we too may confine the term. But it will be well in the next place, before inquiring more closely into their characteristics, to consider for a moment that persistence of preceding modifications which the principle of progressive differentiation implies. This persistence is best spoken of as retentiveness. It is often confused with memory, though this is something much more complex and special; for in memory there is necessarily some contrast of past and present, whereas here there is simply the persistence of the old. But what is it that persists? On our theory we must answer, the continuum as differentiated, not the particular differentiation as an isolated unit. If psychologists have erred in regarding the presentations of one moment as merely a plurality of units, they have erred in like manner concerning the so-called residua of such presentations. As we see a certain colour or a certain object again and again, we do not go on accumulating images or representations of it, which are somewhere crowded together like shades on the banks of the Styx; nor is such colour, or whatever it be, the same at the hundredth time of presentation as at the first, as the hundredth impression of a seal on wax would be. There is no such lifeless fixity in mind. The explanations of perception most in vogue are far too mechanical and, so to say, atomistic; but we must fall back upon the unity and continuity of our presentation continuum if we are to get a better. Suppose that in the course of a few minutes we take half a dozen glances at a strange and curious flower. We have not as many complex presentations which we might symbolize as F₁, F₂,....F₆. But rather, at first only the general outline is noted, next the disposition of petals, stamens, &c., then the attachment of the anthers, position of the ovary, and so on; that is to say, symbolizing the whole flower as [p′ (ab) s′ (cd) o′ (fg)], we first apprehend say [p′ . . s′ . . o′], then [p′ (ab) s′ . . o′.], or [p′ (a . .) s′ (c . .) o′ (f . .)], and so forth. It is because the traits first attended to persist that the later form an addition to them till the complex is at length complete. There is nothing in this instance properly answering to what are known as the reproduction and association of ideas; in the last and complete apprehension as much as in the first vague and inchoate one the flower is there as a primary presentation. There is a limit, of course, to such a procedure, but the instance taken, we may safely say, is not such as to exceed the bounds of a simultaneous field of consciousness. Assuming then that such increase of differentiation through the persistence of preceding differentiations holds of the presentation-continuum as a whole, we conclude that, in those circumstances in which we now have a specific sensation of, say, red or sweet, there would be for some more primitive experience nothing but a vague, almost organic, sensation, which, however, would persist, so that on a repetition of the circumstances it could be again further differentiated. The earlier differentiations, in short, do not disappear like the waves of yesterday in the calm of today, nor yet last on like old scars beside new ones; but rather the two are blended and combined, so that the whole field of consciousness, like a continually growing picture, increases indefinitely in complexity of pattern.
13. Assimilation.—This process, in which later differentiations blend with and thereby further restrict and specialize what is retained of earlier and less definite presentations, is thus a further implication of the principle of the progressive development of the presentational continuum. When not ignored altogether this further process has been commonly regarded as merely a simple form of “association,” its peculiarity being, as it was supposed, that the presentations associated—though numerically distinct—were in quality perfectly identical. In point of fact, both these assumptions seem to be erroneous and due to the so-called psychologist's fallacy.[1] For the experiencing subject there is apparently at this stage-as we have already urged-neither the numerical distinctness nor the qualitative identity which the words “past impression (A₁)” and “present impression (A₂)” suggest. Still the connexion between this process of mere blending or fusion, which we shall call assimilation, and the process of association proper is so close, and the detailed analysis called for so complex, that we must needs defer further discussion till we come to treat of association as a whole (cf. below, § 24). It may then be possible to show that we have here to do with a process much simpler and more fundamental than association. But it is at least clear at once that if the term association is to be correctly used it will imply that the presentations associated are from the first distinct, are attended to as distinct, are associated solely in consequence of such attention, and remain to the last distinguishable.
In view of the intimate connexion between differentiation, retentiveness and assimilation it will sometimes be convenient to refer to all three together as constituting what we may call the plasticity of the presentational continuum.
14. This will be the most convenient place to take note of Relativity. certain psychological doctrines which, though differing in some material respects, are usually included under the term Law of Relativity.
a. Hobbes's Sentire semper idem et non sentire ad idem recidunt is often cited as one of the first formulations of this law; and if we take it to apply to the whole field of consciousness it becomes at once true and trite: a field of consciousness unaltered either by change of impression or of idea would certainly be a blank and a contradiction. Understood in this sense the Law of Relativity amounts to what Hamilton called the Law of Variety: “that we are conscious only as we are conscious of difference.”[2] But, though consciousness involves change, it is still possible that particular presentations in the field of consciousness may continue unchanged indefinitely. When it is said that “a constant impression is the same as a blank,” what is meant turns out to be something not psychological at all, as, e.g., our insensibility to the motion of the earth or to the pressure of the air—cases in which there is obviously no presentation, nor even any evidence of nervous change. Or else this paradox proves to be but an awkward way of expressing what we may call accommodation, whether physiological or psychological. Thus the skin soon adapts itself to certain seasonal alterations of temperature, so that heat or cold ceases to be felt: the sensation ceases because the nervous change, its proximate physical counterpart, has ceased. Again, there is what James Mill calls “an acquired incapacity of attention,” such that a constant noise, for example, in which we have no interest, is soon inaudible. In such a case of psychological accommodation we should expect also to find on the physiological side some form of central reflection or isolation more or less complete. As a rule, no doubt, impressions do not continue constant for more than a very short time; still there are sad instances enough in the history of disease, bodily and mental, to show that such a thing can quite well happen, and that such constant impressions (and “fixed ideas,” which are in effect tantamount to them), instead of becoming blanks, may dominate the entire consciousness, colouring or bewildering everything.
b. From the fact that the field of consciousness is continually changing it has been supposed to follow, not only that a constant presentation is impossible, but—as a further consequence—that every presentation is essentially nothing but a transition or difference. “All feeling,” says Bain, the leading exponent of this view, “is two-sided. . . . We may attend more to one member of the couple than to the other. . . . We are more conscious of heat when passing to a higher temperature, and of cold when passing to a lower. The state we have passed to is our explicit consciousness, the state we have passed from is our implicit consciousness.” But the transition need not be from heat to cold, or vice versa: it can equally well take place from a neutral state, which is indeed the normal state, of neither heat nor cold; a new-born mammal, e.g. must experience cold, having never experienced heat. Again, suppose a sailor becalmed gazing for a whole morning upon a stretch of sea and sky, what sensations are implicit here? Shall we say yellow as the greatest contrast to blue, or darkness as the contrary of light, or both? What, again, is the implicit consciousness when the explicit is sweet; is it bitter or sour, and from what is the transition in such a case? For one thing it seems clear that the transition of attention from one presentation to another and the differences between the presentations themselves are distinct facts. It is strange that the psychologist who has laid such stress on neutral states of surprise
