Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/61

PSYCHOLOGY 49 This will be the most convenient place to take note of certain psychological doctrines which, though differing in some material respects, are usually included under the term Law of Relativity. 1. Hobbes's Idem semper sentire 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 con- sciousness it becomes at once true and trite : a field of consciousness unaltered either by change of impression or of ideas 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 (Reid's Works, p. 932). 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 altera- tions 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 atten- tion," such that a constant noise, for example, in which we have no interest is soon inaudible. As attention moves away from a presentation its intensity diminishes, and when the presentation is below the threshold of conscious- ness its intensity is then subliminal, whatever that of the physical stimulus may be. In such a case of psychological accommodation we should expect also to find on the phy- siological side some form of central reflexion 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. 2. From the fact that the field of consciousness is con- tinually 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 Dr 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 con- sciousness, 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 1 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? It is difficult to avoid suspecting a certain confusion here between the transition of attention from one presentation to another and the qualitative differences among presenta- tions themselves. It is strange that the psychologist who has laid such stress on neutral states of surprise as being akin to feeling, and so distinct from special presentations, should in any way confound the two. The mistake, if mistake indeed it be, is perhaps accounted for by the fact that Dr Bain, in common with the rest of his school, nowhere dis- tinguishes between attention and the presentations that are attended to. To be conscious or mentally alive we must have a succession of shocks or surprises, new objects calling off attention from old ones ; but, over and above these movements of attention from presentation to presentation, do we find that each presentation is also itself but a transi- tion or difference? "We do not know any one thing of itself but only the difference between it and another thing," says Dr Bain. But it is plain we cannot speak of con- trast or difference between two states or things as a contrast or difference if the states or things are not themselves presented, else the so-called contrast or difference would itself be a single presentation, and its supposed "relativity" but an inference. Difference is not more necessary to the presentation of two objects than two objects to the presenta- tion of difference. And, what is more, a difference between presentations is not at all the same thing as the presenta- tion of that difference. The former must precede the latter ; the latter, which requires active comparison, need not follow. There is an ambiguity in the words "know," " knowledge," which Dr Bain seems not to have considered : " to know " may mean either to perceive or apprehend, or it may mean to understand or comprehend. 1 Knowledge in the first sense is only what we shall have presently to dis- cuss as the recognition or assimilation of an impression (see below, p. 53) ; knowledge in the latter sense is the result of intellectual comparison and is embodied in a proposition. Thus a blind man who cannot know light in the first sense can know about light in the second if he studies a treatise on optics. Now in simple perception or recognition we cannot with any exactness say that two things are per- ceived : straight is a thing, i.e., a definite object presented ; not so not-straight, which may be qualitatively obscure or intensively feeble to any degree. Only when we rise to intellectual knowledge is it true to say, "No one could understand the meaning of a straight line without being shown a line not straight, a bent or crooked line." 2 Two distinct presentations are necessary to the comparison that is here implied ; but we cannot begin with such definitional differentiation : we must first recognize our objects before we can compare them. We need, then, to distinguish be- tween the comparativity of intellectual knowledge, which we must admit for it rests at bottom on a purely ana- lytical proposition and the "differential theory of pre- sentations," which, however plausible at first sight, must be wrong somewhere since it commits us to absurdities. Thus, if we cannot have a presentation X but only the presentation of the difference between Y and Z, it would seem that in like manner we cannot have the presentation of T or Z, nor therefore of their difference X, till we have had the presentation of A and B say, which differ by Y, and of G and D, which we may suppose differ by Z. The lurking error in this doctrine, that all presentations are but differences, may perhaps emerge if we examine more closely what may be meant by difference. We may speak of (a) differences in intensity between sensations supposed 1 Other languages give more prominence to this distinction ; compare yvuvai and eldtvai, noscere and scire, kennen and wissen, connaitre and savoir. On this subject there are some acute remarks in a little- known book, the Exploratlo Philosophica, of Professor J. Grote. Hobbes too was well awake to this difference, as, e.g., when he says, "There are two kinds of knowledge; the one, sense or knowledge original and remembrance of the same ; the other, science or know- ledge of the truth of propositions, derived from understanding. " 2 Bain, Logic, vol. i. p. 3. XX. 7