CHAPTER XVI.

ASSOCIATION.

The Order of our Ideas.-After discrimination, association! It is obvious that all advance in knowledge must consist of both operations; for in the course of our education, objects at first appearing as wholes are analyzed into parts, and objects appearing separately are brought together and appear as new compound wholes to the mind. Analysis and synthesis are thus the incessantly alternating mental activities, a stroke of the one preparing the way for a stroke of the other, much as, in walking, a man's two legs are alternately brought into use, both being indispensable for any orderly advance.

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 perfect naturalness and propriety—all this magical, imponderable streaming has from time immemorial excited the admiration of all whose attention happened to be caught by its omnipresent mystery. And it has furthermore challenged the race of philosophers to banish something of the mystery by formulating the process in simpler terms. The problem which the philosophers have set themselves is that of ascertaining, between the thoughts which thus appear to sprout one out of the other, principles of connection whereby their peculiar succession or coexistence may be explained.

But immediately an ambiguity arises: which sort of

connection is meant ? connection thought-of, or connection between thoughts? These are two entirely different things, and only in the case of one of them is there any hope of finding principles.' The jungle of connections thought of can never be formulated simply. Every conceivable connection may be thought of-of coexistence, succession, resemblance, contrast, contradiction, cause and effect, means and end, genus and species, part and whole, substance and property, early and late, large and small, landlord and tenant, master and servant,-Heaven knows what, for the list is literally inexhaustible. The only simplification which could possibly be aimed at would be the reduction of the relations to a small number of types, like those which some authors call the categories' of the understanding. According as we followed one category or another we should sweep, from any object with our thought, in this way or in that, to others. Were this the sort of connection sought between one moment of our thinking and another, our chapter might end here. For the only summary description of these categories is that they are all thinkable relations, and that the mind proceeds from one object to another by some intelligible path.

Is it determined by any laws? But as a matter of fact, What determines the particular path? Why do we at a given time and place proceed to think of b if we have just thought of a, and at another time and place why do we think, not of b, but of c? Why do we spend years straining after a certain scientific or practical problem, but all in vain—our thought unable 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?

The truth must be admitted that thought works under strange conditions. Pure reason' is only one out of a

Who

thousand possibilities in the thinking of each of us. 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 opinions constitute a less bulky part of his mental furniture than his clarified beliefs? And yet, the mode of genesis of the worthy and the worthless in our thinking seems the same.

The laws are cerebral laws. There seem to be mechanical conditions on which thought depends, and which, to say the least, determine the order in which the objects for her comparisons and selections are presented. 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 also come from the same mechanical source as those which hinder it. Hartley accordingly suggested habit as a sufficient explanation of the sequence of our thoughts, and in so doing planted himself squarely upon the properly causal aspect of the problem, and sought to treat both rational and irrational associations from a single point of view. How does a man come, after having the thought of A, to have the thought of B the next moment? or how does he come to think A and B always together? These were the phenomena which Hartley undertook to explain by cerebral physiology. I believe that he was, in essential respects, on the right track, and I propose simply to revise his conclusions by the aid of distinctions which he did not make.

Objects are associated, not ideas. We shall avoid con

fusion if we consistently speak as if association, so far as the word stands for an effect, were between THINGS THOUGHT OF-as if it were THINGS, not ideas, which are associated in the mind. We shall talk of the association of objects, not of the association of ideas. And so far as association stands for a cause, it is between processes in the brain— it is these which, by being associated in certain ways, determine what successive objects shall be thought.

The Elementary Principle.-I shall now try to show that there is no other elementary causal law of association 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 whatever other elementary process it may have excited at any 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 association by similarity, or contrast, or whatever other sorts we may have recognized as ultimate. Its production, however, is, in each one of these cases, to be explained by a merely quantitative variation in the elementary brain-processes momentarily at work under the law of habit.

My thesis, stated thus briefly, will soon become more clear; and at the same time certain disturbing factors, which coöperate 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 of them, on re-occurring, tends to propagate its excitement into the other.

But, as a matter of fact, every elementary process has unavoidably found itself at different times excited in con

junction with many other processes. Which of these others it shall awaken now becomes a problem. Shall bor c be aroused next by the present a? To answer this, we must make a further postulate, based 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 (see p. 128). 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 braincortex 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 excitements; and (3) to the absence of any rival point 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. 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.

Spontaneous Trains of Thought.-Take, to fix our ideas, the two verses from Locksley Hall':

and

"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