lectual elaboration is known as Assimilation. This may be defined provisionally and roughly as the process by which like sensations or other psychical contents "attract" one another and tend to combine or coalesce. In its higher form it involves a "consciousness" or apprehension of a relation of similarity, and thus becomes one of the two leading intellectual functions co-ordinate with conscious discrimination or the apprehension of difference. As a bringing together and a combining of presentative elements assimilation is clearly opposed to differentiation, which in itself tends to a marking off and isolating of psychical contents. All assimilation is thus a mode of uniting or integrating. As we shall see later on, similarity is one great bond of connexion between presentations.

When we say that assimilation is the conjoining of like sensations, we mean by likeness any degree of similarity from the lowest degree of imperfect likeness which is just perceptible. up to perfect likeness or psychical 'equality'. Two sensations may be appreciably like one another yet far from quite or completely similar, as in the case of two adjacent members of the colour- or tone-scale or two adjacent sounds in the scale of intensity or loudness. The relation of likeness is here regarded as a perfectly simple and fundamental relation, co-ordinate with dissimilarity or difference. Perfect likeness, it may be added, whether of quality or of intensity, must be estimated for practical purposes by indistinguishableness when attention is closely directed to the sensations.

It may of course be said, as by Stumpf, that two sensations are never precisely similar or “equal” (gleich), and that consequently we must suppose the sensations which appear even to the severest exertion of attention as indistinguishable to be in reality dissimilar in a measure. This, however, is a subtle point not easily disposed of. We cannot, it is obvious, say that because two physical stimuli are in some degree different in form or energy the central nervous processes must be so also: for certain minimal differences in the stimuli may be inoperative on the central substance. Stumpf's idea is, moreover, beset with the difficulties that attend all theories of sensational content as something absolutely apart and independent of consciousness and attention. A difference between two sensations

1 The term 'identity' is sometimes used to indicate such perfect likeness. But the word is open to the objection that two sensations experienced at different times are not the same' in the sense in which a thing seen to-day is the same as the thing previously seen, The nature of this identity will occupy us later.

that cannot be apprehended, and is out of all relation to consciousness, is as much a paradox as a single unconscious sensation.1

The distinction of perfect and imperfect likeness just spoken of has to do with intensive differences, or differences in degree of the likeness. In addition to these there are extensive differences or differences in the area of the likeness. Thus two colours may resemble one another totally in all points, tint, saturation, etc., or only partially in some one or more of these constituent features. A good deal of what we ordinarily mean by likeness, more particularly when we ascribe likeness to those complexes which we call 'things,' is of this partial character; and, as just shown, even in the case of so-called simple sensations, likeness resolves itself in many cases into partial likeness.

According to the Herbartian psychologists the fundamental relations are not difference and similarity but identity or equality and inequality (Gleichheit and Ungleichheit). According to this view, imperfect likeness as above defined is no simple relation at all, but resolves itself in all cases into partial equality. Thus all assimilation is expressed by the formula AB, AC, where A represents the common identical element in two complexes. This view, however, seems based on speculative hypothesis, and is not in strict accordance with the facts so far as they are known. That imperfect likeness may in many cases be resolved into partial has been conceded above; but this cannot always be done. Physiological analysis' does not enable us to say that two adjacent tones in the scale which are certainly like in pitch and more like than those separated by a wider interval have any common ingredient. And, even if it could be made out that in all cases of like sensations there is a common ingredient, it might be urged that the apprehension of this likeness precedes by a considerable interval any power of abstract fixation or isolation of this ingredient. Thus children and even adults apprehend likeness between tones, as a note and its octave, and between two closely-related colours, as scarlet and crimson red, without being in the least degree able to identify a common element in them.3

1 Stumpf separates in the sharpest manner sensibility to difference (Unterschiedsempfindlichkeit) from discriminative ability (Unterscheidungsfähigkeit). The only meaning I can give to the former is the influence of the organic factor which, as we have seen, co-operates with attention in determining the finest discriminative sensibility to colours, tones, etc. For Stumpf's views see his Tonpsychologie, i. pp. 22, 33 f. and 49 ff. On the difficulties of this theory of unapprehended sensational contents, cf. above, p. 143 f.

2 It would be still less possible to determine a common element in two tones like though not perfectly like in intensity.

The Herbartian view of likeness is connected with the extra-psychological assumption that presentations persist after they sink below the threshold of consciousness, so that what we call a new (similar) presentation may be conceived of as the same presentation re-elevated above this liminal point in the scale. The idea

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A word may be added on the physiological substratum of psychical similarity. said that such a substratum is supplied in the fact of the identity of nervous structure involved in the case of two sensations. This, however, only applies to the case where similarity is perfect. In the case of imperfect likeness we can hardly assume that the same nervous elements and the same mode of functional activity are involved. It is to be added that, even if we could thus clearly conceive of a nervous correlative of two like psychical elements, this would be far from supplying a physiological counterpart of the consciousness or apprehension of a relation of likeness.

§ 6. Automatic Assimilation: Recognition. The simplest form of assimilation is to be found in that process by which a present sensation (or sensation complex) is re-apprehended or 'recognised' as something familiar.1 This assimilation may be illustrated in the effect on the infant consciousness of recurring and interesting sensations of odour, sound, etc., as those of the mother. Such assimilation is automatic or unconscious' in the sense that there is no separate and distinct recalling of a past sensation, and clear awareness of the relation of the present sensation to its predecessor. It does, indeed, involve, as we shall see presently, a germ of what is called retentiveness, as also a certain nascent and imperfect form of revival or reproduction. But the revival not being full and distinct, we cannot in this case speak of a clear, explicit grasp of similarity between two psychical elements. What takes place here is the calling up by a present sensation of the trace or residuum of a past sensation (or sensations), which trace merges in or coalesces with the new sensation, being discernible only through the aspect of familiarity which it imparts to the sensation.

This mark of automatic assimilation, the aspect of familiarity or retrospectiveness in a sensation, will vary according to circumstances. Thus if the sensation has been preceded by a like one shortly before, the trace of this last assuming special distinctness

that all likeness is identity which appears to be shared by Ward (loc. cit., especially p. 46 ff.) is ably criticised by Stumpf. He distinguishes between similarity of simples and of compounds, and argues that in the case of all sensations falling into a scale tones, colours, temperatures-mere likeness (i.e., imperfect likeness) is involved. (Tonpsychologie, i. p. 111 ff.)

1 It may seem premature to introduce the word recognition before we come on to deal with true cognition, i.e., the apprehension of things. But the word is almost unavoidable here, and it may be as well to call attention at this stage to the fact that a simple process of re-cognition is involved in all cognition.

gives the peculiar mode of consciousness signified by 'again' or "over over again". In the case of frequently recurring like sensations, e.g., the taste of everyday dishes, the familiarity takes on the aspect of homeliness or commonplaceness. As already suggested, what becomes very familiar ceases on that account to be noteworthy, that is, to arouse the attention. Hence it may be said that in these cases the effect of automatic assimilation is to render the sensation unimportant or unimpressive.

This automatic assimilation by accumulation of traces plays an important part in early mental development. Recurring sensations, i.e., the occurrence of like sensations or sensationgroups, is, indeed, a necessary condition of this development. A child must begin to bring together and class its sensations; and, indeed, by common consent, it begins to do this hastily and even recklessly, classing things which are only partially alike (provided the like feature is striking and interesting), and overlooking differences. All this shows that assimilation is a prerequisite of the growth of even the most rudimentary knowledge.1

A higher stage is reached when differences are sufficiently attended to to require a special isolating act of attention to the similar ingredient of the complex, as when a child recognises the mother's voice when she is playfully disguising it. This fixing of the attention on a similar feature or features in the midst of diverse elements involves a germ of the higher abstracting attention which will be found to play so prominent a part in the later intellectual processes.2

§ 7. Transition to Comparative Assimilation. This last process forms a transition from automatic assimilation to conscious comparative assimilation, where the relation of similarity begins. to be attended to. Mere recognition with its complete coalescence of the residua of past sensations with the present does not imply such apprehension of relation. In the case of likeness, as in that of difference, this apprehension emerges gradu

1 The effect of successive processes of assimilation or accumulation of traces in giving vividness to sensations was well brought out in Beneke's system of psychology.

The precise nature of recognition is a point that has given rise to a good deal of discussion of late. The matter of dispute will be most conveniently taken up presently when we come on to the reproductive aspect of the process.

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ally, and only becomes steady and clear with the advance of development.

This conscious apprehension of a relation of likeness may take its rise in different ways. Thus one of the first forms would be the noting similarity between two simultaneous presentations, as when a child observes the image of its mother's face in a mirror. Such an unusual reduplication of a familiar object would act as a strong stimulus to the attention, and tend to arouse a vague apprehension of a relation of likeness.1 Along with this may be instanced the simple form of comparative recognition which would arise when a second similar sensation recurs while the after-image of the preceding one still survives, as in the case of the tolling of a bell. As a last startingpoint in the development of such conscious grasp of similarity we have automatic assimilation. In a case where this was checked by the presence of an obstacle, as when a child was puzzled by seeing its mother in a new dress, there would be developed the impulse to separate off the residuum of old impression from the present impression with which it tends to coalesce, and to consciously adjust this last to the first: and this would involve a germ of comparison. Such a process, however, obviously presupposes the advance of another process to be spoken of presently, viz., the distinct recalling or reproduction of past presentative elements under a representative form.

§ 8. Relation of Differentiation to Assimilation. The two processes of differentiation and assimilation, though, as we have seen, in a manner opposed one to another, are carried out together, and in close connexion. And it may be as well to point out the nature of this connexion at once.

First of all, then, since assimilation implies attention to a new sensation, it may be said in every case to involve a measure of differentiation. A child cannot assimilate a taste, a touch, and so forth, till it mentally fixates, and so differentiates, this sensation. Our power of picking out and recognising particular elements in a sensation-complex, e.g., tones in a clang, depends on our differencing these from the other concomitant elements.

1 Cf. what was said above respecting the first development of conscious discrimination.