I have already drawn attention to the fact that the primary end and object of the reception of the influences (stimuli) of the external world, or environment, is to enable the organism to answer or respond to these special modes of influence, or stimuli. In other words, their purpose is to set agoing certain activities. Now, in the unicellular organism, where both the reception and the response are effected by one and the same cell, the activities are for the most part simple, though even among these protozoa there are some which show no little complexity of response. Where, however, the organism is composed of a number of cells, in which a differentiation of structure and a specialization of function have been effected, certain cells are set apart as recipients, while other cells are set apart to respond (respondents). There is thus the necessity of a channel of communication between the two. Hence yet other cells (transmitters), arranged end to end, form a line of connection and communication between the group of receiving cells and the group of responding cells, and constitute what we term a nerve. That which is transmitted may still be called a stimulus, each cell being stimulated in turn by its neighbour. Thus a stimulus must be first received and then transmitted.

But little observation is required to convince us of the fact that, in the higher creatures, a very simple stimulus may give rise to a very complex response. A light pin-prick will cause a vigorous leap in a healthy frog—a leap that involves a most intricate, accurate, and complex co-ordination of muscular activities. And anatomical investigation shows us that in such creatures there is always, in the course of the channel of communication or transmission, a group of closely connected cells, which play the part of co-ordinants. In the vertebrate animals these co-ordinants are collected in the brain and spinal cord. In the insects, crustaceans, and worms they are arranged in a knotted chain running close to the under surface of the body. To this central nervous system, as it is called, nerves (afferent nerves) run inwards from the recipient organs. From it nerves (efferent nerves) run outwards to the organs of response. And in it the transmitted stimuli, brought in by the afferent nerves, are modified, through intervention of the co-ordinants, into stimuli carried out by the efferent nerves. A simple stimulus may create a great commotion among the co-ordinants of the central nervous system, and give rise to many and complex stimuli going out to the muscles and other organs of response. How this is effected is one of the many wonders of the animal mechanism. We believe that the connection and co-ordinations have gradually been established during a long process of development and evolution, reaching back far into the past. How, we can at present scarcely guess.

We must picture to ourselves, then, in the animal organism, a multitude of nerve-fibres running inwards from all the end-organs of the special senses, from the muscles, and from the internal organs, and all converging on the central nervous system. And we must picture to ourselves a multitude of nerve-fibres passing outwards from the central system, and diverging to supply the muscles, glands, and other organs which are to respond to the stimulation from without. We must picture the fibres coming from or going to related parts or organs collecting together to form nerves and nerve-trunks, which are, however, only bundles of isolated nerve-fibres. And, lastly, we must picture the central nerve-system itself co-ordinating and organizing the stimuli brought into it by afferent nerves, from the organs of special sense, and handing over the resultants by efferent nerves to the organs of special activities. So far we have purely physiological effects, many of which occur with surprising accuracy and precision when an organism is in a state of unconsciousness. Place your finger in the palm of a sleeping child, and the fingers will close over it without the child awaking to consciousness. If, in a frog, the brain of which has been extirpated, the side be touched with a drop of acid, the leg of that side will be drawn up, and the foot will be used to wipe away the acid. And if that leg be held and prevented from reaching the side, the other leg will be brought round so as to try and bring the foot within reach of the irritated spot. The actions are, however, in all probability, purely physiological, and are performed in complete absence of consciousness.

When we turn from the physiological to the psychological aspect of the question, we enter a new world, the world of consciousness, wherein the impressions received by the recipient organs (no longer regarded as mere stimuli, but as the elements of consciousness) are co-ordinated and organized, and are built up into those sensations and perceptions through which the objects of the external world take origin and shape. It is with this process that we have now to deal; and we will deal with it first in man.

The first fact to notice is that, apart from sense-stimuli received and exciting consciousness, we have also the revival of past impressions. This revival is the germ of memory. What exactly is the physical basis of memory, how the effects of stimuli in consciousness come to be registered, we do not know. It is clearly a matter that falls under the general law of persistence; but in what organic manner we are largely ignorant. Still, there can be no question of the fact that, quite apart from impressions due to immediate influences of the environment now acting on our recipient organs, we have also revivals of bygone influences of the environment—shadows or after-images of previous modes of influence. Without this process of registration and revival, stimuli could never give rise to sensations and perceptions such as we know them. Without it experience would be impossible.

We may say, then, that impressions (resulting from stimuli) and their revival in memory are the bricks of the house of knowledge; and these are built up through experience into what we call the world of things around us. There may be and is a certain amount of mortar, supplied by the builder, in addition to the elementary bricks. But without the bricks no house of knowledge could be built. Let us now examine the bricks and the building.

From what we have already learnt in the chapter on "The Senses of Animals," it is clear that the impressions and their revivals in memory have differences in quality. Here, on the very threshold of the subject, we must pause. They have differences of quality. But in consciousness these differences must be distinguished. And this involves their recognition and discrimination, presupposing, therefore, a corresponding faculty, however simple, on the part of the recipient. Without cognition and recognition (twin sisters, born in the same hour) we can never get beyond mere impressions; which may, indeed, be differentiated physically, as different stimuli due to diverse action of the environment, but are psychically undifferentiated. This recognition and discrimination is thus the primary activity of the recipient mind. Here is already some of the mortar supplied by the builder. Memory is absolutely essential to the process. The sense-impression of external origin gives rise to an impression of similarity or dissimilarity, which is part of the internal reaction to the external stimulus. Thus impressions are raised to the level of sensations. A sensation is an impression that has been discriminated from others, and recognized as being of such and such a nature. The impressions of the sense-organs as we know them are thus not mere impressions, but impressions raised to the level of sensations, in so far as they are recognized and discriminated.

Let us now glance at some of the differences in quality recognized in sensation. First, we have the broadly distinguished groups of touches and pressures, temperature-sensations, tastes, smells, sounds, sights, muscular sensations, and organic sensations from internal parts of the body. And then, within each of these groups, there are the more or less delicate and distinct shades of quality, well exemplified in vision by the different colour-sensations, in hearing by notes of different pitch, and in smell by the varieties of scents and odours. Many of those sensations, moreover, which are apparently simple, are in reality compound. There are differences of quality in the note A as sounded on a violin, a piano, and a flute; and these differences are due to different admixtures of overtones, which fuse with the fundamental tone and alter its timbre. So, too, with vision. The sensation given by a white disc is a compound sensation, due to waves of different period, which separately would give sensations of colour. Sensations, then, differ in quality.

They also differ in quantity or intensity. This needs little illustration. As evening falls, the sight-sensations derived from the surrounding objects grow more and more feeble. They may remain the same in quality, but the quantity or intensity gradually diminishes. So, too, in music, the pianos and fortes give us differences in intensity of sound-sensations.

Sensations also differ in duration. The stimulation may be either prolonged or instantaneous. Two or more sensations may, moreover, be simultaneous or successive. Just as they may be either similar or different in quality and in intensity, so they may be either simultaneous or successive in time. Simultaneous sensations are best exemplified in vision and through touch; successive sensations are given most clearly by the sense of hearing, through which we recognize a sequence of sounds.

And then, again, sensations not only differ in time, but they seem also to differ in place. A sensation of touch may be referred to different parts of the body—the hand, the foot, or the forehead. But here we open up an important question—Where do we feel a sensation, such as, for example, that of pressure on the skin? Common sense answers, without hesitation, that we feel it at the particular part of the body which is affected by the external stimulus. I feel the pen with which I write with my finger-tips. And common sense is perfectly right from its own point of view. But it is a well-known fact that a person whose leg has been amputated experiences at times tickling and uneasiness in the absent member. This is due to irritation of the nerve-ends in the stump of the limb. But the sensations are referred outwards to the normal source of origin of impressions, the effects of which were carried inwards by the nerve affected. We shall have to consider hereafter the nature of the relation between physiological and psychological processes—the connection of mind and body. Assuming for the present that psychical processes have a physical basis in physiological processes, the fact given above and others of like implication seem to show that the sensation has for its physiological basis some nerve-change in the central nervous system—in us, no doubt, in the brain. Of course, it must be remembered that the sensation, as felt, is a mental fact (using the word "mental" in its broadest sense, as belonging to the psychical as opposed to the physiological series). But it would seem that the physiological accompaniment of this mental fact is some nerve-change in the brain. This nerve-change is caused by a stimulus having its origin in the end-organ of the afferent nerve, and we naturally refer the impression outwards to the place of its source of origin under ordinary and normal conditions. In other words, we localize it. That is what common sense means when it says that we feel pressure at the finger-tips.

To account for this process of localization, it is supposed that every sensation, apart from its special quality as a touch, a taste, or a smell, has a more or less defined spatial quality, or local sign, dependent upon the part of the body to which the stimulus is applied. These local signs have, doubtless, in the long run, been established by experience—if under this term we may include a more or less unconscious process, the outcome of evolution. But they are so rapidly established in the individual, that we are forced to conclude that we inherit very highly developed aptitudes for localization.

The refinement of localization is very different in the different senses. In smell and taste there seems no more than a general localization in the organ affected—the nose or the mouth. In hearing there is not much more, unless we regard the discrimination of pitch as a mode of localization. In touch (and temperature) the refinement is much higher, but it varies with the part of the body affected.

If the back be touched by two points less than two inches and a third apart, the sensation will be that of a single point; the finger-tips, however, can distinguish two points separated by less than one-tenth of an inch; and the tip of the tongue is still more refined in its power of discrimination, distinguishing as two, points separated by less than the twenty-fifth part of an inch. So that the tongue is about sixty times as refined in its discrimination as the skin of the back. Moreover, the delicacy of localization may be cultivated, so that in some cases the refinement may, by practice, be doubled.

When we come to sight, the refinement of localization reaches its maximum, the local signs in the retina showing the highest stage of differentiation, the distance on the retina between two points distinguishable by local signs being, according to Helmholtz, not much more than 1/6000 of an inch (.0044 millimetre), which nearly corresponds with the space between two cones in the yellow spot.

We must remember that the presentations of sense are in all cases given in a stippled form, that is, by the stimulation of a number of separate and distinct points. In vision the stippling is very fine, owing to the minute size and close setting of the retinal cones. In the case of hearing, the stippling, if we may so extend the use of this term, is also very fine, as is shown by the fact that musicians can, according to Weber, distinguish notes separated in the scale of sounds by only one-sixtieth part of a musical tone. In touch the stippling is comparatively coarse. But in all cases there is a stippling; and yet from these stippled sensations the mind in all cases elaborates a continuum. The visual image is continuous, notwithstanding the retinal stippling and the existence of the blind spot. When we lay our hands on a smooth table we fill in the interstices between the sensational points, and feel the surface as continuous. In all cases out of the stippled sense-stimuli we form a continuum.

The next thing that we have to note is that it is not so much the sensation itself, as that which gives origin to it, that we habitually refer outwards to the recipient end of the afferent fibre. In referring a sensation of touch to a certain part of the skin, it is of something touching us that we seem to be immediately conscious. We refer the stimulus to an object in the external world, which we localize, and which we believe to have given rise to the sensation.

This, however, is more clearly seen in the case of vision. When we look through the window and see an object such as a house before us, we do not habitually localize the sensation in a certain part of the retina, but we refer the object to a particular position more or less distant in the world around us. This projection of the object outwards in a right line from the eyes is really a marvellous process, though the wonder of it is lost in its familiarity. It is the outcome of the experience of hundreds of generations. And the experience is not gained through vision alone, but through this in combination with other senses and activities. We see an object, but we have to go to it before we can touch it. It is not in contact with us, but distant from us. Its outness and distance is a matter of what is termed the geometry of the senses; and this geometry has been elaborated through many generations of organized beings, from data given by sight, touch, and the muscular sense. It is true that I can now estimate the distance of the house without going to it; but my eyes go to it, and I can feel them go. The panes of my window are separated by iron bars. As I look from them to the distant house and back to them again, I can feel my eyes going from one to the other. The lens of the eye is adjusted for near or far distance by the action of a ciliary muscle, through which its anterior surface can be flattened, returning again by its own elasticity to the more convex form when the muscle ceases to act. Each eye, moreover, is moved in its orbit by six eye-muscles, and in normal vision the two eyes act as one organ. For near distances they converge; for far distances there is less convergence. Through the muscular sense, which is here extraordinarily delicate, we can feel the amount of accommodation and convergence; and thus we can feel the eyes going to or coming from a near and a distant object. Of course, we are aided in judging or estimating distances by the apparent size of the object when the real size is known, by the clearness of its outlines in a slightly hazy atmosphere, and so forth. But apart from such judgments, it would probably be impossible to perceive that an object is near or distant in the absence of muscles of accommodation and convergence affording the data of the muscular sense. Not only the distance of two objects from the eye, but their distance apart, can be measured by the aid of the muscular sense as we move the eyes from one to the other. And in us this is so delicate that, according to Weber, a distinct muscular sensation is attached to a displacement of a sensitive point of the yellow spot through less than 1/6000 of an inch.

Now, if it be true that the consciousness aroused by objects around us, through sensation, is an accompaniment of certain physiological changes in the brain, it is clear that the localization of their points of origin in special parts of the skin, and the outward projection of the objects exciting vision, is an act of the mind quite distinct from the mere passive response in consciousness which we call an impression, and more complex than that mental activity which, through discrimination and recognition, converts the bare impression into a sensation. It is, in fact, part of that mental process which is called perception.[FP] Sensation has nothing to do with the objects around us as such; it is by perception that we are aware of their existence. Let us now follow the process of perception a little further, always remembering that it involves certain activities of the mind.

These activities are too often ignored. We often speak of the senses as the avenues of knowledge, and John Bunyan, likening the soul to a citadel, spoke of the five gateways of knowledge, Eye-gate, Ear-gate, Mouth-gate, Smell-gate, and Feel-gate. Hence arises a vague notion that through the eye-gate, for example, a sort of picture of the external object somehow enters the mind. And this idea is no doubt fostered by the fact that an inverted image of the object is formed on the retina, though how the inverted image is turned right way up again in passing into the mind bothers some people not a little.[FQ] A much closer analogy is this: Something stands without and knocks at the doorway of sense, and from the nature of the knocks we learn somewhat concerning that which knocks. In other words, at the bidding of certain stimuli from without we construct that mental product which we call the object of sense. It is of these mental constructions—"constructs"[FR] I will call them for convenience—that I have now to speak.

In a fruiterer's shop on the opposite side of a street I see an orange. That is to say, certain cones of the retina of my eye are stimulated by light-waves of a yellow quality, and at the bidding of these stimuli I construct the object which I call an orange. That object is distant, roundish, yellow, resisting and yet somewhat soft, with a peculiar smell, and possessed of a taste of its own. Now, it is obvious that I cannot see all these qualities of the orange, as we call them. I construct the object on reception of certain light-waves which are focussed on the retina of my eye. If I go to the orange, however, I can test the correctness of my construct by the senses of touch, smell, and taste. But what led me to construct an object with these qualities? Experience has taught me that these qualities are grouped together in special ways in an orange. I constructed that particular object through what is termed the principle of association. I have learnt that these qualities are grouped together in certain relations to each other, and when I actually receive sight-stimuli of a certain quality, grouped in certain ways, they immediately call up the memories of the associated qualities. That which is actually received is a mere suggestion, the rest is suggested in memory through association. The object might be suggested through other senses. I come into a dining-room after dessert, and the object is suggested through smell. Or my little son says, "Open your mouth and shut your eyes, and see what the fairies will send you;" and an orange is suggested by taste. In all these cases the object is constructed at the bidding of certain sensations, which suggest to my mind the associated qualities. The object is a construct.

And here let us notice that we ascribe the form, the resistance, the taste, the smell, to the object. We do not say or think, "Sight-sensations inform me that there is something which I call an orange, and which is capable of exciting in me sensations of touch, taste, and smell;" but we say, "There is an orange, which has such and such a taste, smell, and feel." In other words, we refer these sensations, related in certain ways, outwards to the object, and name them qualities of the object that we see. But remember, that we do not necessarily or normally say or think anything about it. We just inevitably construct the object, what we build in to the construct depending upon association through experience.

At this stage, perhaps, Common Sense steps in, and, shaking his head, says, with characteristic bluntness, "Nonsense; you'll never persuade me that the things I see and feel around me are nothing but fictions of my own mind. I don't construct them, as you call it; there they are for me to see and feel and taste if I will." Now, Common Sense is a sturdy, hard-headed individual, with whom I desire to keep on friendly terms. And I therefore hasten to explain that I most fully agree with every word that he says. The orange that I see before me is not a mere fiction of my mind. I can, if I will, take it up, feel it, smell it, and taste it. If it will satisfy Common Sense, I will say that it is the idea of the orange that I construct. Only I think that Common Sense, who has a horror of roundabout and indirect statements, will not like my saying, "I am receiving certain visual sensations related in certain ways, which lead me to construct an idea of an orange." He will prefer my saying simply, "I see an orange." Since what he wants me to call our ideas of things answer point for point to the things as they actually exist for us human-folk, it is not only more satisfactory but more correct to merge the two in one, and speak directly and simply of the object. The object is a thing I construct. That it is real may be proved by submitting it to the test of all the senses that I have.

And what do I mean by "real"? I mean that what it is for me it is also for you and any other normally constituted human being. This is, in truth, the only common-sense criterion of objective reality. Some people are colour-blind, and tell us that a rose is not red, but green. We reply that it is really red, but that, through a defect of sight, they cannot distinguish its redness. Here we take the normal human being as a standard for objective reality. For him the rose is red. And this is the only practical criterion that we have. This, however, does not satisfy some people, who think that the objects around them have the same reality, independent of man, that they have for us human-folk. Annihilate, they say, every human being—nay, all life—and the objects will remain as they are, and retain the same reality. Yes, the same reality; which means that if just one fortunate fellow escaped annihilation, he would find them all just as they were. And this nobody doubts. Nevertheless, it is (to me, at least) inconceivable that things independently of us are what they appear to us. Think of what we learnt about the sensations. They all arose in stimulations of the end-organs of special sense. Thence the explosive waves of change passed inwards to the brain, and somewhere therein gave rise to mental products. These mental products, the accompaniments of nerve-changes, can in no sense be like the outside something which gave rise to them. They are symbols of that outside something. And it is these symbols that we build up into objects. Hence I said that it is not only more satisfactory and convenient, but more correct, to speak directly of the object as constructed, and not our idea of the object. The mental product is the object for us, not only for me, but for you and all normal human beings, since the object is the same for all of us. And hence, also, I said that the analogy of gateways, through which pictures of objects gain access to the mind, was false and misleading, and that a truer analogy is that something stands without and knocks at the doorway of sense, and that from the nature of the knocks we learn somewhat concerning that which knocks. The person inside can never open the door to see what manner of thing it is which knocks. But he can build up a most cunning symbolism of knocks which shall suffice for all practical purposes. In other words, the object-world, symbolic though it is, which you and I and the rest of us construct at the bidding of something without us (the existence of which I assume), is amply sufficient for all our practical needs, and constitutes the only practical reality for human-folk.

I am well aware that there are many people who cannot bring themselves to believe in, or even to listen without impatience to, the view that the world we see around us is a world of phenomena. It is absurd, they say, to tell us that yonder tulip, as an object, is in any sense dependent on our perception of it. There it is, and there it would have been had man never been created. Can one conceive that the new species of fossil, which was only yesterday disentombed from the strata in which it has lain buried for long ages, is dependent on man's observation for its qualities as an object? To say that it was "constructed" by the lucky geologist who was fortunate enough first to set eyes on it is sheer nonsense. Its shelly substance protected a bivalve mollusc millions of years before man appeared upon the earth. When we see the orange in the fruiterer's shop, the sight of it merely reminds us of its other qualities—its taste, its smell, its weight, and the rest, which are essentially its own, and no endowments of ours—nowise bestowed upon it by us.

I have no hope of convincing, and not much desire to convince, one who thus objects. I would merely ask him how and when he stepped outside his own consciousness to ascertain that these things are so. Does he believe that consciousness is an accompaniment of certain nervous processes in the grey cortex of the brain? If so, let him tell us how these conscious accompaniments resemble (not merely symbolize, but resemble) tulips and oranges and fossil molluscs. If not, let him propound his new theory of consciousness.

Let it not be supposed that I am denying the existence, and the richly diversified existence, of the external world. We are fully justified, I think, in believing that, corresponding to the diversity of mental symbolism, there is a rich diversity of external existence. But its nature I hold that we can never know. The objects that we see are the joint products of two factors—the external existence and the percipient mind. We cannot eliminate the latter factor so as to see what the external factor is like without it. Those who, like Professor Mivart,[FS] say that we can eliminate the percipient factor, and that the external world without it is just the same as it is with it, are content to reduce the human mind, in the matter of perception, to the level of a piece of looking-glass.

There are some people who seek to get behind phenomena by an appeal to evolution. It will not do nowadays, they say, to make the human mind a starting-point in these considerations; for the human mind is the product of evolution, and throughout that evolution has been step by step moulded to the external world. The external world has, therefore, the prior existence, and to it our perceptions have to conform. All this is quite true; but it is beside the point. Mind has, throughout the process of evolution, been moulded to the external world; our perceptions do conform to outside existences. But they conform, not in exact resemblance, but in mental symbolism. They do not copy, but they correspond to, external existences. It is just because, throughout the long ages of evolution, mind has lived and worked in this symbolic world that common sense is unable to shake off the conviction that this is the only possible world, and exists as such independently of mental processes. The world of phenomena is the world in which we, as conscious beings, live and move. No one denies it. But it is none the less a symbolic world; none the less a world which mind has constructed in the sense that it is an inalienable factor in its being.

Each of us, when we perceive an object, repeats and summarizes the constructive process which it has been the end of mental evolution to compass. Hence it is that, at the bidding of a simple impression, percepts or constructs take origin and shape in the mind. In taking possession of this faculty in the early years of life, we are entering upon a rich ancestral heritage. But if what I have been urging has truth, what we call objects are human constructs, and cannot by any manipulation be converted into anything else.

I will now take another and more complex case of construction, which will bring out some other facts about what I have termed "constructs." I hear in the street a piercing howl, which suggests a dog in pain. Rising from my seat and going to the window, I see a white terrier with a black patch over the left eye limping down the road on three legs. Now, what was the nature of the construct framed at the bidding of the piercing howl? A dog in pain. But what dog? The nature of the howl suggested a small dog; but there was nothing further to particularize him. The construct was, therefore, exceedingly vague and ill defined, and was not rendered definite and particular till I went to the window, and saw that it was a white terrier with a black patch over the eye. The howl, moreover, suggested certain activities of the dog. The construct was not merely a passive, inanimate object, like the orange, but an object capable of performing, and actually performing, certain actions. Here, again, we can only say that it is through experience that special activities are associated with certain objects. Just as the construct orange is capable of exciting sensations of taste, so the construct dog is capable of doing certain things and performing certain actions, that is, of affecting us in certain further ways.

But, further, the howl suggested a dog in pain. No amount of sensations entering into any manner of relations could give me that element of the construct. I can neither see, touch, taste, smell, nor hear pain in another being. Pain is entirely subjective and known only to the sufferer. But I have been a sufferer. I have experienced pain and pleasure. And just as my experiences, individual and ancestral, lead me to project into inanimate objects certain qualities, the products of my sensations, so do my experiences, individual and ancestral, lead me to project into certain animals feelings analogous to those I have myself experienced. This is sometimes described as an inference. But if we call this an inference, then we must, I think, call the taste, smell, and feel of the orange I see before me inferences. In both cases the inference, if we so call it, enters at once into the immediate construct.

And when I went to the window and saw the dog limping down the street, I saw also a small boy, with arm drawn back, in the act of throwing a stone. In other words, I saw the objects in the scene before me standing in certain relations to each other. I concluded that the boy had thrown a stone at the dog and was about to throw another. In other words, I saw the scene before me as part of a sequence of events.

One more example I will give to bring out another and important feature in the mental process. Strolling before breakfast in early spring in my friend's garden, there is borne to me on the morning air a whiff of violet fragrance. Not only does this lead me to construct violets, but it reminds me of a scene in my childhood with which the scent of these flowers was closely associated. Not only is the object constructed, but a scene with which their fragrant odour has been associated is reconstructed in memory. The violets are immediate constructs or presentations of sense; the remembered scene is a reconstruct or representation in memory. So, too, when I heard a piercing howl in the street, the dog I constructed was a vague presentation of sense; but the street in which I instinctively placed him was a reconstruct or representation in memory. The difference between a construct or presentation of sense, and a reconstruct or representation in memory, is that the former is directly suggested through the immediate action of some quality or activity of the object, while the latter is indirectly suggested through some intermediate agency.

Before proceeding further, let us review the conclusions we have thus far reached. Through the action of certain surroundings on our sensitive organization, we receive certain impressions, and among these impressions and others revived in memory we recognize certain similarities or differences in quality, in intensity, in order of sequence, and in source of origin. The sensations which thus originate are mental facts in no sense resembling their causes, but representing them in mental symbolism. The consciousness of similarity or difference is no part of the impression, but a further mental fact arising out of the impression, and with it giving origin to sensation. It deals with the relation of impressions among each other and to the recipient. It involves recognition and discrimination. Its basis is laid in memory. The sensations are instantly localized, referred to objects, and projected outwards, mainly through the instrumentality of the muscular sense. The mental symbolism is thus built into the objects around us, and constructs are formed. But into the tissue of these constructs are woven, not only the sensations immediately received, but much that is only suggested through association as the outcome of past experience, individual and ancestral. The constructs and their associated reconstructs are thus endowed with qualities which have practical reality, since they are not for me only, but for you and for mankind. They are, therefore, in a sense independent of me, but nowise independent of man.[FT] Some of the constructs are endowed with activities, and some with feelings akin to our own. Finally, in the field of vision which we construct or reconstruct, the objects are seen to stand in relationship to each other, and the scene as a whole is perceived to be part of an orderly sequence of events.

We have already got a long way beyond the impressions with which we started; and yet, if I may trust my own experience, such construction as I have described is direct and immediate. A child of four or five would not only construct as much, but might not improbably go a long way further, and say, "Naughty boy to throw a stone at poor doggie!" It is, I say, direct and immediate, and it implies a wonderful amount of mental activity. Some people seem to imagine that in the simpler forms of perception, as when I see an orange on the table, the mind is as passive as the sensitive plate in a photographer's camera. This surely is not so. It is a false and shallow psychology which teaches it. Just as a light pin-prick may set agoing complex physical activities in the frog, so may comparatively simple visual sensations give rise to complex mental activities in construction and reconstruction. It is to emphasize this mental activity that I have persistently used the terms "construct" and "construction." And I wish to emphasize it still further by saying that without the active and constructive mind no such process of construction or reconstruction is possible or (I speak for myself) conceivable. We might just as well suppose that the frog could leap away on stimulation of a pin-prick in the absence of its complex bodily organization, as that sensation could give rise to construction and reconstruction in the absence of a highly organized mind.

We have seen that when a howl suggested the construct dog, that construct was vague and undefined; but when I went to the window and saw the terrier, the construct became particularized and defined. This seems to me the normal order of development: first the vague, general, and indefinite; then the particular, special, and defined. That which is immediately suggested at the bidding of sensations received is always more or less general; it only becomes specialized on further examination physical or mental—first a dog or an orange; then this dog or this orange. The more unfamiliar the object, the more vague and indefinite the construct. The more familiar the object, and the further our examination of it is carried, the more particular and defined the construct. I would, therefore, mark two stages in the process of construction: first, the formation of constructs by immediate association, more or less vague, indefinite, and ill defined; and, secondly, the definition of constructs by examination, by which they are rendered more definite, particular, and special, and supplemented by intelligent inferences.

I need not stay here to point out the immense importance of this process of defining and particularizing constructs, or the length to which it may be carried; nor need I pause to indicate how, through memory and association, representative or reconstructive elements crowd in to link or weave the constructs into more or less vivid and brilliant scenes. But I have next to notice that out of this intelligent examination arises a new, distinct mental process, the analysis of constructs.

This process involves the paying of special attention to certain qualities of objects, to the intentional exclusion of other qualities. When I cease to examine an orange as a construct, and pay attention to its colour or its taste to the exclusion of other properties, with the purpose of comparing this colour or taste with other colours and tastes, I am making a step in analysis. So, too, when I consider the form of an orange for the purpose of comparing it with the form of the earth, I am making a step in analysis. And, again, when I consider the howl of the dog with the object of comparing it with other sounds, I am making a step in analysis. We may call the process by which we select a certain quality, and consider it by itself to the neglect of other qualities, isolation, and the products of the process we may term isolates.[FU]

This process could not be initiated till a large body of constructive and reconstructive experience had been gained. But once initiated, there is no end to the process. We pick to pieces all the phenomena of nature, all the qualities and relationships of objects, the activities and functions of animals, the mental phenomena of which we are conscious in ourselves. We isolate the qualities, relationships, feelings; and we name the isolates we obtain. Hence arises all our science, all our higher thought. In the terms which we apply to our isolates consists the richness of our language.

We name the isolates; that is, we apply to each an arbitrary symbol to stand for the isolated quality or relation. All words (except the obviously onomatopoetic, such as "bow-wow," "cuckoo," etc.) are arbitrary symbols associated with objects, or qualities, or relations, or other phenomena. And abstract names of isolates are, so to speak, the pegs on which we hang the qualities we have separated by analysis and isolation, while class-names are pegs upon which we can hang a group of similars reached by the process of isolation; for all classing and grouping of objects, or qualities, or relations involves, so far as the process is a conscious one, the principle of analysis. In classing objects, we group them in reference to certain characters which they have in common, disregarding certain other characters in which they differ. We group together, for example, sights, or sounds, or smells, and distinguish them from each other and from tastes and touches. And then we go further, and class all these together as sensations having certain characteristics in common whereby they are distinguished from perceptions of relation and so forth. Perhaps it may be objected that classification comes much earlier in the mental process than I am now putting it. It may be said that the recognition of a sensation as a touch, or a smell, or a sound involves a classification of sensations in these categories, and that the simple perception of an orange involves the placing of the object in this class of bodies. And, undoubtedly, we have here the germs of the process. Sensation and perception give us the materials for classification; the perception of similarity and difference gives us the sine qu non of the process. Nevertheless, although there may be an earlier unconscious grouping of phenomena, it is only when the mind is specially directed to these materials, with the object of grouping them according to their similarities, that we can speak of classification proper—conscious and intentional classification, as opposed to unconscious grouping. And this involves the intentional selection of the points of similarity, and discarding or neglecting the points of difference. It involves the process of analysis or isolation. There is a vast difference between the perceptual recognition of objects as similar, and conceptual classification on grounds of similarity. Just as the recognition of a sensation as now and not then, or here and not there, or as due to something outside us, gives us the germs from which, on ultimate analysis, our ideas of time, space, and causation are reached; so does the recognition of these sensations as of this kind and not that give us the germ from which, on analysis, the process of classification may arise. True, conscious, scientific classification is late in development.

And here let us notice that the conclusions we have reached in this chapter are the outcome of analysis and classification. The sensations with which we started are isolates. In considering their quality, intensity, sequence, we were isolating and classifying these special modes of their existence. Localization and outward projection involved isolation. We simply see the orange before us. To understand and explain how we come to see it as we do see it involves a somewhat subtle analysis. We perceive it to be yellow, round, resistant; and then, isolating these qualities, we reach conceptions of yellowness, roundness, and resistance, quite apart from oranges. Throughout our description the terms we used were very largely terms denoting classified isolates.

Lastly, having enormously increased our knowledge by this process of isolation, we proceed to build in the knowledge thus gained to the structure of our constructs. This is the third and last stage in construction. The first stage is the formation of indefinite constructs by immediate association; the second is the definition of constructs by examination; and the third is the completion of constructs by synthesis.

And the further this process of analysis and isolation is carried, the more we are, so to speak, floated off from the immediate objects of sense into the higher regions of abstract thought. Furthermore, by recombining our isolates in new modes and under new relations, we reach the splendid results of constructive imagination.

In the brief description which I have now given of our mental processes, I have for the most part avoided certain terms which are current in the science of psychology. It will be well here to say a few words concerning these words and their use. The process of sensation is sometimes defined as the mere reception of a sense-stimulus. But it is more convenient, and more in accordance with common usage, to call the simple result of a stimulus an impression, and to apply the term "sensation" to the discrimination and recognition of the impressions as of such and such a quality. Sensation, then, is the reception and discrimination of impressions which result from certain modes of influence (stimuli) brought to bear on our organization. Viewed in this way, therefore, even sensation involves a distinct reaction of the mind; it implies the first stage of mental activity. But when the sensations are given objective significance, when they suggest the existence of an object-world without us, they enter the field of perception. Here the discriminated sense-impression is, to use the words of Mr. Sully, "supplemented by an accompaniment or escort of revived sensations, the whole aggregate of actual and revived sensations being solidified or integrated into the form of a percept; that is, an apparently immediate apprehension or cognition of an object now present in a particular locality or region of space."[FV] Throughout the whole process of the formation of constructs by immediate association, and their definition by examination, we were dealing with perception and percepts. But when we reach the stage when particular qualities were isolated, then we enter the field of conception. The isolates are concepts. Class-names, reached through processes involving isolation, stand for concepts. And completed constructions, involving synthesis of the results of analysis, contain conceptual elements. The word "concept," however, is used in different senses by different authors. Mr. Sully says,[FW] for example, "A concept, otherwise called a general notion, or a general idea, is the representation in our minds answering to a general name, such as 'soldier,' 'man,' 'animal.'... Thus the concept 'soldier' is connected in my mind with the representations of various individual soldiers known to me. When I use the word 'soldier,' ... what is in my mind is a kind of composite image formed by the fusion or coalescence of many images of single objects, in which individual differences are blurred, and only the common features stand out distinctly.... This may be called a typical or generic image." But NoirÉ, quoted by Professor Max MÜller,[FX] taking another illustration, says, "All trees hitherto seen by me leave in my imagination a mixed image, a kind of ideal presentation of a tree. Quite different from this is my concept, which is never an image." I follow NoirÉ; and I hold that the image, in so far as it is an image, whether simple or composite,[FY] is a percept; but that, in so far as there enter into the idea of the soldier or the tree elements which have been isolated by analysis, just in so far does the word "soldier" or "tree" stand for a concept. How far a word stands for a percept, and how far there enter conceptual elements, depends to a large extent on the level of intelligence of the hearer. The moment educated and intellectual folk begin to think about their words, or the objects for which they stand, conceptual elements are sure to crowd in.

There is one more feature of these mental processes in man, and that by no means the least important, that remains for brief consideration. I began by saying that the primary end and object of the reception of the influences of the external world, or environment, is to enable the organism to answer to them in activity. We saw that the sight of an orange suggests, through association, its taste; and that the validity of the association could be verified by going to the orange and tasting it. We saw, too, that when I heard a dog howl in the street, and, going to the window, saw a small boy with a stone in his hand, I concluded that he was going to throw it at the dog. What I wish now to elicit is that out of perceptions through association there arise certain expectations, and that the activities of organisms are moulded in accordance with these expectations.

It is clear that these expectations or anticipations belong partly to the presentative or constructive order, and partly to the reconstructive or representative order. They are in some cases directly suggested by the presentations of sense; they are also built up out of representations which have become associated with the constructs in memory and through experience. But what we have here especially to notice about them is that, in the latter case, they involve more or less distinctly the element which we, in the language of our developed thought, call causation. There is a sequence of events, and the perception of certain of these gives rise, through association and experience, to an expectation of certain succeeding phenomena. Expectations are, therefore, the outcome of the linked nature of phenomena. And when we come eventually to think about the phenomena, and how they are linked together into a chain (successional) or web (coexistent), we reach the conception of causation as the connecting thread. In early stages of the mental process, such a conception does not emerge. Nevertheless, the phenomena are perceived as linked or woven. And the mental process by which we pass from any perceived event or existence to other preceding, concomitant, or subsequent events or existences linked or woven with it in the chain or web of phenomena, we call inference.[FZ] When, for example, I find a footprint in the sand, I infer that a man has passed that way; and when the clouds are heaped up heavy and black, I infer that a storm is about to burst upon us.

Concerning inference, of which I shall have more to say in the next chapter, I have now to note that it is of two kinds: first, perceptual inference, or inference from direct experience; secondly, conceptual inference, or inference based on experience, but reached through the exercise of the reasoning faculties. The latter involves the process of analysis or isolation; the former does not. There is a marked difference between the two. Perceptual inferences are the outcome of practical experience, but do not go beyond such practical experience. Conceptual inferences are also based on experience, but they predict occurrences never before experienced. Perceptual inferences, again, deal with matters practically; but conceptual thought explains them.

The expectation of a storm when the thunder-clouds are heavy is a case of perceptual inference. It is the outcome of a long-established association, and is not reached by a process of reasoning involving an analysis of the phenomena. But if, though the sky is clear, a west wind and a rapidly falling barometer lead me to predict rain, the inference is conceptual, and gained by me or for me by a process of reasoning; for the barometer was the outcome of the analysis of phenomena. In the mind of the rough sailor-lad, however, the fall of the mercury and the succeeding storm may be connected by mere perceptual inference, the phenomena being simply associated together. If, however, there is any attempt at explanation, correct or incorrect, there is so far a conceptual element. In a little fishing-village on our south coast, a benevolent lady presented the fishermen with a Fitzroy barometer. I happened shortly after to remark to one of the men that the summer had been unusually stormy. "Yes, sir," he said, "it has. But then, you see, the weather hasn't no chance against that new glass." Here there was an attempted explanation of the phenomena. The falling glass was conceived as somehow causing bad weather.

It is hard to draw the line between perceptual and conceptual inferences, or rather to say, in this or that case, to which class the inference belongs, because man, through language, lives in a conceptual atmosphere. Moreover, the same result may, in different cases, be reached by perceptual or by conceptual inference. A child who had seen a great number of ascending balloons might, on seeing a balloon, expect it to ascend by a perceptual inference; but a man, knowing that the balloon was full of a gas lighter than air, might expect it to ascend through the exercise of conceptual inference. And just as in adult civilized life our constructs have more and more conceptual elements built into them, so do our inferences become more and more reasoned. It is probable that in an adult Englishman every inference has a larger or smaller dose of the conceptual element.

With the development of language we state our inferences in the form of propositions, and call them judgments. "Every proposition," says Mr. Sully,[GA] "is made up of two principal parts: (1) the subject, or the name of that about which something is asserted; (2) the predicate, or the name of that which is asserted. Thus, when we affirm, 'This knife is blunt,' we affirm or predicate the fact of being blunt of a certain subject, namely, 'this knife.' Similarly, when we say, 'Air corrodes,' we assert or predicate the power of corroding of the subject 'air.'" The proposition always involves conceptual elements; for the predicate of a proposition is always an abstract idea or general notion.

Propositions so formed may then become links in a chain of reasoning. "To reason is," says Mr. Sully,[GB] "to pass from a certain judgment or certain judgments to a new one." And so passing on from judgment to judgment, we may ascend to the higher levels of abstract thought. According to Mr. Sully's definition, therefore, we start from a judgment or judgments in the process of reasoning. The formation of a judgment (conceptual inference) is, however, the first step in a continuous process; and I propose, under this term, "reason,"[GC] to include this first step also. The formation of a conceptual inference I regard as the first stage of reason. Any mental process involving conceptual inference I shall call rational.

In contradistinction to this, I shall use the term "intelligence" for the processes by which perceptual inferences are reached. An intelligent act is an act performed as the outcome of merely perceptual inference. A rational act is the outcome of an inference which contains a conceptual element.