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SENSATION] or what the more careful of them call irritability; and, true again, that this irritability is invariably preceded by a physical process called stimulation. But it may be urged, why not recognize a connexion that actually obtains, since otherwise sensation must remain unexplained? Well, in the first place, such “psychophysical” connexion is not a psychological explanation: it cannot be turned directly to account in psychology, either analytic or genetic. Next the psychological fact called sensation always is, and at bottom always must be, independently ascertained; for the physiological “neurosis” or irritation has not necessarily a concomitant “psychosis” or sensation and, strictly dealt with, affords no hint of such. Finally, this inexplicability of sensation is a psychological fact of the utmost moment: it answers to what we call reality in the primary sense of the term. The psychophysicist, in setting out to explain sensation, has—unawares to himself—left this fundamental reality behind him. For it belongs essentially to individual experience, and this—in assuming the physical standpoint—he has of course transcended. Nevertheless the mistake of method that here reveals itself was perhaps inevitable, for the facts of another's sense-organs and their physical excitants must have obtruded themselves on observation long before the reflective attitude was advanced enough to make strictly psychological analysis possible. The psycho physical standpoint, that is to say, was attained before the purely psychological; and the consequent bias is only now in process of correction. A series of physical processes, first without and then within the organism—ethereal or aerial vibrations, neural and cerebral excitations—was the starting point. What comes first, immediately, and alone, in the individual's experience, and is there simply and positively real, was then misinterpreted as subjective modification, mental impression, species sensibiles, or the like. For from the days of Democritus to our own the same crude metaphor has prevailed without essential variation. And here the saying holds: Vestigia nulla retrorsum. Into the man's head the whole world goes, including the head itself. Such thoroughgoing “introjection” affords no ground for subsequent “projection.” Thus the endeavour to explain sensation overreaches itself: the external object or thing that was supposed to cause sensations and to be therefore distinct from them, was in the end wholly resolved into these and regarded as built out of them by association (Mill) or by apperceptive synthesis (Kant). But no “mental chemistry,” no initial alchemy of “forms,” can generate objective reality from feelings or sense-impressions as psychophysically defined. A's experience as it is for B is not real but inferential; and if the grounds of the inference, which are the only realities for B, are to be regarded as the causes of which A's experiences are merely the effects, then the two experiences are on a wholly different footing. When A treats B in the same fashion we get the world in duplicate: (1) as original and outside, i.e. as cause, and (2) as copied within each percipient's head, i.e. as effect. But when B interprets his own experience as he had interpreted A's we seem to have lost the real world altogether. In presence of this dilemma, the philosophers of our time, as already said, are feeling it needful to revise their psychology. The question of method is vital. If the psychophysical standpoint were the more fundamental, psychology would be based on physiology, and the old definition of sensation might stand. If, on the other hand, it is the exclusive business of psychology to analyse and trace the development of individual experience as it is for the experiencing individual, then—however much neurological evidence may be employed as a means of ascertaining psychological facts—the facts themselves must be scrupulously divested of all physical implications, the psychophysical method takes a secondary place, and the objective reality of “sensory” presentations stands unimpeached.

The duality of subject and object in experience compels us also to object to the description of sensations as “states of consciousness.” Since it is the subject, not the object that is conscious, the term state of consciousness implies strictly a subjective reference; and so it is only applicable to sensations, if they are regarded as subjective modifications, either affective or active. The former would identify sensation with feeling, and this—for reasons already given—we must disallow. But it is true that a sensation, like other presentations, implies the subjective activity we call attention; it is not, however, a modification or state of this activity, but the object of it. This relation is expressed in German by means of the distinction generally of Vorstellen and Vorstellung and in the present case of Empfinden and Empfindung; and German psychology has gained in clearness in consequence. The distinction of conception and concept (conceit) is to be found in older English writers and was revived by Sir W. Hamilton, who suggested also the analogous distinction of perception and percept. It would be a great gain if there were a corresponding pair of terms to distinguish between “the sensing act” and the object “sensed,” as some have been driven to say. Reception and recept at once occur and seem unexceptionable—apart, of course, from their novelty. At any rate, if we are to rest content with our present untechnical terminology we must understand sensations to mean objective changes as they first break in upon the experience of our psychological individual; in this respect Locke's term “impression” has a certain appropriateness.

What we ordinarily call a single sensation has not only a characteristic quality but it is also quantitatively determined in respect of intensity, pro tensity (or duration) and extensity. A plurality of properties, it may be said, straightway implies

complexity of some sort. This is obvious and undeniable; psychological—as distinct from psychical —analysis of simple sensations is possible, and the description just given is reached by means of it. Such analysis, however, presupposes the comparison of many sensations; but to the complexity it discloses there is no answering plurality discernible in the immediate experience of a single sensation. To make this clearer let us start from a case in which such plurality can be directly verified. In a handful of rose petals we are aware at once of a definite colour, a definite odour and a definite “feel.” Here there is a plurality (a+b+c), any part of which can be withdrawn from our immediate experience without prejudice to the rest, for we can close the eyes, hold the nose, or drop the petals on the table. Let us now turn to the colour alone; this we say has a certain quality, intensity, extensity, &c. But not only have we not one sense for quality, another for intensity, &c., but we cannot reduce the intensity to zero and yet have the quality remaining; nor can we suppress the quality and still retain the extensity. In this case then what we have is not a plurality of presentations (a+b+c), but a single presentation having a plurality of attributes (a b c) so related that the absence of any one annihilates the whole. But though, as already said, such single presentation gives, as it stands, no evidence of this plurality, yet it is to be remembered that in actual experience we do not deal with sensations in isolation; here, accordingly, we find evidence in plenty to justify our psychological analysis. In innumerable cases we experience varieties of intensity with little or no apparent change of quality, as happens, for example, when a sounding pitch-pipe is moved towards or away from the ear; and continuous changes of quality without any change of intensity, as happens when the pipe is shortened or lengthened without any alteration of position. We may have tactual or visual sensations which vary greatly in extensity without any striking change of quality, and we may have such sensations in every possible variety of quality without any changes of extensity.

The numerous and striking diversities among our present sensations are obviously not primordial; what account then can we give of their gradual differentiation? Some psychologists have assumed the existence of absolute “units of