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IN THE study of exceptional and residual phenomena, it is always necessary to have some standard by which to measure them and to make them intelligible, and, unless they in some way embody the same general laws and functions, they must forever remain outside the ken of the understanding. The slightest examination of many abnormal phenomena reveals the action of familiar laws and causes, and suggests that, if these exceptional and residual facts were better known, they would exhibit less mystery, though they remain just as exceptional as before. To ascertain the extent to which this is true, and to which we may apply the interpretations of normal mental phenomena to the abnormal as simply disturbances in the action of very complex functions, we must go to the study of our normal mental processes, where much the largest part of our average experience is found. We shall then better understand the real and apparent variations from these normal occurrences, and the reluctance with which the scientific mind accepts any such deviation from them as is implied in supernormal phenomena. For this reason I shall devote a little time to the analysis and interpreting of the elementary processes of knowledge, as presented in our normal experience. I begin with sensation and perception, which represent the first stages of our knowledge.
The senses are the channels through which comes our knowledge of the external world. I do not here say or imply that this knowledge is correct, or that we form from it immediately right conceptions of this external world, but that, in some way, we obtain it
through sensory experience. Whatever its nature, it would not be normally acquired in any other way, and hence sense-perception confines our knowledge of external things to sense-impressions. There is no proposition of psychology on which men are more agreed than on this. They may dispute about the nature of our knowledge, about the nature of matter, and about the limits of sensory experience, of its contents and of its certitude; but they are agreed that we can have such knowledge as we do possess only through the agency of sense-perception, and that this agency consists of the organs or media represented by the senses. Now how do the senses give us this knowledge? The answer for the layman is that we get it by sensations. But what are sensations, and what do we "know" as a result of them?
The answer to this question also seems very simple. We are accustomed to have it said that sensations are the mental states by which we get our knowledge of the material world. Here, then, we are going round in a circle and make no progress with the problem. The means of getting external knowledge is sensations, and sensations are the means of getting our external knowledge, and we are just where we started. But the curious mind will not stop with any such answers, and insists on a more thorough description of the process, especially as man's experience has revealed to him a large number of illusions and errors of judgment associated with his sensations, a fact which has suggested to many the question whether we know anything at all independently of our mental states. That is, they would say we can know only the states themselves. Illusion and error seem to have the same source as our assumed truth. This creates a problem for us which is how to know when we can accept sensory deliverances and when we can disregard them. We require some criterion by which to distinguish one type from another and to determine the nature and limits of sense-experience. The need of discriminating between his normal sensations and his dreams, for instance, on the one band, and between his sensations and his inferences on the other, forces man into a most careful study and definition of his elementary mental states. His first aim, therefore, is a theory of how his sensations occur and what they mean. The hope, in thus studying them, is to find the laws which determine or regulate the order of both the normal and the abnormal states associated with sensory functions. Their superficial resemblances are clear, and the conviction of an external reality in one and of illusion in the other is as tenacious as their apparent identity is clear. Consequently, investigation of some kind is rendered necessary for understanding the meaning Of all of them and for distinguishing the one type from the other.
An ancient Greek philosophy formed a very simple theory of sense-knowledge, which probably represents the most natural conception of the untrained mind when it is called on to explain how sensation can take place. The majority of lay minds probably do not imagine that there is any problem in the matter, but simply take sensations for granted as facts which, whatever their explanation, are not particularly mysterious. But when asked to treat them as puzzling phenomena they will probably give a naive explanation of them. Such was the theory of Empedoeles and Democritus, the ancient Greeks, to whom I have just referred. Their view, while it was a tacit explanation of sensation, was less such than it was a theory of knowledge aimed to give an intelligible account of how we came to know an external world of matter. Democritus thought that objects threw off little
eidola, or images of themselves, corpuscula, as they were also called when the doctrine was translated into Latin, and that these little bodies, simulacra of the objects themselves, impinged upon the soul, or sensorium, as we should say, and in this manner we came to know these external objects which threw off such images. This view was tantamount to saying that the reason that we could know objects was that they succeeded in impressing upon us some simulacra of themselves, and, of course, if our sensations were only impressions Eke objects, it would be natural to feel that there was nothing puzzling about our seeing them or knowing them. They were
there, one and the same in kind, with the knowing process and the known object.
But it was not long before this naive view was modified. It took but little skeptical reflection to discover that there was no sense-evidence for the flight of these
eidola, or images, and for their impingement on the soul. Such a theory might seem possible on certain assumptions, and might conform to some speculative demand to bridge the chasm between the sensorium and objects at a distance; but the theory wanted the necessary evidence for its truth to the very senses under consideration, and
so had to succumb to a view which was not so easily attacked, even though the corpuscular theory might have been refined to suit the situation.
Hence the view of sense-knowledge which followed the corpuscular theory of Empedoeles and Democritus was that objects set up some motion between themselves and our senses, and that the immediate stimulus or cause of sensations was this motion, and in connection with this stimulus our perceptive knowledge arose. This view dispensed with the difficulties of the corpuscular theory, and permitted objects to retain their bodily integrity while the idea of contact could still remain to explain the occurrence of knowledge. Action at a distance was regarded as inconceivable, and hence the theory of Democritus, which assumed that contact and similarity of the sense-impression to the object were necessary to perception. But the idea of corpuscular emanations soon became as absurd as action at a distance, and to save the situation, the conception of motion, intervening between things and sense, was substituted for that of corpuscular impressions, and the assumption Of contact was preserved, while that of flying eidola was abandoned. The theory of motion has survived ever since its assumption.
This view serves very well for sight and hearing, where we have come to think, whether rightly or wrongly it is not necessary to say, that there is an interval of space between the object and the sensorium, and that the light and sound Which are their respective stimuli are motional or undulatory in nature. But antiquity had no scientific knowledge of light and sound to substantiate its speculations, hence its only guide was the anomaly of action at a distance, which it overcame by the supposition of eidola or motion. In accepting motion instead of corpuscular impressions, it gave up contact of the object with the sense affected and assumed some sort of influence conveyed across the interval of space admitted to intervene between object and sensorium. This conception, however, was not necessary, even if true. in the case of touch. Here the object was supposed to be in contact with the organism affected. It was not necessary to invoke motion from the object to the sensorium. Hence the analogy here was that of the seal or stamp on wax, the seal corresponding to the stimulus and the wax to the sensorium. In this view the conception was much the same as that of Empedocles and Democritus, except that the assumption of
eidola was unnecessary.
It is probable that Aristotle was better satisfied with this analogy than with that of motion or of the
corpuscula. For he compared all sensation to the impression of a seal on wax. Both views had the common conception that objects acted On sense, but they did not agree upon the manner of this causal action or upon the conditions under which sensations occurred. Each view had its own perplexities, but it is curious to remark that the theories adopted assumed a point of view which did not cover the whole field of sensation. One formed its theories upon the senses of sight and hearing, and the other upon that of touch. In one, space intervened between sense and the object, and this chasm had to be spanned, and in the other space did not intervene; contact was the condition of the case. Neither the flight of
eidola nor the transmission of motion satisfied the terms of both situations, hence the separate schools had to choose one sense as the functional type and ignore the perplexities proposed by the unity of sensory experience. This is still a problem for us, though we have probably decided for undulatory stimuli for sight and hearing.
It is probable that the uncritical mind does not feel any perplexities in the case. In our normal and unreflective experience we probably do not incline to ask how we come to know things. We are so familiar with our sense-experiences that we are satisfied to say that we see objects, that we hear them, that we touch them, that we taste them, that we smell them, etc. We do not have any theory about sensation. We take the perception of external objects as a matter of course. We do not think of them as causing sensations. We do not even think of causal action at all. It is enough to think that objects are there, and that we perceive them. We admit "sensations" in touch, but never think of them in sight and hearing until philosophic reflection drives us into it. The very fact that we can give no intelligible account of the manner in which we can see or hear objects at a distance, the fact, indeed, not involving any conscious problem for us, makes us satisfied with the mere perception of them; hence we do not think of our knowledge as an effect like the passive result of a cause. We distinguish radically between our tactual experience or "sensation" and our visual and auditory perceptions. We may come to think of the two different agencies of knowledge, or all of them in the physiological field, as senses, but we do not confuse their action. We may readily distinguish in the one between the object and the sensation, namely, in touch, though this is an unconscious admission of conceptions from another sense, but in the others, namely, sight and hearing, we have no "sensations," or are not aware of any such thing as we conceive the term in reference to touch. We simply perceive the object in touch, and this without any direct knowledge of intermediate causal influences. We do not pretend to give any philosophic reasons for considering that all sensations are essentially the same in kind when classifying them as if they were, and so feel no perplexities that assume an anomalous difference between touch and sight and hearing.
This was probably the general state of mind after the decline of Greek philosophy and until modern times. But at the first awakening of scientific reflection, men began to study the perplexities of senseperception, and, though they did not return to the naive views of Empedoeles and Democritus, with their supposition of
eidola or corpuscular emanations from objects impinging on the organism, or to the equally unsatisfactory comparison of Aristotle, namely, that of the seal and wax, they did apply the theory of vibrations and motion in some of the senses and the idea of causal agency in all of them, but they left unsolved the apparent anomaly between touch and sight and hearing. Their wider view of connection was that of causal agency, which was more abstract and intangible than the ancient attempts to unify sense-perception by ignoring the anomaly mentioned, though, in fact, this general assumption of causal agency quite as much ignored the real perplexity as did the Greeks when they chose one sense as the measure of external knowledge and disregarded the others. However this may be, men began to look at sensation and sense-perception as an effect to be primarily accounted for by the causal action of objects on the sensorium, and the unique character of this effect as an activity of the mental or. cerebral subject was either unknown or neglected for the time, or at least was subordinated to the causal action of objects, until idealism came forward to emphasize ,the internal or subjective factor of knowledge. Of this again, as I am not at present concerned with that movement which began to surmise or assert a larger number of intermediate steps in knowledge, though it was in fact an attempt to eradicate the anomaly which had perplexed both Greeks and later philosophers in the relations between the different senses. I shall have to approach that attempted solution of the problem through the anomaly itself and the substitution of the conception of causality for the supposed essential identity of different sensations. This conception of causality was the general one at the basis of the assumed contact of touch and of motion or vibration for sight and hearing. It was an interesting scientific circumstance that gave them the first place in psychological theories of senseperception.
The application of motion to the phenomena of sensation and perception in sight and hearing was demonstrated by the physical discovery that light and sound were undulatory and not corpuscular in their nature. For a long time light was supposed to consist of minute corpuscles thrown off from radiant matter. But finally certain phenomena seemed to prove that it was some form of undulatory or vibratory motion of the ether, and soon it was proved that sound was also due to undulations or wavelike vibrations in the air or other matter. These discoveries at once revived the older theory of sense-perception in the sensations of sight and hearing, and perhaps all other sensations were affected by this assumption of undulatory stimuli. However this may be, the doctrine of intermediate causal action between objects and sensations in these two cases has taken a fixed place in psychology and philosophy, and suggests that we must reckon with its conceptions in the other senses when accepting their general identity with sight and hearing.
The naive view of the man who does not reflect upon the various steps involved in our knowledge of external objects naturally assumes, as I have already said, that there are no mediating influences in the phenomena. This view is favored by our natural ignorance of what those intervening causes are. As the undulations of light and sound are not immediately known by him, they are ignored in his judgment of reality until investigation discovers indirectly that they are there. Hence we naturally assume that the object of perception is indirectly known when these intermediate influences are known to exist, and at the same time that we come to this view, we often or always retain the conception of these objects which characterized our ideas before we suspected an indirect knowledge of them. With many reflective minds this system of intervening agencies between objects and sensation suggests a theory which conceives objects as "mental constructs," that is, products of the mind or brain upon which the motion or vibrations act. Of this view presently. But with the majority of men who do not reflect upon it, the object remains the same in their conception of it after the explanation of perception and sensation by intermediate agencies as it had appeared before, and their minds may feel puzzled to account for a phenomenon which is mediate instead of immediate. But puzzled or not, earlier habits prevail to protect conceptions which the facts ought to modify, and the problem of sensation and perception takes on a complicated form for the man who wants to insist upon the retention of his earlier ideas while he admits the existence of causal agencies not identical with the objects known, and admits them indeference to the assumption that causal action can never occur at a distance. Confined to this maxim, and not being able to suppose, as he might do, that, however causality requires contact for its effects, knowledge might not require this for its judgments, he feels an embarrassment in his problem which practical life does not experience, and he remains between the acceptance of his natural conceptions and skeptical influence of scientific facts about intermediate agencies in his view of sense-perception.
But the discovery of these intermediate agencies and their causal influence, such as vibrations transmitted from objects to the organism, gives rise to inquiry about what goes on in the organism itself. If we do not perceive objects without motional agencies intervening between them and the senses, and if these agencies are different from the objects, we may begin to suspect that there may be as much difference between what takes place in the organism after the action of stimulus as we assume exists between the object and the undulations which it radiates. Men we get into this state of mind we must be prepared for almost anything.
Right at this stage of reflection an important circumstance occurs. Many of the sensations, especially those of touch, seem to occur at the periphery of the organism, that is, on the external area of the body presumably affected, while we have reasons to believe that there is more than the periphery to be taken into account. We have discovered, during the progress of reflection on the matter at issue, that we have a central nervous system with various branches and ramifications distributed throughout the bodily tissue, and various evidences go to show that, somehow, all states of consciousness, whether sensory or intellectual, whether localized on the periphery in perception or not, are connected with this central nervous system. I shall not indicate the evidence for this, as the fact is too generally known and accepted to require this. The fact gives rise to inquiry about the apparent source of sensation in affections of the periphery, and so the question whether it really occurs there or in central brain tissues. The supposition sometimes is that the peripheral localization of the sensation is an illusion and that it is really a central affair. But the difficulty is at least partly solved by the supposition of molecular action of the nerves between the periphery and the brain. The phenomena of reaction time seem to prove this fact of transmission from surface to centre, and possibly in return, as the phenomena of peripheral localization after the amputation of a limb seem to prove a central origin for all peripherally localized sensations. Reaction time is the period elapsing between the moment when stimulus touches the sensorium and the moment when the sensation occurs. This is invariably a measurable period, and seems to show beyond a doubt that a certain amount of time, insensible to our rough measures of sense-experience, is required for the transmission of stimulus to the brain and the occurrence of the sensation. This interval is supposed to be filled by molecular vibrations intervening between the periphery and the brain-centres, much as luminous and sonorous vibrations, outside the organism and acting as stimulus, intervene between the object and the sensorium. Additional complications are thus introduced into the already perplexing problem.
Where the naive view supposed that we simply saw and felt objects, that is, perceived them directly, and where it was not troubled by anomalies about action at a distance, intervening space, or differences between mental and material phenomena, the later view recognizes several distinct phenomena which may be described in the following manner. First, we have the object, often at a distance, perhaps always so, except in the cases of touch and taste. In the thermal sense there is the capacity of perceiving its object either in contact or at a distance. Then there is the system of motions or undulations intervening between the object and sense. There is next the impression upon the periphery of the organism, and this is followed by a conjectured molecular action in the nerve-filaments leading to the central nervous system. When these "impressions," or influences, are received in the brain or nerve-centres there is a reaction, or process so named metaphorically at least, and presumably again some transmission of molecular action back to the periphery to cause either sensation or some motor action in the muscular system. What these inward and outward transmissions are we do not know, at least in any sensible way. They are described as molecular because this is all that we can conjecture of media that are known or supposed to be molecular in structure and function. But whatever they are, they are conjectural and not immediately known. They seem, however, quite as well assured as if they were directly known. Hence there several different steps in the production of sensations and perceptive knowledge where the naive view had supposed the process a very simple one; and each step is supposed to have a different character from the preceding one, it is natural to raise the query whether we actually perceive the object at all as it is ordinarily conceived to be. This suspicion is further confirmed by the doctrine of specific nerve-energies, which shows that the same stimulus acting on different sense-organs will produce different sensations, and different stimuli acting on the same sense-organ will produce the same sensation, indicating that the sensory organism and its mode of action are factors in what is often taken for the object itself. Thus a shock to the retina will produce a sensation of light as well as luminous vibrations will produce it, and a touch on the tympanum of the ear will produce a sensation of sound as well as undulations of the air will produce it.
This complexity of the process, taken with this peculiarity of specific nerve-energies, gives rise to many curious questions in the reflective mind. The first question is, how can we know objects by such a mediating process. This query appears to have much force where it suggests an answer opposed to the naive view which, even when it recognizes the indirectness of the process, is quite satisfied with the assumption that the thing known remains intact, And that the mediation of vibration between it and sense creates no serious problems.
The most of us, trained or untrained, naturally accept our familiar conception of the object as beyond revision or denial, and so assume that the various steps supposed to explain it do not involve any modification of our idea of the place and nature of the object. But the very fact that we suppose, or once supposed, that the object is immediately known, - and certainly that which usually passes for such an object is immediately known, -while we have no immediate knowledge of the intervening motion or activity affecting the sensorium and nerve-centres, at once suggests the question how we can really know the object when this is assumed not to come into contact with sense and when there is presumably no resemblance between this supposed object and the motion or molecular phenomena that give rise to sensations. All these intermediate steps which appear to have no representative character for things at a distance, and which are not directly known, tend to suggest that we do not really know objects at all, or that there is no such direct knowledge as we had naively supposed. Consequently many minds come to the conclusion that what we do directly know is the sensation. the subjective state of the sensorium, and hence, with its non-representative character, that we have to infer the existence of the external object, which can only affect the mind by agencies that are modified all along the line between the external and internal worlds.
Two schools of thought arise here. One still insists that we know objects immediately, and the other that we do not "know" them, but that we infer their existence. When this controversy, however, is reduced to its final terms, the difference is mainly whether we directly and certainly know the nature of reality or not, one holding that we do in some sense, and the other that we know only the "appearance" of it, the way in which the sensorium is affected by stimulus. The former school tends to think that this phenomenal nature of the object involves the assumption that our knowledge of reality as naturally represented is illusory and not to be trusted.
But I shall not settle the controversy between these two schools, as it is not important to the purposes of this discussion, which is to be concerned with mental phenomena and their relations to each other, with criteria for determining those which have a normal practical value and those which do not. It would take us far into metaphysics to decide the dispute between the realist and the idealist, between the man who thinks we know reality directly and the man who thinks we know it only indirectly; between the man who thinks we know the nature of things and the man who thinks we know only their appearance or our mental states. But I have alluded to the controversy for the purpose of making intelligible a view of our mental states which can hardly be made clear in any other way, and this was suggested by the enormously complex processes giving rise to sensations. The moment that it was called upon to suppose that objects retained their immediate integrity, after a whole series of intermediate agencies quite different from them was necessary to arouse conscious perception, it was inevitable that the naïve view which had accepted the direct testimony of consciousness as to the nature of objects should be troubled by the apparent illusory character of the judgment involved. The discovery of the several steps to knowledge brought to the front the fact that the whole matter could be looked at from the standpoint of the mind as well as from that of the object. Whatever the presumed causal influence of objects in exciting sensation, the nature of the sensation was at least apparently the product of the mind, that is, a subjective function, and was in no respect a facsimile or simulacrum, of the object, and much less was it supposed to be the object itself. The difference between the stimulus, or at least the conception of what that stimulus was, intervening between the object and the mind, namely, the motion emanating from the object, and still further the difference between the molecular action of the nervous system and what appeared to consciousness in sensation, made it difficult to suppose that we actually saw or heard objects when we did not directly know the admittedly immediate causes of the sensation, without which the perception of the object would not take place. Hence arose the feeling that sensation is purely a product of the mind, in so far as its nature is concerned, though its occurrence depended on external stimulus.
Various actual experiences also seem to point conclusively to the same result. For instance, if we look at the sun for a few moments and then turn toward the blue sky or some similar background, we shall see a distinct image of the sun projected on this field, and for a few seconds it cannot be distinguished from the real sun. It will then fade into what is called the negative after-image, an image which is in all respects like the sun except in color and brightness, the positive after-image not being distinguishable from the real perception of the sun, except in its not representing a real or supposed objective fact. The negative after-image may take a red or a green, or even a dark color. But in all cases the phenomenon shows a continued brain or mental activity like the real percept, after the removal of the stimulus, and hence without the actual presence of that stimulus in any normal form. Again if we place the finger on the ball of the eye and move it so that the effect will be to shift the mental images present there, the landscape or objects at which we are looking will seem to move, when in fact they are not moving at all, according to the standard of normal judgment. The image in a mirror does not represent the right object at the real point of space at which it is situated, and certain kinds of mirrors will distort objects beyond all recognition. If we look at objects through colored glass they do not seem the same as in normal vision. Color-blindness illustrates the inability of the sensorium to perceive the object as in normal perception. The prism will produce color-distortion, and the microscope will magnify the size of objects.
These phenomena are not new. They are very familiar examples in the experience of all of us, and perhaps might be multiplied in various ways. But familiar as they are, we do not always think of their significance for our views of sense-perception. Even after we have discovered their subjective character we still think and act as if our normal experience, which is supposed to have retained its real character, is not to be compared with these illusory instances. But all these and many other facts show that our sensations are modifications of mental action, and that "objects" appear according to the way the mind is made to act by influences intervening between the supposed object and the subject or mind. Hence we are forced to recognize a subjective factor in our elementary states of consciousness that is neither the object nor representative of it in any sense involving identity of kind. This conception of the matter precipitates the feeling that our ordinary judgments are perfectly illusory, if we reflect on the evident resemblance between the normal and these illusory experiences. The consequence is that the question is raised regarding a test for the reality and validity Of any Of our sensory knowledge. If we cannot trust such primitive and tenacious judgments as those of sense-perception, what can we trust? We seem forced by the facts to think of sensations as reactions of the mind and not in any way presentative or representative of objects at all. That is, they are not facsimiles of them, and we either know nothing of external reality, or we have to obtain our knowledge by some form of indirect, inferential, or implicative act of the mind about it. Sensations are activities of the subject, not images of the object, even though we have reason to believe that they are in some way due to external agency.
The reactions of physical objects under impact afford good analogies of the same thing. The sound of a bell is not like the hammer or the motion of the hammer that produces the sound. The impact of the same kind of a blow on very different objects produces different effects. On a bell it is a musical sound, and on different bells it will be different sounds; on an ivory billiard-ball it is a clear, sharp sound, on clay or wood it is a dull thud. The re~ action in all such cases is determined by the nature of the subject or substance affected, or on which the action is directed, quite as much as by the external cause and perhaps more. It is the same with the mind or brain. Its response to stimulus is not like the stimulus, and what we take for reality in our naive way of looking at the matter appears to be only the mind's own product or "construct." What we have supposed to be an external object thus seems to be a mere phenomenon or internal fact.
What, then, do we know about external reality? How do we know that our experiences in sense are not illusions or hallucinations? In what way are we different from the abnormal or insane mind? What criterion have we for our belief in external objects? The insane mind apparently sees objects which examination shows to be creations of his own mind or brain, and which are not objectively real at all. In what respect are our normal experiences different from these?
The answers to these questions have given rise to two schools of thought. One of them calls itself the realistic school, and means in some way to insist that our normal sensations and perceptions stand for at least something outside the organism which we denominate external reality. What its reasons are for this judgment 1 am not concerned at present to discuss. They are not important for the purposes of this work, which is to study mental phenomena primarily in their relation to the distinction between the normal and the exceptional. Hence I am interested in the problem of Realism only in so far as it represents a class of thinkers who suppose they have a means of defending the integrity and validity of our primitive judgments, based upon sensation, and in so far as it represents the effort to distinguish between two distinct types of mental phenomena that have different relations to our practical life. But this realistic school divides between two interpretations of experience. One division holds that senseperception correctly reports the nature of external reality and that objects are as we see them. This school may be called that of Presentative Realism, meaning that objects are presented to and "in" sense as they appear. The other division of the school holds that we do not directly perceive external reality, but that we infer its existence from our sensations. This view is called Hypothetical Realism. It makes some concession to the idea that sensations are more or less subjective affairs, while the alternative view tends to emphasize the result from the standpoint of the object and perhaps does not appreciate the subjective nature of sensation, though neither denying nor assuming it consciously.
The second general type of thought, opposed to Realism, calls itself the idealistic, and aims to judge of experience from the subjective point of view. It assumes an opposition of some kind between sensation and what it betokens, or is supposed to betoken. This school, Idealism, divides also into two views. One of them admits the existence of an external reality, but denies that our knowledge of it is direct or presentative and immediate, and so explains that the knowledge is inferential or hypothetical. This view is virtually identical with that of Hypothetical Realism, and differs only in that it is inclined to emphasize the antithesis between sensation and reality. But in essential particulars the view is identical with hypothetical realism. The second type of idealism is more emphatic still in its representation of the limitation of knowledge to sensations or phenomena, and inclines to abandon all antithesis between the subjective and objective, so that in so far as it admits the existence of external reality at all, it makes it the same in kind with the subjective, and to that extent approximates Presentative Realism, save that it inclines to make the real mental instead of material. But it insists on maintaining that we know nothing about the nature of the external cause, if it is not mental. Its favorite formula is that we know only appearances or phenomena; that we know things only in terms of consciousness, etc. This view does not wholly escape the belief in something other than sensations, though it tends either to deny all possible knowledge of this reality, or assumes that it is mental in nature. Hence, though there is a point of reconciliation between this view and either form of Realism, it has certain aspects of skeptical difference that distinguishes its way of looking at things from that of naive Realism.
I shall not undertake here to solve the problem discussed by these two schools. It is a problem that involves more than the criteria to distinguish between the normal and the abnormal or exceptional in mental phenomena, though it is closely connected with this in some respects. The question in dispute between these two schools primarily regards the nature of reality, the limits of
presentative knowledge, rather than the fact of external objects, and the question of illusions arises incidentally. Illusion is suggested by the necessity of reviewing our primitive and naive judgments when we come to admit the creative agency in what it knows or seems to know, if creative agency is the proper term for describing the act or product. Hence, though controversy between realism and idealism concerns the mode of explaining knowledge, and does not in fact represent the question regarding the distinction between valid and illusory mental states, it gave rise to this problem and associated or confused it with the metaphysical issue. This has been the reason for discussing it as much as
I have done, because it is the historical line of thought about it that represents the way in which it has been approached. Though we may abandon the specific way in which the dispute is carried on between these two modes of speculation, we can hardly escape the use which it has for the problem of deciding between what has an objective and what has a subjective origin.
The realist has always supposed himself assured of a criterion for distinguishing valid judgments from illusions. Whenever he discovered or suspected an illusion in vision, he tested his experience by an appeal to touch which was supposed to give reality unmistakably. Any apparent object which could not affect touch was an illusion in the sense to which it appeared. Thus the normal and the real became the same thing. But as the psychologist could assert the subjectivity of tactual sensations quite as well as the visual, the aural, or the thermal, and as illusions are occasionally discoverable in tactual experience, the security against illusion had to be sought by some other means than touch alone. In our ordinary experience tactual phenomena are our test of what is real when we find the need of asking whether any other has such a meaning or not, and its practical value in the various adjustments of life need not be disputed or doubted when asking whether it is any better expression of the nature of things than any other sense. Whatever reasons we may have for an appeal to tactual experiences for testing our relation to things, we do not require to suppose that its superior importance for this end indicates its right to estimate the nature of things to the exclusion of vision, hearing, and the other senses. Reflection on the common relation of all the senses to our knowledge, and on the occasional illusions of touch, shows that this sense no more gives the "real" directly, as the naive view conceives it, than the other senses, and the consequence is that it becomes necessary to distinguish between the real and the normal as a means of evading the philosophical controversy. Hence we may relegate the dispute between the realist and the idealist to the domain of metaphysics or to epistemology, and seek the explanation of illusory and abnormal phenomena in some other way. This new way actually came into recognition with modern science with its emphasis upon the relation of phenomena and the laws of their occurrence rather than upon their metaphysical causes.
This new way of solving the problem of illusion had nothing to do with the nature of things, interesting as this question may be to the human mind, and however important it may be to certain types of reflective speculation affecting wider than immediate practical issues. Ignoring this metaphysical question, it sought to determine the practical question by ascertaining the
laws of mental action their relation to daily life, in which there was no and dispute between idealist and realist. In the last analysis we may have to resort to the principle assumed by both these schools, namely, that of external causality, for deciding when a phenomenon is purely subjective in its origin and when it originates outside the subject. But in regard to the question whether our knowledge of reality is direct or indirect, mediate or immediate, whether we know things as they are or only as they appear, we may find a common field for scientific investigation in the uniformities of coexistence and sequence in mental phenomena, where we may find at least a preliminary and provisional criterion for distinguishing between the normal and abnormal until a better be found, if it be required. But if we are not seeking the causes of Phenomena, we may be satisfied with a means of measuring the expectation of their occurrence and relation to welfare by something else than their explanation. In this view we do not ask for the nature of objects, or perhaps even for their existence, as a test for the normal in the first degree, but for the association of different sensations and the relative frequency of their association as a means of fixing their place in regulating our actions. In other words, our provisional test is the relation of experience to the practical affairs of daily life and immediate adjustment to environment. The limitations of this criterion may be seen in the conclusion. But for practical emergencies, as they are affected by the immediate demands of action, the various associations of sensation and the observed experience of other persons are the main test of what is "real" and what is illusory.
In applying it we shall still correct the judgments of one sense by those of another, but we shall not involve ourselves in the problem of the nature of things. We shall confine ourselves to the relations of phenomena. Our ordinary practical life has to be regulated in the same way under all theories of the world, whether we believe in the existence of matter or spirit, whether in an external world or only, in subjective states. Even if vision, for instance, is illusory in its data, we cannot persist in the act of looking steadfastly at what we call the burning sun. Nor can we ignore considering our footsteps in our behavior toward what we appear to see. We have to at least preserve caution and to see that our expectation of associated experiences has some law for its guidance. If sense-perception generally be illusory, and if we have no criterion to distinguish between the nature of purely subjective and the nature of the objective facts of knowledge, there is a common means of distinguishing between different subjective experiences and of determining their relation to survival in the struggle for existence. This means is suggested by the illustration mentioned above. No matter, for instance, how subjective tactual perception is or may be, we cannot act toward a stone as we would toward a figure behind a mirror, No matter how subjective heat-sensations may be, we cannot treat them as we would after-images or stereoscopic pictures. We have to regulate our conduct to suit certain consequences, or, if not consequences, certain recurrent phenomena and associations that are related to our welfare. Hence it is certain uniform relations between one set of sensations and another, coexistent or sequent, that constitutes the First test of the illusory, the illusory being merely that which can be safely neglected in the immediate adjustment of ordinary conduct. The full meaning of this view will be apparent at the close of the next chapter. For the present we must be content with the general fact that the investigation of the normal and the abnormal in mental phenomena can he carried on without any prior solution of the metaphysical problem, and that the practical test of the distinction between them will be some law of their recurrence and
association.
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