as being akin to feeling and so distinct from special presentations, should in any way confound the two. The mistake is perhaps accounted for by the fact that Bain, in common with the rest of his school, nowhere distinguishes between attention and the presentations that are attended to. If “change of impression” and being conscious or mentally alive are the same thing, it is then manifestly tautologous to say that one is the indispensable condition of the other. If they are not the same thing, then the succession of shocks or surprises cannot wholly determine the impressions which successively determine them.
But we have still to consider whether the impressions themselves are nothing but differences or contrasts. “We do not know any one thing of itself but only the difference between it and another thing,” said Bain. But it is plain we cannot speak of contrast or difference between two states or things as a contrast or difference, if the states or things are not themselves presented; the so-called contrast or difference would then be itself 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 presentation of difference. And, what is more, a difference between presentation is not at all the same thing as the presentation 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 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 discuss as the recognition or assimilation of an impression (see below, § 18); 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 perceived: straight is a thing, i.e. a definite object presented; not so not-straight, which answers to no definite object at all. 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 must first recognize our objects before we can compare them, and this further step we may never take. We need, then, to distinguish between the comparativity of intellectual knowledge, which we must admit—for it rests at bottom on a purely analytical proposition—and the “differential theory of presentations,” 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 Y 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 C 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 to be qualitatively identical, as e.g. between the taste of strong and weak tea; or of (b) differences in quality between presentations of the same sense, as e.g. between red and green; or of (c) differences between presentations of distinct senses, as e.g. between blue and bitter. Now as regards (a) and (b), it will be found that the difference between two intensities of the same quality, or between two qualities of the same order, may be itself a distinct presentation, that is to say, in passing from a load of 10 ℔ to one of 20 ℔, for example, or from the sound of a note to that of its octave, it is possible to experience the change continuously, and to estimate it as one might the distance between two places on the same road. But nothing of this kind holds of (c).[3] In passing from the scent of a rose to the sound of a gong or a sting from a bee we have no such means of bringing the two into relation—scarcely more than we might have of measuring the length of a journey made partly on the common earth and partly through the looking-glass. In (c), then, we have only a diversity of presentations, but not a special presentation of difference; and we only have more than this in (a) or (b) provided the selected presentations occur together. We say that we know the difference between a sound and a taste; but what we mean is simply that we know what it is to pass from attending to the one to attending to the other. It is simply an experience of change. Change, however, implies continuity, and there is continuity here in the movement of attention and the affective state consequent on that, but not directly in the qualities themselves.
c. If red follows green we may be aware of a greater difference than we could if red followed orange; and we should ordinarily call a 10 ℔ load heavy after one of 5 ℔ and light after one of 20 ℔. Facts like these it is which make the differential theory of presentations plausible. On the strength of such facts Wundt has formulated a law of relativity, free, apparently, from the objections just urged against Bain’s doctrine. It runs thus: “Our sensations afford no absolute but only a relative measure of external impressions. The intensities of stimuli, the pitch of tones, the qualities of light, we apprehend (empfinden) in general only according to their mutual relation, not according to any unalterably fixed unit given along with or before the impression itself.”[4]
But if true this law would make it quite immaterial what the impressions themselves were: provided the relation continued the same, the sensation would be the same too, just as the ratio of 2 to 1 is the same whether our unit be miles or millimetres. In the case of intensities, e.g. there is a minimum sensible and a maximum sensible. The existence of such extremes is alone sufficient to turn the flank of the thoroughgoing relativists; but there are instances enough of intermediate intensities that are directly recognized. A letter-sorter, for example, who identifies an ounce or two ounces with remarkable exactness identifies each for itself and not the first as half the second; of an ounce and a half or of three ounces he may have a comparatively vague idea. And so generally within certain limits of error, indirectly ascertained, we can identify intensities, each for itself, neither referring to a common standard nor to one that varies from time to time—to any intensity, that is to say, that chances to be simultaneously presented; just as an enlisting sergeant will recognize a man fit for the Guards without a yard measure and whether the man’s comrades are tall or short. As regards the qualities of sensations the outlook of the relativists is, if anything, worse. In what is called Meyer’s experiment (described under Vision) what appears greenish on a red ground will appear of an orange tint on a ground of blue; but this contrast is only possible within certain very narrow limits. In fact, the phenomena of colour-contrast, so far from proving, distinctly disprove that we apprehend the qualities of light only according to their mutual relation. In the case of tones it is very questionable whether such contrasts exist at all. Summing up on the particular doctrine of relativity of which Wundt is the most distinguished adherent, the truth seems to be that, in some cases where two presentations whose difference is itself presentable occur in close connexion, this difference—as we indirectly learn—exerts a certain bias on the assimilation or identification
- ↑ Other languages give more prominence to this distinction; compare γνῶναι and εἲδέναι, noscere and scire, kennen and wissen, connaître and savoir. On this subject there are some acute remarks in a little-known book, the Exploratio 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 knowledge of the truth of propositions, derived from understanding.”
- ↑ Bain, Logic, i. 3.
- ↑ Common language seems to recognize some connexion even here or we should not speak of harsh tastes and harsh sounds, or of dull sounds and dull colours and so forth. All this is, however, superadded to the sensation, probably on the ground of similarities in the accompanying organic sensations.
- ↑ Physiologische Psychologie, 1st ed., p. 421; the doctrine reappears in later editions, but no equally general statement of it is given.
