ASSOCIATION OF IDEAS, or MENTAL ASSOCIATION, is a general name used in psychology to express the con-ditions under which representations arise in consciousness, and also is the name of a principle of explanation put forward by an important school of thinkers to account generally for the facts of mental life. The more common expression, from the time of Locke, who seems to have first employed it, has been Association of Ideas; but it is allowed or urged on all hands that this phrase contains too narrow a reference; association, in either of the senses above noted, extending beyond ideas or thoughts proper to every class of mental states. In the long and erudite Note D**, appended by Sir W. Hamilton to his edition of Reid's Works, and offered as a contribution towards a history of the doctrine of mental suggestion or association, many anticipations of modern statements are cited from the works of ancient or mediaeval thinkers, and for Aristotle, in particular, the glory is claimed of having at once originated the doctrine and practically brought it to perfection. Aristotle's enunciation of the doctrine is certainly very remarkable. As translated by Hamilton, but without his interpolations, the classical passage from the tract Be Memoria et Reminiscentia runs as follows :
" When, therefore, we accomplish an act of reminiscence, we pass through a certain series of precursive movements, until we arrive at a movement on which the one we are in quest of is habi-tually consequent. Hence, too, it is that we hunt through the mental train, excogitating from the present or some other, and from similar or contrary or coadjacent. Through this process reminis-cence takes place. For the movements are, in these cases, some-times at the same time, sometimes parts of the same whole, so that the subsequent movement is already more than half accomplished."
The passage is obscure (leaving open to Hamilton to suggest a peculiar interpretation of it, that may be noticed in connection with the elaborate doctrine of association put forward by himself, as if to evince the shortcomings rather than the perfection of Aristotle's), but it does in any case indicate the various principles commonly termed Contiguity, Similarity, and Contrast; and, though the statement of these cannot be said to be followed up by an effective exposition or application, it quite equals in scope the observations of many a modern inquirer. Zeno the Stoic also, and Epicurus, according to the report of Diogenes Laertius (vii. § 52, x. § 32, overlooked by Hamilton), enumerated similar principles of mental associa-tion. By St Augustin, at the end of his long rhapsody on the wonders of memory in book x. of his Confessions, it was noted (c. 19) that the mind, when it tries to remember something it knows it has forgotten, has, as it were, hold of part and thence makes quest after the other part. Meanwhile and later, Aristotle's doctrine received a more or less intelligent expansion and illustration from the ancient commentators and the schoolmen ; and in the still later period of transition from the age of scholasticism to the time of modern philosophy, prolonged in the works of some writers far into the 17th century, Hamilton, from the stores of his learning, is able to adduce not a few philosophical authorities who gave prominence to the general fact of mental associationthe Spaniard Ludo-vicus Vives (1492-1540) especially being most exhaustive in his account of the conditions of memory. This act of justice, however, once rendered to earlier inquirers, it is to modern views of association that attention may fairly be confined.
In Hobbes's psychology so much importance is assigned to what he called, variously, thé succession, sequence, series, consequence, coherence, train, «fcc., of imaginations or thoughts in mental discourse, that he has not seldom been regarded, by those who did not look farther back, as the founder of the theory of mental association. He did, indeed, vividly conceive and illustrate the principle of Contiguity, but, as Hamilton conclusively shows, he repro-duced in his exposition but a part of the Aristotelian doctrine, nor even this without wavering ; representing the sequence of images, in such states as dreams, now (in his Human Nature) as casual or incoherent, now (in Levia-than), following Aristotle, as simply unguided. Not before Hume, among the moderns, is there express question as to a number of distinct principles of association. Locke had, meanwhile, introduced the phrase Association of Ideas as the title of a supplementary chapter incorporated with the fourth edition of his Essay, meaning it, however, only as the name of a principle accounting for the mental pecu-liarities of individuals, with little or no suggestion of its general psychological import. Of this last Hume had the strongest impression, and thinking himself, in forgetfuluess or ignorance of Aristotle's doctrine of reminiscence, the first inquirer that had ever attempted to enumerate all the modes of normal association among mental states, he brought them to threeEesemblance, Contiguity in time and place, Cause and (or) Effect. Without professing to arrive at this result otherwise than by an inductive con-sideration of instances, he yet believed his enumeration to be exhaustive, and sought to prove it so by resolving Contrastone of Aristotle's heads, commonly received as a mixture of causation and resemblance. Viewed in relation to his general philosophical position, it must always remain a perplexing feature of Hume's list of principles, that he specified Causation as a principle distinct from Contiguity in time, while otherwise the list has no superiority to Aristotle's. Hume's fellow-countrymen, Gerard and Beattie, in opposition to him, recurred accord-ingly to the traditional enumeration ; and, in like manner, Dugald J Stewart put forward Resemblance, Contrariety, and Vicinity in time and place, though he added, as another obvious principle, accidental coincidence in the sounds of Words, and farther noted three other cases of relation, namely, Cause and Effect, Means and End, and Premisses and Conclusion, as holding among the trains of thought under circumstances of special atten-tion. Reid, preceding Stewart, was rather disposed, for his own part, to make light of the subject of association, vaguely remarking that it seems to require no other original quality of mind but the power of habit to explain the spontaneous recurrence of trains of thinking, when become familiar by frequent repetition (Intellectual Bowers, p. 387). The counter-observation of his editor, Hamilton, that we can as well explain habit by association as association by habit, might with reason have been pointed more sharply.
Hamilton's own theory of mental reproduction, sugges-tion, or association, given in outline in Note D***. following the historical note before mentioned, at the end of his edition of Reid's Works, calls for more special notice, as perhaps the most elaborate expression yet devised for the principles involved in the phenomena of mental repre-sentation. It is a development, greatly modified, of the doctrine expounded in his Lectures on Metaphysics (vol. ii. p. 223, seq.), which in agreement with some foreign authorities, reduced the principles of association first to twoSimultaneity and Affinity, and these farther to one supreme principle of Redintegration or Totality. In the ultimate scheme he posits no less than four general laws of mental succession concerned in reproduction: (1.) Associa.-
bility or possible co-suggestion (all thoughts of the same mental subject are associable, or capable of suggesting each other); (2.) Repetition or direct remembrance (thoughts coidentical in modification, but differing in time, tend to suggest each other); (3.) Redintegration, direct remembrance or reminiscence (thoughts once coidentical in time, are, however, different as mental modes, again suggestive of each other, and that in the mutual order which they originally held); (4.) Preference (thoughts are suggested not merely by force of the general subjective relation subsisting between themselves, they are also suggested in proportion to the relation of interest, from whatever source, in which they stand to the individual mind). Upon these follow, as special laws :A, Primarymodes of the laws of Repetition and Redintegration(1), law of Similars (Analogy, Affinity); (2), law of Contrast; (3), law of Coadjacency (Cause and Effect, &c.); B, Secondarymodes of the law of Preference, under the law of Possibility(1), laws of Immediacy and Homogeneity; (2), law of Facility. Such is the scheme; and now may be understood what interpretation Hamilton desires to put upon Aristotle's doctrine, when he finds or seeks in it a parallel relation to that established by himself between the general laws, more especially Redintegration, and his special ones. But, though the commentary of The-mistius, which he cites, lends some kind of support to the position, it cannot be maintained without putting the greatest strain on Aristotle's language, and in one place it is as good as surrendered by Hamilton himself (footnote, p. 900, b). Nor is the ascription of such a meaning at all necessary to establish Aristotle's credit as regards the doctrine of mental association.
Thus far the principles of association have been con-sidered only as involved in mental reproduction and repre-sentation. There has grown up, however, especially in England, the psychological school above mentioned, which aims at explaining all mental acquisitions, and the more complex mental processes generally, under laws not other than those determining simple reproduction. Hamilton also, though professing, in the title of his outline just noticed, to deal with reproduction only, formulates a num-ber of still more general laws of mental successionlaw of Succession, law of Variation, law of Dependence, law of Relativity or Integration (involving law of Conditioned), and, finally, law of Intrinsic or Objective Relativityas the highest to which human consciousness is subject; but it is in a sense quite different that the psychologists of the so-called Associationist School intend their appropriation of the principle or principles commonly signalised. As far as can be judged from imperfect records, they were antici-pated to some extent by the experientialists of ancient times, both Stoic and Epicurean (cf. Diogenes Laertius, as above). In the modern period, Hobbes is the first thinker of permanent note to whom the doctrine may be traced. Though he took, as has been seen, anything but an exhaustive view of the phenomena of mental succession, yet, after dealing with trains of imagination, or what he called mental discourse, he sought in the higher depart-ments of intellect to explain reasoning as a discourse in words, dependent upon an arbitrary system of marks, each associated with, or standing for, a variety of imaginations; and, save for a general assertion that reasoning is a reckoningotherwise, a compounding and resolvinghe had no other account of knowledge to give. The whole emotional side of mind, or, in his language, the passions, he, in like manner, resolved into an expectation of consequences based on past experience of pleasures and pains of sense. Thus, though he made no serious attempt to justify his analysis in detail, he is undoubtedly to be classed with the associationists of the next centuryHartley and the others. They, however, were wont to trace the first
beginnings of their psychological theory no farther back than to Locke's Essay. If this seems strange, when Locke did little more than supply them with the word Association, it must be remembered in what ill repute the name of Hobbes stood, and also that Locke's work, though not directly concerned with the question of psychological development, being rather of metaphysical or logical import, was eminently psychological in spirit, and might fairly be held to contain in an implicit form the principle or principles evolved later by the associationists. P>erkeley, dealing, immediately after Locke and altogether in Locke's spirit, with the special psychological problem of visual perception, was driven to posit expressly a principle of suggestion or association in these terms :" That one idea may suggest another to the mind, it will suffice that they have been observed to go together, without any demonstra-tion of the necessity of their coexistence, or so much as knowing what it is that makes them so to coexist" (New Theory of Vision, § 25) ; and to support the obvious applica-tion of the principle to the case of the sensations of sight and touch before him, he constantly urged that association of sound and sense of language which the later school has always put in the foreground, whether as illustrating the principle in general or in explanation of the supreme importance of language for knowledge. It was natural, then, that Hume, coming after Berkeley, and assuming Berkeley's results, though he reverted to the larger inquiry of Locke, should be more explicit in his reference to association; and, not only explicit, he was original also, when he spoke of it as a " kind of attraction which in the mental world will be found to have as extraordinary effects as in the natural, and to show itself in as many and as various forms " (Human Nature, i. 1, § 4). Other inquirers were, in fact, appearing about the same time, who con-ceived of association with this breadth of view, and set themselves to track, as psychologists, its effects in detail.
Hartley's Observations on Man, published in 1749 (eleven years after the Human Nature, and one year after the better-known Inquiry, of Hume), opened the path for all the investigations of like nature that have since that time become so characteristic of the English name in psychology. According to his own statement, his attention was first turned to the subject about eighteen years before, through what he heard of an opinion of the " Rev. Mr Gay," that it was possible to deduce all our intellectual pleasures and pains from association. Gay is known only by a disserta-tion on the fundamental principles of virtue, prefixed, at first anonymously, in 1731, to Archdeacon (afterwards Bishop) Law's translation of King's Origin of Evil, wherein it was maintained, with considerable force, that by associa-tion the feelings belonging to ends may come to attach themselves to means, and give rise to action for the means as if they were ends, as seen (the instance has become a commonplace) in the passion for money-making. In this vein, but on a very different scale, Hartley proceeded to work. A physician by profession, and otherwise well versed in science, he sought to combine with an elaborate theory of mental association a minutely detailed hypothesis as to the corresponding action of the nervous system, based upon the suggestion of a vibratory motion within the nerves thrown out by Newton in the last paragraph of the Principia. So far, however, from promoting the acceptance of the psychological theory, this physical hypothesis proved to have rather the opposite effect, and it began to be dropped by Hartley's followers (as Priestley, in his abridged edition of the Observations, 1775) before it was seriously impugned from without. When it is studied in the original, and not taken upon the report of hostile critics, who would not, or could notat all events, who did not understand it, no little importance must still be accorded to
the first attempt, not seldom a curiously felicitous one, to carry through that parallelism of the physical and psychical, which since then has come to count for more and more in the science of mind. Nor should it be forgotten that Hartley himself, for all his paternal interest in the doctrine of vibrations, was careful to keep separate from its fortunes the cause of his other doctrine of mental association. Of this the point lay in no mere restatement, with new precision, of a principle of coherence among "ideas," but in its being taken as a clue by which to follow the progressive development of the mind's powers. Holding that mental states could be scientifically understood only as they were analysed, Hartley sought for a principle of synthesis to explain the complexity exhibited not only in trains of representative images, but alike in the most involved combinations of reasonings and (as Berkeley had seen) in the apparently simple phenomena of objective perception, as well as in the varied play of the emotions, or, again, in the manifold conscious adjustments of the motor system. One principle appeared to him sufficient for all, running, as enunciated for the simplest case, thus : "Any sensations A, B, C, &c, by being associated with one another a sufficient number of times, get such a power over the corresponding ideas (called by Hartley also ves-tiges, types, images) a, b, c, <fcc, that any one of the sensa-tions A, when impressed alone, shall be able to excite in the mind b, c, <fcc., the ideas of the rest." To render the principle applicable in the cases where the associated elements are neither sensations nor simple ideas of sensa-tions, Hartley's first care was to determine the conditions under which states other than these simplest ones have their rise in the mind, becoming the matter of ever higher and higher combinations. The principle itself supplied the key to the difficulty, when coupled with the notion, already implied in Berkeley's investigations, of a coales-cence of simple ideas of sensation into one complex idea, which may cease to bear any obvious relation to its con-stituents. So far from being content, like Hobbes, to make a rough generalisation to all mind from the phenomena of developed memory, as if these might be straightway assumed, Hartley made a point of referring them, in a subordinate place of their own, to his universal principle of mental synthesis. He expressly put forward the law of association, endued with such scope, as supplying what was wanting to Locke's doctrine in its more strictly psycho-logical aspect, and thus marks by his work a distinct advance on the line of development of the experiential philosophy.
The new doctrine received warm support from some, as Law and Priestley, who both, like Hume and Hartley him-self, took the principle of association as having the like import for the science of mind that gravitation had acquired for the science of matter. The principle began also, if not always with direct reference to Hartley, yet, doubtless, owing to his impressive advocacy of it, to be applied systematically in special directions, as by Tucker (1768) to morals, and by Alison (1790) to aesthetics. Thomas Brown (d. 1820) subjected anew to discussion the question of theory. Hardly less unjust to Hartley than Reid or Stewart had been, and forward to proclaim all that was different in his own position, Brown must yet be ranked with the associationists before and after him for the prominence he assigned to the associative principle in sense-perception (what he called external affections of mind), and for his reference of all other mental states (internal affections) to the two generic capacities or susceptibilities of Simple and Relative Suggestion. He preferred the word Suggestion to Association, which seemed to him to imply some prior con-necting process, whereof there was no evidence in many of the most important Gases of suggestion, nor even, strictly speaking, in the case of contiguity in time where the term seemed least inapplicable. According to him, all that could be assumed was a general constitutional tendency of the mind to exist successively in states that have certain re-lations to each other, of itself only, and without any external cause or any influence previous to that operating at the moment of the suggestion. Brown's chief contribution to the general doctrine of mental association, besides what he did for the theory of perception, was, perhaps, his analysis of voluntary reminiscence and constructive imagination faculties that appear at first sight to lie altogether beyond the explanatory range of the principle. In James Mill's Analysis of the Phenomena of the Human Mind (1829), the principle, much as Hartley had conceived it, was carried out, with characteristic consequence, over the psychological field. With a much enlarged and more varied conception of association, Professor Bain has re-executed the general psychological task in the present generation, while Mr Herbert Spencer has revised the doctrine from the uew point of view of the evolution-hypothesis. John Stuart Mill made only occasional excursions into the region of psychology proper, but sought, in his System of Logic (1843), to determine the conditions of objective truth from the point of view of the associationist theory, and, thus or otherwise being/lrawn into general philosophical discussion, spread wider than any one before him its repute.
It is remarkable that the Associationist School has been composed chiefly of British thinkers, but in France also it has had distinguished representatives. Of these it will suffice to mention Condillac, the author of the sensationalist movement in the 18th century, who professed to explain all knowledge from the single principle of association (liaison) of ideas, operating through a previous association with signs, verbal or other. At the present day the later English school counts important adherents among the younger French thinkers. In Germany, before the time of Kant, mental association was generally treated in the traditional manner, as by Wolff. Kant's inquiry into the foundations of knowledge, agreeing in its general purport with Locke's, however it differed in its critical procedure, brought him face to face with the newer doctrine that had been grafted on Locke's philosophy; and to account for the fact of synthesis in cognition, in express opposition to associationism, as represented by Hume, was, in truth, his prime object, starting, as he did, from the assump-tion that there was that in knowledge which no mere association of experiences could explain. To the extent, therefore, that his influence prevailed, all such inquiries as the English associationists went on to prosecute were discounted in Germany. Notwithstanding, under the very shadow of his authority a corresponding, if not related, movement was initiated by Herbart. Peculiar, and widely different from anything conceived by the associationists, as Herbart's metaphysical opinions were, he was at one with them, and at variance with Kant, in assigning fundamental importance to the psychological investigation of the develop-ment of consciousness, nor was his conception of the laws determining the interaction and flow of mental presentations and representations, when taken in its bare psychological im-port, essentially different from theirs. In Beneke's psycho-logy also, and in more recent inquiries conducted mainly by physiologists, mental association has been understood in its wider scope, as a general principle of explanation.
Associationists differ not a little among themselves in the statement of their principle, or, when they adduce several principles, in their conception of the relative importance of these. Hartley took account only of Con-tiguity, or the repetition of impressions synchronous or immediately successive; and the like is true of James Mill, though, incidentally, he made an express attempt to
resolve the received principle of Similarity, and through this the other principle of Contrast, into his fundamental lawlaw of Frequency, as he sometimes called it, because upon frequency, in conjunction with vividness of impres-sions, the strength of association, in his view, depended. In a sense of his own, Brown also, while accepting the common Aristotelian enumeration of principles, inclined to the opinion that " all suggestion may be found to depend on prior coexistence, or at least on such proximity as is itself very probably a modification of coexistence," provided account be taken of " the influence of emotions and other feeliugs that are very different from ideas, as when an analogous object suggests an analogous object by the influence of an emotion which each separately may have produced before, and which is, therefore, common to both." (Upon which view it obviously occurs to remark, that, except in the particular case, plainly not intended, where the objects are experienced in actual succession with the emotion common to both, a suggestion through similar emotions must still be presumed.) To the contrary effect, Mr Spencer maintains that the fundamental law of all mental association is that presentations aggregate or cohere with their like in past experience, and that, besides this law, there is in strictness no other, all further phenomena of association being incidental. Thus in particular, he would explain association by Contiguity as due to the circumstance of imperfect assimilation of the present to the past in consciousness; a presentation in as far as it is distinctly cognised is in fact recognised through cohering with its like in past experience, but there is always, in consequence of the imperfection of our perceptions, a certain range within which the classing of the present experience with past is doubtfula certain cluster of rela-tions nearly like the one perceived, which become nascent in consciousness in the act of assimilation; now contiguity is likeness of relation in time or in space, or in both, and, when the classing, which, as long as it is general, goes easily and infallibly forward, becomes specific, a presenta-tion may well arouse the merely contiguous, instead of the identical, from former experience. Midway between these opposed views should be noted, finally, the position of Professor Bain, who regards Contiguity and Similarity, logically, as perfectly distinct principles, though in actual psychological occurrence they blend intimately with each other; contiguous trains being started by a first (it may be, implicit) representation through Similarity, while the express assimilation of present to past in consciousness is always, or tends to be, followed by the revival of what was presented in contiguity with that past.
That Similarity is an ultimate ground, of mental associa-tion cannot seriously be questioned, and to neglect or discount it, in the manner of the older representatives of the school, is to render the associationist theory quite inadequate for purposes of general psychological explana-tion. It is simply impossible to over-rate the importance of the principle, and, when Mr Spencer, by way of supporting his position, maintains farther, that the psychological fact of conscious assimilation corresponds with the fundamen-tally simple physiological fact of re-excitation of the same nervous structures, the force as well as pertinence of the observation is at once evident. Nevertheless, it is one question whether a representation, upon a particular occasion, shall be evoked by Similarity, and another question what shall be raised into consciousness along with it; nor for this is there any help but in positing a distinct principle of Contiguity. The phenomena of presentative cognition or objective perception on which Mr Spencer bases his argument, are precisely those in which the function of Contiguity is least explicitly mani-fested, but only because of the certainty and fixity it has assumed through the great uniformity and trequency of such experience. Let the series of presentative elements, as in formal education, be less constant in composition, and less frequently recurrent, than are those aggregates of sensible impressions that, in the natural course of experi-ence, become to us objects in space with a character com paratively fixed, and then the function of Contiguity starts-out with sufficient prominence, being found as often as not to fail in determining a revival of the corresponding repre-sentative series. All the phenomena, too, of coalescence, in which a variety of elements become fused to a result in consciousness as heterogeneous as any chemical compound in relation to its constituentsphenomena that have re-mained the very property of the Associationist School since they first were distinctly noted by Hartleyhow are these to be explained by the principle of Similarity 1 Involved as it incontestably is in every repeated apprehension, whether of the elements, or of the product, or of the relation between them, Similarity of itself is powerless to determine a relation the essence of which lies not more in the hetero-geneous character of the result than in the diversity of the elements brought together. Nor, in order to support the claim of the principle of Contiguity to an equally funda-mental position with that of Similarity, is it more difficult to find an expression in terms of physiology corresponding with the subjective process. The fact that different nerve-centres are excited together, synchronously or successively, along definite lines of connection, will leave them, being so connected, in a state of relative instability, which, other things equal, will vary in proportion to the frequency and strength of the excitation ; and thus, when one of them is, in whatever way, again aroused, the rest will tend to be re-affected also by reason of the instability that has remained. The process of psychological representation, running parallel with the nervous events here supposed, involves assimilation at every stage from and including the first ; it is also con-stantly happening, in contiguous trains, that a break occurs at a particular stage through an express suggestion, by Similarity, of something foreign to the train. But in the one case, as in the otheralike coincident with the implicit action of Similarity, and in the pauses of express assimila-tionthe principle of Contiguity has a part to play, not to be denied or confounded with any other.
A minor question, also disputed, is whether by the side of Contiguity and Similarity, Contrast should be held, as by Aristotle, an independent principle of association. That things contrasted may and do often suggest each other in consciousness iB on all hands allowed, but ever since Hume attempted, however infelicitously, to resolve the principle into others, its independence has not ceased to lie under sus-picion. When the question is approached without preju-dice, it cannot but appear strange that mental states which suggest each other because of likeness, should suggest each other because of unlikeness also. In that case anything might suggest everything else, since like and unlike con-scious states are all that are possible ; nay, unlike states alone are all, as there must always be some difference be tween any two. Now it is true, in one sense, that anything may suggest anything be it ever so unlike, namely, if the things have been once or repeatedly experienced in con-junction ; but then the bond of association is the contiguity, and not the unlikeness, which obviously cannot be a ground for suggesting this one other thing more than any other thing. By contrast, however, is not generally meant bare unlikeness. Genuine contrasts, as black-white, giant-dwarf, up-down, are peculiar in having under the difference a foundation of similarity, the two members lying within the sphere of a common higher notion, and only being distin-guished the more impressively by reason of the accompany-ing unlikeness. Clearly, in the case of mutual suggestion,
if it be not the similarity itself that is here the ground of association, it may again be Contiguity, the sharpest expe-rience of each member of the contrast having been when there was experience also of the other ; or both grounds may conspire towards the result, the association being then what Professor Bain has marked as Compound. On the whole, it must be concluded that only in a secondary sense can Contrast be admitted as a principle of mental association.
The highest philosophical interest, as distinguished from that whic uore strictly psychological, attaches to the mode of mental association called Inseparable. The coales-cence of mental states noted by Hartley, as it had been assumed by Berkeley, was farther formulated by James Mill in these terms :
" Some ideas are by frequency and strength of association so closely combined that they cannot be separated ; if one exists, the other exists along with it in spite of whatever effort we make to disjoin them."(Analysis of the Human Mind, 2d ed. voL i. p. 93.)
J- S. Mill's statement is more guarded and particular :
" When two phenomena have been very often experienced in eon-Junction, and have not, in any single instance, occurred separately either in experience or in thought, there is produced between them what has beeD called inseparable, or, less correctly, indissoluble, association ; by which is not meant that the association must inevitably last to the end of lifethat no subsequent experience or process of thought can possibly avail to dissolve it ; but only that as long as no such experience or process of thought has taken place, the association is irresistible ; it is impossible for us to think the one thing disjoined from the other. "(Examination of Hamilton's Philo-sophy, 2d ed. p. 191.)
Even this statement, however, is somewhat lacking in precision, since there never is any impossibility of thinking the things apart, in the sense of considering them as logi-cally distinct ; the very fact of association implies at least such distinctness, while there may be evident, besides, a positive difference of psychological origin, as when, in the case of visual extension, the colour of the field is referred to the passive sensibility of the eye, and the expanse to it3 mobility. The impossibility is of representation apart, not of logical consideration or thought. It is chiefly by J. S. Mill that the philosophical application of the principle has been made. The first and most obvious application is to so-called necessary truthssuch, namely, as are not merely ana-lytic judgments but involve a synthesis of distinct notions. Again, the same thinker has sought, in the work just cited, to prove Inseparable Association the ground of belief in an external objective world. The former application, especially, is facilitated, when the experience through which the associa-tion is supposed to be constituted is understood as cumula tive in the race, and transmissible as original endowment to individualsendowment that may be expressed either, subjectively, as latent intelligence, or, objectively, as fixed nervous connections. Mr Spencer, as before suggested, is the author of this extended view of mental association.
For a detailed exposition of the psychological theory of the Associationist School, the reader is referred to the works of its latest representatives named above. The question is still under discussion, how far the theory avails to account for the facts of intelligence, not to say the complex phases of mental life in general in all their variety ; nor, were the theory carried out farther than it has yet been by any one, and formulated in terms com-manding more general assent than any expression of it has yet obtained even from professed adherents, is it likely to be raised above dispute. Yet it must be allowed to stand forward with a special claim to the scientific charac-ter ; as already in his time Laplace (who, though an outsider, could well judge) bore witness, when, speaking of the principle of association (Contiguity) as applied to the explanation of knowledge, he declared it la partie réelle de la métaphysique (Essai phil. sur Us Probabilités, uvres, vol. vii p. cxxxvii.) If in the physical sciences the object of the inquirer is confined to establishing laws expressive of the relations subsisting amongst phenomena, then, however different be the internal world of mindhowever short such treatment may seem to come of expressing the depth and fulness even of its phenomenal naturea corresponding object is as much as the scientific psychologist can well set to himself. The laws of association express undoubted relations holding among particular mental states, that are the real or actual facts with which
the psychologist has to deal, and it becomes a strictly scientific task to inquire how far the whole complexity of the internal life may receive an explanation therefrom. Understood in this sense, Hume's likening of the laws of mental association to the principle of gravitation in external nature L perfectly justifiable. It is to the credit of the associationists to have grasped early, and steadily maintained, such a conception of psychological inquiry, and, whatever their defects of execution may have been or remain, their work retains a permanent value as a serious attempt to get beyond barren description of abstract mental faculties to real and effective explanation. The psychologists that, in the related point of view, have earned the title of the Analytical School, from holding before their eyes the exemplar of the method of the positive sciences, are precisely those that have fastened upon the principles of association as the ground of mental synthesis ; and, till it is shown that the whole method of procedure is inapplicable to such a subject as mind, their conception is entitled to rank as a truly scientific one. (0. 0. B.)