The Principles of Psychology, Vols. 1-2

of the laws of habit in the nervous system; in other words, it is to ascribe it to a physiological cause. If it be truly a law of those nerve-centres which co-ordinate sensory and motor processes together that paths once used for coupling any pair of them are thereby made more permea ble, there appears no reason why the same law should not hold good of ideational centres and their coupling-paths as well.* Parts of these centres which have once been in action together will thus grow so linked that excitement at one point will irradiate through the system. The chances of complete irradiation will be strong in proportion as the previous excitements have been frequent, and as the present points excited afresh are numerous. If all points were originally excited together, the irradiation may be sensibly simultaneous throughout the system, when any single point or group of points is touched off. But where the original impressions were successive — the conjugation of

* The difficulty here as with habit uberJiaupl is in seeing how new paths come first to be formed (cf. above, 109). Experience shows that a new path is formed between centres for sensible impressions whenever these vibrate together or in rapid succession. A child sees a certain bottle and hears it called ' milk,' and thenceforward thinks the name when he again sees the bottle. But why the successive or simultaneous excitement of two centres independently stimulated from without, one by sight and the other by hearing, should result in a path between them, one does not im mediately see. We can only make hypotheses. Any hypothesis of the specific mode of their formation which tallies well with the observed facts of association will be in so far forth credible, in spite of possible obscurity. Herr Mimsterberg thinks (Beitriige zur exp. Psychologic, Heft 1, p. 132) that between centres excited successively from without no path ought to be formed, and that consequently all contiguous association is between simultaneous experiences. Mr. Ward (loc. cit.) thinks, on the contrary, that it can only be between successive experiences : " The association of objects simultaneously presented can be resolved into an association of objects successively attended to. ... It seems hardly possible to mention a case in which attention to the associated objects could not have been successive. In fact, an aggregate of objects on which attention could be focussed at once vrould be already associated." Between these extreme possibilities, I have refrained from deciding in the text, and have described contiguous association as holding between both successively and coexistently pre sented objects. The physiological question as to how we may conceive the paths to originate had better be postponed till it comes to us again in the chapter on the Will, where we can treat it in a broader way.

It is enough here to have called attention to it as a serious problem. a Greek verb, for example— awakening nerve-tracts in a definite order, they will now, when one of them awakens, discharge into each other in that definite order and in no other way. The reader will recollect all that has been said of in creased tension in nerve-tracts and of the summation of stimuli (p. 82 ff.). We must therefore suppose that in these ideational tracts as well as elsewhere, activity may be awakened, in any particular locality, by the summation therein of a number of tensions, each incapable alone of provoking an actual discharge. Suppose for example the locality M to be in functional continuity with four other localities, K, L, N, and O. Suppose moreover that on four previous occasions it has been separately combined with each of these localities in a common activity. M may then be indirectly awakened by any cause which tends to awaken either K, L, N, or O. But if the cause which awakens K, for instance, be so slight as only to increase its tension without arousing it to full discharge, K will only succeed in slightly increasing the tension of M. But if at the same time the tensions of L, N, and O are simi larly increased, the combined effects of all four upon M may be so great as to awaken an actual discharge in this latter locality. In like manner if the paths between M and the four other localities have been so slightly excavated by previous experience as to require a very intense excitement in either of the localities before M can be awakened, a less strong excitement than this in any one will fail to reach M. But if all four at once are mildly excited, their com pound effect on M may be adequate to its full arousal.

The psychological law of association of objects thought of through their previous contiguity in thought or experience would tJirts lie an effect, within the mind, of the physical fart that nerve-currents propayaic themselvex easiest through those tracts of conduction which have been already most in use. Des cartes and Locke hit upon this explanation, which modern science has not yet succeeded in improving. "Custom," says Lycke, "settles habits of thinking in the under standing, as well as of determining in the will, and of motions in tinbody ; all which seem to l>c but trains of motion in the animal sjiirftn

[by this Locke meant identically what we understand by neural pro cesses] 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." * Hartley was more thorough in his grasp of tlie prin ciple. The sensorial nerve-currents, produced when objects are fully present, were for him * vibrations/ and those which produce ideas of objects in their absence were ' miniature vibrations.' And he sums up the cause of mental associa tion in a single formula by saying :

"Any vibrations, A, B, C, etc., by being associated together a suffi cient Number of Times, get such a Power over a, b, c, etc. , the corre sponding Miniature Vibrations, that any of the Vibrations A, when impressed alone, shall be able to excite 6, c, etc., the Miniatures of the rest."f It is evident that if there be any law of neural habit similar to this, the contiguities, coexistences, and succes sions, met with in outer experience, must inevitably be copied more or less perfectly in our thought. If A B C D E be a sequence of outer impressions (they may be events

* Essay, bk. n. chap, xxxin. § 6. Compare Hume, who, like Locke, only uses the principle to account for unreasonable and obstructive mental associations : " 'Twould have been easy to have made an imaginary dissection of the brain, and have shown why, upon our conception of any idea, the animal spirits run into all the contiguous traces, and rouse up the other ideas that are related to it. But though I have neglected any advantage which I might have drawn from this topic in explaining the relations of ideas, I am afraid I must here have recourse to it, in order to account for the mistakes that arise from these relations. I shall therefore observe, that as the mind is endowed with a power of exciting any idea it pleases ; whenever it dis patches the spirits into that region of the brain in which the idea is placed, these spirits always excite the idea, when they run precisely into the propel1 traces, and rummage that cell which belongs to the idea. But as their mo tion is seldom direct, and naturally turns a little to the one side or the other: for this reason the animal spirits, falling into the contiguous traces, pre sent other related ideas in lieu of that which the mind desired at first to survey. This change we are not always sensible of ; but continuing still the same train of thought, make use of the related idea which is presented to us, and employ it in our reasoning, as if it were the same with what we demanded. This is the cause of many mistakes and sophisms in philoso phy; as will naturally be imagined, and as it would be easy to show, if there was occasion."

or they may be successively experienced properties of an object) which once gave rise to the successive ' ideas,'a bcde, then no sooner will A impress us again and awaken the a, than bode will arise as ideas even before BCDE have come in as impressions. In other words, the order of impressions will the next time be anticipated ; and the men tal order will so far forth copy the order of the outerworld. Any object when met again will make us expect its tormer concomitants, through the overflowing of its braintract into the paths which lead to theirs. And all these suggestions will be effects of a material law.

Where the associations are, as here, of successively ap pearing things, the distinction I made at the outset of the chapter, between a connection thought of and a connection of thoughts, is unimportant. For the connection thought of is concomitance or succession ; and the connection between the thoughts is just the same. The ' objects ' and the * ideas ' fit into parallel schemes, and may be described in identical language, as contiguous things tending to be thought again together, or contiguous ideas tending to recur together.

Now were these cases fair samples of all association, the distinction I drew might well be termed a Spitzfindigkeit or piece of pedantic hair-splitting, and be dropped. But as a matter of fact we cannot treat the subject so simply. The same outer object may suggest either of many realities for merly associated with it — for in the vicissitudes of our outer experience we are constantly liable to meet the same thing in the midst of differing companions — and a philosophy of association that should merely say that it will suggest one of these, or even of that one of them which it has oftenest accompanied, would go but a very short way into the ra tionale of the subject. This, however, is about as far as most associationists have gone with their ' principle of con tiguity.' Granted an object, A, they never tell us before hand which of its associates it will suggest ; their wisdom is limited to showing, after it has suggested a second object, that that object was once an associate. They have had to supplement their principle of Contiguity by other priuci-

pies, such as those of Similarity and Contrast, before could begin to do justice to the richness of the facts. I shall try to show, in the pages which immediately follow, that there is no other elementary causal law of asso ciation than the law of neural habit. All the materials of our thought are due to the way in which one elementary process of the cerebral hemispheres tends to excite what ever other elementary process it may have excited at some former time. The number of elementary processes at work, however, and the nature of those which at any time are fully effective in rousing the others, determine the character of the total brain-action, and, as a consequence of this, they determine the object thought of at the time. According as this resultant object is one thing or another, we call it a product of association by contiguity or of as sociation by similarity, or contrast, or whatever other sorts we may have recognized as ultimate. Its production, how ever, is, in each one of these cases, to be explained by a merely quantitative variation in the elementary brain-pro cesses momentarily at work under the law of habit, so that psychic contiguity, similarity, etc., are derivatives of a sin gle profounder kind of fact.

My thesis, stated thus briefly, will soon become more clear ; and at the same time certain disturbing factors, which co-operate with the law of neural habit, will come to view. Let us then assume as the basis of all our subsequent reasoning this law : When two elementary brain-processes have been active together or in immediate succession, one oj them, on reoccurring, tends to propagate its excitement into the other. But, as a matter of fact, every elementary process has found itself at different times excited in conjunction with many other processes, and this by unavoidable outward causes. Which of these others it shall awaken now be comes a problem. Shall b or c be aroused next by the present a ? We must make a further postulate, based, how ever, on the fact of tension in nerve-tissue, and on the fact

of summation of excitements, each incomplete or latent in itself, into an open resultant* The process 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-cor tex 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 accompanied that of the point in question; (2) to the intensity of such excite ments ; and (3) to the absence of any rival point functionally disconnected with the first point, into ivhich the discharges might be diverted.

Expressing the fundamental law in this most compli cated way leads to the greatest ultimate simplification. Let us, for the present, only treat of spontaneous trains of thought and ideation, such as occur in revery or musing. The case of voluntary thinking toward a certain end shall come up later. Take, to fix our ideas, the two verses from ' Locksley Kail ' : "I, the heir of all the ages in the foremost tiles of time," and — " For I doubt not through the ages one increasing purpose runs."

Why is it that when we recite horn 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 fol lows the ages has its brain-process awakened not simply by the brain-process of the ages alone, but by it plus the brainprocesses of all the words preceding the ages. The word ages at its moment of strongest activity would, per se, indif ferently 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 dis-

charge into either of a large number ol other words with which they have been at different times combined. But when the processes of ' /, the heir of all the ages,' simul taneously vibrate in «he brain, the last one of them in a maximal, the others in a fading phase of excitement ; then the strongest line of discharge will be that which they all alike tend to take. ' In ' and not ' one ' or any other word wi]l be the next to awaken, for its brain-process has previ ously vibrated in unison not only with that of ages, but with that of all those other words whose activity is dying away. It is a good case of the effectiveness over thought of what we called on p. 258 a ' fringe.'

But if some one of these preceding words — 'heir,' for example — had an intensely strong association with some brain-tracts entirely disjoined in experience from the poem of ' Locksley Hall ' — if the reciter, for instance, were tremu lously awaiting the opening of a will which might make him a millionaire — it is probable that the path of discharge through the words of the poem would be suddenly inter rupted at the word * heir.' His emotional interest in that word would be such that its own special associations ivoidd 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 alphabeti cal order in a lecture-room. He finally learns to call them by name, as they sit in their accustomed places. On meet ing one in the street, however, 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 con sequently his general alphabetical position ; and then, usually as the common associate of all these combined data, the student's name surges up in his 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 re ply, from which the child cannot 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-f or answer, " I calls it vertical." All the concomitants of the Kindergarten ex perience had to recombine their effect before the word ' vertical ' could be reawakened.

Professor Bain, in his chapters on ' Compound Associa tion,' 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 con crete 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 in stance, be the elementary nerve-tracts excited by the last act 01 the dinner-party, call this act A, and I, 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, 65 c, d, e, will each and all discharge into I through the paths by which their original discharge took place. Similarly they will discharge into w, n3 o, and p ; and these latter tracts will also each reinforce the other's action because, in the experience B, they have already vibrated in unison. The lines in Fig. 40, p. 570, 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 y to desig nate all association. Such processes as we have just de- *I strongly advise the student to read his Sense* and Intellect, pp. 544- scribed might in an emphatic sense be termed redintegra tions, 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 redintegra tion 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 elemen tary brain-tracts to discharge independently into an aber rant 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. Let us call this process impartial redintegration. Whether it ever occurs in an 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 gar rulous old women, those dry and fanciless beings who spare you no detail, however petty, of the facts they are recount ing, and upon the thread of whose narrative all the irrele vant items cluster as pertinaciously as the essential ones,

the slaves of literal fact, the stumblers over tlie 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 char acters 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 ' Em- nia.' Hear how she redintegrates :

u ' 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 cannot 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 Fatty 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 1 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 Hawtins—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 con sists 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 contempla tion.

This case helps us to understand why it is that the ordinary spontaneous flow of our ideas does not foHow the law of impartial redintegration. In no revival of a past ex perience are all the items of our thought equally operative in determining ivliat the next thought shall be. Always some in gredient 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 revery. Just as in the original sensible experience our attention focalized it self upon a few of the impressions of the scene before us, so here in the reproduction of those impressions an equal partiality is shown, and some items are emphasized above the rest. What these items shall be is, in most cases of spontaneous revery, hard to determine beforehand. In subjective terms we say that the prepotent items are those which appeal most

Expressed in brain-terms, the law of interest will be : some one brain-process is alivays prepotent above its concomi tants 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 repre sentation remains long before consciousness in the same state, but fades, decays, and becomes indistinct. Those parts of the object, how ever, which possess an interest resist this tendency to gradual decay of the whole object. . . . This inequality in the object — some parts, the un interesting, 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. * Time and Space, p. 266. Compare Coleridge : " The true practical general lav/ of association is this : that whatever makes certain parts of a total impression more vivid or distinct than the rest will determine the mind to recall these, in preference to others equally linked together by the com mon condition of contemporneity or of contiguity. But the will itself, by confining and intensifying the attention, may arbitrarily give vividness or distinctness to any object whatsoever. " (Biographia Litteraria, Chap. V.)

our musings pursue an erratic course, swerving continu ally into some new direction traced by the shifting play of interest as it ever falls on some partial item in each complex representation that is evoked. Thus it so often comes about that we find ourselves thinking at two nearly adjacent moments of things separated by the whole diam eter 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 (1879), I found myself thinking of a recent resolution in the Senate about our legal-tender notes. The clock called up the image of the man who had repaired its gong. He suggested the jeweller'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 beau tiful tone, it had become discordant and aroused disap pointment. But for this the clock might have suggested the friend who gave it to me, or any one of a thousand cir cumstances connected with clocks. The jeweller'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 conti guity 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 Another example of it is given by Hobbes in a passage which has been quoted so often as to be classical :