resolve the received principle of Similarity, and through this the other principle of Contrast, into his fundamental law law 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 feelings 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 doubtful a 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, aud 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 frequency 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 f 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 constituents phenomena that have re mained the very property of the Associationist School since they first were distinctly noted by Hartley how 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 other alike coincident with the implicit action of Similarity, and in the pauses of express assimila tion the principle of Contiguity has a part to play, not to be denied or confounded with any other.
Contiguity and Similarity, Contrast should be held, as by Aristotle, an independent principle of association. Thafc things contrasted may and do often suggest each other in consciousness is on all hands allowed, but ever since Hume attempted, however iufelicitously, 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 sta f es 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, arid 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 bara 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-
in"- unlikeness. Clearly, in the case of mutual suggestion,