Popular Science Monthly/Volume 16/March 1880/The Association of Ideas
By WILLIAM JAMES, M.D.,
ASSISTANT PROFESSOR OF PHYSIOLOGY IN HARVARD COLLEGE.
THE manner in which trains of imagery and consideration follow each other through our thinking, the restless flight of one idea before the next, the transitions our minds make between things wide as the poles asunder, transitions which at first sight startle us by their abruptness, but which, when scrutinized closely, often reveal intermediating links of thought of perfect naturalness and propriety—all this magical, imponderable streaming has from time immemorial excited the admiration of every living man whose attention happened to be caught by its omnipresent mystery. And it has furthermore challenged the race of philosophers to try to banish something of the mystery by formulating the process in somewhat simpler terms.
Two great philosophic efforts to this end have been made. The one is called the associationist philosophy of England, the other the Herbartian system of Germany. Professor Bain’s books are generally regarded as the most successful expression of the first movement. Volkmann’s “Psychology” is perhaps the most finished utterance of the last. These schools differ as to their theoretic basis (the one being ontological and the other phenomenal), but they agree in almost all besides; especially in the attempt to show how all the different kinds of mental activity (such as memory, judgment, reasoning, self-consciousness, desire, etc., etc., which were formerly classed as distinct and original “faculties”) may be explained as resultants of the manner in which, by the working of two or three simple elementary laws of revival between images, these latter are grouped into certain characteristic forms.
In fact, the easiest way of describing the entire industry of these schools would be to say that they seek to explain the forms of consciousness by means of its materials.
Now, to another class of minds any such attempt seems so preposterously absurd that they pour out the child with the bath, and disdain even a modest ambition which should content itself with tracing out in the jungle of the mind a few of the trails by which its materials are brought together. As this article is born of the latter ambition, and as its author thinks he has succeeded in making the trails broader and smoother than previous writers have left them, it behooves him to defend himself and his purpose by a few preliminary words addressed to this class of critics. They are recruited mainly from the school of Hegel, but we find even as fertile and acute a writer as Lotze sharing their prejudices and negations in this respect.
The intuition they start from is that thought is not a sand-heap of juxtaposed images with associating links outside of them and between them. It is a unitary continuum of which the items, and the logical relations between the items, form alike integral parts, equally imbedded, equally essential, equally interdependent. Any relation may carry us from one item to another, and according as we follow one or the other relation we shall traverse the field of thought in this way or in that, have one train of images or its opposite. But all the relations are logical, are relations of reason. A thing may suggest its like, or its opposite, its genus or its species, its cause or its effect, its means or its purpose, its habitual neighbors in space or in time, its possibilities or its impossibilities, its changes or its resistance to change—in short, it may call up every consideration to which it can have a possible logical relevancy, and call up each in its turn. And the only summary formula that can be applied to all these infinite possibilities of transition is that, as transitions of Thought, they are all alike acts of Reason. This monotonous appeal to "Thought" with a capital T and Reason with a capital R is apt to irritate the ear of him bent on analysis, very much as the stereotyped "Allah is great" of the Mussulman irritates the ear of the scientific traveler. It is true enough, but sterile. And, when it interdicts discrimination and the search for secondary causes, it performs as obstructive a function as that of our dear old friend the dog in the manger.
For these so-called "transitions of Reason" are far from being all alike reasonable. If pure Thought runs all our trains, why should she run some so fast and some so slow, some through dull flats and some through gorgeous scenery, some to mountain-heights and jeweled mines, others through dismal swamps and darkness?—and run some off the track altogether, and into the wilderness of lunacy? Why do we spend years straining after a certain scientific or practical problem, but all in vain—Thought refusing to evoke the solution we desire? And why, some day, walking in the street with our attention miles away from that quest, does the answer saunter into our minds as carelessly as if it had never been called for—suggested, possibly, by the flowers on the bonnet of the lady in front of us, or possibly by nothing that we can discover? If Reason can give us relief then, why did she not do so earlier?
The truth must be admitted that pure Thought works under conditions imposed ab extra. The great law of habit itself—that twenty experiences make us recall a thing better than one, that long indulgence in error makes right thinking almost impossible—seems to have no essential foundation in reason. The business of pure Thought is with Truth—the number of experiences ought to have nothing to do with her hold of it; and she ought by right to be able to hug it all the closer, after years wasted out of its presence. Such arrangements seem quite fantastic and arbitrary, but nevertheless are part of the very bone and marrow of our minds. Reason is only one out of a thousand possibilities in the thinking of each of us. Who can count all the silly fancies, the grotesque suppositions, the utterly irrelevant reflections he makes in the course of a day? Who can swear that his prejudices and irrational beliefs constitute a less bulky part of his mental furniture than his clarified opinions? It is true that a presiding arbiter seems to sit aloft in the mind, and emphasize the better suggestions into permanence, while it ends by dropping out and leaving unrecorded the confusion. But this is all the difference. The mode of genesis of the worthy and the worthless seems the same. The laws of our actual thinking, of the cogitatum, must account alike for the bad and the good materials on which the arbiter has to decide, for wisdom and for folly. The laws of the arbiter, of the cogitandum, of what we ought to think, are to the former as the laws of ethics are to those of history. Who but an Hegelian historian ever pretended that reason in action was per se a sufficient explanation of the political changes in Europe?
There are, then, mechanical conditions on which Thought depends, and which, to say the least, determine the order in which is presented the content or material for her comparisons, selections, and decisions. It is a suggestive fact that Locke, and many more recent Continental psychologists, have found themselves obliged to invoke a mechanical process to account for the aberrations of Thought, the obstructive prepossessions, the frustrations of Reason. This they found in the law of habit, or what we now call Association by Contiguity. But it never occurred to these writers that a process which could go the length of actually producing some ideas and sequences in the mind might safely be trusted to produce others too; and that those habitual associations which further thought may come from the same mechanical source as those which hinder it. Hartley accordingly suggested habit as an all-sufficient explanation, but failed to dispose of the difficulty which comes in when we notice that in the highest flights of Reason habit does not seem the link between one item and the next. Rather are the transitions of genius distinguished by their express defiance of all that is habitual.
This led to the erection of other laws to supply the gaps in explanation left by the law of habit alone. No sensible man now considers the habit-philosophy of Hartley, Priestley, and James Mill to be adequate to its task. Professor Bain, reverting to Hume’s standpoint, supplements the law of Contiguity by that of Similarity, and, in a subordinate degree, by that of Contrast. All the materials of thought, without conception, are in his psychology pushed or drawn before the footlights of consciousness by the working of these laws and by them alone.
Mr. Hodgson, ablest of recent (if not of all) English philosophers, supplements Bain’s laws by an important principle, that of Interest.
And every one before whose consciousness, when falling asleep, trains of faces and other disconnected images are wont to pass, and who, moreover, after his attention has once been called to the subject, surprises vestiges of the same process at work during his waking hours, in the form of a sort of meteoric shower of random images, visual or verbal, which cross the main current of thought, but are so faint that they ordinarily arrest no attention and are forthwith forgotten—every such person, I say, will plead for the admission of a principle of spontaneity or accidental arousal, along with the principles already mentioned.
In the pages that follow I accept all these laws save that of contrast; and that I do not reject, but simply ignore and disregard on the present occasion. I try to show how they all may follow from certain variations in a fundamental process of activity in the brain. In particular I reduce Contiguous and Similar Associations to one, by exhibiting their most pronounced forms as mere extremes of a common mode. But the reader is requested to remember that in thus trying to explain, by laws of matter, what ideas shall be presented to consciousness at any moment, I expressly repudiate the pretension to explain the form of consciousness itself. Consciousness, as I understand it, is always in the midst of the present aware of the past as that from which the present came; and, out of the materials which the present furnishes, she is always comparing one part with another, to select that which most fits her ends. These peculiarities of consciousness were referred to above, when it was spoken of as a “presiding arbiter.” I am wholly unable to picture this strange discriminating industry, this bringing of things together in order to keep them apart, this setting of ends and choosing from equal possibilities, in terms of any physical process whatever. The laws of association to be treated of here might, for aught we can see, be true in a creature wholly devoid of memory or comparison. Each of his ideas would vanish in the act of awakening its successor; his mind (if such it could be called) would be shut up to the punctiform instant; he would obey, without noticing, the current which swept him on; drift to his conclusions, but never know why; and act upon the suggestions of experience with a fatality which would be inwardly all the blinder in proportion as it was the more rational to outward semblance. I simply assume for his benefit the possession of a consciousness. I beg that much from the reader’s liberality; and limit my ambition to showing (the consciousness being granted) with what objects it is at any given moment most likely to be filled.
The laws of motor habit in the lower centers of the nervous system are disputed by no one. A series of movements repeated in a certain order tend to unroll themselves with peculiar ease in that order for ever afterward. Number one awakens number two, and that awakens number three, and so on, till the last is produced. A habit of this kind once become inveterate, like the manipulations of certain trades, the balancings of the body in standing or walking, the varying pressure of the legs in response to the swayings of a horse’s gait, may go on automatically while the mind concerns itself with far other affairs. And so it is with thoughts. Not only poems, but the multiplication-table, Greek verbs, and formulas of gibberish like "ana, mana, mona, mike," etc., cohere in the self-same order in which they have once been learned. If we have blundered once in a certain place, we are prone to repeat the mistake again. The higher and the lower nerve-centers, then, are subject to one and the same law; and the reason of the law must be in both cases the same. The fact that there are isolated tracts of conduction in all the centers, and that as we pass from below upward the different centers have in the main different characteristic functions, leads to the notion that each function, ideational or motor, is dependent on a certain tract localized somewhere, which tract when once excited may propagate the excitement to other outlying tracts. The reason for the law of habit would, then, seem to be that the propagation occurs easiest through those tracts of conduction which have been already most in use. Descartes and Locke hit upon this explanation, which modern science has not yet succeeded in improving. "Custom," says Locke, "settles habits of thinking in the understanding as well as of determining in the will, and of motions in the body; all which seem to be but trains of motion in the animal spirits (by this Locke meant identically what we understand by the words neural process), which, once set agoing, continue in the same steps they have been used to, which by often treading are worn into a smooth path, and the motion in it becomes easy and as it were natural."
Let us, then, assume as the basis of all our subsequent reasoning the following law: When two brain tracts or processes have occurred together or in immediate succession, any one of them, on reoccurring, tends to propagate its excitement into the other.
Now, as a matter of fact, things in the brain are much less simple than this. Every elementary tract or process has found itself at different times excited in conjunction with many other tracts or processes, and this by unavoidable outward causes. Which of these others it shall awaken now becomes a problem. Shall b or c be aroused next by the present a? We must make a further postulate, based, however, on the undeniable fact of tension in nerve-tissue, and the summation of excitements, each incomplete or latent in itself, into an open resultant; b rather than c will awake, if in addition to the vibrating tract a some other tract d is in a state of sub-excitement, and formerly was excited with b alone and not with a. In short, we may say:
The amount of activity at any given point in the brain-cortex is the sum of the tendencies of all other points to discharge into it, such tendencies being proportionate (1) to the number of times the excitement of each other point may have coexisted with that of the point in question; (2) to the intensity of such excitements; and (3) to the absence of any rival locality or process functionally disconnected with the first point, into which the discharges might be diverted.
Expressing the fundamental law in this most complicated way leads to the greatest ultimate simplification. This will now be seen; but the reader will bear in mind that our limits only allow us to treat of spontaneous trains of thought and ideation, such as occur in reverie or musing. The case of voluntary thinking toward a certain end must be postponed to another opportunity.
Take, to fix our ideas, the two verses from "Locksley Hall":
"I, the heir of all the ages in the foremost files of time,"
"For I doubt not through the ages one increasing purpose runs."
Why is it that when we recite from memory one of these lines and get as far as the ages that portion of the other line which follows, and, so to speak, sprouts out of the ages, does not also sprout out of our memory, and confuse the sense of our words? Simply because the word that follows the ages has its brain-process awakened not simply by the brain-process of the ages alone, but by it plus the brain-processes of all the words preceding the ages. The word ages at its moment of strongest activity would, per se, indifferently discharge into either "in" or "one." So would the previous words (whose tension is momentarily much less strong than that of ages) each of them indifferently discharge into either of a large number of other words with which they have been at different times combined. But when the processes of "So I doubt not through the ages" simultaneously vibrate in the brain, the strongest line of discharge will be that which they all alike tend to take. "One" and not "in" or any other word will be the next to awaken, for its brain-process has previously vibrated in unison not only with that of ages, but with that of all those other words whose activity is just dying away.
In case of some one of these preceding words—"heir," for example—having an intensely strong association with some brain-tracts entirely disjoined in experience from the poem of "Locksley Hall"—in case the reciter, for instance, was tremulously awaiting the opening of a will which might make him a millionaire or leave him penniless—it is probable that the path of discharge through the words of the poem would be suddenly interrupted at the word "heir." His emotional interest in that word would be such that its own special associations would prevail over the combined ones of the other words. He would, as we say, be abruptly reminded of his personal situation, and the poem would lapse altogether from his thoughts.
The writer of these pages has every year to learn the names of a large number of students who sit in alphabetical order in a lecture-room. On meeting one in the street, early in the year, the face hardly ever recalls the name, but it may recall the place of its owner in the lecture-room, his neighbors’ faces, and consequently his general alphabetical position; and then, usually as the common associate of all these combined data, the student’s name surges up in my mind.
A father wishes to show to some guests the progress of his rather dull child in Kindergarten instruction. Holding the knife upright on the table, he says, "What do you call that, my boy?" "I calls it a knife, I does," is the sturdy reply, from which the child can not be induced to swerve by any alteration in the form of question, until the father, recollecting that in the Kindergarten a pencil was used, and not a knife, draws a long one from his pocket, holds it in the same way, and then gets the wished-for answer, "I calls it vertical." All the concomitants of the Kindergarten experience had to recombine their effect before the word "vertical" could be reawakened.
Professor Bain, in his chapters on Compound Association, has treated in a minute and exhaustive way of this type of mental sequence, and what he has done so well need not be here repeated.
The ideal working of the law of compound association, were it unmodified by any extraneous influence, would be such as to keep the mind in a perpetual treadmill of concrete reminiscences from which no detail could be omitted. Suppose, for example, we begin by thinking of a certain dinner-party. The only thing which all the components of the dinner-party could combine to recall would be the first concrete occurrence which ensued upon it. All the details of this occurrence could in turn only combine to awaken the next following occurrence and so on. If a, b, c, d, e, for instance, be the elementary nerve-tracts excited by the last act of the dinner-party, call this act A, and l, m, n, o, p be those of walking home through the frosty night, which we may call B, then the thought of A must awaken that of B, because a, b, c, d, e, will each and all discharge into l through the paths by which their original discharge took place. Similarly they will discharge into m, n, o, and p, and these latter tracts will each re-enforce the other’s action because, in the experience B, they have already vibrated in unison. The lines in the diagram symbolize the summation of discharges into each of the components of B, and the consequent strength of the combination of influences by which B in its totality is awakened.
Hamilton first used the word "redintegration" to designate all association. Such processes as we have just described might in an emphatic sense be termed redintegrations, for they would necessarily lead, if unobstructed, to the reinstatement in thought of the entire content of large trains of past experience. From this complete redintegration there could be no escape save through the irruption of some new and strong present impression of the senses or through the excessive tendency of some one of the elementary brain-tracts to discharge independently into an aberrant quarter of the brain. Such was the tendency of the word "heir" in the verse from "Locksley Hall," which was our first example. How such tendencies are constituted, we shall have soon to inquire with some care. Unless they are present, the panorama of the past, once opened, must unroll itself with fatal literality to the end, unless some outward sound, sight, or touch divert the current of thought.
I prefer to discard the word "redintegration" altogether, and to give to this unobstructed process the name of Complete Association by Contiguity. Whether it ever occurs in this absolutely complete form is doubtful. We all immediately recognize, however, that in some minds there is a much greater tendency than in others for the flow of thought to take this form. Those insufferably garrulous old women, those dry and fanciless beings who spare you no detail, however petty, of the facts they are recounting, and upon the thread of whose narrative all the irrelevant items cluster as pertinaciously as the essential ones, the slaves of literal fact, the stumblers over the smallest abrupt step in thought, are figures known to all of us. Comic literature has made her profit out of them. Juliet’s nurse is a classical example. George Eliot’s village characters and some of Dickens’s minor personages supply excellent instances.
Perhaps as successful a rendering as any of this mental type is the character of Miss Bates in Miss Austen’s "Emma." Hear how she redintegrates: "‘But where could you hear it?’ cried Miss Bates. ‘Where could you possibly hear it, Mr. Knightley? For it is not five minutes since I received Mrs. Cole’s note—no, it can not be more than five—or at least ten—for I had got my bonnet and spencer on, just ready to come out—I was only gone down to speak to Patty again about the pork—Jane was standing in the passage—were not you, Jane?—for my mother was so afraid that we had not any salting-pan large enough. So I said I would go down and see, and Jane said: "Shall I go down instead? for I think you have a little cold, and Patty has been washing the kitchen." "Oh, my dear," said I—well, and just then came the note. A Miss Hawkins—that’s all I know—a Miss Hawkins, of Bath. But, Mr. Knightley, how could you possibly have heard it? for the very moment Mr. Cole told Mrs. Cole of it, she sat down and wrote to me. A Miss Hawkins—’"
But in every one of us there are moments when this complete reproduction of all the items of a past experience occurs. What are those moments? They are moments of emotional recall of the past as something which once was, but is gone for ever—moments, the interest of which consists in the feeling that our self was once other than it now is. When this is the case, any detail, however minute, which will make the past picture more complete, will also have its effect in swelling that total contrast between now and then which forms the central interest of our contemplation.
This case helps us to understand why it is that the ordinary spontaneous flow of our ideas does not follow the law of "complete" Association by Contiguity. In no revival of a past experience are all the items of our thought equally and impartially operative in determining what the next thought shall be. Always some ingredient is prepotent over the rest. Its special suggestions or associations in this case will often be different from those which it has in common with the whole group of items; and its tendency to awaken these outlying associates will deflect the path of our reverie. Just as in the original sensible experience our attention focalized itself upon a few of the impressions of the scene before us, so here in the reproduced representation of those impressions the same partiality is shown, and some items emphasized above the rest. What these items shall be is, in most cases of spontaneous reverie, hard to determine beforehand. In subjective terms we say that the prepotent items are those which appeal most to our interest.
Expressed in brain-terms, the law of interest will be: some one brain-process is always prepotent above its concomitants in arousing action elsewhere.
"Two processes," says Mr. Hodgson, "are constantly going on in redintegration. The one a process of corrosion, melting, decay; the other a process of renewing, arising, becoming. . . . No object of representation remains long before consciousness in the same state, but fades, decays, and becomes indistinct. Those parts of the object, however, which possess an interest, that is, those which are attended by a representation of pleasure or pain, resist this tendency to gradual decay of the whole object. . . . This inequality in the object—some parts, the uninteresting, submitting to decay; others, the interesting parts, resisting it—when it has continued for a certain time, ends in becoming a new object." Only where the interest is diffused equally over all the parts (as in the emotional memory just referred to, where, as all past, they all interest us alike) is this law departed from. It will be least obeyed by those minds which have the smallest variety and intensity of interests—those who, by the general flatness and poverty of their aesthetic nature, are kept for ever rotating among the literal sequences of their local and personal history.
Most of us, however, are better organized than this, and our musings pursue an erratic course, swerving continually into a new direction traced out by the shifting play of interest as it irradiates always some partial item in each complex representation that is evoked. Thus it commonly comes about that we find ourselves thinking at two nearly adjacent moments of things separated by the whole diameter of space and time. Not till we carefully recall each step of our cogitation do we see how naturally we came by Hodgson’s law to pass from one to the other. Thus, for instance, after looking at my clock just now, I found myself thinking of Senator Bayard’s recent resolution about our legal-tender notes. The clock called up the image of the man who had repaired its gong. He suggested the jeweler’s shop where I had last seen him; that shop, some shirt-studs which I had bought there; they, the value of gold and its recent decline; the latter, the equal value of greenbacks, and this naturally the question of how long they were to last, and of the Bayard proposition. Each of these images offered various points of interest. Those which formed the turning-points of my thought are easily assigned. The gong was momentarily the most interesting part of the clock, because, from having begun with a beautiful tone, it had become discordant and aroused disappointment and perplexity. But for this, the clock might have suggested the friend who gave it to me, or any one of a thousand circumstances connected with it. The jeweler’s shop suggested the studs, because they alone of all its contents were tinged with the egoistic interest of possession. This interest in the studs, their value, made me single out the material as its chief source, etc., to the end. Every reader who will arrest himself at any moment and say, "How came I to be thinking of just this?" will be sure to trace a train of representations linked together by lines of contiguity and points of interest inextricably combined. This is the ordinary process of the association of ideas as it spontaneously goes on in average minds. We may call it Partial or Mixed Association.
Another example of it is given by Hobbes in a passage which has been quoted so often as to be classical: "In a discourse of our present civil war, what could seem more impertinent than to ask (as one did) what was the value of a Roman penny? Yet the coherence to me was manifest enough. For the thought of the war introduced the thought of the delivering up the King to his enemies; the thought of that brought in the thought of the delivering up of Christ; and that again the thought of the thirty pence, which was the price of that treason: and thence easily followed that malicious question; and all this in a moment of time; for thought is quick."
Can we determine now when a certain portion of the going thought has, by dint of its interest, become so prepotent as to make its own exclusive associates the dominant features of the coming thought—can we, I say, determine which of its own associates shall be evoked? For they are many. As Hodgson says: "The interesting parts of the decaying object are free to combine again with any objects or parts of objects with which at any time they have been combined before. All the former combinations of these parts may come back into consciousness; one must; but which will?" Mr. Hodgson replies: "There can be but one answer: that which has been most habitually combined with them before. This new object begins at once to form itself in consciousness, and to group its parts round the part still remaining from the former object; part after part comes out and arranges itself in its old position; but scarcely has the process begun, when the original law of interest begins to operate on this new formation, seizes on the interesting parts and impresses them on the attention to the exclusion of the rest, and the whole process is repeated again with endless variety. I venture to propose this as a complete and true account of the whole process of redintegration."
In restricting the discharge from the interesting item into that channel which is simply most habitual in the sense of most frequent, Hodgson’s account is assuredly imperfect. An image by no means always revives its most frequent associate, although frequency is certainly one of the most potent determinants of revival. If I abruptly utter the word swallow, the reader, if by habit an ornithologist, will think of a bird; if a physiologist or a medical specialist in throat-diseases, he will think of deglutition. If I say date, he will, if a fruit-merchant or an Arabian traveler, think of the produce of the palm; if an habitual student of history, figures with a. d. or b. c. before them will rise in his mind. If I say bed, bath, morning, his own daily toilet will be invincibly suggested by the combined names of three of its habitual associates. But frequent lines of transition are often set at naught. The sight of C. Göring’s "System der kritischen Philosophie" has most frequently awakened in me thoughts of the opinions therein propounded. The idea of suicide has never been connected with the volumes. But a moment since, as my eye fell upon them, suicide was the thought that flashed into my mind. Why? Because but yesterday I received a letter from Leipsic informing me that this philosopher’s recent death by drowning was an act of self-destruction. Thoughts tend, then, to awaken their most recent as well as their most habitual associates. This is a matter of notorious experience, too notorious, in fact, to need illustration. If we have seen our friend this morning, the mention of his name now recalls the circumstances of that interview, rather than any more remote details concerning him. If Shakespeare’s plays are mentioned, and we were last night reading "Richard II.," vestiges of that play rather than of "Hamlet" or "Othello" float through our mind. Excitement of peculiar tracts, or peculiar modes of general excitement in the brain leave a sort of tenderness or exalted sensibility behind them which takes days to die away. As long as it lasts, those tracts or those modes are liable to have their activities awakened by causes which at other times might leave them in repose. Hence, recency in experience is a prime factor in determining revival in thought.
Vividness in an original experience may also have the same effect as habit or recency in bringing about likelihood of revival. If we have once witnessed an execution, any subsequent conversation or reading about capital punishment will almost certainly suggest images of that particular scene. Thus it is that events lived through only once, and in youth, may come in after-years, by reason of their exciting quality or emotional intensity, to serve as types or instances used by our mind to illustrate any and every occurring topic whose interest is most remotely pertinent to theirs. If a man in his boyhood once talked with Napoleon, any mention of great men or historical events, battles or thrones, or the whirligig of fortune, or islands in the ocean, will be apt to draw to his lips the incidents of that one memorable interview. If the word tooth now suddenly appears on the page before the reader’s eye, there are fifty chances out of a hundred that, if he gives it time to awaken any image, it will be an image of some operation of dentistry in which he has been the sufferer. Daily he has touched his teeth and masticated with them; this very morning he brushed them, chewed his breakfast and picked them; but the rarer and remoter associations arise more promptly because they were so much more intense.
A fourth factor in tracing the course of reproduction is congruity in emotional tone between the reproduced idea and our mood. The same objects do not recall the same associates when we are cheerful as when we are melancholy. Nothing, in fact, is more striking than our utter inability to keep up trains of joyous imagery when we are depressed in spirits. Storm, darkness, war, images of disease, poverty, and perishing afflict unremittingly the imaginations of melancholiacs. And those of sanguine temperament, when their spirits are high, find it equally impossible to give any permanence to evil forebodings or to gloomy thoughts in general. In an instant the train of association dances off to flowers and sunshine, and images of spring and hope. The records of Arctic or African travel perused in one mood awaken no thoughts but those of horror at the malignity of Nature; read at another time they suggest only enthusiastic reflections on the indommitable power and pluck of man. Few novels so overflow with joyous animal spirits as "The Three Guardsmen" of Dumas. Yet it may awaken in the mind of a reader depressed with sea-sickness (as the writer can personally testify) a most dismal and woful consciousness of the cruelty and carnage which heroes like Athos, Porthos, and Aramis make themselves guilty of.
Habit, recency, vividness, and emotional congruity are, then, all reasons why one representation rather than another should be awakened by the interesting portion of a departing thought. We may say with truth that in the majority of cases the coming representation will have been either habitual, recent, or vivid, and will be congruous. If all these qualities unite in any one absent associate, we may predict almost infallibly that that associate of the going thought will form an important ingredient in the coming thought. In spite of the fact, however, that the succession of representations is thus redeemed from perfect indeterminism and limited to a few classes whose characteristic quality is fixed by the nature of our past experience, it must still be confessed that an immense number of terms in the linked chain of our representations fall outside of all assignable rule. To take the instance of the clock given on page 586. Why did the jeweler’s shop suggest the shirt-studs rather than a chain which I had bought there more recently, which has cost more, and whose sentimental associations were much more interesting? Both chain and studs had excited brain-tracts simultaneously with the excitement of others by the general aspect of the shop. The only reason why the nerve-stream from the shop-tract switched off into the stud-tract rather than the chain-tract must be that the stud-tract happened at that moment to lie more open, either because of some accidental alteration in its nutrition or because the incipient sub-conscious tensions of the brain as a whole had so distributed their equilibrium that it was more unstable here than in the chain-tract. Any reader’s introspection will easily furnish similar instances. It thus remains true that to a certain extent, even in those forms of ordinary Mixed Association which lie nearest to Pure Association by Contiguity, which associate of the interesting item shall emerge must be called largely a matter of accident—accident, that is, for our intelligence. No doubt it is determined by cerebral causes, but they are too subtile and shifting for our analysis.
In Partial or Mixed Association we have all along supposed that the interesting portion of the disappearing thought was of considerable extent, was sufficiently complex to constitute by itself a concrete object. Sir William Hamilton relates that after thinking of Ben Lomond he found himself thinking of the Prussian system of education, and discovered that the links of association were a German gentleman whom he had met on Ben Lomond, Germany, etc. The interesting part of Ben Lomond, the part operative in determining the train of his ideas was the complex image of a particular man. But now let us suppose that that selective agency of interested attention, which may convert in the way we have seen complete contiguous association into partial association—let us suppose that it refines itself still further and accentuates a portion of the passing thought, so small as to be no longer the image of a concrete thing, but only of an abstract quality or property. Let us, moreover, suppose that the part thus accentuated persists in consciousness (or, in cerebral terms, has its brain-process excited) after the other portions of the thought have faded. This small surviving portion will then surround itself with its own associates after the fashion we have already seen, and the relation between the new thought and the faded one will be a relation of similarity. The pair of thoughts will form an instance of what is called "Association by Similarity." To make this perfectly plain we must understand exactly what constitutes similarity between two things. The moon is similar to a gas-jet, it is also similar to a foot-ball; but a gas-jet and a foot-ball are not similar to each other. When we affirm the similarity of two things, we should always say in what respect it obtains. Moon and gas-jet are similar in respect of luminosity, and nothing else; moon and foot-ball in respect of rotundity, and nothing else. Foot-ball and gas-jet are in no respect similar—that is, they possess no common point, no identical attribute. Objects are really identical with each other in that point with respect to which they are called similar. Similarity is partial identity. When the same attribute appears in two phenomena, though it be their only common property, the two phenomena are similar in so far forth. To return now to our associated representations. If the thought of the moon is succeeded by the thought of a foot-ball, and that by the thought of one of Mr. Vanderbilt’s railroads, it is because the attribute rotundity in the moon broke away from all the rest and surrounded itself with an entirely new set of companions—elasticity, leathery integument, swift mobility in obedience to human caprice, etc.; and because the last-named attribute in the foot-ball in turn broke away from its companions, and, itself persisting, surrounded itself with such new attributes as make up the notions of a "railroad king," of a rising and falling stock-market, and the like.
The gradual passage from Complete Contiguous to Similar Association
through what we have called Partial Association may be symbolized by diagrams. Fig. 2 is Pure Contiguous, Fig. 3 is Mixed, and Fig. 4 Similar, Association. A in each is the passing, B the coming thought. In "Contiguous," all parts of A are equally operative in
calling up B. In "Mixed," most parts of A are inert. The part M alone breaks out and awakens B. In "Similar," the focalized part M is much smaller than in the previous case, and after awakening its
new set of associates, instead of fading out itself, it continues persistently active along with them, forming an identical part in the two ideas, and making these, pro tanto, resemble each other.
Why a single portion of the passing thought should break out from its concert with the rest and act, as we say, on its own hook, why the other parts should become inert, are mysteries which we can ascertain but not explain. Possibly a minuter insight into the laws of neural action will some day clear the matter up; possibly neural laws will not suffice, and we shall need to invoke a dynamic reaction of the form of consciousness upon its content. But into this we can not enter now.
Thus the difference between the three kinds of association reduces itself to a simple difference in the Amount of that portion of the nerve-tract supporting the going thought which is operative in calling up the thought which comes, but the modus operandi of this active part is the same, be it large or be it small.
The items constituting B waken in every instance because their nerve-tracts once were excited continuously with those of A or its operative part. This ultimate physiological law (supra, p. 583) is what runs the train. The direction of its course and the form of its transitions, whether contiguous or similar, are due to unknown regulative or determinative conditions which accomplish their effect by opening this switch and closing that, setting the engine sometimes at half speed, and coupling or uncoupling cars.
This last figure of speech affords itself an excellent instance of association by similarity. I was thinking of the deflections of the course of ideas. Now, from Hobbes’s time downward English writers have been fond of speaking of the train of our representations. This word happened to stand out in the midst of my complex thought with peculiarly sharp accentuation, and to surround itself with numerous details of railroad imagery. Only such details became clear, however, as had their nerve-tracts besieged by a double set of influences—those from train on the one hand, and those from the movement of thought on the other. It may possibly be that the prepotency of the suggestions of the word train at this moment were due to the recent excitation of the railroad brain-tract by the instance chosen a few pages back of a railroad king playing foot-ball with the stock-market.
It is apparent from such an example how inextricably complex are all the contributory factors whose resultant is the line of our reverie. It would be folly in most cases to attempt to trace them out. From an instance like the above, where the pivot of the Similar Association was formed by a definite concrete word, train, to those where it is so subtile as utterly to elude our analysis, the passage is unbroken. We can form a series of examples. When Mr. Bagehot says that the mind of the savage, so far from being in a state of nature, is tattooed all over with monstrous superstitions, the case is very like the one we have just been considering. When Sir James Stephen compares our belief in the uniformity of nature, the congruity of the future with the past, to a man rowing one way and looking another, and steering his boat by keeping her stern in a line with an object behind him, the operative link becomes harder to dissect out. It becomes a real puzzle when the color pale-blue is said to have feminine, and blood-red masculine affinities. And if I hear a friend describe a certain family as having voices like blotting-paper, the image, though immediately felt to be apposite, baffles the utmost powers of analysis. The higher poets all use abrupt epithets, which are alike intimate and remote, and, as Emerson says, sweetly torment us with invitations to their inaccessible homes.
In these latter instances we must suppose that there is an identical portion in the similar ideas and that it is energetically operative, without, however, being sufficiently accentuated in consciousness to stand out per se, attract the attention to itself and be abstracted. We can not even by careful search see the bridge over which we passed from the heart of one representation to that of the next. In some brains, however, this mode of transition it extremely common. It would be one of the most important of physiological discoveries could we assign the mechanical or chemical difference which makes the thoughts of one brain cling close to Pure Contiguity while those of another shoot about in all the lawless revelry of Similarity. Why in these latter brains action should tend to focalize itself in small spots, while in the others it fills patiently its broad bed, it seems impossible to guess. Whatever the difference may be, it is what separates the man of genius from the prosaic creature of habit and routine thinking. Professor Bain, more profusely and cogently than any one else, has illustrated the truth that the leading fact in what we call genius in every department of life is a high development of the power of Similar Association. I therefore refer the reader to his work on the "Study of Character," Chapter XV., and to Chapter II., sections 25 to 45, of the portion entitled "Intellect" of his treatise on "The Senses and the Intellect."
Into the study of voluntary trains of thought there is no space to enter. The student will find in Hodgson’s "Theory of Practice," vol. i., pp. 394-400, the best account with which I am acquainted. Meanwhile he will no doubt admit that the promise with which this article set out has been fulfilled, and that the processes of spontaneous association have become already a little more intelligible to his mind.