy is easily able to show that, physically, man is but the last term of a long series of forms, which lead, by slow gradations, from the highest mammal to the almost formless speck of living protoplasm, which lies on the shadowy boundary between animal and vegetable life; so, comparative psychology, though but a young science, and far short of her elder sister's growth, points to the same conclusion.

In the absence of a distinct nervous system, we have no right to look for its product, consciousness; and, even in those forms of animal life in which the nervous apparatus has reached no higher degree of development, than that exhibited by the system of the spinal cord and the foundation of the brain in ourselves, the argument from analogy leaves the assumption of the existence of any form of consciousness unsupported. With the super-addition of a nervous apparatus corresponding with the cerebrum in ourselves, it is allowable to suppose the appearance of the simplest states of consciousness, or the sensations; and it is conceivable that these may at first exist, without any power of reproducing them, as memories; and, consequently, without ideation. Still higher, an apparatus of correlation may be superadded, until, as all these organs become more developed, the condition of the highest speechless animals is attained.

It is a remarkable example of Hume's sagacity that he perceived the importance of a branch of science which, even now, can hardly be said to exist; and that, in a remarkable passage, he sketches in bold outlines the chief features of comparative psychology.

" ... any theory, by which we explain the operations of the understanding, or the origin and connexion of the passions in man, will acquire additional authority if we find that the same theory is requisite to explain the same phenomena in all other animals. We shall make trial of this with regard to the hypothesis by which we have, in the foregoing discourse, endeavoured to account for all experimental reasonings; and it is hoped that this new point of view will serve to confirm all our former observations.

"First, it seems evident that animals, as well as men, learn many things from experience, and infer that the same events will always follow from the same causes. By this principle they become acquainted with the more obvious properties of external objects, and gradually, from their birth, treasure up a knowledge of the nature of fire, water, earth, stones, heights, depths, &c., and of the effects which result from their operation. The ignorance and inexperience of the young are here plainly distinguishable from the cunning and sagacity of the old, who have learned, by long observation, to avoid what hurt them, and pursue what gave ease or pleasure. A horse that has been accustomed to the field, becomes acquainted with the proper height which he can leap, and will never attempt what exceeds his force and ability. An old greyhound will trust the more fatiguing part of the chase to the younger, and will place himself so as to meet the hare in her doubles; nor are the conjectures which he forms on this occasion founded on anything but his observation and experience.

"This is still more evident from the effects of discipline and education on animals, who, by the proper application of rewards and punishments, may be taught any course of action, the most contrary to their natural instincts and propensities. Is it not experience which renders a dog apprehensive of pain when you menace him, or lift up the whip to beat him? Is it not even experience which makes him answer to his name, and infer from such an arbitrary sound that you mean him rather than any of his fellows, and intend to call him, when you pronounce it in a certain manner and with a certain tone and accent?

"In all these cases we may observe that the animal infers some fact beyond what immediately strikes his senses; and that this inference is altogether founded on past experience, while the creature expects from the present object the same consequences which it has always found in its observation to result from similar objects.

"Secondly, it is impossible that this inference of the animal can be founded on any process of argument or reasoning, by which he concludes that like events must follow like objects, and that the course of nature will always be regular in its operations. For if there be in reality any arguments of this nature they surely lie too abstruse for the observation of such imperfect understandings; since it may well employ the utmost care and attention of a philosophic genius to discover and observe them. Animals therefore are not guided in these inferences by reasoning; neither are children; neither are the generality of mankind in their ordinary actions and conclusions; neither are philosophers themselves, who, in all the active parts of life, are in the main the same as the vulgar, and are governed by the same maxims. Nature must have provided some other principle, of more ready and more general use and application; nor can an operation of such immense consequence in life as that of inferring effects from causes, be trusted to the uncertain process of reasoning and argumentation. Were this doubtful with regard to men, it seems to admit of no question with regard to the brute creation; and the conclusion being once firmly established in the one, we have a strong presumption, from all the rules of analogy, that it ought to be universally admitted, without any exception or reserve. It is custom alone which engages animals, from every object that strikes their senses, to infer its usual attendant, and carries their imagination from the appearance of the one to conceive the other, in that particular manner which we denominate belief. No other explication can be given of this operation in all the higher as well as lower classes of sensitive beings which fall under our notice and observation."—(IV. pp. 122-4.)

It will be observed that Hume appears to contrast the "inference of the animal" with the "process of argument or reasoning in man." But it would be a complete misapprehension of his intention, if we were to suppose, that he thereby means to imply that there is any real difference between the two processes. The "inference of the animal" is a potential belief of expectation; the process of argument, or reasoning, in man is based upon potential beliefs of expectation, which are formed in the man exactly in the same way as in the animal. But, in men endowed with speech, the mental state which constitutes the potential belief is represented by a verbal proposition, and thus becomes what all the world recognises as a belief. The fallacy which Hume combats is, that the proposition, or verbal representative of a belief, has come to be regarded as a reality, instead of as the mere symbol which it really is; and that reasoning, or logic, which deals with nothing but propositions, is supposed to be necessary in order to validate the natural fact symbolised by those propositions. It is a fallacy similar to that of supposing that money is the foundation of wealth, whereas it is only the wholly unessential symbol of property.

In the passage which immediately follows that just quoted, Hume makes admissions which might be turned to serious account against some of his own doctrines.

"But though animals learn many parts of their knowledge from observation, there are also many parts of it which they derive from the original hand of Nature, which much exceed the share of capacity they possess on ordinary occasions, and in which they improve, little or nothing, by the longest practice and experience. These we denominate Instincts, and are so apt to admire as something very extraordinary and inexplicable by all the disquisitions of human understanding. But our wonder will perhaps cease or diminish when we consider that the experimental reasoning itself, which we possess in common with beasts, and on which the whole conduct of life depends, is nothing but a species of instinct or mechanical power, that acts in us unknown to ourselves, and in its chief operations is not directed by any such relations or comparison of ideas as are the proper objects of our intellectual faculties.

"Though the instinct be different, yet still it is an instinct which teaches a man to avoid the fire, as much as that which teaches a bird, with such exactness, the art of incubation and the whole economy and order of its nursery."—(IV. pp. 125, 126.)

The parallel here drawn between the "avoidance of a fire" by a man and the incubatory instinct of a bird is inexact. The man avoids fire when he has had experience of the pain produced by burning; but the bird incubates the first time it lays eggs, and therefore before it has had any experience of incubation. For the comparison to be admissible, it would be necessary that a man should avoid fire the first time he saw it, which is notoriously not the case.

The term "instinct" is very vague and ill-defined. It is commonly employed to denote any action, or even feeling, which is not dictated by conscious reasoning, whether it is, or is not, the result of previous experience. It is "instinct" which leads a chicken just hatched to pick up a grain of corn; parental love is said to be "instinctive"; the drowning man who catches at a straw does it "instinctively"; and the hand that accidentally touches something hot is drawn back by "instinct." Thus "instinct" is made to cover everything from a simple reflex movement, in which the organ of consciousness need not be at all implicated, up to a complex combination of acts directed towards a definite end and accompanied by intense consciousness.

But this loose employment of the term "instinct" really accords with the nature of the thing; for it is wholly impossible to draw any line of demarcation between reflex actions and instincts. If a frog, on the flank of which a little drop of acid has been placed, rubs it off with the foot of the same side; and, if that foot be held, performs the same operation, at the cost of much effort, with the other foot, it certainly displays a curious instinct. But it is no less true that the whole operation is a reflex operation of the spinal cord, which can be performed quite as well when the brain is destroyed; and between which and simple reflex actions there is a complete series of gradations. In like manner, when an infant takes the breast, it is impossible to say whether the action should be rather termed instinctive or reflex.

What are usually called the instincts of animals are, however, acts of such a nature that, if they were performed by men, they would involve the generation of a series of ideas and of inferences from them; and it is a curious, and apparently an insoluble, problem whether they are, or are not, accompanied by cerebral changes of the same nature as those which give rise to ideas and inferences in ourselves. When a chicken picks up a grain, for example, are there, firstly, certain sensations, accompanied by the feeling of relation between the grain and its own body; secondly, a desire of the grain; thirdly, a volition to seize it? Or, are only the sensational terms of the series actually represented in consciousness?

The latter seems the more probable opinion, though it must be admitted that the other alternative is possible. But, in this case, the series of mental states which occurs is such as would be represented in language by a series of propositions, and would afford proof positive of the existence of innate ideas, in the Cartesian sense. Indeed, a metaphysical fowl, brooding over the mental operations of his fully-fledged consciousness, might appeal to the fact as proof that, in the very first action of his life, he assumed the existence of the Ego and the non-Ego, and of a relation between the two.

In all seriousness, if the existence of instincts be granted, the possibility of the existence of innate ideas, in the most extended sense ever imagined by Descartes, must also be admitted. In fact, Descartes, as we have soon, illustrates what he means by an innate idea, by the analogy of hereditary diseases or hereditary mental peculiarities, such as generosity. On the other hand, hereditary mental tendencies may justly be termed instincts; and still more appropriately might those special proclivities, which constitute what we call genius, come into the same category.

The child who is impelled to draw as soon as it can hold a pencil; the Mozart who breaks out into music as early; the boy Bidder who worked out the most complicated sums without learning arithmetic; the boy Pascal who evolved Euclid out of his own consciousness: all these may be said to have been impelled by instinct, as much as are the beaver and the bee. And the man of genius, is distinct in kind from the man of cleverness, by reason of the working within him of strong innate tendencies—which cultivation may improve, but which it can no more create, than horticulture can make thistles bear figs. The analogy between a musical instrument and the mind holds good here also. Art and industry may get much music, of a sort, out of a penny whistle; but, when all is done, it has no chance against an organ. The innate musical potentialities of the two are infinitely different.

CHAPTER VI.

The names of simple impressions and ideas, or of groups of co-existent or successive complex impressions and ideas, considered per se, are substantives; as redness, dog, silver, mouth; while the names of impressions or ideas considered as parts or attributes of a complex whole, are adjectives. Thus redness, considered as part of the complex idea of a rose, becomes the adjective red; flesh-eater, as part of the idea of a dog, is represented by carnivorous; whiteness, as part of the idea of silver, is white; and so on.

The linguistic machinery for the expression of belief is called predication; and, as all beliefs express ideas of relation, we may say that the sign of predication is the verbal symbol of a feeling of relation. The words which serve to indicate predication are verbs. If I say "silver" and then "white," I merely utter two names; but if I interpose between them the verb "is," I express a belief in the co-existence of the feeling of whiteness with the other feelings which constitute the totality of the complex idea of silver; in other words, I predicate "whiteness" of silver.

In such a case as this, the verb expresses predication and nothing else, and is called a copula. But, in the great majority of verbs, the word is the sign of a complex idea, and the predication is expressed only by its form. Thus in "silver shines," the verb "to shine" is the sign for the feeling of brightness, and the mark of predication lies in the form "shine-s."

Another result is brought about by the forms of verbs. By slight modifications they are made to indicate that a belief, or predication, is a memory, or is an expectation. Thus "silver shone" expresses a memory; "silver will shine" an expectation.

The form of words which expresses a predication is a proposition. Hence, every predication is the verbal equivalent of a belief; and, as every belief is either an immediate consciousness, a memory, or an expectation, and as every expectation is traceable to a memory, it follows that, in the long run, all propositions express either immediate states of consciousness, or memories. The proposition which predicates A of X must mean either, that the fact is testified by my present consciousness, as when I say that two colours, visible at this moment, resemble one another; or that A is indissolubly associated with X in memory; or that A is indissolubly associated with X in expectation. But it has already been shown that expectation is only an expression of memory.

Hume does not discuss the nature of language, but so much of what remains to be said, concerning his philosophical tenets, turns upon the value and the origin of verbal propositions, that this summary sketch of the relations of language to the thinking process will probably not be deemed superfluous.

So large an extent of the field of thought is traversed by Hume, in his discussion of the verbal propositions in which mankind enshrine their beliefs, that it would be impossible to follow him throughout all the windings of his long journey, within the limits of this essay. I purpose, therefore, to limit myself to those propositions which concern—1. Necessary Truths; 2. The Order of Nature; 3. The Soul; 4. Theism; 5. The Passions and Volition; 6. The Principle of Morals.

Hume's views respecting necessary truths, and more particularly concerning causation, have, more than any other part of his teaching, contributed to give him a prominent place in the history of philosophy.

"All the objects of human reason and inquiry may naturally be divided into two kinds, to wit, relations of ideas and matters of fact. Of the first kind are the sciences of geometry, algebra, and arithmetic, and, in short, every affirmation which is either intuitively or demonstratively certain. That the square of the hypothenuse is equal to the square of the two sides, is a proposition which expresses a relation between these two figures. That three times five is equal to the half of thirty, expresses a relation between these numbers. Propositions of this kind are discoverable by the mere operation of thought without dependence on whatever is anywhere existent in the universe. Though there never were a circle or a triangle in nature, the truths demonstrated by Euclid would for ever retain their certainty and evidence.

"Matters of fact, which are the second objects of human reason, are not ascertained in the same manner, nor is an evidence of their truth, however great, of a like nature with the foregoing. The contrary of every matter of fact is still possible, because it can never imply a contradiction, and is conceived by the mind with the same facility and distinctness, as if ever so conformable to reality. That the sun will not rise to-morrow, is no less intelligible a proposition, and implies no more contradiction, than the affirmation, that it will rise. We should in vain, therefore, attempt to demonstrate its falsehood. Were it demonstratively false, it would imply a contradiction, and could never be distinctly conceived by the mind."—(IV. pp. 32, 33.)

The distinction here drawn between the truths of geometry and other kinds of truth is far less sharply indicated in the Treatise, but as Hume expressly disowns any opinions on these matters but such as are expressed in the Inquiry, we may confine ourselves to the latter; and it is needful to look narrowly into the propositions here laid down, as much stress has been laid upon Hume's admission that the truths of mathematics are intuitively and demonstratively certain; in other words, that they are necessary and, in that respect, differ from all other kinds of belief.

What is meant by the assertion that "propositions of this kind are discoverable by the mere operation of thought without dependence on what is anywhere existent in the universe"?

Suppose that there were no such things as impressions of sight and touch anywhere in the universe, what idea could we have even of a straight line, much less of a triangle and of the relations between its sides? The fundamental proposition of all Hume's philosophy is that ideas are copied from impressions; and, therefore, if there were no impressions of straight lines and triangles there could be no ideas of straight lines and triangles. But what we mean by the universe is the sum of our actual and possible impressions.

So, again, whether our conception of number is derived from relations of impressions in space or in time, the impressions must exist in nature, that is, in experience, before their relations can be perceived. Form and number are mere names for certain relations between matters of fact; unless a man had seen or felt the difference between a straight line and a crooked one, straight and crooked would have no more meaning to him, than red and blue to the blind.

The axiom, that things which are equal to the same are equal to one another, is only a particular case of the predication of similarity; if there were no impressions, it is obvious that there could be no predicates. But what is an existence in the universe but an impression?

If what are called necessary truths are rigidly analysed, they will be found to be of two kinds. Either they depend on the convention which underlies the possibility of intelligible speech, that terms shall always have the same meaning; or they are propositions the negation of which implies the dissolution of some association in memory or expectation, which is in fact indissoluble; or the denial of some fact of immediate consciousness.

The "necessary truth" A = A means that the perception which is called A shall always be called A. The "necessary truth" that "two straight lines cannot inclose a space," means that we have no memory, and can form no expectation of their so doing. The denial of the "necessary truth" that the thought now in my mind exists, involves the denial of consciousness.

To the assertion that the evidence of matter of fact, is not so strong as that of relations of ideas, it may be justly replied, that a great number of matters of fact are nothing but relations of ideas. If I say that red is unlike blue, I make an assertion concerning a relation of ideas; but it is also matter of fact, and the contrary proposition is inconceivable. If I remember[26] something that happened five minutes ago, that is matter of fact; and, at the same time, it expresses a relation between the event remembered and the present time. It is wholly inconceivable to me that the event did not happen, so that my assurance respecting it is as strong as that which I have respecting any other necessary truth. In fact, the man is either very wise or very virtuous, or very lucky, perhaps all three, who has gone through life without accumulating a store of such necessary beliefs which he would give a good deal to be able to disbelieve.

It would be beside the mark to discuss the matter further on the present occasion. It is sufficient to point out that, whatever may be the differences, between mathematical and other truths, they do not justify Hume's statement. And it is, at any rate, impossible to prove, that the cogency of mathematical first principles is due to anything more than these circumstances; that the experiences with which they are concerned are among the first which arise in the mind; that they are so incessantly repeated as to justify us, according to the ordinary laws of ideation, in expecting that the associations which they form will be of extreme tenacity; while the fact, that the expectations based upon them are always verified, finishes the process of welding them together.

Thus, if the axioms of mathematics are innate, nature would seem to have taken unnecessary trouble; since the ordinary process of association appears to be amply sufficient to confer upon them all the universality and necessity which they actually possess.

Whatever needless admissions Hume may have made respecting other necessary truths he is quite clear about the axiom of causation, "That whatever event has a beginning must have a cause;" whether and in what sense it is a necessary truth; and, that question being decided, whence it is derived.

With respect to the first question, Hume denies that it is a necessary truth, in the sense that we are unable to conceive the contrary. The evidence by which he supports this conclusion in the Inquiry, however, is not strictly relevant to the issue.

"No object ever discovers, by the qualities which appear to the senses, either the cause which produced it, or the effects which will arise from it; nor can our reason, unassisted by experience, ever draw any inference concerning real existence and matter of fact."—(IV. p. 35.)

Abundant illustrations are given of this assertion, which indeed cannot be seriously doubted; but it does not follow that, because we are totally unable to say what cause preceded, or what effect will succeed, any event, we do not necessarily suppose that the event had a cause and will be succeeded by an effect. The scientific investigator who notes a new phenomenon may be utterly ignorant of its cause, but he will, without hesitation, seek for that cause. If you ask him why he does so, he will probably say that it must have had a cause; and thereby imply that his belief in causation is a necessary belief.

In the Treatise Hume indeed takes the bull by the horns:

" ... as all distinct ideas are separable from each other, and as the ideas of cause and effect are evidently distinct, 'twill be easy for us to conceive any object to be non-existent this moment find existent the next, without conjoining to it the distinct idea of a cause or productive principle."—(I. p. 111.)

If Hume had been content to state what he believed to be matter of fact, and had abstained from giving superfluous reasons for that which is susceptible of being proved or disproved only by personal experience, his position would have been stronger. For it seems clear that, on the ground of observation, he is quite right. Any man who lets his fancy run riot in a waking dream, may experience the existence at one moment, and the non-existence at the next, of phenomena which suggest no connexion of cause and effect. Not only so, but it is notorious that, to the unthinking mass of mankind, nine-tenths of the facts of life do not suggest the relation of cause and effect; and they practically deny the existence of any such relation by attributing them to chance. Few gamblers but would stare if they were told that the falling of a die on a particular face is as much the effect of a definite cause as the fact of its falling; it is a proverb that "the wind bloweth where it listeth;" and even thoughtful men usually receive with surprise the suggestion, that the form of the crest of every wave that breaks, wind-driven, on the sea-shore, and the direction of every particle of foam that flies before the gale, are the exact effects of definite causes; and, as such, must be capable of being determined, deductively, from the laws of motion and the properties of air and water. So again, there are large numbers of highly intelligent persons who rather pride themselves on their fixed belief that our volitions have no cause; or that the will causes itself, which is either the same thing, or a contradiction in terms.

Hume's argument in support of what appears to be a true proposition, however, is of the circular sort, for the major premiss, that all distinct ideas are separable in thought, assumes the question at issue.

But the question whether the idea of causation is necessary, or not, is really of very little importance. For, to say that an idea is necessary is simply to affirm that we cannot conceive the contrary; and the fact that we cannot conceive the contrary of any belief may be a presumption, but is certainly no proof, of its truth.

In the well-known experiment of touching a single round object, such as a marble, with crossed fingers, it is utterly impossible to conceive that we have not two round objects under them; and, though light is undoubtedly a mere sensation arising in the brain, it is utterly impossible to conceive that it is not outside the retina. In the same way, he who touches anything with a rod, not only is irresistibly led to believe that the sensation of contact is at the end of the rod, but is utterly incapable of conceiving that this sensation is really in his head. Yet that which is inconceivable is manifestly true in all these cases. The beliefs and the unbeliefs are alike necessary, and alike erroneous.

It is commonly urged that the axiom of causation cannot be derived from experience, because experience only proves that many things have causes, whereas the axiom declares that all things have causes. The syllogism, "many things which come into existence have causes, A has come into existence: therefore A had a cause," is obviously fallacious, if A is not previously shown to be one of the "many things." And this objection is perfectly sound so far as it goes. The axiom of causation cannot possibly be deduced from any general proposition which simply embodies experience. But it does not follow that the belief, or expectation, expressed by the axiom, is not a product of experience, generated antecedently to, and altogether independently of, the logically unjustifiable language in which we express it.

In fact, the axiom of causation resembles all other beliefs of expectation in being the verbal symbol of a purely automatic act of the mind, which is altogether extra-logical, and would be illogical, if it were not constantly verified by experience. Experience, as we have seen, stores up memories; memories generate expectations or beliefs—why they do so may be explained hereafter by proper investigation of cerebral physiology. But, to seek for the reason of the facts in the verbal symbols by which they are expressed, and to be astonished that it is not to be found there, is surely singular; and what Hume did was to turn attention from the verbal proposition to the psychical fact of which it is the symbol.

"When any natural object or event is presented, it is impossible for us, by any sagacity or penetration, to discover, or even conjecture, without experience, what event will result from it, or to carry our foresight beyond that object, which is immediately present to the memory and senses. Even after one instance or experiment, where we have observed a particular event to follow upon another, we are not entitled to form a general rule, or foretell what will happen in like cases; it being justly esteemed an unpardonable temerity to judge of the whole course of nature from one single experiment, however accurate or certain. But when one particular species of events has always, in all instances, been conjoined with another, we make no longer any scruple of foretelling one upon the appearance of the other, and of employing that reasoning which can alone assure us of any matter of fact or existence. We then call the one object Cause, the other Effect. We suppose that there is some connexion between them: some power in the one, by which it infallibly produces the other, and operates with the greatest certainty and strongest necessity.... But there is nothing in a number of instances, different from every single instance, which is supposed to be exactly similar; except only, that after a repetition of similar instances, the mind is carried by habit, upon the appearance of one event, to expect its usual attendant, and to believe that it will exist.... The first time a man saw the communication of motion by impulse, as by the shock of two billiard balls, he could not pronounce that the one event was connected, but only that it was conjoined, with the other. After he has observed several instances of this nature, he then pronounces them to be connected. What alteration has happened to give rise to this new idea of connexion? Nothing but that he now feels those events to be connected in his imagination, and can readily foresee the existence of the one from the appearance of the other. When we say, therefore, that one object is connected with another we mean only that they have acquired a connexion in our thought, and give rise to this inference, by which they become proofs of each other's existence; a conclusion which is somewhat extraordinary, but which seems founded on sufficient evidence."—(IV. pp. 87-89.)

In the fifteenth section of the third part of the Treatise, under the head of the Rules by which to Judge of Causes and Effects, Hume gives a sketch of the method of allocating effects to their causes, upon which, so far as I am aware, no improvement was made down to the time of the publication of Mill's Logic. Of Mill's four methods, that of agreement is indicated in the following passage:—

" ... where several different objects produce the same effect, it must be by means of some quality which we discover to be common amongst them. For as like effects imply like causes, we must always ascribe the causation to the circumstance wherein we discover the resemblance."—(I. p. 229.)

Next, the foundation of the method of difference is stated:—

"The difference in the effects of two resembling objects must proceed from that particular in which they differ. For, as like causes always produce like effects, when in any instance we find our expectation to be disappointed, we must conclude that this irregularity proceeds from some difference in the causes."—(I. p. 230.)

In the succeeding paragraph the method of concomitant variations is foreshadowed.

"When any object increases or diminishes with the increase or diminution of the cause, 'tis to be regarded as a compounded effect, derived from the union of the several different effects which arise from the several different parts of the cause. The absence or presence of one part of the cause is here supposed to be always attended with the absence or presence of a proportionable part of the effect. This constant conjunction sufficiently proves that the one part is the cause of the other. We must, however, beware not to draw such a conclusion from a few experiments."—(I. p. 230.)

Lastly, the following rule, though awkwardly stated, contains a suggestion of the method of residues:—

" ... an object which exists for any time in its full perfection without any effect, is not the sole cause of that effect, but requires to be assisted by some other principle, which may forward its influence and operation. For as like effects necessarily follow from like causes, and in a contiguous time and place, their separation for a moment shows that these causes are not complete ones."—(I. p. 230.)

In addition to the bare notion of necessary connexion between the cause and its effect, we undoubtedly find in our minds the idea of something resident in the cause which, as we say, produces the effect, and we call this something Force, Power, or Energy. Hume explains Force and Power as the results of the association with inanimate causes of the feelings of endeavour or resistance which we experience, when our bodies give rise to, or resist, motion.

If I throw a ball, I have a sense of effort which ends when the ball leaves my hand; and if I catch a ball, I have a sense of resistance which comes to an end with the quiescence of the ball. In the former case, there is a strong suggestion of something having gone from myself into the ball; in the latter, of something having been received from the ball. Let any one hold a piece of iron near a strong magnet, and the feeling that the magnet endeavours to pull the iron one way in the same manner as he endeavours to pull it in the opposite direction, is very strong.

As Hume says:—

"No animal can put external bodies in motion without the sentiment of a nisus, or endeavour; and every animal has a sentiment or feeling from the stroke or blow of an external object that is in motion. These sensations, which are merely animal, and from which we can, a priori, draw no inference, we are apt to transfer to inanimate objects, and to suppose that they have some such feelings whenever they transfer or receive motion."—(IV. p. 91, note.)

It is obviously, however, an absurdity not less gross than that of supposing the sensation of warmth to exist in a fire, to imagine that the subjective sensation of effort or resistance in ourselves can be present in external objects, when they stand in the relation of causes to other objects.

To the argument, that we have a right to suppose the relation of cause and effect to contain something more than invariable succession, because, when we ourselves act as causes, or in volition, we are conscious of exerting power; Hume replies, that we know nothing of the feeling we call power except as effort or resistance; and that we have not the slightest means of knowing whether it has anything to do with the production of bodily motion or mental changes. And he points out, as Descartes and Spinoza had done before him, that when voluntary motion takes place, that which we will is not the immediate consequence of the act of volition, but something which is separated from it by a long chain of causes and effects. If the will is the cause of the movement of a limb, it can be so only in the sense that the guard who gives the order to go on, is the cause of the transport of a train from one station to another.

"We learn from anatomy, that the immediate object of power in voluntary motion is not the member itself which is moved, but certain muscles and nerves and animal spirits, and perhaps something still more minute and unknown, through which the motion is successively propagated, ere it reach the member itself, whose motion is the immediate object of volition. Can there be a more certain proof that the power by which the whole operation is performed, so far from being directly and fully known by an inward sentiment or consciousness, is to the last degree mysterious and unintelligible? Here the mind wills a certain event: Immediately another event, unknown to ourselves, and totally different from the one intended, is produced: This event produces another equally unknown: Till at last, through a long succession, the desired event is produced."—(IV. p. 78.)