The Place of Illusory Experience in a Realistic World
Edwin B. Holt
ILLUSION, hallucination, and the erroneous experience in general, we are told, can have no place in a universe where everything is non-mental or real: and they cannot be satisfactorily accounted for by realistic philosophy. Such is the challenge that has been repeatedly thrown out from the idealist to the realist camp. And although it has recently been taken up and admirably answered in two all but impeccable articles by Professor Alexander and Mr. Nunn, I propose to take up the issue once more and to add something if possible to the measure of satisfaction already vouchsafed by these two gentlemen. A closer definition of the terms used in the dispute is not necessary at the outset, for they are offered and may be accepted as the current names for fairly unambiguous phenomena. Sharper definitions, however, for these and other terms will emerge in the course of the argument.
ILLUSIONS OF PERCEPTION AND THOUGHT
Erroneous experiences have been assumed to come under four heads, according as the error is one of space, of time, of ('secondary') quality, or of judgment (thought).
1. Errors of Space. —An object is frequently seen as nearer or farther, as larger or smaller than it really is; it may be seen inverted in position or distorted in shape, it may be seen double or triple (spatially reduplicated) ; and the same frailties attach to the senses of hearing and touch and to other modes of appre-
(304) -hension, such as that, for an instance, in which the semicircular canals area contributory factor. The person sees what is not there, — hence the act of seeing is constitutive in the case, hence the illusory object (however it may be with a correctly perceived one) is essentially mental and subjective. Thus if the two eyes are sharply converged and then one eye is closed, near objects (far ones are now out of focus) are seen as both nearer and smaller than ordinarily, or than they really are. ('Really are' just happens not to be a realist's phrase, as shall be explained later, but I shall use it and still refrain from quotation marks out of deference to the opponent, who, to judge by his actions, is unable to state his case against realism except he be granted handy access to some things that 'really are.') Now there is a machine for manufacturing the lasts on which shoes are made. A model last is placed in contact with one end of an arm and the machine at once carves out of a block of wood a second last which is like the model. The machine at work has quite the air of seeing its model. Indeed, the comparison between duplicate and model has an uncanny resemblance to the subject-object relation. However that may be, there is an adjustment which can be effected such that the duplicate last is turned out smaller than the original, but otherwise still like it, and the same adjustment brings any point that shall be geometrically defined as the center of the last nearer to the important part of the machine, the cutting edge. I forbear to press the analogy : the essential point is, merely, that a mechanical manipulation of the eyes which brings things nearer and makes them smaller argues nothing for mentality or subjectivity, for there is another machine at hand which can be as readily manipulated with the very same effect. And in the shoe-last machine I imagine that our opponent, so far from discovering the subject-object relation and so forth, will even feign to evade the comparison.
However, our next case is his own favorite out of a not too varied repertory. If a person presses one of his eye-balls out of place, and keeps both eyes open, he will see double. He sees,
(305) for instance, a second mare's nest which isn't really there. This demonstrates a remarkable creative function inherent in mental process. A too literally-minded person might ask if it did not somehow depend on there being two eyes, and this the more as the direction given for setting this creative function of mind in operation was distinctly physical, i.e. a jab on the eye-ball. Indeed, it could almost be said to be directed on the eye rather than addressed to the mind. This notion becomes even more plausible when one remembers that the stereoscopic camera habitually sees double. The notion becomes a certainty from the circumstance that in the case of a person with two eyes of which one is blind, with, however, a creative mental apparatus equal to any the best you may find, — in such a case the charm works not at all. (It does not work even if a normal-sighted person closes one eye-lid during the experiment.) This is proof by the Baconian canon, so long as our opponent adduces only two factors — the pair of eyes and the mental process. Or, to return to concrete experience, I will ask the opponents of realism this : Do they indeed think that of the two images of one object which are given in the stereoscopic camera one of the images is 'illusory' because but one outer object is really there? Does the camera lie ? If not, why is one of the two images on occasion given in human vision, any the more illusory? "Ah, but," is the reply, "no one asserts that the image in the camera is the object out in front." To which I say that realism asserts just this, —the image is genuinely (a part only, but a true part, of) the object photographed. The professional photographer asserts it, saying, in the manner of his trade, " We have caught your exact expression, Madame." And we all speak, as Robert Louis Stevenson spoke, of "just that secret quality in a face that is apt to slip out somehow under the cunningest painter's touch, and leave the portrait dead for lack of it" ("An Autumn Effect"). The physicist or astronomer absolutely asserts that his photograph of a spectrum is integrally the spectrum under study. Now the realist contends that when we say such things we mean them ;
(306) the opponent, that we do not. Yet everybody except this perverse school of philosophers continues to assert the same in any case whatsoever of 'reproduction' in art or craft ; and the philosophers of that school assert it the instant they have doffed their professional perruque and descended from the cathedra. Whether they admit this or not, the point which they must admit is that reduplication, if only of 'images,' is a common feature of purely physical systems, and that therefore the occurrence of reduplication as a function of the human organs of sense argues nothing for subjectivity lying behind that sense. The relation of 'image' to the object and then to knowledge we shall presently examine.
Or again an astigmatic eye distorts its object; so does a roughly cast glass lens, and so do the innumerable facets on the surface of troubled waters. A stimulation of the two sacs in the inner ear translocates one part of perceived space within an otherwise perceived space; just so every mirror and other reflecting surface makes a new translocated space, which is in all ways geometrically viable and is within the original real space : and so on for every one of the spatial illusions and hallucinations.
Our opponent must withdraw from his citation of cases in which the organs of sense yield multiplied or distorted images, because of the invariable parallel to strictly physical systems. And he must stand on a ground further back; which would be, as several of our opponents have indeed made their particular point, that not the distorted image as such, but the distorted image which asserts itself to be, or which the realist asserts to be the real object, —that this is the crux for realism. In order to be fair I hasten to add that not a few of the opponents of realism have not to retreat to this ground, since it is their original position. And I am only too eager to meet them there, as I shall do in due course. Meanwhile many of our opponents have undertaken to occupy the ground which I claim that we have just covered, and all opponents are to be reckoned with. Indeed, it remains true that in nearly every case where the idealist has ventured within the somewhat unfamiliar and ticklish region of the concrete,
(307) he has brought against realism the charge which I have just partially refuted. I say 'partially,' not because I account the physical parallels of illusion as inconclusive, but because we have so far considered only the spatial cases. We now proceed to the next group.
2. Errors of Time. — An object is not only frequently, hut invariably seen at a moment of time later than that when it had the position and other circumstances which it still has in our vision of it. The illustration hallowed by the tenderest association for the idealist seems to be the case of seeing the sun or other heavenly bodies some millions of years behind time, or indeed millions of years after it may have ceased really to exist. But now what advantage over us has the photographic plate, as plainly physical and as little mental or illusory as we all grant that to be? And if it be paradoxical and for realism ominous that we can see a real thing long after it has ceased to be real, how much more paradoxical and ominous must it be for physics if it is obliged to concede that each smallest physical object remains under the direct and real influence of other physical objects which have not been existent or real for millions of years. It seems to me that this argument proves either all or nothing. It may, I fancy, open up magnificent vistas to theosophists and clairvoyants ; but my imagination halts when I try to conceive what it can open up to a sane and sober philosopher. Nevertheless such a passage as the following is characteristic of the greater number of writers who are just now so superbly stooping to take notice of realism. "The 'real' object always exists earlier in time than the perceived object, which we hastily assume to be the 'real' object, yet which is really but an element in our own experience, and not the object, or eject, which exists in and for itself."  Succinctly stated, the astonishing argument is that the mental image is not a part of the real world, but is distinctly non-physical and non-real, and belongs intrinsically to another, the subjective order of being,
(308) because it lags in time behind the real order of things : and this is urged notwithstanding the fact that every case of image which can be cited from the strictly physical world lags in exactly the same way behind its real physical prototype.
Some of our opponents, as in the previous case of spatial illusions, stand on the safer ground of affirming that not the delayed image as such, but the delayed image which asserts itself to be, or which the realist asserts to be the real object, —is the crux for realism. Thus one critic affirms that "In the face of intervening machinery (of sense-perception) and the lapse of time, realism cannot persist in saying that the very object thrusts itself in amongst the contents of consciousness." We shall consider this latter argument in due course, but for those who find something in the former argument I wish to suggest an illustration which they may find useful in their future animadversions on this point, since it will be more novel than the somewhat threadbare case of seeing the non-existing sun, and furthermore in their eyes more damaging to the cause of realism. One discovers in the psychological laboratory a kind of lapse of attention during which sensory stimulations are prevented from reaching the sensorium, or from coming to consciousness ; yet if the lapse is brief, say not over five-tenths of a second, sensory stimulations given during the lapse reach consciousness afterwards and are then perceived in the reverse of their true time order. This is, of course, hard on realism, although the same reversal happens to a bunch of delayed telegrams, letters, or express parcels.
3. Errors in Secondary Qualities. — The detachment of secondary qualities from physical objects has seemed so conspicuous to the makers of history, that these qualities are rather generally deemed to exist in minds and nowhere else, to be in very essence mental. On the other hand, there is a group of thinkers who assert that the secondary qualities are not in minds at all, neither ideas nor even sensations being endowed with these qualities. In this case either they are spoken of as if they were a part of the physical objects, or else no status or habitat whatsoever, so far
(309) as I have been able to discover, is assigned to them. I take it that in urging the case of secondary qualities against realism, our opponent assumes the case (for him) contrary to fact, that the qualities are out there on the objects, and undertakes to argue to a reductio ad absurdum.
The larger part of illusory instances here in question needs but brief comment, for their case is still parallel to the cases already considered. As one passes down a dark street and past a lighted window, the darkness of the street seems more profound, although the night is really no darker : but just so a photographic plate carried past the light of the window is thenceforward less sensitive to the faint illumination of the darkness beyond, and this illumination is for it one of reduced intensity. But in such a simple fact of modified physical process no one sees raised at all the issue between reality and unreality, or between the material and the mental. The hill and wood that one looks out upon are practically invariable in their chemical properties, yet as the day progresses they are seen in a perpetual variety of light, shade, and hue : but their luminous properties, although invariable, are invariable functions of the incident illumination, functions whose particular values vary therewith ; so that the light that is reflected is in reality ever changing. Since it is reflected light that is perceived in this case, and not the invariable functions, it would be a falsification of reality if the light were not seen in perpetual flux. The orthochromatic moving film will record this diurnal flux in an entirely parallel way. The change of 'appearance' as an object is carried from peripheral to foveal vision is only a case of one light differently affecting differently sensitized surfaces : and the 'brightness distribution' of the totally color-blind eye is photographed outright by exposing a tube filled with a solution of visual purple from the eyes of frogs, to the several wave-lengths of the spectrum.
A feeble tone sounds fainter when a stronger tone is sounded so too it will yield less physical sound when occurring simultaneously with other sounds (owing to partial interferences). The intense stillness after explosions has its counterpart in the 'fatigue'
( 310) of physical mechanisms. In binaural diplacusis one given pitch is heard by the two ears as two different pitches (generally less than one third of a scale-interval apart) : but so will one tone set up overtones of different pitches in as many resonant bodies ; as one may note by listening to several telephone transmitters which are connected with one receiver. It may be alleged that auditory 'beats' falsify the perception of physical sounds, but 'beats' take place in every damped membrane, and are in human audition nothing but the true perception of what is going on in the tympanum of the middle ear. Likewise, in some measure, at least, auditory 'attention waves' are the true record in consciousness of interrupted function of the tympanum, owing to rhythmical changes in the latter's tension, which prevent it from vibrating responsively to some pitches. (Similarly visual attention waves are in part at least due to like rhythmical changes in the shape of the lens.)
The phenomena of dizziness and other peculiar affections in our sense of orientation have found a singularly satisfactory explanation in the Mach-Breuer theory, wholly in terms of the inertia and elasticity of bodies. And a model has been constructed which manifests in the real world many of the very same false responses to changes of orientation that the human being perceives by virtue of the labyrinth of his two ears. An almost identical organ has been found in plants. One can only regret, in this connection, that none of our sense-organs contain gyroscopes, for then there would be material startling enough to prove to the satisfaction of some a dozen anti-realisms.
The case of all the other senses is exactly parallel, and I will mention only the sadly overworked instance of the bowl of water which feels hot to one hand and cold to the other, adding merely that if our learned opponents who find this experiment so significant will heat one thermometer and put a second for a time on ice, the first will record as objectively as one pleases that the bowl is really cold, while at the same time the second thermometer will record that the bowl is really hot. In connection with
( 311) all of the phenomena so far cited, the admirable papers of Professor Alexander and Mr. Nunn, already referred to, will be found most illuminating.
But I have not yet mentioned hallucinatory secondary phenomena, cases in which a color or sound comes in all distinctness to consciousness, while nevertheless no such color or clue to it is out there in the physical world. In a way positive, negative, and complementary after-images seem to belong here ; and yet they are really cases like the foregoing. A positive afterimage has of course a thousand parallels in the physical world, and indeed it depends certainly on the nervous 'after-discharge,' which has been well made out by physiology. The image is therefore a true perception of a real process, which in its turn constitutes a part of the real properties of a real thing (as shall be more amply brought out later). Likewise a negative after-image is paralleled by the photographic 'negative.' The complementary after-image seems indeed a purely subjective hallucination. The yellow candle-flame is not blue as it looks in the afterimage. Vision after santonin poisoning shows objects, again, suffused with an illusory or hallucinatory yellow cast. This latter case is nearly paralleled by fluorescent bodies which increase the wave-length of all light that comes to them. It is not probable that santonin vision depends on fluorescence (although the visual purple of the retina happens to be a fluorescent substance), but it would be explained in physical terms, and given a real status like that of our other instances, by any physiological process which should have the effect of a yellow light-screen interposed between the object and the sensorium. Although the means for this have not been discovered, it too clearly rests on a subtraction from consciousness (as it were a selective eye-lid) to be of interest in the present connection.
The complementary after-image still looks more like a subjective creation. Now it will be recalled that Helmholtz plotted a
( 312) curve showing the wave-lengths of the complementary colorpairs,  and I have learned from Professor G. W. Pierce that when the capacity of the receiving mast of a wireless telegraph system is tuned to a given length of Hertzian wave, it is ipso facto tuned to a second wave-length as well; and for each new tuning it becomes sensitive to a similar pair of waves : that, further, the curve of these wave-pairs shows precisely such a function as the plot of the complementary color-pairs. The complementary or antagonistic colors are comparable, then, not to the octaves in audition (as some serious but abortive speculations have tried to show), but to the complementary pairs of Hertzian waves. Now it is not known how the cones of the retina pick up lightwaves and send them on as nervous impulses, but it is improbable that they do this by virtue of any photo-chemical substance (as is the case with the rods), for in spite of repeated investigation of the cones no such substance has been found. (The question of 'visual substance,' as raised by Helmholtz and Hering, is not necessarily involved here.) But it is most probable for a variety of reasons which have been advanced by Meisling, that the cones resonate to waves of light, as in Helmholtz's theory of audition the radial fibers and organs of Corti are believed to resonate to sound. Now light-waves and Hertzian waves are closely related physically, so that if the view of Meisling is correct, —and it is not only the most reasonable view so far offered, but it is itself well supported by facts, —the complementary colors of vision are nothing but a true presentation in consciousness of the fact of complementary attunement of light-resonators. This is not an assured fact, but it is a view possessing too high a degree of probability to leave any interest attaching to the case of complementary colors as a special difficulty in the path of realism.
The case of pure hallucination involving no peripheral stimu-
( 313) -lation whatsoever, the case, that is, of centrally induced sensations and images, or, as Johannes Müller called them, "fantastical visual phenomena," is more unmistakably to our purpose. And I confess that this is the first of the arguments allotted to me in which I can see enough plausibility to enable me to meet the adversary with either amiability or patience. I heartily grant the propriety of our opponent's question, How can realism pretend to assert the reality of the color, sound, and perhaps tactile or olfactory sensations which are vividly present in the dreams of a person sleeping, it maybe, in a box no bigger than his coffin? The case has still two aspects : first, how can these purely hallucinatory secondary qualities have, even in themselves alone, any sort of being other than a subjective and mental being? Second, the argument already twice referred to, how can they pretend to assert themselves to be, or how can the realist pretend to assert them to be the real object ?
The former difficulty first. It must have occurred even to the idealist, in a ruminative moment, what a singular thing that cleavage in our universe, the sharp division between primary and secondary qualities that is ordinarily attributed to Locke, after all is. Whether one views our 'universe' as a material system, a scheme of relations, a subjective realm, an 'Absolute' system, or whatsoever, one is ever confronted by the strange apartness of the secondary from the primary qualities, a cleft that is bridged only by the bare one-to-one correlation of some of the colors, sounds, and so forth with certain vibratory wave magnitudes found in the primary system. Since this is a bare one-to-one relation, not even for instance admitted to be a true causal relation, the case presents even to the thought of our own day as clean and gratuitous a 'preëstablished harmony' as was ever dreamt of by Leibnitz. This cleavage and the mystery of error constitute, I take it, the chief empirical motives (as opposed, say, to temperamental motives) which have led thinking men into some form of subjectivism. Since, however, subjectivism by no means clears up this inscrutable correlation, it remains to
(314) me personally a mystery that, so far as I know, no explanation has been attempted of this harmonious accident — so uniform and inveterate. But is this fixed correlation a fixed accident? This is a question which must be answered on solely empirical grounds, if our adversary grants that term to have any meaning, and without regard to realistic or anti-realistic prepossessions.
For the empirical psychologist the unique and isolated position of secondary qualities is enunciated in Johannes Müller's doctrine of the specific energy of nerves, for which Müller himself gave various formulations, one of which is substantially the theory generally believed to-day. The germ of the doctrine descends to us from Locke through Hume to Kant, for it was Kant's epistemology that Müller, by his theory, aimed to exhibit in concrete operation. (He hoped thus to confirm Kantian metaphysic, and although the work turned out, unconsciously to Müller, a caricature, we still note among idealists a real affection for the 'Sonderstellung der sekundären Qualitäten.') Nevertheless, explicitly Miller proceeded empirically, and based his theory on two groups of phenomena; the 'fantastical visual phenomena,' or in general the central excitation of mental processes ; and the fact that some nerves when stimulated by sonic other than their normal stimulus still respond by yielding the same sensation as when exposed to their normal or 'adequate' stimulus. Thus, it was believed that a surgical severing of the optic nerve produced a confusedly brilliant burst of light and color sensations. Clearly the world outside the body contained only primary qualities and, more pertinently, vibration-rates, while the secondary qualities were certainly found only in the nervous system and undoubtedly (but this was pure assumption in the supposed Kantian interest) only in the mind. And it was a specific energy of nerve fiber 'or' brain center (the latter being the modern view), that, although having nothing about it that resembled a secondary quality, had the power of arousing the secondary qualities in the mind. Thus the specific energies were the physiological counterpart of a Kantian category.
But obviously the specific energy of the optic nerve must differ from that of the acoustic nerve in order to account for the different effects of the two on the mind. Müller spoke somewhat roughly of specific energies, qualitatively differing, for each of the several senses. The assumption was later made by Helmholtz, and not without reason, of a specifically different energy not merely for the modes of light, sound, heat, and so forth, but for many of the qualitative differences within these modes as well. Thus we have the sundering of primary and secondary qualities with the harmonious accident of their correlation, restated in the terms of mind and body or rather of mind and the cortical cells of the cerebrum, with nothing done to explain the steady correlational accident. (And as for the Kantians, it is hard to see how they can feel grateful to Johannes Müller for exhibiting so definitely the slender cortical threads by which the mind is held in touch with a contrastingly non mental world, even though the latter was devoid of secondary qualities.)
The point about this theory which interests us now is that nerve physiology has not been able to discover any trace of specific nerve-energies. All nervous impulses seem to be of quite the same 'qualitative' order, differing only in intensity : sensory impulses are even not different from motor impulses. Yet the question remains, — How can the mind (to continue Miller's conception of the case) be affected to different modes of sensation by nervous impulses which are all qualitatively alike? And it is a question not merely of understanding the cases of centrally induced hallucinations and of normal sensations caused by abnormal, 'inadequate,' stimulation, but a question of still broader import, — How can any physical stimuli whatsoever, whether normal
(316) or abnormal, produce different qualitative sensations when the differences between the stimuli, the differences of wave-length or vibration-rate, are merged and lost on their way to the brain in nervous impulses which appear to be all alike.
The readiest answer should seem to be that the differences required are not differences in impulse but in nerve-fibril : each nerve fibril different from every other might, whenever excited, give the cue to the mind for one specific secondary quality. But no such differences between nerve fibrils have ever been discovered; any more than between nerve impulses. Might then the differences be in the cortical cells at which the fibrils terminate? This has been somewhat investigated and a very slight difference in the chemical composition of different lobes of the brain found. Even this has not been confirmed, and I believe that no investigator has ever claimed to find chemical, histological, or other differentiations between homologous cells of one lobe ; as our assumption requires. (Differences between the cells of different cortical layers will not serve our purposes, since these differences between layers extend practically unmodified over the whole cortex.) Professors Sherrington and McDougall have shown that not the cell-bodies but the synapses between neurones are in other respects (such as duration and fatigue phenomena) significant for consciousness ; but here again no differences between synapses even remotely approximating what we require have been adduced. The only course remaining is that taken by Professor Münsterberg in his 'action theory,' a where the correlation between neural impulse and secondary quality in the mind is conceived as a bare
(317) one-to-one correlation, no other differentiation in the nervous substratum being suggested than one of spatial position. And this view again brings us back to the unexplained preëstablished harmony ; and to the mind of a realist, at least, nature abhors a preestablished harmony. But another and strictly empirical reason makes impossible the assumption which we have just considered. In the words of the late Professor Nagel, "Unquestionably an hypothesis which should permit us to ascribe to individual nerve-fibers a single qualitatively determined and unvarying mode of excitation (Erregungsart, and the context shows that he is referring not to the form of stimulation, but to the nature of the sensational response) would be by far more satisfactory, and would stand in closer accord with other investigations. The special investigations in sense physiology, however, are not at present favorable to such an assumption." The evidence is as follows. Müller left his theory in a crude form, inasmuch as he thought of a 'specific energy' for each 'sense' — sight, hearing, and so forth; but each 'sense' gives us several qualities (as four for taste, at least several thousand for hearing, and an indefinitely large number each for sight and smell) ; and every argument that speaks for specific energy at all for the several sensory modes, speaks just as imperatively for a separate energy for each quality within the mode. This 'undoubtedly influenced Helmholtz, in his theory of audition, to assign to each fibril of (the cochlear branch of) the eighth nerve, the work of transmitting a separate auditory sensation of pitch. The fact that these fibrils are connected serially with the graded series of organs of Corti made the
(318) theory very plausible. Helmholtz was similarly influenced (although the evidence is here less obvious) in his assumption of three fundamental qualities of vision. Now the extension of the theory of specific energies to the sensory qualities, as required if the theory is to explain the facts which it undertakes to explain, has been thoroughly unsuccessful, and has been put by recent investigations quite out of question.
In the first place the theory never has, in spite of several efforts, been extended with any degree of completeness to the qualities. The greatest success was attained in Helmholtz's theory of audition. This theory conceives the series of pitches as the qualitative auditory series (of which the justice has been disputed), shows the different pitches to be carried to the brain by different nerve-fibrils : and in spite of some doubts on the score of difference- and summation-tones was on the whole a credible theory. The theory still meets with several difficulties, nevertheless, a rather serious one being the difficulty of conceiving how the radial fibers with their almost microscopic dimensions can 'resonate' to so great a range of pitches as are included in the audible range of hearing, and specially how such resonance is possible between the little fibers and the lower audible wave-lengths which are little short of sixty-four feet. Furthermore these radial fibres are transversely bound together, so that any true resonance must be made more difficult, and a specific resonance of individual fibers to respective individual tones seems quite out of question. Were this not the case, it is estimated that the radial fibers would be numerous enough to correspond to the number of distinct audible pitches if this latter is taken as the same as the number of successive pitch differences discriminable in an ascending or descending continuous series of tones. In fact, however, the series of pitch sensations is continuous, and so includes infinitely more pitches than are brought out in the step-wise series yielded
(319) by the discrimination experiment. Helmholtz himself admitted, if I recall aright, that many intermediate pitches must be accounted for by the simultaneous activity of adjacent organs of Corti excited severally in differing degrees of intensity. This rather stretches a point in order to prop up the general theory of a nervefibril to a sensory quality : and yet one is tempted to let it pass, owing to the close resemblance between near-lying pitches.
But in vision the case is less favorable. The color series is also a continuous one, and since on the red-green zone of the normal retina (a very considerable area) every hue can be perceived at every point, it was from the outset out of question to look for, or to assume, a cable of nerve-fibrils going to every point and large enough to provide a separate fibril for each of the discriminable color differences, to say nothing of the actually continuous series of such differences. So here Helmholtz stretched still further (and very far) the point which just now we let pass. He assumed, in effect, three fibrils going to what is practically each point of the red-green zone, and assumed one of the three colors red, green, and blue to be aroused in the mind by activity of one or other of the three fibrils. Intermediate colors, as in the dubious point conceded in the case of audition, were aroused in the mind by the simultaneous excitation in different relative amounts of two or even three of the fibrils. Thus yellow, in which few persons recognize any resemblance to either red or green, must nevertheless be understood as the mental result of simultaneous and equal excitations of red and green fibrils : and white, which resembles no color, as the mental result of equal excitations of red, green, and blue fibrils together. Now here surely the matter has been stretched too far, for if yellow and white are not sufficiently distinct qualities to have special fibrils assigned them, then the theory of a nerve-fibril to a sensory quality has simply failed. The case is furthermore worse than in audition, for the mind must be inexplicably aroused to perceive different qualities on the excitation of different fibrils, and intermediate qualities according to relative and exactly discriminated quantities of excitation;
( 320) and now, per contra, it must be aroused to apprehend the same quality on the excitation of several thousand different red, or green, or blue fibrils. When the point is stretched so far, the principle of a nerve-fibril to a quality is squeezed to vanishing ; it is lost.
Moreover, continuous qualitative series quite bridge in many cases the gaps which the older psychology rather jauntily assumed to exist between the 'five senses.' There are innumerable sensations which are aroused by the simultaneous excitation of taste and smell fibrils ; indeed, all but four of the so-called tastes are due to the cooperation of olfactory excitations, and yet it is notorious that none but the trained, and few of these, can mentally resolve these sensations into taste plus smell. For nearly every one they are as unanalyzable as is white unanalyzable into red, green, and blue. Again the variety of tastes is greatly increased by the (mentally) unsuspected assistance of the touch sense. The senses of touch, pain, warmth, and cold (known to have separate end-organs) are inextricably co-involved in the production of a vast variety of 'dermal' sensations; while, according to Professor von Frey, the sensation of heat is due to the simultaneous action of organs which if excited severally would yield sensations of warmth and cold. The number of instances could be increased to any length, but I will further mention but one sensation which I may call the still, small voice of psychology : the sensation which has no namable quality. It is familiar, I think, to every trained introspector, and certainly to every observant one ; one seeks in vain to assign it to any of the familiar senses, and it is distinctly not visceral or otherwise of a proprio-ceptive order. Thus I have several times been as assured as the nature of the case allowed, that the stimulation which yielded the experience was either visual or auditory, and still I was quite unable to recognize the result in consciousness as either a color or a sound ; yet the sensation was moderately intense and it held its own well under the process of introspection. By way of introspective description I can only say that its quality suggests
(321) something primal and unelaborated. I mention this at some length because it will interest us later : and also because it is so little suggestive of a rough and ready scheme of specific energies.
And thus it is that the theory of specific energies of nerve, twist and refine it as one will, encounters so many difficulties and ends up with such a bland profession of ignorance, that one must go back, and indeed for economy of thought much prefers to go back, to the original facts, perplexing as they are. The considerations which I shall now adduce seem to me to plunge the merciful bodkin into the Müllerian theory and also to throw a flood of light on the seemingly baffling facts.
If nerve physiologists have been unable, for the support of Müller's theory, to discover anything like a qualitative difference among nervous impulses, nor yet suitable chemical or histological differences among cortical cells and synapses, certain recent discoveries have shown something about the nervous impulse which both does away with old conceptions and introduces rather extraordinary new ones. That something is, that the nervous impulse, and particularly the sensory nervous impulse, presents periodic fluctuations of a frequency vastly higher than was hitherto suspected. In the words of Professor Sherrington, "The number of separable excitatory states (impulses) engendered in a nerve-trunk by serially repeated stimuli corresponds closely with the stimuli in number and rhythm. Whether the stimuli follow each other once per second or five hundred times per second, the nervous responses follow the rhythm of stimulation. Using contraction of skeletal muscle as index of the response the correspondence at rhythms above thirty per second becomes difficult to trace, because the mechanical effects tend at rates beyond that to fuse indistinguishably. The electrical responses of the muscle can with ease be observed isolatedly up to faster rates : their rhythm is found to agree with that of stimulation : thus at eighty per second their responses are eighty per second. If the muscle note be accepted as an indication of the response of the muscle, its pitch
(322) follows pari passu the rate of stimulation of the nerve through a still greater range." "The refractory period in nerve-trunk conduction seems to last not longer than lo—." The last sentence is equivalent to the statement that the periodicity of the nerve impulse can go as high as one thousand per second ; and it leaves the question whether the frequency does not go higher, unprejudiced, for further investigation. Almost all of the recent work on axis-cylinder conduction, muscle-tone, tetanus, 'Treppe,' and refractory phase gives indication of a similar oscillation of the nervous impulse at rates quite unsuspected by physiologists of an earlier day. Thus, for instance, Professor Piper finds that in voluntary contraction (under virtually normal conditions, then) the flexor muscle of the lower arm receives fifty nervous impulses per second. The reason why this discovery has been reserved until so recent a date is of the simplest, and is the one hinted at by Dr. Sherrington in the passage just quoted : the mechanical inertia of the recording instruments hitherto used in studying the nervous impulse has been such as to 'fuse indistinguishably' anything but slow fluctuations of the nerve-current intensity. But the mass and variety of evidence already on hand, together with its unquestioned authority, make it certain that as the use of finer electrical recording instruments progresses (particularly the oscillograph, which is a relatively new instrument in physiological laboratories), we shall become acquainted with a large field of phenomena relating to high frequencies of the nervous impulse.
Now, as has so often happened, evidence of the same fundamental fact has been simultaneously accumulating from another source, that of specifically sense physiology or psychology. In 1907 Lord Rayleigh  published a paper in which he showed conclusively
( 323) that sounds of lower pitch than 128 d.v. per second, at least, (and perhaps of pitch as high as 512 d.v.) could not be localized by means of differences between their heard intensities; but that they could be and were localized on the basis of their relative phases as they entered the two ears. Lord Rayleigh adds, "It seems no longer possible to hold that the vibratory character of sound terminates at the outer ends of the nerves along which the communication with the brain is established. On the contrary, the processes in the nerve must themselves be vibratory, not of course in the gross mechanical sense, but with preservation of the period and retaining the characteristic of phase — a view advocated by Rutherford, in opposition to Helmholtz, as long ago as 1886" (loc. cit., pp. 224-225). Now earlier, but unfortunately either not published or not adequately emphasized and therefore unnoticed, work had already been done which proved the importance of phase-differences in the localization of sound, by Sylvanus Thompson, Professor L. T. More, and Mr. M. Greenwood; and the fact has received further confirmation from subsequent experiments of Lord Rayleigh,  Professors Myers and Wilson, Mr. Bowlker, and Professor More. The last named author finds that phase-differences are effective up to pitches in the vicinity of 1024 d.v. (loc. cit., p. 314). Professors Myers and Wilson have tried to subsume the new facts under the old intensity-ratio theory, by alleging that phase is operative only as it is correlated with intensity, but their explanation is too patently a case of ingenuity expended to save a preconception. If the nerve-impulse were known not to show phases of the periods here involved, one would perhaps let the explanation in terms of
(324) the intensity-ratio theory stand, however improbable. Since, however, the very periodicities which are prerequisite have been independently proved to exist, the view of Lord Rayleigh and Professor More is altogether the natural one. Professor More pertinently says (loc. cit., p. 319), "The only objection to the idea that the ear is capable of detecting the phase of a sound or at least the difference in the phase of two sounds, is that it is difficult to reconcile with our theories of audition."
But the experiment showing that phase-differences govern the localization of the lower pitches is one in which no 'hypothesis' and indeed very little deduction has entered, whereas the Helmholtz theory of audition (to which Professor More must mainly if not exclusively have referred) involves a grave hypothesis, in the much-disputed resonance assumption, and was furthermore framed not a little in the interests of Müller's 'specific energies,' —a theory which we have already seen to be valueless. I say that it is the Helmholtz theory to which Professor More must have referred, because of the three other prominent theories, Ewald's in no sense depends on the Müllerian tradition, and Rutherford's and Meyer's are irreconcilable with that tradition. And the new facts regarding auditory phase are not difficult to reconcile with these theories. Indeed, Dr. Rutherford's theory consists in little else than an interesting, and to my mind valid, protest against specific energies, and in favor of the view that sensory qualities are conveyed to the sensorium by vibratory nerve-impulses whose rates are closely related to those of the impinging physical stimuli. The considerations adduced by either Dr. Rutherford or Professor Ewald are hardly complete enough to be called a 'theory' of audition; those of Professor Max Meyer better deserve the title. This investigator has offered a theory which takes into account and plausibly explains all the important peculiarities of audition (specially some of those which Helmholtz found most difficult), except the phenomenon of pitch ('quality'), which generally is the first point that a psychological theory
(325) undertakes to explain. I cannot discover that Professor Meyer has once made explicit mention of pitch, or how he understands it to be transmitted to the brain. And yet his theory is positive on this point; what it requires is to suppose that pitch is transmitted not by specifically different nerve-fibrils (as in the Müller-Helmholtz conception), but by nerve-impulses, along any or all fibrils, which consist of periodic vibrations identical in rate with the vibrations of the outer sound stimulus. I have never understood what I must call Professor Meyer's mysterious reticence on this point ; unless, indeed, one may suppose that, unaware of the arguments in his favor adduced by Dr. Rutherford and many other physiologists, he has hesitated to give explicit prominence to a feature of his theory which so widely departs from the Müllerian tradition. Indeed, the views of Meyer and Rutherford are not rival, but complementary and entirely harmonious theories. Together they form a compact, complete, and very promising theory of audition ; which, for that matter, would seem in no wise to jar with the fragmentary and somewhat whimsical speculations of Professor Ewald, although I can assign no immense value to these latter. In short, I have no hesitation in affirming that what we may call the Rutherford-Meyer theory is an adequate theory of audition, and that in view of recent discoveries in nerve physiology, it has the distinct advantage over the theory of Helmholtz. I could substantiate this conclusion in much greater detail, but in our present connection I have wished only to show that all considerations require us to abandon 'specific energies,'  that the facts of nerve physiology point unmistakably to the view that the quality of sensations is transmitted to the brain by vibratory nerve-impulses, that certain facts of sense psychology prove this in the field of audition, and further that here the vibration-rate corresponds to that of the
(326) outer sound stimulus, and lastly that this is not "difficult to reconcile with our theories of audition."
How may such a view, now, fare in the field of vision? — the only other sense which has been at all exhaustively investigated. The reply is that it fares very well. In a paper already referred to Mr. Meisling has presented very urgently the following considerations regarding color (cone) vision. Heat, light, and Hertzian waves belong to the same physical order, all being electro-magnetic vibrations and differing in the one essential of wavelength or rate. These waves can and do affect substances photochemically, as they have hitherto been conceived to affect the rods and cones of the retina; that is, by means of so-called visual substances. But there must be a photo-chemical substance to be affected. In the case of the rods such a substance is found in the visual purple, and the conscious result is white or gray sensation. In the cones no photo-chemical substance has been demonstrated, although the purple of the rods was discovered relatively early (by Boll in 1876), and three or more visual substances have eagerly been looked for in the cones. Now the 'visual substances' were always purely hypothetical in our color theories, and were conceived merely by analogy with the pigmented cells of rudimentary vertebrate eyes and with the visual purples of the rods in vertebrates. This analogy was not unreasonable, but it is unreasonable to cling to it when almost a half century of investigation has failed to bear it out, by demonstrating not even one of the supposedly requisite photo-chemical substances. Now the cones need not be conceived of as actinometers ; they may be thermometers (bolometers), or resonators. They are probably not thermometers, since then they would be more sensitive to red than to yellow light, and still more to the slower heat waves than to red. But the cones may very well be resonators. If they are, the fact would account for their remarkable unfatiguability, a point which Hering emphasized in his arguments against Helmholtz, and to provide for which (in part) Hering conceived his antagonistic ana- and katabolic visual processes : a conception
(327) which was applied by Hering to the temperature sense, and which was overturned by the discovery of separate warmth and cold spots. Now Meisling adduces facts concerning the structure of the cones, their several types, the structure of the several layers of the retina, the contraction of cones under light stimulation, and concerning the rest-currents and action-currents of the retina, showing how these facts well agree with the view that the cones are electromagnetic resonators.
Perhaps the most interesting confirmation of this view lies in the complementary attunement of those instruments which receive Hertzian waves; a point which I have already touched on. This would account inevitably for the complementariness of colors, and in this regard both of the present theories of color are unsatisfactory. Helmholtz's 'errors of judgment' are in many phenomena of antagonism altogether far-fetched : and Hering's kata- and anabolic processes are unconfirmed hypotheses ; they meet special difficulties in regard to the white-black series, and they contravene sound physiological analogy. For, as has been pointed out before, it is as unprecedented that an ana-bolic process should directly yield sensation, as that it should directly cause muscular contraction.
It is admitted on all sides that neither the Helmholtz nor the Hering theory of vision had ever the authority of Helmholtz's theory of audition, and that neither is to-day an acceptable theory. It is generally believed that each contains errors so radical that it would take elimination as well as supplementation to transform it into a definitive theory. Such a transformation, of either theory, Meisling offers when he suggests in place of 'visual-substances' three or more differently attuned types of retinal resonators. And, as we have seen, the same suggestion contains the foundation for an explanation for the so-far unexplained antagonism of colors. Whatever the result may be for color the-
( 328) -ory in general, our present point is that we have cogent arguments for believing that the visual impulse traveling along the optic nerve is, as in the case of audition, a vibratory impulse whose period corresponds with the vibration rate of the impinging stimulus. And the opposing view of photo-chemical substances with 'qualitative specific energies' has no direct evidence to support it and a considerable body of evidence to refute it. Mr. Meisling's position, I believe, is conservative, and more secure than any other.
When we come to the other senses much less can be said on either side of our question. I cannot discover that anything pertinent, and I might almost say anything at all, is known of the actual physiology of the remaining organs of sense. Certainly all details of the processes of stimulation here are veiled in mystery. These other senses are generally thought to be either mechanical or chemical as to their immediate stimulation. Rodvision remains a chemical sense of which no further details are known concerning the nervous impulse that the bleaching of the visual purple initiates. Yet the minute hairs on the olfactory and gustatory cells have given rise to some speculation as to whether the ultimate stimulus here might not be mechanical after all. The temperature organs may well be resonators to heat waves, but that is pure hypothesis. The pain, touch, and joint senses are almost certainly mechanical in their mode of stimulation, but that statement has no special significance for one who is trying to understand the physiological processes involved in their stimulation. The fact that mechanical stimulation of the chorda tympani, a gustatory nerve which passes through the middle ear, produces a sensation of taste, remains the one undisputed case in the series that was adduced by Müller. It does not
(329) prove the existence of a qualitative specific energy, but it may squint that way, and must be borne in mind in a dispassionate survey of the whole situation. We are woefully ignorant of all these matters, and in science imagination is no counter-irritant for ignorance. The Müllerian theory of specific energies receives no support from the total ignorance prevailing in this field, while it is refuted by much that we do know about vision and audition. If conjectures are to be made as to the nervous impulse in the mechanical and chemical senses, the safest way will be to draw some analogy with what we do know about the light and sound senses. I personally believe that gratuitous conjectures (as opposed to grounded deductions) are mischievous, and I have no interest in them, whether they are pro- or anti-Müllerian. There is a general consideration, however, which may properly be mentioned here. The specific energies, whether in nerve-fiber, brain-cell, or synapse, are conceived of as differing qualitatively from one another. Now science has so frequently found that examination of what appear to be qualitative differences shows them to be really quantitative differences, that it has come to be a maxim of science that there are no 'qualitative' differences. This, I think, oversteps the mark : there are qualitative differences, obviously, but these are usually analyzable into quantitative differences ; precisely as every starch is a starch, but can be analyzed into one of a series of quantitatively related carbohydrates. The maxim should then be, simply, that quality is not an ultimate category of natural science, and this maxim is universally acknowledged save by a small group of persons of a certain, possibly
(330) rather vague, type of mind, such as, for instance, the neo-vitalists. Now it follows from this that the specific energies can hardly hope (or desire) to retain their peculiar, strictly 'qualitative' status, and I should like to ask the believers in specific energies if they can think of any other quantitative interpretation for these qualitative differences, than one which I have been arguing for. If I have spoken against specific energies in toto, it was solely because most of the followers of Müller cling tenaciously to their unanalyzable 'qualities' and account them the palladium of their sect. It is significant indeed that Helmholtz, who did more than any one else to substantiate Miller's theory by physiological evidence, held that the energies differed only in quantitative ways. And it is only fair to add that in Müller's own writings the word 'quality' is used only in a casual fashion, as if it slipped in while his attention was focussed on other matters. I do not think that Müller anywhere proposes to exclude the resolution of these 'qualitative' into quantitative differences. And it is a matter of indifference whether the arguments which I have presented shall be said to oppose or to interpret and extend the original theory of specific energies. The real purpose of this all too tedious digression into physiology, is to show that there is excellent and abundant evidence of minute periodic fluctuations in the nerveimpulse, and of a close correspondence, in the cases of audition and color-vision, between these fluctuations and the vibration rates of the impinging physical stimuli.
We have next to examine the secondary qualities from the so-called subjective or introspective point of view: and here we shall presently see the bearing of the foregoing discursus on the realistic issue.
Our urbane adversary adduces secondary qualities, and perhaps even deigns to mention his favorite red, yellow, or blue, quite as if these matters contained no intricacies worthy of his closer attention, and none that could throw any light on his own pro-
( 331) found views as to their 'subjective' nature. Indeed our adversaries, particularly of the present generation, are so emancipated from allegiance to anything that can be called empirical, look to it so little for guidance, and argue on grounds so a priori, that they can only expect some day or other to be punished for indolence and frivolity. The blessed Absolute will certainly strike out at them with a burst of novelties : for the Absolute is a powder-magazine as well as a precious pot of slumbering ineffables. Now the secondary qualities present interrelations both fixed and intelligible, so that those persons who seriously study them begin to see that they form a system like the systems discovered in mathematics, and this fact alone, as some one has said, already sets them off from the purely 'subjective,' individual, and incalculable. Unquestionably the most comprehensive single treatise on these interrelations is the remarkable work of Dr. Brentano, "Untersuchungen zur Sinnespsychologie." He dwells primarily on the relation of similarity between the qualities. Thus in the spectral series of colors, every hue has a position intrinsic to itself by virtue of its similarity to the adjacent hues : a particular orange has no place in the series except just between a certain yellowish red on the one side and a certain reddish yellow on the other. To assign it any other position would be like trying to assign to the number 3 a position in the number series between 528 and 529. (I know that some subjectivists declare with their usual license that this can be done, but before they stake great hopes on doing it I urge that they actually try and then report to us from time to time on progress made. One can place orange in space among the reddish purples, but it hits back at one because the spatial order has been made discrepant with the 'intrinsic,' logical color order.) And the case is the same with grays, with auditory pitches and timbers, with warmth and cold sensations, to some extent (which increases with careful study) with tastes and odors : the same thing is true of all intensities in whatever field of sensation.
Now why, asks Brentano, is this relation of similarity so rigid
( 332) and inexorable? The reply has often been that the question admits of no answer, that namely this qualitative similarity is an ultimate, unanalyzable category; the very answer that for centuries was made regarding the similarities between plant and animal species and between chemical substances. God made them so ; voilà tout. The modern answer is identical save that, agreeably to the whim of the day, God is left out. But Dr. Brentano is something of an empiricist, and knows the empirical grounds for the maxim that quality is not an ultimate category of science. He looks then, but only looks and does not a priori argue, for some quantitative resolution of these qualitative relations of similarity. And he finds them in profusion. It happens that ever since the day when Helmholtz made a group of tuning-forks pronounce the vowels, and he and Stumpf showed that musical chords can be analyzed, not merely physically but as purely 'subjective' phenomena, it has been generally conceded in psychology that a quality may seem as unitary as possible, and that it may nevertheless be, still merely as a conscious phenomenon, complex. It is admitted in short, though sometimes grudgingly, that even consciousness requires careful study, like any other phenomenon, and that a seemingly simple quality may only need practised scrutiny to be resolved into separate elements. The merest novice may have an inkling of this if he will strike the prongs of a fork from the dinner table, press his finger very lightly thereon, and ask himself carefully whether he feels a simple quality of roughness or a microtactile succession of impacts. In fact, the analysis of conscious qualities is precisely like the analysis of chemicals; if careful study yields an analysis, the phenomenon was not simple ; if components are not isolated, the phenomenon may be simple, or it may yet be analyzed by further study.
This principle is now endorsed by the most conservative authorities, for the entire range of musical chords, timbers, and every other variety of auditory quality, except pitches, and including (with a few dissenting opinions) noises. The principle is not so
( 333) universally admitted in the field of color, and here Brentano commences his investigation — "Concerning Phenomenal Green." Is green a simple quality with 'similarities' to yellow and blue, or is the green composed of two elements, yellow and blue? Introspective reports differ, and the question arises whether this is because the judgments are based merely on associations (as in some careless investigations in aestheties) and are subject to various 'illusions of judgment,' or whether the divergence arises because the individuals reporting have varying degrees of skill at introspective analysis, as in the case of the analysis of a chord by musical and unmusical individuals. For Brentano the latter is the case here, and in my opinion he thoroughly substantiates his opinion  with a wealth of fact and a scrupulous precision of treatment, which leave nothing to be desired. The concensus of opinion among painters, who are here the trained musicians, is that green is composite, and phenomenally is yellow and blue. This is not owing to the fact that they often make their greens by mixing yellow and blue pigments, for on the one hand they very often make green by mixing yellow and black ; and on the other hand, while they as often make yellow by mixing orange and green pigments, they never see in the phenomenon yellow - orange and green. They make 'fine gray' (S. 153) too by mixing red and green, and another gray by mixing yellow and blue, yet they never see in the resulting gray these pairs of colors. Brentano's argument touches every conceivable aspect of the case, and I must here refer the skeptical reader to the original work.
Green is, in short, an interesting, because disputed, case like others which are more generally admitted. More persons admit that they see orange as red and yellow, that purple is red and blue, that greenish blue is green (or yellow) and blue, than admit that green is a composite quality. There is, on the other hand, a striking unanimity of opinion among the practiced as well as the unpracticed, that white resembles no color, that gray resembles nothing
( 334) except white and black, and that red, and yellow, and blue are phenomenally simple. Thus the rudiments of a mathematical system among the colors begin to emerge, as once analytical chemistry emerged, by virtue of unanimity among the penetrating and expert, and in spite of some dissent from those less experienced. Brentano brings out many other analyses of color qualities into their simpler components : but of these I will mention but one. Is it true, he asks, that red and green are as antagonistic as Hering, for instance, declares them to be when he says that they can never be perceived together at one place? And if so why is it that olive-green seems to so many persons to contain a red component? Brentano says much more about it, but I will leave the question here to the reader's introspection ; admitting for myself that I have always seen red in olive-green and have never dared to say so.
In the field of audition Professor Brentano takes up an analysis by Professor Mach  a of the pitch series, into merely two qualities — ' Dumpf' and 'Hell'; such that the various pitches consist solely of these two qualities combined in varying proportions. Brentano does not fully agree with this, but agrees so far as to admit the qualities, dull and bright, and that the lower and higher pitch ranges are always tonally unsaturated by reason of an admixture with one of these qualities, precisely as dark and light colors are always unsaturated by reason of admixture with black or white respectively. There follows an incisive and careful account of the matter, based on introspective judgments, which is not wholly out of joint with the valuable contributions of Stumpf in this same
(335) field. On these and many other purely introspective empirical analyses of the qualities Brentano bases his principle of 'compound qualities' (multiple Qualität), the principle, namely, that the qualities presented in consciousness are generally not simple, not even 'phenomenally' simple, but are composed of two or more qualities which careful introspection enables us to apprehend as integral parts of the presented quality. This principle is by no means new, being merely an extension to the entire field of conscious qualities of the principle of analysis already brought to approval and acceptance through their work on musical chords and timbers, by Helmholtz and Stumpf. And I think that an unbiased survey of the facts adduced by Brentano must convince any one of the correctness of this extension of qualitative analysis which is offered in the principle of compound qualities.
Now in recent years the traditional distinction between the 'different senses,' i.e. the modes, has been generally breaking down. It is at best based on nothing but the gross anatomy of sense-organs, and has just about that weight of authority which we concede to the popular 'five senses of man.' Apart from the facts that the 'sense of touch' is supplied with at the very least four different sets of nerves and sense-organs, and the tongue with at least three types of sense-organ and three distinct cranial nerves, we have innumerable conscious units, phenomenally considered, which at first sight seem as simple as colors or musical chords, but for which we know that the physiological apparatus of production involves a variety of different senses. The most familiar case of this is the so-called 'taste' sensations, of which all but four (sweet, salt, bitter, and sour) involve the coöperation of an indefinite number of olfactory fibrils, besides, very often, that of touch, warmth, cold, and pain fibers as well. Thus a taste which until analyzed seems as simple as the color yellow is yielded by no less than three of the 'five senses' working in coöperation; or, in the modern terminology, by the action of the taste, smell,
(336) tactile, and perhaps the warmth, cold, and pain 'modes' all together. Almost every familiar touch sensation (smoothness, wetness, et cetera) is recognized as being similarly compounded of two or more dermal modes. And the number of such seemingly simple, yet physiologically complicated, sensations is beyond reckoning; and were it to come to such conscious entities as "the feeling of triangularity," which several psychologists have asserted to be simple, the variety exceeds all bounds. In short the modal boundaries, perfunctorily taught in many elementary textbooks, has no meaning at all for a psychology which has outgrown its swaddling clothes (cf. Nagel, op. cit.). Here too Brentano comes in with fresh arguments, and notably in the matter of intensity. Now intensity is admittedly a feature of all sensations and perceptions, and in so far binds together the different modes. Yet only rather recently has it been shown that the intensities of two different qualities even within a mode can be accurately compared and a judgment pronounced of more and less. Professor von Kries now says that this is undoubtedly possible for colors however distinct in quality. Dr. Brentano goes further, showing that in such cases as of a very faint odor compared with a loud noise, it is possible to judge that the latter is more intense than the former. How far practiced introspection may enable us to go toward the refinement of such judgments, nobody as yet may know. There are also other communities between the different modes : "A sound that approaches a noise in character we . . . pronounce a less saturated tone sensation than another which is less like a noise. In the field of taste, indeed, Aristotle correctly remarks that sweet is related to bitter as is a brighter to a darker color. And similarly several persons whom I have asked have definitely pronounced the cool sensation of a breeze blowing on the hand as brighter than the feeling of a warm breath. A sensation of coolness compared with that of sweetness or with the odor of a lily, is as un
(337) saturated as white compared with a color in the narrower sense, or as a hiss or other noise compared with a vibrant tone.'  By such examples this author shows not only that the infinity of qualities within the mode consists, phenomenally, of combinations of elementary qualities, but also that the modes themselves merge into one another and present, in part at least, common elements such as intensity, saturation, brightness, and so forth. Lastly I will mention Professor Brentano's thesis that no quality which has intrinsically a position between two other qualities can be simple. It must rather be a compound of the qualities between which it so obviously lies. For in what, otherwise, should the two similarities, this necessary betweenness, consist? Here he takes, as unequivocally as possible, the accepted position of science, that qualitative 'similarity' is never an ultimate category.
However one may agree or disagree here with some of the particular cases, enough is proved, and I think very amply proved, to show that nearly if not quite all of the so-called secondary qualities are, taken merely as phenomena, complex; that careful introspection enables us to analyze out many, more elementary qualities ; and that, furthermore, we cannot as yet seethe limits to the possibilities of such analytical procedure. Such a psychological 'atomism,' for this is what the whole matter points to, has been shown by other writers to be the course which the facts are clearly leading psychology into. Professor Münsterberg is one who has urged this. "Are these sensations," he writes, " the ultimate elements of our consciousness, or is that which we call a blue or a hot sensation, a sweet taste, a tone C, a muscle sensation or a pain sensation itself a complex affair which consists of more elementary parts : in short, have we in the mind ultimate elements which are simpler than the sensations? It is the inquiry for a radical psychological atomism." (pp. 4-5). "The psychological fact which stands immediately in the foreground of such considerations is 'the fact of the similarity of the
(338) sensations. . . . Similarity from the point of view of description is community of parts : . . . The logical conclusion by analogy is that two sensations also are similar to each other only when they contain various component parts of which some are common to both. These parts are of course not sensations but inexperienceable factors like the atoms, and as we do not know a sensation which is not in some way similar to some other one, we can say that no known sensation is an ultimate element" (p. 11). Thus for Professor Münsterberg the ultimate elements will necessarily be 'absolutely dissimilar' from one another, since so long as any similarity subsisted, it would indicate the presence of some yet similar common ingredient. The same should indeed seem to follow from Professor Brentano's principle that no quality is simple which (by similarity) lies between two others. Both writers agree that all the traditional modal "demarcation lines which existed for the sensations have now disappeared. . . . The similarity between smell and taste, or between touch and muscle sensation, and so on, appears then not different from the similarity of two tones" (p. 13). Professor Münsterberg adds that only the ultimate elements, "the psychic-atoms can rightly be correlated with the physiological units" (p. 16), meaning to suggest, clearly, something like cortical cells or synapses.
This is a very promising program, but one point needs further examination. We seem to come out with a set of 'utterly dissimilar' psychic elements, and we seem to have no clue as to how many of these we are likely to find ; it will apparently not be less than the number of cortical elements. This must be, of course, as it empirically is found to be; and yet an analysis with so stated a limit is so different from all other scientific analyses, that one is prompted to look through the argument once again. Besides, scientific analysis arrives at similars and not at differents. Will it pay us to undertake the analysis at all if at the end the number of irreducible elements is to be not less, and perhaps far more, than the number of brain-cells or synapses ? Will that be a kind of science to which the human mind shall advisedly address
(339) itself ? We have already seen that introspective analysis is precisely comparable to chemical analysis, and Professor Münsterberg's program promises as its goal very much that thing which chemistry had attained when it had reduced all substances to some seventy not further reducible types of atom. But we now see that this was not to be the goal of chemistry ; the periodic law, largely, dissolved these 'atoms.' A further comparison with chemistry shows the miscalculation in this psychological program. And this lies in the neglect of an important aspect of analysis.
If it is true that a quality which lies between two others must have a common ingredient with them, it does not necessarily follow that for the original three qualities the total number of ingredients is now four (one common and three proprial). Such cases occur, but they are utterly atypical. Typically the three qualities are at first found to consist of two ingredients only, combined in different numerical proportions ; and finally of only one substantial ingredient, such as one kind of atom, variously organized, such as three sizes of molecule. And science has the best empirical evidence for accounting no analysis complete until it has reduced all qualitative differences to different arrangements of elements which are all alike in quality. (And 'quality' here is presently seen no longer to have a meaning.) In physics and chemistry these arrangements are confessedly numerical values organized in time and space. Now it is here, probably, that Professor Münsterberg finds the rub, for he denies (for reasons of a somewhat metaphysical character) that psychic atoms exist in time and space, or can be organized therein. It should seem to be for this reason that he sets so singular a goal to psychological analysis. Now we can for the moment grant him the timeless aspatiality of psychic atoms, since a merely numerical, or, as I should perfer to say, logical principle of organization is quite enough for our purpose; — of which the number system itself is an instance. This principle alone will give, from one type of element, all the variety which we require, as any one shall see who will trouble to enumerate all the positive whole numbers, to say nothing of the
(340) negative, fractional, irrational, and 'unreal' numbers. There seem, then, to be no reasons of a general nature why we should not hope to reduce by analysis all of the conscious qualities to different forms of organization of one sort of element. So much for theory; how are the concrete facts?
They are most patently that psychic entities in general (and not merely elements) are organized into higher units precisely in time and space. The 'Gestaltqualitäten' are precisely such higher units : any rapidly phrased sequence of a few tones yields a form-quality which psychologists have repeatedly declared to be a new, unique, independent, and unanalyzable quality ; and yet it is a thing of which the structure remains conspicuous. New and unique it may be, but it is neither independent nor unanalyzable ; indeed, the conscious analysis cannot be inhibited except by the most purblind votary of preconceptions. Certainly there is novelty about a new form of organization ; water is, indeed, more than oxygen and hydrogen, it is these with organization added. And this is precisely what the analyst says, — water is hydrogen and oxygen and organization. So with the form-qualities. Their number, too, is without end in all the fields of sensation where succession can be perceived, and I make bold to affirm that none can deny that here the psychic components are organized in time (just like 'ether' vibrations) except after an a priori metaphysical preamble which is deliberately calculated to obscure the salient empirical fact.
Now we have form-qualities in space as well as in time. The late Professor James has dwelt on the integral aspect of such 'feelings' as that of triangularity, rotundity, squareness, and one quite grants this as one grants the integral aspect of water. Indeed I should add millions more, for I discover a similar integral aspect to the comic and the tragic, to the picturesque, the blithe, the wholesome, the inquisitorial, and the horrific. (While the unanalyzed aspects of the canonic-pretentious, the idiotic-fallacious, the obscurantic, and the conscious-deceptive are units to keep well in mind so that one may recognize and name them when one
(341) meets them —whether in one's self or in another.) These all, however, have their disintegral aspects as well ; they are clearly complexes organized temporally, spatially, or logically, or in more than one of these ways at once. The beauty, however, of the purely temporal or spatial form-qualities is that they reveal more clearly than any instance ever shown in chemistry, that the peculiar flavor of the whole does not devour and supersede the distinctness of the parts, or that the relatedness of the parts is not repugnant to the unity of the whole. If one finds it at all within one's powers to believe that the water which one drinks is oxygen and hydrogen spatially combined, how much more should one see that the Graal Motiv is a temporal succession of tones, and that the triangle is perceptions of line and angle spatially ordered : for the water does appear to supersede its gaseous components, whereas in the form-qualities the synthesis and analysis are to be observed simultaneous and amicable. Once more I affirm that one cannot deny the spatiality of the organization of the conscious elements of a triangle, except one close one's empirical eye-lids in sleep.
But these cases seem remote from the secondary qualities, our theme. I mention them merely because their temporal and spatial organization is so indubitable. Yet from these form-qualities we can pass directly down to the qualities where the formal element almost or quite defies introspection, and we shall find examples at every step. A paradigm than which nothing clearer can be desired is a series of light touch stimuli given at an ever increasing rate. The single tap is called a conscious (secondary) quality. A pair in slow succession is already a form-quality, with all the vaunted charms of novelty, uniqueness, and what not ; yet I will not believe that even amid such delights any one can for an instant find there anything more than two taps plus temporal organization (I grant that this last consists of more than mere twoness). A pair given in more rapid succession is another form-quality, 'entirely different' from the first, as we may read in many of the textbooks. It is not entirely different, but it is different, and by just as much as the difference of temporal or-
(342) -ganization has altered it. Here too the unity of the whole does not infringe on the distinctness of the parts. As the taps are given in faster and faster succession, however, there comes a time when encroachment sets in (at somewhere around 3 taps per sec). The integral aspect is approaching that to which we give the name roughness (but is not yet roughness), and the attention is drawn ever and anon from this to the other aspect, which now consists in an attempt to count the taps and to articulate the number with the tongue. The two aspects have begun to behave precisely like the two aspects of water —either H2O or water. The incompatibility of the two aspects depends, however, on no feature of the new form-quality, but on a definitely physiological defect of the time-sense which has begun to be flustered and calls in the tongue to its aid and so spasmodically wins to itself the balance of attention. This is precisely comparable to those time-errors mentioned in an earlier part of this paper. Even here favorable moments arise when the integral and disintegral aspects are apprehended together and as not antagonistic. As now the rate of tapping increases the unified aspect approaches the (form-) quality of roughness, and more and more tends to usurp the attention; while the succession-of-parts aspect becomes vaguer. Articulation is outstripped, then the count is lost, then a sympathetic, voluntary, inner rhythm (of the vocal cords?) which replaced lingual articulation falters and fails, leaving a bare and nonparticipating awareness of succession. This last persists up to very much higher rates, dying down only at about 600 taps per second. Meanwhile the roughness has become a distinct quality in its own right, so that some psychologists describe it as subsisting with, but 'utterly independent' of, the awareness of succession. They are the same who find water utterly independent or hydrogen and oxygen ; while the truth is merely that with the increasing rate of the taps comes increasing (logical and temporal) complexity of relations, to meet which the attention (with its time-sense and other auxiliary implements), no longer able to survey the whole intricacy, covers such parts as it best
(343) can. Again (to resort to my all but evaporated simile) this is like the many properties of water, all of which are deducible from, and logically bound up in, the properties of oxygen and hydrogen and their form of combination ; yet so intricate is the whole manifold, that the scientist thinks himself fortunate if in a lifetime he can make a survey of even the vapor-pressure properties of oxygen or the rôle played by water in dropsy of the mammalian heart. This is what there is, and all that there is, in the current semi-mystical rubbish about the incorruptibility of wholes into their parts. A whole is different from and independent—of its parts for precisely those persons who find the word 'independent' so censurable when uttered by the realist.
Thus in the experience of tactual roughness the properties of the ordered whole gradually supersede in attention the properties of the parts ordered, not because the whole, as the rate of tapping increases, is coming to be anything other than the ordered sum of its parts, but because the quicker succession soon eludes the sense of time, and so leaves other features of the succession (which moreover is itself now a more complicated thing, per time unit if not also otherwise) to occupy the attention. This is merely to say, what we have found all along, that the faculty of attentive introspection (and notably in so far as this relies on the time-sense) has its distinct limitations. Stated with less concreteness but with more logical precision, the case is this. Even a slow succession of taps (and even were each of these logically simple like a geometrical point) is already a logical system of no mean complexity; as one sees from the number of derivatives discovered by differential calculus where a rate of succession is involved. It has therefore distinct parts which I have in deference to a bad tradition called 'aspects.' Now the case of the rather slow tapping shows us that the series is at one and the same time both a division of time and a quality, roughness; by which I do not mean that the quality is anything over and above, or added to the pure succession of taps. It is some intrinsic feature of that succession, logically bound up in it. The quality part may be
(344) related to the time-division part as the mere arithmetical number of railroad ties to the mile is to the spatial distance between the ties : these two values are simple functions of each other, of course, and yet mathematically not identical. Indeed, the actual experience of the taps strongly suggests that the quality is the number of taps per unit of time (i.e. their density) as distinguished from the (perceived) time interstices between them ; for as this time-perception wanes, the (to be sure uncounted, which is a still different matter) number-quality, if I may so call it, waxes. To show that this is by no means whimsical hair-splitting, I may remind the reader that in railroad construction one speaks of a cheap or expensive road-bed, quite as if these were 'qualities' of the bed. Now this quality of expense is held to vary directly with the number of ties to the mile (for one of the factors); while the very different quality of safety of traffic is held to vary directly (for one factor) with the nearness of the ties to one another. And even to a layman it would seem less direct to state the safety of traffic in terms of the number of ties to the mile, or the expense of construction in terms of the spatial vacancies between the ties, although either could be done and by some accountants doubtless is. Similar niceties abound in the computation of trafficdensity, train-load, and so forth.
Again a rate of motion is a rate of motion, yet it has, not by way of additions but by way of inclusion and inalienably, first, second and n derivatives of space with regard to time : these are parts of it just as number of taps per time unit and the divided time intervals are parts of the tap-sequence. Yet as intimately as the rate of motion and its first derivative are related, so that to loose thinking "one is merely a different aspect of the other," the rate of motion may be very great while the first derivative is zero;
( 345) the body is moving rapidly, but accelerating not at all. And when this little mathematical scheme of relations is found to prevail in concrete affairs it often determines extreme qualitative contrasts. A man may be very rich (a form-quality surely) and happy (another and very different form-quality), yet the beingrich depends on his rate of income while the being—happy or unhappy depends on the first derivative of the rate of income — the rate of accumulation; for however rich a man is he sees and feels his fortunes bright if his rate of income is increasing (i.e. if the first derivative is positive); but he sees them dwindling and feels that ruin is only a matter of time if the first derivative of his rate of income is negative.
I hold it then to be no academic act of logic-chopping if I say that the experience of the tactual rhythm shows that time-division and number ('Anzahl') of taps per time-unit are distinct though inseparable parts of this sequence, and that this latter feature is just the quality of roughness. At some rates the attention may be given to both features simultaneously or to either at will; at other rates the powers of attention (introspection) prove inadequate and only the quality can be apprehended. This reveals a limitation of the power of introspection, and more specifically of the time-sense, but not any cleavage between the inseparable features of time-division and tap-frequency.
Now as the rate of tapping becomes still faster the quality of roughness changes continuously toward the quality of smoothness (just as in the spectrum red changes to yellow), until eventually it has run its gamut and becomes the steady quality of continuous touch ; which under other complications is a component of the form-quality solidity. The precisely parallel experience is to be had in the field of audition where a slow sequence of faint thuds or hisses passes over into a musical pitch. Here too there is a rate (best gotten with a siren of governable speed) at which the sound sequence and pitch are experienced together, as distinct but inseparable. Here too careful scrutiny shows that the marked-off time-intervals are time perceptions, while the repeated
( 346) hisses are the quality of pitch : the two are just as distinct but just as inseparable parts of the given succession as are the first and second derivatives of a rate of motion. In perception they are separable (as in mathematics distinguishable) just as in perception the form is separable from the size of a concrete object : — so specific is the action of the nervous system in selecting what features of a complex shall enter consciousness. The same experience is had again when the beats between two tones (nearly alike, but steadily departing from each other in pitch) gradually pass over (with a disagreeable transitional stage of dissonant roughness) into a third pitch, the difference-tone. Anent which we have some amusing speculations, called introspections, by persons whose logic has vitiated their introspection. These persons say that because the beats and the difference-tone can at a certain rate be apprehended simultaneously, the two "must be utterly independent" entities — a point which we have already dealt with. The parallel experience can be had in vision where an intermittent color stimulus is seen with increasing rate of flicker. At first it is succession without the flicker quality, then succession and a form-quality of flicker, then less obvious succession and more distinct (form-) quality, then the quality of (rough) flicker, then the quality of smooth flicker, then the end. This series is run through rapidly, since flicker entirely disappears at 60 to 70 alternations per second. The plain lesson of all these cases is that what we call secondary qualities are in truth form-qualities, simple psychic entities in temporal organization (rate of sequence) and we are tempted to view them as qualities instead of form-qualities because for all but the most absurdly slow rates of succession the time-sense is inadequate to its task. The successive 'aspect' is unperceived while the multitude 'aspect' (it might be by mere summation) gains on the attention. The time-sense throws over its duty so preposterously early that it is no wonder that for the upper range of pitches and for all the colors (which we know are 'correlated with,' and which I am aiming to show are identical with, extraordinarily rapid successions) every
(347) trace whatsoever of a form-quality should elude the introspection.
We are now in a position to sum up what I fear will have been a tedious and apparently aimless array of evidence. The prevalent form of the specific energy theory, or the view that the secondary qualities present ultimate unresolvable 'qualitative differences' (like the immutable species deposited by the hand of God in the Garden of Eden), has utterly broken down. It is actually the view that the qualities are independent, unanalyzable, psychic substances, and there is no good evidence that Johannes Müller ever intended his theory to take this shape. These qualities, considered merely as phenomena, reveal to introspection compound structure (musical chords, timbres, colors like blue-green, orange, violet, sensations such as roughness), 'similarities' (odors), and other affinities and repugnancies which prove that these qualities are not so independent as was supposed, but are at least related as different species are related in a genus. Further, the field of consciousness presents innumerable instances of psychic components organized into higher unities by means of spatial or temporal relations (form-qualities). Indeed, the entire field of consciousness presents nothing but such complex entities in which the principle of organization is either spatial, temporal, or logical, and a class reputed to stand quite apart, of entities alleged to be simple and independent —the 'secondary qualities.' These complex entities have indeed a unified 'aspect,' on which alone some writers are prone to dwell, and otherwise they were not units at all ; but they each and every one, as I have tried to bring out, reveal unmistakably the unity of the whole undispelled by the relatedness of the parts, and the ordering of the parts constitutive of the unity of the whole, as even no example of chemistry or physics so reveals. To any but the most purblind gaze they utterly scatter and quench the neo-Hegelian imbecilities about vital,' 'organic,' unanalyzable, and altogether ineffable 'wholes.' Alone the secondary qualities maintain their hereditary Sonderstellung. But we have found a breach in their wall and now know
(348) how defenseless is their position behind it. Any form-quality of which the principle of organization is time is, like any other content, dependent on the mechanism of perception for its entry into consciousness. And when time is the formal principle, this form, if perceived at all, must be perceived by aid of the time sense (of which the physiological mechanism is so far not in the least understood) ; and this time-sense is utterly inadequate to perceive the form-qualities when the time divisions therein involved are very small.
One hears that the time-sense is most acute : and the most favorable case that can be cited is that of bare succession. A single pair of auditory stimuli can be perceived as two, even when they succeed each other by two thousandths of a second. But this is not in truth a time-perception; it is one of mere 'twoness,' i.e. bare numerical as opposed to a truly temporal discrimination. And if the stimuli continue at anything like this rate of succession, the conscious result becomes at once a mere burred sensation akin to the quality of roughness. The time interval involved is not apprehended (as time). Tactual roughness can still be apprehended when the stimuli are as frequent as 600 per second, and this, again, is cited as a feat of the time-sense. But such it is not. There is no more consciousness of time involved in the quality of roughness than in that of smoothness or in the quality red, as the most casual introspection proves. What is interesting about roughness is that its quality varies so immediately with the number, of stimuli given in a time-unit that it shows conclusively that the nerve is able to carry an impulse of this same frequency number, and that the roughness quality is precisely this frequency magnitude and with the time element specifically omitted from consciousness. Just this, now, is what I contend is the case with all of the secondary qualities : they are all form-qualities in which the temporal subdivisions are so small that the time-sense cannot discriminate them, whereas the frequency magnitude or the density still remains perceivable : and density is different from time, since we have it in spatial and even in mathematical manifolds.
Now if the secondary qualities are all such densities, it must be
( 349) that, however inadequate the time-sense, the nerve-fibril is at least able to carry these densities or frequency magnitudes to the brain (even those of the highest frequencies, which are the violet end of the spectrum). And this is precisely what physiology is now showing to be the case. Rayleigh and More have proved that the auditory nerve carries sound-frequencies, up to 512, if not 1024, per second. And Meisling has adduced facts and arguments of great weight to show that the visual cones are electromagnetic resonators, and that the optic nerve must carry impulses of a frequency proportioned to that of waves of light. Everywhere, moreover, physiology, as distinct from sense physiology, is finding in the phenomena of 'Treppe,' refractory phase, et caetera, that the nerve current shows oscillations which can be measured only in a few thousandths of a second. If physiology has been late in discovering this, it is because such frequencies, to say nothing of higher ones, could by no possibility have been discovered prior to certain very recent improvements of instrumental technique, and specially the introduction of the oscillograph or string-galvanometer. I hold it, then, to be a view which is amply supported by facts, that the secondary qualities, instead of being unanalyzable psychological elements are all form-qualities of which the time-sense is inadequate to perceiving the form, while the density is perceived for very high frequencies by a process which is perhaps related to physiological summation. It is to be noted that the secondary qualities seem to engage the attention roughly in proportion to their density, as from our present view we should be led to expect. Tactual roughness is readily driven from attention (inhibited) by a sound of moderate pitch, this by a higher pitch, and so on up. But a color of anything like the same intensity, when presented, makes it difficult to attend to a sound.
Our argument comes out to a psychological atomism which is substantially like that proposed by Spencer. "Although the individual sensations and emotions, real or ideal, of which consciousness is built up, appear to be severally simple, homogeneous, unanalyzable, or of inscrutable natures, yet they are not so. There is at least one kind of feeling [musical sound] which, as ordinarily experienced, seems elementary, that is demonstrably not elementary. And after resolving it into its proximate components, we can scarcely help suspecting that other apparently-elementary feelings are also compound, and may have proximate components like those which we can in this one instance identify " (pp. 148-149). There follows an account of the beats going over into a difference-tone, and so forth. Now "if the different sensations known as sounds are built out of a common unit, is it not to be rationally inferred that so likewise are the different sensations known as tastes, and the different sensations known as odors, and the different sensations known as colors? Nay, shall we not regard it as probable that there is a unit common to all these strongly-contrasted classes of sensations ? If the unlikenesses among the sensations of each class may be due to unlikenesses among the modes of aggregation of a unit of consciousness commonto them all; so, too, may the much greater unlikenesses between the sensations of each class and those of other classes. There may be a single primordial element of consciousness, and the countless kinds of consciousness may be produced by the compounding of this element with itself and the recompounding of its compounds with one another in higher and higher degrees so producing increased multiplicity, variety, and complexity" (p. 150).
"Have we any clue to this primordial element? I think we have. That simple mental impression which proves to be the unit of composition of the sensation of musical tone, is allied to certain other simple mental impressions differently originated.
( 351) The subjective effect produced by a crack or noise that has no appreciable duration, is little else than a nervous shock " (p. 150). Quite so, and I think that the experience which I before called the still small voice of psychology, somewhat approximates this primitive nervous shock. Spencer gives many further illustrations. "The fact that sudden brief disturbances thus set up by different stimuli through different sets of nerves, cause feelings scarcely distinguishable in quality," he continues, "will not appear strange when we recollect that distinguishableness of feeling implies appreciable duration; and that when the duration is greatly abridged, nothing more is known than that some mental change has occurred and ceased. . . . It is possible, then -may we not even say probable - that something of the same order as that which we call a nervous shock is the ultimate unit of consciousness ; and that all the unlikenesses among our feelings result from unlike modes of integration of this ultimate unit" (p. 151).
In view of the time at which this was written (about 1855), the speculation seems astonishingly bold. Even more so, to me, seem certain remarks (pp. 152-153) on the oscillatory nature of the nervous impulse, and I should much like to know what physiological investigations were then available, which justified the belief in nervous frequencies at anything like the rate of sound or light. Nevertheless subsequent investigations have remarkably confirmed Spencer's view (I had almost said, intuition), and it seems to me that to-day this atomistic theory of consciousness, hardly modified from the form which Spencer gave it, must be looked on as a very shortly to be demonstrated fact. Most substantially supported by empirical investigations it already is. For myself I quite adhere to this view, while dissenting from Spencer's further remarks as to the nature of the primordial conscious unit, and from other features of his philosophy of mind. In weighing this theory one should never forget the phenomenon of roughness, which (whatsoever the sense-organ that originates it) is to introspection a quality, and is at the same time nothing else
( 352) than the density of a succession of conscious shocks, which seem individually to be of quite infral-modal primitiveness.
This completes our argument. And now I can reply to the anti-realist's questions: How can realism pretend to assert the reality of the color, sound, and so forth which are vividly present in the dreams of a person sleeping, it may be, in a box no bigger than his coffin? Realism, I say, can assert this because the nervous system, even when unstimulated from without, is able to generate within itself nerve-currents of those frequencies whose density factor is the same as in ordinary peripheral stimulation. I have not said, be it noted, that the density factor of the nervous impulse is the secondary quality : it is the density of the series of some relatively primitive sensation which is the secondary quality ; and nerve impulses may also have such a density, as also may Hertzian waves and many other things. The case, then, of sensory hallucinations, whether due to the 'inadequate' stimulation of nerves or to so-called central excitation, is entirely comparable to the cases of illusion which we considered in the earliest sections of this paper. In this connection I should not quite say with Professor Alexander that, "The illusory character of the appearance is the defect of our quality. With an organ adapted to see red we can see only red, no matter how the organ is set a-working." The hallucinatory quality needs to be explained more specifically, and this, I think, we have done. We could, of course, be more specific yet and suggest that such sensory resonators as the retinal cones would resonate in their own period to the electricity released by any of the various metabolic processes going on in their vicinity (as a brass resonator will sound its own tone in response to any tap) : we could suggest that the cortical synapses have much to do with the periodicity of
(353) nerve-impulses : or that nerve-impulses of various periods coming together in the central nervous system must often produce an impulse of a new and perhaps higher frequency. But speculation on the minuter details ought to wait on investigation. Certain it is that the nervous impulse at large is oscillatory ; and that the oscillations do sometimes (without external aid) become very rapid, is no ground for astonishment.
I must here forestall an erroneous inference that will almost certainly be made from the foregoing paragraph : this is, that hallucinatory and other consciousness is in the skull. Quite on the contrary, consciousness, whenever localized at all (as it by no means always is) in space, is not in the skull, but is 'out there' precisely wherever it appears to be. This is, for me at least, one of the cardinal principles of realism, and a realist would say with Berkeley that "the rose is really red" and so forth, just as it appears to be. The idea that consciousness is within the skull, current as it is, has arisen from the obvious connection between modifications of the nervous system and changes in consciousness. But this connection can be in other ways than that of a spatial inclusion of consciousness by the nervous system. Suppose, for instance, that the latter is like a search-light which, by playing over a landscape and illuminating now this object and now that, thus defines a new collection of objects all of which are integral parts of the landscape (and remain so), although they have now gained membership in another manifold — the class of all objects on which the illumination falls. Here, too, there would be a direct connection between the members of the illuminated class and the movements of the light : as there is between the contents of consciousness and changes of the nervous system. Any class that is formed from the members of a given manifold by some selective principle which is independent  of the principles which have organized the
(354) manifold may be called a cross-section. And such a thing is consciousness or mind, — a cross-section of the universe, selected by the nervous system. The elements or parts of the universe selected, and thus included in the class mind, are all elements or parts to which the nervous system makes a specific response. It responds thus specifically to a spatial object if it brings the body to touch that object, to point toward it, to copy it, and so forth. It responds to a secondary quality which is 'on' a particular object by, firstly, a similar (and physiologically very complicated) response to this special color and no other. This last is effected, the facts seem to show, by the nerves being capable of carrying a nervous impulse of the same frequency as the vibrations which are sent through the intervening space by that color. If the nervous system can pick these up and transmit them, it can specifically respond to them : otherwise not. This puts the colors or qualities into the nervous system neither less nor more than the fact of ether or air vibrations of the same period or density existing all through the intervening space puts these qualities into that intervening space. We are little tempted to believe that the color of a flower fills all the space between the flower and the eye : and neither less nor more does it fill, or enter into, the peripheral nerves and skull. The entity responded to is the color out there, two factors which involve two factors of response; but that color out there is the thing in consciousness selected for such inclusion by the nervous system's specific response. Consciousness is, then, out there wherever the things specifically responded to are. Now in cases of hallucination, indeed, the colors, shapes, and positions responded to are not in 'real Space,' as we are accustomed to say; but they are in a space which is in all respects comparable to mirror space, and which is just as objective. Of their reality I shall say more in connection with thinghood and contradiction.
But one more point here. In calling the primitive entity whose density constitutes a secondary quality a 'sensation,' I meant in no wise a thing within the skull, nor a thing at all mental or
( 355) subjective in substance. To introspection itself this simple entity is as objective as anything else; it is simpler, truly, than a concrete object like a shell or fossil, and so may seem more abstract. But it has all of the objectivity of other abstractions such as points and numbers (which are as little subjective as the starry heavens). I have discussed at length in another place  the ultimate substance of mental and physical elements, and endeavored to show that no difference of substance exists between the two groups. Professor Stout has well called the qualities "secondary attributes of matter." Mind and matter consist of the same stuff, and the little entity that in aggregates of various densities constitutes the secondary qualities is not far removed from the little atom that constitutes physical bodies, and in point of substance there is no distinction at all. So, it seems to me, we get an intelligible picture of how the secondary qualities are as objective as the primary. Their being included or not being included in the class of things which we name a consciousness, depends for both alike, on their being specifically responded to by a nervous system. But consciousness is in no sense at all within the nervous system.
4. Illusions of Thought. — In the matter of errors of thought —
( 356) contradicted opinions, fallacies exposed, disappointed expectations, and outstanding perplexities—we meet again a difficulty which can honestly be urged against realism, one where the anti-realist challenges and still more inspires the thoughtfulness and zeal of the realist. Such contradictions subsist, it is quite true, and if realism took on itself to explain them away realism would, in my opinion, be no better than several other obliteration-philosophies which I could name. The task for realism or for any philosophy is not to show that evil is only quintessential good, the imperfect - perfect, and so on, but to acknowledge the empirical subsistence of errors and contradictions and to show the significance and place of these things in the tissue of the universe. And precisely here I believe realism achieves one of its most signal triumphs.
We have already found, and left still outstanding, a charge against realism which is now just a case in point. Not the illusory or hallucinatory image as such, it was rightly said by our opponent, but such an image when it asserts itself to be or when the realist asserts it to be a real object, is the crux for realism. And the sting of this situation would of course be that such a thought would soon find itself contradicted. The illusion that proclaimed itself real would soon encounter a higher authority to show up conclusively its unreality. Or the realist who declared these unrealities to be real could soon be confronted with the contradictory empirical evidence that they are unreal. And he certainly could be. The difficulty in either case is clearly one of contradictory assertions or opinions — errors of thought — and so we can discuss these issues together, and in doing so we shall have left from our previous arguments no other objections outstanding. The issue includes all illusions of thought, but is more comprehensive still, and therefore it logically introduces a new section.
1. Images Assert Nothing. — Our first case shall be the abovementioned 'crux.' Now it is not true that an image or other content 'asserts itself' to be real, although I am aware that several neo-realists and other persons who may be said to evince some leanings toward realism, have declared this. I cannot see with what right a person asserts that a "truth which the sensation 'reveals' is its own extra-mental existence." This is certainly revealed, but not by the sensation content itself. Nor can I conceive that any content asserts, for or about itself, truth, reality, objectivity, or anything else ; such content simply is, and anything asserted for or about it is another content and one of a propositional nature : this is a thought or opinion and it may or may not be a true one. The former content simply is, and is in itself neither true nor false. As Professor Dewey has said, "Truth and falsity [and I should add reality and unreality] are not properties of any experience or thing, in and of itself or in its first intention" : that is, in its capacity as a bare subsistent. The fallacy in this notion of the self-qualification of mental contents lies in a failure to discriminate the bare content as it subsists, from (propositional) assertions about it which may coexist with it in the mind, either explicitly or subconsciously. The first content is what logic knows as a term, the second is one or more propositions. To confuse the two is absurd. But the same confusion is present wherever we find it said that a sensation or idea is 'aware of,' 'refers to,' 'points at,' or 'means' its object. The content does not refer to its object in any way; it is a part of the object. Any such assertion about objectivity or about reality is another (and propositional) content ; it is also
(358) supplied by experience, and it may itself be further qualified as to truth and reality by another propositional content. It is important to discriminate in every case between what has been called the content and intent, or more accurately between terms in the mind and propositions in the mind; and after that, in the words of Professor Alexander, the intent is for description another and special part of the content." I do not admit, then, that the image, whether it is true or illusory, asserts anything about itself. Such an image may, however, exist in the mind together with mutually contradictory propositions about it ; — another case of errors of thought, which we are to examine.
2. What the Realist Asserts. —The realist does also not assert that an unreal thing (image or whatsoever) is a real thing. And here the realist insists on the conscientious observance of a distinction which logic and mathematics have long since known and scrupulously observed, which even some idealists have perhaps heard of, but which not one anti-realist nor yet all realists seem even remotely to appreciate. This is the distinction between reality and being or subsistence. Here is a typical case of 'reality' confused with being. Professor MacKenzie writes, "and so the new realist seems to be in truth one who is persuaded that things are just as he apprehends them. The idealist, on the other hand, maintains that what is directly perceived is never in itself real." Thus when the realist says that as things are perceived so they are, the idealist stupidly misunderstands him to say "as things are perceived so they are really," i.e. all perceived things are real things. But while all perceived things are things, not all perceived things are real things. Stupid as such a confusion is, it will be found to have been made at some point in every anti-realist argument. This abuse involves two of Perry's fallacies, pseudo-simplicity
(359) and verbal suggestion : 'reality' is taken to be a simple qualification connoting no more than being (as if there were no unreality to be accounted for, as there is no non-being) ; and, again, the fulsome delights experienced by most minds on mention of the 'real' (especially when exasperated by idealistic futilities and untruths), make it a welcome epithet which can be slipped in unprotested anywhere. Small wonder that idealistic arguments which provide so little of the article should make the most of a pleasant verbal suggestion : for however troubled the sea of debate, the comfortable word 'real' gives one a sense of being at home.
Now for realism by no means everything is real ; and I grant that the name realism tends to confuse persons who have not followed the history of the term. For the gist of realism is not to insist that everything is real, far from it, but to insist that everything that is, is and is as it is. Not a dangerous heresy, this, it should seem; but it just happens that every form of idealism has maintained the contrary, has maintained, to use a term of Professor Dickinson Miller's, some kind of 'false-bottom' theory of the universe. Idealism has either said that since some things are demonstrably erroneous they are not as, on the same authority, they are (i.e. erroneous) — and this is the German way ; or it has said that everything is erroneous, nothing is as, on the very same authority, it is — the way of Mr. Bradley and his school. The approaches to idealism are extraordinarily diverse, or at least are so represented by their expounders ; but these latter are in fact primarily engaged with the problem of error, and either they profess to discover that it is not, and so find themselves rather busied with an uneasy conscience ; or else they are obsessed with error everywhere, and consequently fold their hands in despair. For if I dare profess at all to grasp these anthropological mysteries, the differentia of idealistic philosophers is their common assignment of first importance to the problem of knowledge, and this problem has been, from the earliest Greek times to our own, primarily the problem of error. Realism neither succumbs to this problem with the non-possumus of the modern
(360) English school, nor tries to explain error away with the solemn circumstance of the German schools. It meets, if I may venture at all to speak for it, the problem of error by borrowing from logic and mathematics the well-authenticated distinction between reality and being. The universe is not all real ; but the universe all is. Two more distinctions, and we proceed : being is to be distinguished not merely from being real, but from being true, and from being perceived or thought. Realism has a just and proper place for the functions of perception and thought, but the subjectivist's contention that "being means always in some sense or other [sic] being perceived or thought," rests solely, as Perry has demonstrated, on the fallacy of the ego-centric predicament.
3. Contradiction and Being. — The earliest (and very ancient) 'solution' of the problem of error seems to have been that errors are all matters of opinion, are merely subjective, found only in consciousness: but that the objective world is error-free, so that no one need worry lest the universe totter and collapse. This remains to-day the comfortable popular view of the matter. Nor can I see that the triumphal progress of idealism has brought enlightenment. Rather has idealism thrown us back on the original difficulty by asserting that everything is subjective, from which the conclusion must be that error is again ubiquitous. Yet many idealists, and especially the leather-patch school of
Professor Karl Pearson and his associates, profess not to draw this conclusion, since they continue to dispose comfortably of error on the ground of its 'subjectivity.' It is true that Hegel undertook to treat error much more responsibly, but his solution seems to have evolved a checkmate of thought and intellection überhaupt, so that his followers have no course left to them save to sing the cradle-song of the Absolute, and, so lulled, to surmount error by oblivion. Yet error remains a problem for persons who have kept awake, and one observes that the hated name of realism
(361) suffices to arouse even the Hegelians to a disturbed consciousness : "If you won't repose ineffably  in the Absolute, what are you going to do with error?"
Now it may be admitted that 'errors' are all of knowledge, or are in experience; but the important point is another : that all errors are cases of contradiction or contrariety. One has met error who has experienced that A is B and that the same A is not B. But the experiencing is not the significant fact, and that all errors are of knowledge is true merely by definition, since contrariety or contradiction is called 'error' only when it occurs in some person's field of consciousness. The actual problem is the contradiction or contrariety itself what is the significance of a universe that holds such things? And here, once more, the only solution which appeals in practice to any one is the ancient one : that only one of two incompatible propositions is in the universe, the other is 'only subjective.' It is for this reason that every one of the recent writers against realism centers his attack about the problem of error or contradiction. I shall base my remarks on their own assumption that there can be no contradiction in an objective (or 'real') universe.
This last proposition is always expressed, or tacitly implied, with an assurance which shows that these gentlemen assign to it axiomatic validity ; and if they were to be asked how they know so interesting a fact about the universe, they would infallibly reply that it is self-evident. On which I should remark that so far from being self-evident, it is categorically untrue. "Are you," say they, "crazy enough to think that you have ever seen an existing object move both up and down at the same moment? Have you ever met the round-square, or the A that was at the same time not-A?" and I reply, "No; are you so crazy as to be able to think these objects?"
An answer to this is, that while it may not be easy to visualize
( 362) or image an A-not-A, yet that one can easily think of an A that should be, or might be, also not-A. This is a mere defect of imagery, just as it is an accident of vita brevis that one cannot enumerate an infinite series although one thinks it readily enough. Now this is the core of the matter. It is not a "defect of imagery" which prevents us from visualizing the round-square or the A-not-A as readily as we visualize a hippogriff, the whale discussing Jonah, or even a Cook at the north pole. The thought of the round-square is a propositional content about a strictly unthinkable IT : — that it is to be square, and it is to be round, and so forth. Further than this even thought cannot go : even the inner eye cannot grasp the square which is also round. One can think of a point which should move up and move down at the same moment, but when one images the point, it moves either up or down, or the two successively. Now this "defect of imagination" is not a psychological matter at all, but rests on a fundamental distinction which symbolic logic and mathematics have more or less recently made out, between propositions or postulates on the one hand and terms in relation on the other. It is found here that propositions may subsist together in a set although they are mutually contradictory, but that such contradictory propositions can never generate, or be realized in, a system of terms in relation. Indeed, so harmless, oftentimes, are the contradictions between propositions that the only certain test that propositions are not contradictory is the discovery of a system of terms in relation of which the propositions all hold true, or in which they are exemplified. Thus if one undertook to define a figure such that it should be the portion of a plane surface included between three straight lines ; that it should possess four (internal) angles ; that the sum of these should equal 180 degrees ; and that the sum of its external angles should equal ten times 180 degrees ; — one would have no means of discovering whether a contradiction  had been
(363) posited except by appealing to the corresponding system of terms (plane, lines, et caet.) which such a set of postulates undertakes to define. This is of course an appeal neither to physical existents, nor to the faculty of imagination : nor are propositions more 'subjective' than terms. This distinction between sets of propositions and systems of terms is of the most profound importance; it sheds light, for instance, on analysis and synthesis, the meaning of verification, concreteness, empiricism, and on the triviality of the 'geometrical method,' or any other, when the propositional sequence of the argument swings free from the patient exhibition of terms in their relations. Now this fact that propositions oppose one another freely while such opposition or contradiction is never exemplified in a system of terms in relation, does not, I admit gladly, tell us all that we wish to know about contradiction and negation. On the contrary, it merely opens up a field of study most stimulating to the appetite, and one which at the present juncture I conceive to be the most promising of any, for both logic and philosophy. But the considerations just adduced are important in two respects; they do not purport to explain 'error' (contradiction) away; and they do show that the problem of contradiction (error) has nothing whatsoever to do with the problem of knowledge or epistemology.
The dichotomy proposition-term, fundamental as it may be, coincides in no wise with the dichotomy mind-matter, subject-object, nor yet with unreal-real. Conscious images, like physical objects, are terms in relation, and as the round square or A-not-A is not found among physical systems of terms, so it is (and for precisely the same reason) not found among mental systems of terms. What is in the one case called physically impossible ('unreal') is in the other case found to be mentally impossible, i.e. unthinkable. On the other hand, the mind can and does entertain the most contradictory propositions about terms, precisely as physical laws, which have obviously the nature of propositions, are habitually in a state of contradiction.
I say 'habitually,' although I know how shocking a heresy it is to speak of contradiction in any connection with the physical
(364) world. This does not contain, it is true, A's that are not-A's. Neither does the mental world contain them; and the expression A-not-A, or round-square, has no meaning at all save as symbol for a little pair of contradicting propositions. But having discovered this valuable fact, apparently, at some pains, natural science conceived such an animus against the name 'contradiction' that it devised means for disguising the true cases of (propositional) contradiction among natural laws; of which every case of collision, interference, acceleration and retardation, growth and decay, equilibrium, et caetera, et caetera, is an instance. This is as follows. A law of motion states always that a physical particle (or series of them) moves (or shall move) thus and so. If now two wave-motions are progressing along the same straight line and toward each other, there will be a moment when a certain particle will be 'acted on' by both motions at once. The law of one motion will state that the particle moves up (or shall move up), while that of the other motion states that it moves down (or shall move down) at the same moment. Each law opposes the other, and although the relation is called one of contrariety, this contrariety is in fact more than contradiction; for if one law says up, the other not only says not-up, but further specifies down Logic cannot show a negation more thorough. And while the impossible-unthinkable does not happen, the result which is characteristic of all contradictions ensues, namely, zero motion ; or in the cases of different amounts of energy one motion is reduced toward zero by as much as the opposing motion has energy to contradict it. To say that because no energy has been 'lost' there has been no contradiction is nothing whatsoever to the point. Two laws of motion have met in contradiction, and this is precisely the appointed signal for energy of one sort to be transformed into energy of another. Because a third law can be framed (in terms of transformation, strain, or elasticity) to describe what shall continue to happen when a contradiction arises, should not blind us to the fact that it is not until the first two laws do meet in contradiction that the third law goes into operation. The case is paralleled in
(365) the game of chess, where the laws governing the moves of the several men often come in contradiction with the rule that no two men shall simultaneously occupy one square. To meet this case a further law declares that the second comer shall 'take' or annihilate the earlier occupant; and the whole game hinges on such contradictions. To imagine that in this way contradiction has been forestalled, is to do like the fatuous master who commands: "Stand up, but if you won't stand up, lie down; my orders shall be obeyed." Not even from the point of view of a static logic is contradiction in this way avoided ; and modern logic is not static. Contradiction is after all a tame and harmless thing, although a very interesting one. The pretensions of many natural scientists that they find no contradictions is uncommonly absurd, because in fact they find little else. That is, all natural motions are the result of so many partially contradictory laws operating together that it requires a fabulously clever technique to produce a motion which is simple or uncontradicted enough to allow any one of the component laws (or constant functions) to be determined. The natural scientist may conceive this as he likes, but if our idealist opponents object to the above considerations I will beg them to take down the gospel according to Kant and read what the latterday Immanuel had to say in his "Essay toward the Introduction of the Concept of Negative Quantities into Natural Science", it is one, but only one, of the authorities for what I have ventured to present above.
The gist of the whole matter is, that the impossible-unthinkable never happens anywhere, but that every variety of contradiction, contrariety, repugnance, opposition, and negation which logic itself recognizes is quite as plentifully manifested in the objective physical world as it is in the subjective sphere of mind. A thought, then, which negates another thought is neither more nor less significant than a physical law which negates another
( 366) law. The problem of error, as that of 'reality,' is in no way involved in the problem of knowledge.
Now the image in consciousness does not assert anything about itself, nor does the realist, as it seems to me, assert of it that it is necessarily real; still less would he assert that all the propositional contents of consciousness are real. But what I suppose that realism insists on is that every content, whether term or proposition, real or unreal, subsists of its own right in the all-inclusive universe of being ; it has being as any mathematical or physical term or proposition has being ; and that this being is not "subjective in its nature" (a phrase indeed to which in this connection I can attach no meaning). I believe, further, that no content is 'constituted' by a metaphysical knower or ego, for I believe that no knower, or ego, such as metaphysics means, exists. I believe also that no conscious content is 'constituted' even by the knowing process, in the sense commonly attached by metaphysics to the word 'constitute.' If the knowing process ever constitutes its content, it is, I believe, only as a ripple of water in assuming successive forms may be said to constitute these forms (if that appears either significant or interesting to any one, as it does not to me). But particularly meaningless is the assertion of idealism that a mental content is 'subjective' in its substance or nature, or is constituted by a metaphysical knower or ego.
As to what reality is, I take no great interest ; nor do most other persons, for if they had done so, they would have taken more pains to define it sharply as against the equally and perhaps even more prevalent unreality. But if challenged, I should hazard the guess that perhaps reality is some very comprehensive system of terms in relation. For by reality we seem to mean the thing most remote from contradiction, and this is with certainty found only in systems of terms. This would make reality closely related to what logic knows as 'existence.' If this is correct, probably all of the terms found in the physical world, also some and possibly all of the terms found in minds, are real. But all this, so far as
(367) I know, has been far too little studied. Certain it is that unreality is no more subjective than reality ; for a thing may be objective and yet unreal, as is commonly asserted of certain numbers and of some systems of geometry.
4. Contradiction and Realism. — Let us now return to some arguments of our opponents. In a somewhat over-ingenious paper Professor Lovejoy brings up at length the case of hallucination. "While it lasts, the hallucination is for the victim of it as good 'content' as any other of his perceptions." But "it was not at the time an object perceived by others. . . . In fact, it turns out that the other percipients at that time perceived as vacant, or as otherwise occupied, the very space which the hallucinatory object ostensibly occupied . . . and since the testimony of many witnesses and of the general uniformities of experience is against his object, the victim of the hallucination, when here,covers, proceeds to call his object somehow 'unreal,' and to declare that the 'content' that was truly in the space in question was that beheld by the other percipients. . . . Be it observed that the corrective judgment, through the making of which the conception of consciousness is generated, predicates 'unreality'—now interpreted as 'existence merely for consciousness'—of the object of the hallucination at the moment when that object was present" (p. 595). Professor Lovejoy grants it as possible that the "new realism . . . does not maintain that the same portion of real space can be at once both empty and filled," but he does not see "what account a new realist can consistently give of the status of the hallucinatory object at that time, or of the difference between it and the coexisting 'real' objects" (p. 596). Now I should not call the hallucinatory object necessarily 'unreal,' still less an existent "merely for consciousness," nor need anybody hasten to the conclusion that the other object is 'real' since collective hallucinations are also possible. It is to be noted that a "corrective judgment" (i.e. a proposition) in opposition to one or more previous
(368) judgments is that which carries the difficulty, and I look on a conflict of judgments precisely as on any other propositional conflict.
If now it is asked how one surveying the whole situation (as if this were possible without implicitly or subconsciously making many judgments  ) can interpret it in the spirit of realism, the answer is simple. One interprets it precisely as Professor Lovejoy probably interprets mirrored space in connection with the space behind the mirror. The case is parallel to our own in all respects germane to our argument; and I have yet to hear that mirrored space gives rise to grave difficulties about reality or about "existence merely for consciousness." It does, however, show in exactly the same degree to which hallucinations show that "the same portion of real space can be at once both empty and filled." Lest the opponent have no ready interpretation of such a mystery, I will offer one.
Mirror-space is a cross-section of ordinary space and of the bodies therein ; it has all the pure-space properties of the other save for a geometrically definable mode of reversal, and it includes the surfaces and shapes of the mirrored objects (reversed) with their colors. But it does not include the ponderability and many other physical properties of these objects. As in the case of all cross-sections (of which one case is consciousness), a new manifold is formed, consisting of certain parts, and integral parts, of objects; and here, as usually, such partition and analysis of the objects reveals that they are made up, of elements which are not in the popular sense 'physical,' but rather conceptual or mathematical, or, as I prefer to say, neutral —because neither physical nor mental. These mirrored parts remain objects, but they lack many properties, such as ponderability, et caetera, which pertain only to the original entire object in its natural state of organization. All this is precisely what natural science has discovered from its own analysis of the same objects ; —matter analyzes out completely into mathematical entities, and leaves no residue by way of little
(369) material brickbats. A block of wood is ponderable, et caetera, but the shape, volume, physical masses, and electrical charges of which it is composed are not ponderable ; ponderability being a property of, and deducible from, just these things in their organized completeness. This circumstance gives rise to what Professor Lovejoy and others have remarked as the "wide denotation which the realist gives to the term object," a denotation which physical science itself imposes. It is true that in the case of mirrored space reproduction is involved, but it is a reproduction of identicals without change of their 'nature'; and while it presents, indeed, interesting problems concerning particulars and universals, it affords no footing for speculations as to a subjective realm of representations. And no more do the cases in which consciousness involves reproduction (as it sometimes but by no means always does); they are invariably entirely comparable to physical reproductions. Yet they have given rise to no end of silly talk, which, when applied to the equally eligible case of the mirror, reads as follows : " You say that the mirror does not alter its objects. Where then does it get its reproduction of them? Must it not make them? But if it makes them, they must derive their nature from the mirror itself, and be intrinsically subjective mirror-stuff. The mirrored reality cannot be other than of the nature of the mirroring spirit." Or if there are two actively imaging mirrors we read : "Data which are qualitatively different cannot be numerically identical; and no 'this' in the one mirror can ever be exactly the same, qualitatively, as any 'this' in the other mirror at the same moment, could not be unless the two mirrors were exactly alike and occupied the same place in space, i.e. in idealistic terms, unless every element pictured in the two mirrors were identical ; in which case they would be one and the same mirror." Thus it is proved to the satisfaction of idealists that two mirrors cannot image the same object. I say, then, that the case of hallucinations, as cited by Professor Lovejoy, is paral
(370) -leled by such cases as that of mirrored space, wherein sundry mirrored objects occupy the same spatial positions as are occupied by other 'real' objects situated behind the mirror. It is admitted that such physical cases give rise to no difficulties about 'unreality' or a separate subjective status. In some cases of hallucination and illusion the error consists solely in the entertainment in the mind of mutually contradictory propositions; and while one of these may be for some reason preferred or assigned a superior value, neither is more subjective than the other; nor are both subjective, because, as we have seen, the entire universe is brimming full of just such mutually contradictory propositions. In other cases of hallucination and illusion (as with the two eyes asquint) a certain actual interpenetration of terms in relation is experienced, which is precisely paralleled by the interpenetration of mirrored objects with the objects behind the mirror. This is not a case of the impossible-unthinkable realized, but it is merely a case which shows that the neutral cross-sections of objects possess properties of interpenetrability and so forth which differ from the properties of the entire objects. So, too, fire burns, while the idea of fire does not, just as it still burns although the magnetic properties of flame do not. Thus, whatever practical terminology may be found most convenient for the case of hallucinations, these afford no grounds for an argument toward subjectivism. The realistic account of them is clear, simple, and straightforward, even if it is admitted that reproduction is involved. In many if not most cases of consciousness reproduction is not involved, and the realistic account is still simpler.
A word may here be in place on the realist's "wide denotation of the word object or thing." A common anti-realistic argument is that since fire burns and the idea of fire does not, since an object has no perspective foreshortening, while the visual image of it has, an object has definite position in space, and the memory image of it has not, and position in time, while the idea comes always subsequently; — that for these reasons realism makes itself absurd in asserting that the idea is 'qualitatively' and in
(371) many cases 'numerically' the object. I think that it was probably this argument mainly which led Mr. G. E. Moore to the view that consciousness and its objects are distinct existents, that even color qualities are never content of sensations, and then on to a belief in a fundamental unresolvable relation of awareness; from all of which I should emphatically dissent. Now to the argument above stated it might be replied that fire burns but the shape of the flame does not, that an object is not foreshortened but that its geometrical projections are, that the object has position in space but that, say, the nth derivative of its physical motion has not, and that while the object has position in time the value of its physical mass is timeless. Thus the argument rests entirely on a singularly crude brickbat notion of physical object. This is that the object is a sort of indivisible brickbat, of which any and every property of the object can under any and all circumstances be predicated; or that if the brickbat has parts, all of its properties can be predicated of each of its parts. The absurdity of this is patent, and yet one can see how far such an error may go from the astonishing words of Dr. Drake, who after remarking the many aspects presented to different spectators by a tree, continues, "If we believe, then, that each of these 'thises' that we have in experience is a permanent existence [he should say a subsisting entity], we have a marvelously multiplied world. A thousand, a million different 'thises' permanently exist as 'this tree P Disparate as they are, they cannot be squeezed down into one simple object [indivisible brickbat], and we have a world reduplicated ad infinitum. . . . We ['critical realists'] give him [the 'natural man'] a simple, homogenous external world ; 'natural' realism does not." I should hope not ! And I can conceive no better advertisement for what Dr. Drake calls 'natural' realism. But what, meanwhile, can he possibly be thinking of the infinity of actual geometrical projections of his tree, to say nothing of its innumerable other actual relations ? Can these
(372) all be "squeezed down into one simple object" ? Surely the tree is, with its relations, all of these things : and even more. For, as Professor Alexander says, of a straight stick which looks bent when a part of it is under water, "There is illusion only if we deny that the bent and the straight appearance in the two different sets of conditions belong to the same stick." Certainly they belong to it, and so does every other of its projective properties (and these are not merely spatial, but temporal and logical as well). For it must not be forgotten that while the object itself, if a physical thing, is far from simple, we are always perceiving it in a complicated setting of (spatial, temporal, and logical) relations, which is a still more complicated thing. But the conscious cross-section is always a group of the integral (neutral) components of the object and of its innumerable relations. And since, firstly, it is seldom possible to say just where the object itself terminates and its relations to other entities commences (Is, for instance, the first derivative of motion a part of the moving object or one of the object's relations?), and since, secondly, any discriminable entity may be 'object' of consciousness (i.e. a member of the class of entities to which the nervous system specifically responds), realism has good grounds for extending the denotation of object or thing.
This completes my argument, and more than fills the space allotted to me in this volume. The picture which I wish to leave is of a general universe of being in which all things physical, mental, and logical, propositions and terms, existent and non-existent, false and true, good and evil, real and unreal subsist. The entities of this universe have no substance, but if the spirit is weak to understand this, then let the flesh, for a season, here predicate a neutral substance. These entities are related by external relations, and man has as yet no just ground for doubting that the analytic method of empirical science can proceed without limit in its investigation of this universe. The dimensions of this universe are more than the three dimensions of space and the one of time : how
( 373) many more is not known. The line that separates the existent and the non-existent, or the false and the true, or good and evil, or the real from the unreal, seldom coincides, and never significantly coincides with the line that distinguishes mental and non-mental, subject and object, knower and known. A mind or consciousness is a class or group of entities within the subsisting universe, as a physical object is another class or group. One entity or complex of entities can belong to two or more classes or groups at the same time, as one point can be at the intersection of two or more lines so that an entity can be an integral part of a physical object, of a mathematical manifold, the field of reality, and one or any number of consciousnesses, at the same time. As the class of physical objects is defined within the subsistent universe by principles known to science, so the class of consciousnesses is defined within this universe by principles which are partly known, and which are coming to be more fully known, by empirical psychology. A consciousness is the group of (neutral) entities to which a nervous system, both at one moment and in the course of its life history, responds with a specific response.