THE
PRESENTATIVE POWER

SENSE OR PERCEPTION BY THE SENSES.

§ I.—General Observations.

This Faculty the Foundation of our Knowledge.—Of the cognitive powers of the mind, the first to be noticed, according to the analysis and distribution already given, is the Presentative Power—the power of cognizing external objects through the senses. This claims our first attention, inasmuch as it lies, chronologically at least, at the foundation of all our cognitive powers, and in truth, of our entire mental activity. We can, perhaps, conceive of a being so constituted as to be independent of sense, and yet possess mental activity; and we can even conceive such a mind as taking cognizance, in some mysterious way, of objects external to itself. But not such a being is man—not such the nature of the human mind. Its activity is first awakened through sense; from sense it derives its knowledge of the external world, of whatever lies without and beyond the charmed circle of self; and whether all our knowledge is, strictly speaking, derived from sense, or not—a question so much disputed, and which we will not here stay to discuss—there can be no doubt that the activity of sense, and the knowledge thus acquired, is at least the beginning and foundation of all our mental acquisitions. We are constantly receiving impressions from without through the senses. In this way the mind is first awakened to activity, and from this source we derive our knowledge of the external world.

General Character of this Faculty.—In its general character the faculty now under consideration, as the name indicates, is presentative and intuitive. It presents rather than represents objects, and what the mind thus perceives it perceives intuitively, rather than as the result of reflection. The knowledge which it gives is immediate knowledge, the knowledge of that which is now and here present, in time and space.

Involves a twofold Element.—Looking more closely at the character of this faculty, we find it to involve a twofold element, which we cannot better indicate than by the terms subjective and objective. There is, in the first place, the knowledge or consciousness of our own sentient organism as affected, and there is also the knowledge of something external to, and independent of the mind itself, or the me, as the producing cause of this affection of the organism. We know, by one and the same act, ourselves as affected, and the existence and presence of an external something affecting us. This presupposes, of course, the distinct independent existence of the me and the not-me—of ourselves as thinking and sentient beings, and of objects external to ourselves, and material,—a distinction which lies at the foundation of all sense-perception. All perception by the senses involves, and presupposes, the existence of a sentient being capable of perceiving, and of an object capable of being perceived. It supposes, also, such a relation between the two, that the former is affected by the presence of the latter. From this results perception in its twofold aspect, or the knowledge, on the part of the sentient mind, at once of itself as affected, and of the object as affecting it. According as one or the other of these elements is more directly the object of attention, so the subjective and the objective character predominate in the act of perception. If the former, then we think chiefly of the me as affected, and are scarcely conscious of the external object as the source or the producing cause; if the latter, the reverse is true.

§ II—Analysis of the Perceptive Process.

Simple Sensation.—The nature of the presentative power may be better understood by observing closely the different steps of the process. As we come into contact with the external world, the first thing of which we are conscious, the first step in the process of cognition, is doubtless simple sensation. Something touches me, my bodily organism is thereby affected, and I am conscious, at once, of a certain feeling or sensation. I do not know as yet what has produced the sensation, or whether any thing produced it. I do not as yet recognize it as the result of an affection of the bodily organism, or even as pertaining to that organism in distinction from the spiritual principle. I am conscious only of a certain feeling. This is simple sensation—a purely subjective process.

Recognition of it as such.—We do not, however, stop here. The mind is at once aroused by the occurrence of the phenomenon supposed, the attention is directed to it. I cognize it as sensation, as feeling. If it be not the first instance of the kind in my experience, I distinguish it from other sensations which I have felt.

Distribution of it to the Parts affected.—More than this; I am conscious not only of the given sensation, but of its being an affection of my bodily organism, and of this or that part of the organism; I distinguish the body as the seat of the sensation, and this or that part of the body as the part affected. The organism as thus affected becomes itself an object of thought as distinct from the thinking mind that animates and pervades it. It becomes to me an externality, having extension and parts out of and distinct from each other. As thus viewed, and brought now for the first time under the eye of consciousness, it becomes known to me as the non-ego, still connected, however, by sensation with the ego, the sentient principle and as thus viewed, I become aware that the sensation which I feel is an affection of that organism, and of a certain portion of it, as the hand, or the foot. This cognizance of the sensation as such, as pertaining to the organism, and to this or that part of the same, and the consequent cognizance of the organism as such, as distinct from the sentient mind, and as thus and thus affected, is no longer simple sensation, it is perception.

Cognition of something external to the Organism itself.—This is the most simple form of immediate perception. The process does not, however, necessarily stop here. I am conscious not only of this or that part of my organism as affected, but of something external to the organism itself, in contact with and affecting it. This organism with which I find myself connected, the seat of sensation, the object of perception, is capable of self-movement in obedience to my volitions. I am conscious of the effort to move my person, and conscious also of being resisted in those movements by something external in contact with my organism. This yet unknown something becomes now the object of attention and perception—this new phenomenon—resistance, something resisting. To perceive that I am resisted, is to perceive that something resists, and to perceive this is to perceive the object itself which offers such resistance. I may not know every thing pertaining to it, what sort of thing it may be, but I know this respecting it, that it exists, that it is external to my organism, that it resists my movements. Thus the outer world becomes directly an object of perception—passes under the immediate eye of consciousness.

In what Sense these several Steps distinct.—In the preceding analysis, in order more clearly to illustrate the nature of the process, we have regarded the act of perception as broken into several distinct parts, or steps of progress. This, however, is not strictly correct as regards the psychology of the matter. Logically, we may distinguish the simple sensation as mere feeling, from the reference of the same to this or that part of the bodily organism as affected, and each of these again, from the cognizance of the external object, which by contact or resistance produces the sensation. Chronologically, the act is one and indivisible. The sensation and the perception are synchronous. We cannot separate the act of sense-perception into the consciousness of a sensation, the consciousness of the bodily organism as affected by that sensation, and the consciousness of an external something as the proximate cause of that affection. To experience a sensation, is to experience it as here or there in the sentient organism, and to perceive contact or resistance, is to perceive something in contact or resisting. There may, however, be sensation without cognizance of the external producing cause.

Restricted Sense of the term Perception.—According to the view now advanced, perception is immediate; not a matter of inference, not a roundabout reflective process. It is a cognizance direct and intuitive of the bodily organization as thus and thus affected, and of an external something in correlation with it, affecting and limiting that organism in its movements.

Usually, however, a wider range has been given to the term, and the faculty thereby denoted. It has been made to comprehend any mental process by which we refer a specific sensation to something external as its producing cause. It is thus employed by Reid and Stewart, and such has been in fact the prevalent use of the term. According to this, when we experience the sensation of fragrance, and refer that sensation to the presence of a rose, or the sensation of sound, and refer it to the stroke of a bell, or a passing carriage, we exercise the faculty of perception. Evidently, however, our knowledge in these cases is merely a matter of inference, of judgment, not of immediate direct perception, not in fact of perception at all. All that we properly perceive in such a case, all that we are directly conscious of is the fragrance or the sound. That these are produced by the rose and the bell is not perceived, but only conceived, inferred—known, if at all, only by the aid of previous experience.

Sensation as distinguished from Perception.—According to the view now presented, sensation, as distinguished from perception, is the simple feeling which results from a certain affection of the organism. It is known to us merely as feeling. Perception takes cognizance of the feeling as an affection of the organism, and also of the organism as thus affected, and consequently as external to the me, extended, having parts, etc. It apprehends also objects external to the organism itself limiting and affecting its movements. Sensation is the indispensable condition of perception. If there were no sensation, there would be no perception. The one does not precede, however, and the other follow in order of time, but the one being given, the other is given along with it. The two do not, however, coexist in equal strength, but in the relation, as stated by Hamilton, of inverse ratio; that is, beyond a certain point, the stronger the sensation, the weaker the perception, and vice versÂ.

Sensation as an Affection of the Mind.—It has been common to speak of sensation as lying wholly in the mind. Primarily, however, it is an affection of the nervous organism, and through that organism, as thus affected, an impression is made on the mind. If it were not for the mind present with the organism, and susceptible of impression from it, and thus cognizant of changes in it, the same changes might be produced in the organism as now, but we should be entirely unconscious of and insensible to them. In certain states of the system this actually happens, as in sound sleep, the magnetic state, the state produced by certain medicinal agents as ether, chloroform, opium, and the intoxicating drugs of the East. In those cases, the connection between the mind and the nervous organism seems to be in some manner interrupted or suspended, and consequently there is for the time no sensation. The nerves may be irritated, divided even, and still no pain is felt.

It is not true, however, that the sensation is wholly in the mind. It is in the living animated organism, as pervaded by the mind or spiritual principle, mysteriously present in every part of that organism, and cognizant of its changes; and neither the body alone, nor the mind alone, can be said to possess this faculty, but the two united in that complex mysterious unity which constitutes our present being.

§ III.—Analysis and Classification of the Qualities of Bodies.

Difference of Qualities.—The qualities of bodies as known to us through sensation and perception are many and various. On examination, a difference strikes us as existing among these qualities, which admits of being made the basis of classification. Some of them are qualities which strike us at once as essential to the very existence of matter, at least in our notion of it, so that we cannot in thought divest it of these qualities, and still retain our conception of matter. Others are not of this nature. Extension, divisibility, size, figure, situation, and some others, are of the former class. If matter exists at all, it must, according to our own conceptions, possess these qualities. We cannot think them away from it, and leave matter still existing. But we can conceive of matter as destitute of color, flavor, savor, heat, cold, weight, sound, hardness, etc. These are contingent and accidental properties not necessary to its existence.

How named and distinguished.—Philosophers have called the former class primary, the latter secondary qualities. The former are known À priori, the latter by experience. The former are known as qualities, in themselves, the latter only through the affections of our senses.

The primary qualities then have these characteristics:

1. They are essential to the very existence of matter, at least in our conception.

2. They are to be known À priori.

3. They are known as such, or in themselves.

The secondary, on the contrary, are:

1. Accidental, not essential to the notion of matter.

2. To be known only by experience.

3. To be learned only through the affection of the senses.

Further Division of secondary Qualities.—A further division, however, is capable of being made. The secondary qualities, as now defined, comprise, in reality, two classes. There are some, which, while known to us only through the senses, have still an existence as qualities of external objects, independent of our senses. As such they are objects of direct perception. Others, again, are known, not as qualities of bodies, but only as affections of sense, not as objective, but only as subjective, not as perceptions, but only as sensations. Thus I distinguish the smell, the taste, and the color of an orange. What I distinguish, however, is after all only certain sensations, certain affections of my own organism. What may be the peculiar properties or qualities in the object itself which are the exciting cause of these sensations in me, I know not. My perception does not extend to them at all. It is quite otherwise with the qualities of weight, hardness, compressibility, fluidity, elasticity, and others of that class. They are objects of perception, and not of sensation merely.

These Classes, how distinguished.—The class first named, are qualities of bodies as related to other bodies. The other class are qualities of bodies as related only to our nervous organization. The former all relate to bodies as occupying and moving in space, and come under the category of resistance. The latter relate to bodies only as capable of producing certain sensations in us. We may call the former mechanical, the latter physiological.

Connection of Sensation with the external Object.—From long habit of connecting the sensation with the external body which produces it, we find it difficult to persuade ourselves that taste and smell are mere affections of our senses, or that color is really and simply an affection of the optic nerve of the beholder, and that what is actually perceived in these instances is not properly a quality of the external object. A little reflection, however, will convince us that all which comes to our knowledge in these cases, all that we are properly cognizant of, is the affection of our own nervous organism, and that whatever may be the nature of the qualities in the object which are the producing cause of these sensations in us, they are to us occult and wholly unknown.

Power of producing these Sensations.—It is not to be denied, of course, that there is in external objects the power of producing these sensations in us, under given circumstances; but to what that power is owing, in what peculiarity of constitution or condition it consists, we know not. We have but one name, moreover, for the power of producing, and the effect produced. Thus the color, taste, smell, etc., of an object may denote either the sensation in us, or the unknown property of matter by virtue of which the sensation is awakened. It is only in the sense last mentioned, that the qualities under consideration may properly be called qualities of bodies.

Enumeration of the several Qualities as now classed.—According to the classification now made, the qualities of bodies may be thus enumerated.

I. Primary.—Extension, divisibility, size, density, figure, absolute incompressibility, mobility, situation.

II. Secondary.—A. Objective, or mechanical—as heavy or light, hard or soft, firm or fluid, rough or smooth, compressible or incompressible, resilient or irresilient, and any other qualities of this general nature resulting from attraction, repulsion, etc.

B. Subjective or physiological—as color, sound, flavor, savor, temperature, tactual sensation, and certain other affections of the senses of this nature.

§ IV.—Organs of Sense.—Analysis of their Several Functions

Number of the Senses.—The different senses are usually reckoned as five in number. They may all be regarded, however, as modifications of one general sense, that of touch—or, in other words, the susceptibility of the nervous system to be excited by foreign substances brought into contact with it. This is the essential condition of sensation in any case, and the several senses, so called, are but so many variations in the mode of manifesting this excitability. There is a reason, nevertheless, for assigning five of these modifications and no more, and that is, that the anatomical structure indicates either a distinct organ, as the ear, the eye, etc., or at least a distinct branch of the nervous apparatus, as in the case of smell and taste, while the whole nervous expansion as spread out over the surface of the body contributes to the general sense of touch.

The Senses related to each other.—Distinct Office of each.—It is evident enough that these several senses sustain a certain relation to each other. They are so many and no more, not merely by accident; not merely because so many could find room in the bodily organization; not merely because it might be convenient to have so many. Let us look at the office performed by each, and we shall see that while each has its distinct function, not interchangeable with that of any other, it is a function more or less necessary to the animal economy. Remembering that the design and use of the several senses is to put us in possession of data, by means of which, directly or indirectly, we may gain correct knowledge of the external world, let us suppose the inquiry to be raised, What senses ought man to have for this purpose? What does he need, the material universe remaining what it is?

Function of the Sense of Touch.—Things exist about us in space, having certain properties and relations. We need a sense then, first and chiefly, that shall acquaint us with objects thus existing, taking cognizance of what lies immediately about us in space. This we have in the general sense of touch, making us acquainted with certain objective or mechanical qualities of external objects.

This Sense, how limited.—This, however, avails only for objects within a short distance, and capable of being brought into contact. It operates also synthetically and slowly, part after part of the object being given as we are brought into contact with different portions of it successively until the process is so far complete that, from the ensemble of these different parts, our understanding can construct the whole.

Possibility of a Sense that shall meet these Limitations.—We can conceive of a sense that should differ in both these respects—that should take cognizance of distant objects, not capable perhaps of being brought into contact—and that should also operate analytically, or work from a given whole to the parts, and not from the parts to a whole, thus giving us possession at once of a complete object or series of objects. Such a sense, it is easy to see, would possess decided advantages, and in connection with the one already considered, would seem to bring within the sphere of our cognizance almost the complete range of external nature. This we have, and this exactly, in the sense of vision. It takes in objects at a distance, and takes in the whole at a glance.

This new Sense still limited.—This new sense, however convenient and useful as it is, has evidently its limitations. It is available only through a given medium, the light. Strictly speaking, it is the light only that we see, and not the distant object; that is known indirectly by means of the light that variously modified, travels from it to the eye. When this fails, as it does during several hours of the twenty-four, or when it is intercepted by objects coming between and shutting out the forms on which the eye seeks in vain to rest, then our knowledge from this source is cut off.

Still another Sense desirable.—Under these circumstances, might it not be well, were there given an additional sense, of the same general nature and design, but operating through a different medium, sure to be present wherever animal life exists, so that even in the darkness of the night, or the gloom of the dungeon, we might still have means of knowing something of the surrounding objects. And what of this medium, or avenue of sense, were of such a nature as to be capable of modification, and control, to some extent, on our part, and at our pleasure, so as to form a means of voluntary communication with our fellow-beings. Would not such an arrangement be of great service? Exactly these things are wanted; exactly these wants are met, and these objects accomplished, by a new sense answering to these conditions—the sense of hearing—the cognizance of sound. This we produce when we please by the spoken word, the vocal utterance, whether of speech, or musical note, or inarticulate cry, varied as we please, high, low, loud, soft—a complete alphabet of expression, conveying thus by signals, at once rapid and significant, the varying moods and phases of our inner life to other beings that had else been strangers, for the most part, to the thoughts and feelings which agitate our bosoms.

Senses for another Class of Qualities.—The senses, as thus far analyzed, have reference primarily to the number magnitude, and distance of objects as occupying space—to quantities rather than qualities. Were it possible now to add to these a sense, or senses that should take cognizance of quality, as well as existence and quantity—that should detect, to some extent at least, the chemical properties of bodies as connected especially with the functions of respiration and nutrition—the list of senses would seem to be complete. This addition is made, this knowledge given, in the senses of smell and taste.

Possibility of additional Senses.—To those already named, other senses might doubtless have been added by the Creator, which would have revealed, it may be, properties of matter of which we have now no conception. It is not to be supposed that we know every thing respecting the nature and qualities of even the most familiar and common objects. Many things there may be, actual, real, in the world about us, of which we know nothing, because they come not within the range of any of our senses. But all that is essential to life, and happiness, and highest welfare is doubtless imparted by the present arrangement; and when closely studied, no one of these senses will be found superfluous, no one overlapping the province of another, but working each its specific end, and all in harmony.

The proper Office of Psychology in respect to the Senses.—It is the province of the anatomist and the physiologist to explain the mechanical structure of the several organs of sense, and their value as parts of the physical system. The psychologist has to do with them only as instruments of the mind, and it is for him to show their connection and proper office as such. This has been attempted in the preceding analysis.

The kind of Knowledge afforded by the Senses.—It is to be noticed, in addition, that with the exception of the tactual sense, and possibly of sight, these senses give us no direct, immediate knowledge of external things. They simply furnish data, signs, intimations, by the help of which the understanding forms its conclusions of the world with out. They are the receiving agents of the mind. This is, in fact, the chief office of sense, to receive through its various avenues the materials from which the understanding shall frame conceptions of things without; to convey, as it were, a series of telegraphic despatches along those curious and slender filaments that compose the nervous organization, by means of which the soul, keeping her hidden seat and chamber within, may receive communication from the distant provinces of her empire. These signs the understanding interprets; and in so far as this is the true nature of the process, it is not a process of immediate and proper perception. I hear, for example, a noise. All that I really perceive in this case is the sensation of sound. I refer it, however, to an external cause, to a carriage passing in the street. I specify, moreover, the kind of carriage, perhaps a coach, or a wagon with iron axles. I have observed, have learned by experience, that sounds of this nature are produced in this way, that is, by carriages passing, and by such carriages. Hence I judge that the sound which I now hear is produced in the same way. It is an inference, a conception merely. All that sense does is to receive and transmit the sign, which the understanding interprets by the aid of former experience. And the same is true of the other senses, with the exceptions named.

Not therefore of little Value.—We are not to infer, however, that these senses are on this account of no special value or importance to us. They do precisely what is needed. They put us in possession of just the data wanted in order to the necessary information concerning external things. It is only the theorist who undervalues the senses, and he only in his closet. No man, in the full possession of his reason, and his right mind, can go forth into this fair and goodly world, and not thank God for every one of those senses—sight, hearing, taste, touch, and smell. Their true and full value, however, we never learn till we come to be deprived of their use; till with Milton we exclaim,

§ V.—Amount of Information Derived from the Respective Senses

A further Question as to one Class of the Senses.—The relations and specific functions of the several senses have been already described. Some further questions arise, however, respecting the precise amount and kind of information afforded by that class of the senses which; as we have seen, relates to the spatial properties of bodies, in distinction from the chemical, viz.: hearing, sight, and touch.

What is given in Hearing.—And first, as to the sense of hearing. What is it precisely that we hear? When we listen to a sound, we speak of hearing the object that produces the sound; we say, I hear a bell, a bird, a gun, etc. Strictly speaking, we do not hear the object, but only the sound. It is not the bell or the bird that we hear, but the vibration of the air produced by bell and bird. This has been already illustrated by reference to a carriage passing in the street. It is only by experience, aided by other senses, that we learn to refer the sound to its producing cause.

Hearing not properly Perception.—Is hearing then a sensation merely, or is it a perception? If by perception we mean a direct knowledge of the external object—which is the proper sense of the word—hearing certainly is not perception. It gives us no such immediate knowledge. What we perceive in hearing is merely the sensation of sound. It may be doubted whether by this sense alone we should ever get the idea that what we hear is any thing external to ourselves.

Affords the means of Judging.—As it is, however, we judge, not only of the existence and nature, but of the distance and direction of the external object whence the sound proceeds. We learn to do this with great correctness, and with great facility. No sooner do we hear a sound, in most instances, than we form an opinion at once, from what direction it comes, and what produces it; nor are we often mistaken in our judgment. The faculty of judging by the ear as to the direction of the sound, and the nature of the object producing it, may be cultivated by care and practice to a remarkable degree of accuracy. Napoleon was seldom mistaken as to the direction and distance of a cannonade. It is said that the Indian of the north-western prairies by applying his ear to the ground, will detect the approach of a body of cavalry at a distance beyond the reach of vision, and distinguish their tread from that of a herd of buffaloes.

Number of Sounds.—The number of sounds which the ear can distinguish is almost without limit. There are, it is said, five hundred distinct tones which an ear of usual accuracy can recognize, and each of these tones admits of five hundred variations of loudness, giving, in all, two hundred and fifty thousand different sounds.

Power of Sound over the Mind.—The power of sound to affect the mind, and especially the feelings, is too well known to require specific statement. The note of an instrument, the tone of a human voice, the wild warbling of a bird, the tinkling of a bell, the variations of speech and of song, from the high and shrill to the low and heavy intonation, from the quick and impetuous to the slow and plaintive movement, these simple varieties of tone affect powerfully the heart, and find their way at once and irresistibly to the feelings. Hence the power of music over even the uncultivated mind; hence too in no small degree the power of the skilful orator over the feelings of his audience. It is not merely, nor so much, the thing said, in many cases, as the way of saying it, that touches and sways the assembled multitude. Tones and sounds have a natural meaning. They are the natural language of the heart. They express emotion, and hence awaken emotions in others.

The Question as to Sight.—Turning now from the sense of hearing to that of sight, the question arises, What is it precisely that we perceive by the eye? When we fix the eye upon any object, more or less remote, what is it, strictly speaking, that we see, extension and figure, or only color? Is it by vision that we learn primarily the distance of objects and their locality? These are points requiring investigation.

Does Sight give Extension and Figure.—As to the first of these questions, whether extension and figure are objects of direct visual perception. No doubt they are associated in our minds with the act of vision, so that the moment we see an object we obtain an idea of it as extended, and of such and such dimensions and figure. The question is, whether it is really through the sense of sight that we obtain this idea, or in some other way. Had we no other means of information, would sight alone give us this? When we first open our eyes on external objects, do we receive the idea of extension and figure, or only of color? The fact that as matters are, we cannot in our experience separate the notion of some surface extension from the sensation of color, is not decisive of these questions. We cannot, as Dr. Brown observes, separate the color from the convexity and magnitude of an oak before us, but this does not prove that convexity and magnitude are objects of immediate and original perception. If every surface in nature had been convex, suggests the same writer, we should probably have found the same difficulty in attempting to conceive of color as separate from convexity, that we now find in attempting to conceive of it as separate from length and breadth. As it is, however, our sensation of color has not always been associated with convexity, while it has been always associated with surface extension. Hence it is, he maintains, that we seem to perceive, by the eye, the length, and breadth, and objects along with their color.

Argument from the Affection of a Portion of the Retina.—The fact that in vision a certain portion of the retina in length and breadth is actually affected by the light falling on it, has been supposed by some to be conclusive of the fact that we perceive the length and breadth of the external object by the eye. This does not necessarily follow. As Dr. Brown contends, it is equally true that a certain part of the organ of smell is affected by odors, and a certain part of the auditory nerve is affected by sounds, yet we are not conscious of any perception of extension by either of these organs; we neither smell nor hear the length, and breadth, and magnitude of objects; nor is there any reason to suppose that the particular portion of the retina affected has any thing to do with the original sensation of sight.

Amount of the preceding Arguments.—These arguments however, do not strike me as conclusive. They merely show the possibility that extension and figure may be acquired rather than original perceptions. They do not amount to positive evidence that they are so.

An Argument to the Contrary.—On the other hand, there is one consideration of a positive character, which to most minds will be likely to outweigh the merely negative arguments already adduced. Color is a property of light, and light comes to us reflected from objects occupying space; we perceive it only as we perceive it spread over and reflected from some surface. Extension, then, surface expansion of the reflecting object, is the indispensable condition of the visibility of light itself, and so of color, as reflected from the object. Now it is difficult to persuade ourselves that what we know to be an essential condition of the perception of color, and what we seem to perceive along with the color, and cannot, even in thought, wholly separate from it, is not, after all, really perceived by the eye.

Argument from recent Discoveries.—Indeed, recent discoveries in science seem to vindicate that not only surface extension, but trinal extension, or solidity, may be an object of direct perception by the eye. I refer to the researches of Wheatstone, in binocular vision, which go to show, that in consequence of the difference of the images formed upon the right and the left eye, as occupying different positions with reference to the object seen, we are enabled by the eye to cognize the solidity as well as the extension of objects. The difference of figure in the two images gives us this. That such is the case is shown by an instrument, the stereoscope, so constructed as to present separately the image as formed on each eye, which, when separately viewed, appear as mere plane surfaces, but when viewed together, the right image with the right eye, and the left one with the left eye, at the same time, present no longer the appearance of plane surfaces, but the two images combine to form one distinct figure, and that a solid, having length, breadth, thickness, and standing out with all the semblance of the real object.

It is hardly necessary to say that if extension is an object of perception by the eye, so also is figure, which is merely the limitation of extension in different directions.

Second Question—Does Sight give Distance?—Is it also by vision that we obtain the idea of the distance of objects and their externality? Does vision alone give the idea that what we see is numerically distinct from ourselves, and that it occupies this or that particular locality? So it would seem, judging from the impression left upon the mind in the act of vision. We seem to see the object as here or there, external, more or less distant in space. We distinguish it from ourselves.

The negative View.—This is denied by some. All that we see, they contend, is merely the light coming from the object, and from the variations and modifications which this exhibits we learn to judge by experience of the distance and locality of the object. It is a matter of judgment and not of perception. We have learned to associate the two things, the visual appearance and the distance.

Argument in the Negative.—In proof of this they adduce the fact that we are frequently mistaken in our estimate of the distance of objects. If there be more or fewer intervening objects than usual, if the atmosphere be more or less clear than usual, or any like circumstance affords a variation from our ordinary experience, we are misled as to the distance of the object. Hence we mistake the distance of ships at sea, or of objects on a prairie or a desert, the width of rivers, the height of steeples, towers, etc.

Further Argument in the Negative.—It is further contended that facts show that the impressions of sight alone, uncorrected by experience, do not convey the idea of distance at all, but that what we see seems to be in connection with the eye itself, until we learn the contrary by the aid of other senses. This, it is said, is the experience of persons who have been operated upon for cataract, particularly of a patient whose case is described by Cheselden, and who thought every thing which he saw, touched his eyes. It is said also to have been the same with Caspar Hauser, when first liberated from the long confinement of his dungeon, and permitted to look out upon the external world. The goodly landscape seemed to him to be a group of figures, drawn upon the window.

Force of this Argument.—This, however, is not inconsistent with the perception of externality by vision, since even what seems to be in contact with the eye, nay, what is known to be so, may still be known as external. Contact implies externality. It is very much to be doubted, moreover, whether the cases now referred to, coincide with the usual experience of those who are learning to see. The little child seems to recognize the externality and remoteness from his own person of the objects which attract his attention, as soon as he learns to observe surrounding objects at all, and, though he may not judge correctly of their relative distance from himself, never seems by his movements to suppose that they are in contact with his eye or with any part of his person. The young of animals, also, as soon as they are born, seem to perceive by the eye, the externality, the direction, and the distance of objects, and govern their movements accordingly. It is not, in these cases, a matter of experience, but of direct perception. These facts render it doubtful, to say the least, whether the common impression—that which in spite of all arguments to the contrary, is, and always will be made upon the mind in the act of vision, viz., that we see objects as external, as having locality, and as more or less remote from us—is not, after all, the correct impression.

Learning to judge of Distance not inconsistent with this View.—- Nor does it conflict with this view that we learn to judge of the true distance of objects, and are often deceived in regard to it. The measurement of distance, the more or less of it, is of course a matter of experience, a thing to be learned by practice. It does not follow, however, that we may not by the eye directly, and at first, perceive an object to be external, and removed from us, in other words distant, though we may not know at first how distant. The rays of light that come to us from this external object, may give us direct perception of the object as external, as extended, and as occupying apparently a given locality in space more or less remote, while at the same time it may be left to other senses and to experience to determine how great that distance is.

Questions as to Touch.—Passing now from the sense of sight to that of touch, we find similar questions discussed among philosophers respecting the precise information afforded by this sense. Does touch give us immediate perception of externality, extension, form, hardness, softness, etc., including the various mechanical properties of bodies? To this sense it has been common to ascribe these faculties of perception. They are so attributed by Reid, Upham, Wayland, and, I believe, by modern writers generally, with the exception of Brown and Hamilton.

Probability of another Source of Information.—It may be questioned, I think, whether, as regards some of these qualities at least, it is not rather the consciousness of resistance to muscular effort, than the sense of touch, properly speaking, that is the informing source. So, for example, as to hardness; the application of an external body lightly to the hand awakens the sense of touch, but conveys no idea of hardness. Let the same object be allowed to rest with gradually increasing weight upon the hand until it becomes painful, and we get the idea of weight, gravitation, but not of the hardness or impenetrability of the object. It is only when our muscular effort to move or penetrate the external body is met and resisted by the same, that we learn the impenetrability of the opposing body.

Other Perceptions attributable to the same Source.—So with regard to externality, extension, and form. When an external object, a cube, for example, or an ivory ball, is placed on the palm of the hand, sensation is awakened, but is that sensation necessarily accompanied with the perception of the external object as such? Does the mere tactual sensation, in the first instance, and of itself, inform us that there is something external to ourselves, that what we feel is not a part of our own organism? We are conscious of a change in the sensation of the part affected, but are we immediately conscious that this change is produced by something external? Let there be given, however, the consciousness of resistance to our muscular movements, as when the cube or ball, for instance, prevents the effort to close the hand, or when our locomotion is impeded by the presence of some obstacle, and will not the same resistance inform us of the extension of the resisting body, and so of its form and figure? We learn whereabout in space this resistance occurs, and where it ceases. The tactual sensation would indeed very soon come to our aid in this cognition, and serve as a guiding sense, even in the absence of the former. The question is, whether this alone would, in the first instance, give us such cognitions?

Our first Ideas of Extension, how derived.—We have had reference in this discussion only to the qualities of external bodies. There can be little question that our first ideas of extension are derived from our own sentient organism, the consciousness of sensations in different parts of the body, distinct from, and out of each other, thus affording the knowledge of an extended sentient organization. The idea of externality, or outness, and extension, thus acquired, the transition is easy from the perception of our own bodies as possessing these qualities, to the cognizance of the same qualities in external objects.

§ VI.—Credibility of our Sensations and Perceptions.

Denied by some.—There have always been those who were disposed to call in question the testimony of the senses. Such were the Eleatics and the Skeptics among the Greek philosophers, and there have not been wanting among the moderns minds of acuteness and ingenuity that have followed in the same path. While admitting the phenomena of sense, the appearance of things as being so and so, they have called in question the corresponding objective reality. Things appear to me to be thus and thus—such and such impressions are made on my senses—that I cannot deny; but how do I know that the reality corresponds to my impressions, or, in fact, that there is any reality? How know we our senses to be reliable? What evidence have we that they do not habitually deceive us?

Evidence demanded.—It were perhaps a sufficient answer to this question to reply, What evidence have we, or can we have, that they do deceive us? In the absence of all evidence to the contrary, is it not more reasonable to suppose that our perceptions correspond to realities, than that they are without foundation, uncaused, or caused by something not at all answering to the apparent object of perception; more reasonable to suppose that there is a real table or book answering to my perception of one, than that I have the perception while there is no such reality? It remains with those, then, who question and deny the validity of sense-perception, to show reasons for such denial. And this becomes the more imperative on them, inasmuch as they contradict the common belief and universal opinion of mankind—nay, what, in spite of all their arguments, is still, by their own confession, their own practical conviction and belief.

Evidence impossible.—But whence is this evidence to come? Where is it to be sought? How are we to prove that sense deceives us, except by arguments drawn from sense? And if sense is not reliable in the first instance, why rely upon it in the second, to prove that it is not reliable? If the senses do habitually deceive us, manifestly it can never be shown that they do. And, even if this could be shown, it would be impossible to find any thing better to rely upon in their stead. We have these guides or none. We have these instruments of observation provided for the voyage of life. We may pronounce them worthless and throw them into the sea, but we cannot replace them.

Inconsistent and contradictory Testimony of Sense.—But it may be replied that the testimony of sense is often inconsistent with itself, and contradictory of itself. What is sweet to one is sour and bitter to another. What seems a round tower in the distance becomes a square one as you approach; and the straight stick that you hold in your hand appears crooked when thrust into the water. There is in reality, however, no contradiction or inconsistency in the cases supposed. The change of circumstances accounts in every instance for the change of appearance. In the case of the stick, for example, the different density of the water accounts for the refraction of the rays of light that pass through it, and this accounts for the crooked appearance of the stick that is only partially submerged. So in the other cases; it is no contradiction that an object which appears round at a distance of ten miles, should appear square at the distance of so many rods—or that the taste of two persons should not agree as to the savor of a given object.

Deceptions of Sense.—It may be further objected that in certain states of the physical organism, sensations are experienced which seem to be of external origin, but are really produced by internal changes; and that in such cases we have the same perceptions, see the same objects, hear the same things, that we should if there were a corresponding external reality, while nevertheless there is no such reality, and it can be proved that there is none. If this may happen in some cases, why not in others, or in all?

Reply.—I reply, the simple fact, that in the case supposed the deception can be detected and proved, shows the difference between that and ordinary perception. If the senses were not habitually reliable, we could not detect the mistake in this particular instance. If all coin were counterfeit, how could we detect a counterfeit coin? We know, moreover, how to account for the mistake in the case before us. It occurs, by the supposition, only in a certain state of the organism, that is, only in a diseased, abnormal condition of the system. The exception proves the rule.

Distinction of direct and indirect Testimony.—A distinction is to be made, in the discussion of this subject, between the direct and indirect testimony of the senses, between that which is strictly and properly perception, and that which is only conception, judgment, inference. What I really perceive, for example, in the case of the distant tower, or the stick partially under water, is only a given appearance; I infer from that appearance that the tower is round and the stick crooked, and in that inference I am mistaken. My judgment is at fault here, and not my senses. They testified truly and correctly. They gave the real appearance, and this was all they could give, all they ever give. This has been well stated by Dr. Reid, and, long before him, the same ground was taken, in reply to the same objection, by Aristotle and also by Epicurus.

Direct Perception gives what.—In regard to direct and immediate perception, the case is different. Here the testimony is positive to the existence of the object. When something resists my voluntary movement, I am conscious of that resistance, conscious of something external and resisting. I cannot deny the fact of that consciousness. I may, however, deny the correctness, the truthfulness of what consciousness affirms. To do this, however, is to put an end to all reasoning on the subject, for, when we give up consciousness as no longer reliable, there is nothing left to fall back upon. If any one chooses to leap from this precipice, we can only say finis.

§ VII.—HISTORICAL SKETCH.

I. Of Different Divisions of the Qualities of Bodies.

The Greek Philosophers.—The distinction of the qualities of bodies into two classes, differing in important respects, is by no means a modern one. It was recognized by some of the earlier Greek philosophers, who held that the sweet, bitter, hot, cold, etc., are rather affections of our own senses than proper qualities of matter, having independent existence. Subsequently the view was adopted by Protagoras, and by the Cyrenean and Epicurean schools. Plato held it, and especially and very fully, Aristotle, who calls the qualities to which we have referred, and which are usually denominated secondary, affective qualities, because they have the power of affecting the senses, while the qualities now usually termed primary, as extension, figure, motion, number, etc., he regards as not properly objects of sense. The former class he calls proper sensibles, the latter, common.

The Schoolmen.—The schoolmen made much of this distinction, and held, with Aristotle, that the qualities now called primary, require, for their cognition, other faculties than those of sense.

Doctrine of Galileo.—Galileo points out the true ground and philosophy of this distinction, and also gives the name primary to the class referred to, viz., those qualities which are necessary to our conception of body, as for example, figure, size, place, etc., while, on the contrary, colors, tastes, etc., are not inherent in bodies, but only in us, and we can conceive of body without them. The former are real qualities of bodies, while the latter are only conceptions which give us no real knowledge of any thing external, but only of the affections of our own minds.

The Moderns.—Descartes and Locke merely adopted these distinctions as they found them, without essential modification. So also did Reid and Stewart, although both included among the primary qualities some which are properly secondary, as roughness, smoothness, hardness, softness. Indeed Stewart restricted the primary qualities to those and such as those just named.

Hamilton.—No writer has so fully elaborated this matter as Sir William Hamilton, to whom we are indebted mainly for the historical facts now stated, and whose dissertations are and must ever remain an invaluable thesaurus on the philosophy of perception. So complete and elaborate is his classification of the qualities of matter, that I shall be pardoned for giving a synopsis of its principal points in this connection.

Hamilton's Scheme—General Divisions.—He divides the qualities of bodies into three classes, which he calls primary, secundo-primary, and secondary. The primary are thought as essential to the very notion of matter, and may be deduced À priori, the bare notion of matter being given; while the secundo-primary and the secondary, being accidental and contingent, must be deduced À posteriori, learned by experience. His deduction of the primary qualities is as follows:

Primary Qualities.—We can conceive of body only as, I. Occupying space; II. Contained in space. Space is a necessary form of thought, but we are not obliged to conceive of space as occupied, that is, to conceive of matter. When conceived it must be under the conditions now named.

I. The property of occupying space is Simple Solidity, which implies, a. Trinal extension, or length, breadth, and thickness; b. Impenetrability, or the property of not being reduced to non-extension. Trinal extension involves, 1. Number, or Divisibility; 2. Size, including Density; 3. Shape.

II. The attribute of being contained in space, affords the notion, 1. Of Mobility; 2. Of Position.

The essential and necessary constituents then of our notion of matter are, 1. Extension (comprising under it, 2. Divisibility; 3. Size; 4. Density; 5. Figure); 6. Ultimate Incompressibility; 7. Mobility; 8. Situation. These are the primary qualities, products, in a sort, of the understanding, developing themselves with rigid necessity out of the given notion of substance occupying space.

Secundo-Primary Qualities.—The secundo-primary are contingent modifications of the primary, all have relation to space, and motion in space, all are contained under the category of resistance, or pressure, all are learned or included as results of experience, all have both an objective and subjective phase, being at once qualities of matter, and also affections of our senses.

Considered as to the sources of resistance, there is, I. That of Co-attraction, under the forms of a, Gravity, b, Cohesion; II. That of Repulsion; III. Inertia; all which are capable of minute subdivision. Thus from cohesion follow the hard and soft, firm and fluid, tough and brittle, rigid and flexible, rough and smooth, etc., etc. From repulsion are derived compressible and incompressible, resilient and irresilient.

Secondary Qualities.—The secondary qualities are, as apprehended by us, not properly attributes of body at all, but only affections of our nervous organism. They belong to bodies only so far as these are furnished with the power of exciting our nervous organism to the specific action thus designated. To this class belong color, sound, flavor, savor, tactile sensation, feeling of heat, electricity, etc. Such also are titillation, sneezing, shuddering, and the various sensations, pleasurable or painful, resulting from the action of external stimuli.

These Classes further distinguished.—Of the qualities thus derived, the primary are known immediately in themselves, the secondary only mediately in their effects on us, the secundo-primary both immediately in themselves, and mediately in their effects on us. The primary are qualities of body in relation to body simply, and to our organism as such; the secundo-primary are qualities of body in relation to our organism, not as body in general, but as body of a particular sort, viz.: propelling, resisting, cohesive; the secondary are qualities of body in relation to our organism as excitable and sentient. The primary may be roundly characterized as mathematical, the secundo-primary as mechanical, the secondary as physiological.

Reasons for retaining the twofold Division.—Such, in brief outline, are the principal points of Hamilton's classification. While following in the main the distinctions here indicated, I have preferred to retain the old division into primary and secondary, as at once more simple, and sufficiently accurate, merely dividing the secondary into two classes, the mechanical (secundo-primary of Hamilton), and physiological. We are thus enabled, not merely to retain a division and nomenclature which have antiquity and authority in their favor, and are well-nigh universally received, but we avoid the almost barbarous terminology of Sir William's classification—while, at the same time, we indicate with sufficient precision the important distinction between the so-called secundo-primary and secondary qualities.

II. Of Different Theories of Perception.

Realists and Idealists.—There are two leading theories, quite distinct from each other, which have widely prevailed, and divided the thinking world, as to the philosophy of perception. The one maintains that in perception we have direct cognizance of a real external world. This is the view taken in the preceding pages, and now generally held by psychologists in this country, and to some extent in Europe But for a long period, the prevalent, and in fact, until the time of Reid in Scotland, and Kant in Germany, the almost universally-received opinion was the reverse of this—that in perception, as in any and all other mental acts, the mind is conscious only of its own ideas, cognizant of itself and its own states only, incapable, in fact, of knowing any thing external to itself. Those who hold the former view are termed Realists, the latter Idealists.

Further division of the latter.—The latter, however, are of two classes. The Absolute Idealists hold that the notion we have of external things is purely subjective, having no external counterpart, no corresponding outward reality. In distinction from this the greater part maintain that while we are cognizant, directly and strictly, of nothing beyond our own minds, nevertheless there is an external reality corresponding to the idea in our minds, and which that idea represents. Hence they have been designated Representative Idealists, or, as Sir William Hamilton terms them, Cosmothetic Idealists.

Further Distinction.—Of these latter, again, some hold the idea which we have of an external world to be merely a state or modification of the mind itself; others regard it as a sort of intermediate connecting link between mind and matter. The former may be called egoistic, and the latter non-egoistic.

Summary of Classes.—We have then these three great classes—the Natural Realists, the Absolute Idealists, and the Representative Idealists comprising the Egoistic and Non-Egoistic divisions.

Distinguished Writers of the different Classes.—On the roll of absolute idealism are names of no small distinction: Berkley and Hume, in England, Fichte and Hegel, in Germany, are of the number; while among the representative idealists one finds Descartes, Arnauld, Malebranche, Leibnitz, Locke, in fine, the greater number of philosophic writers from Descartes onward to the time of Reid. Subsequently even, we find a writer of no less repute than Dr. Brown assuming, as the basis of his philosophy of perception, the exploded theory of representative idealism, under the egoistic form. Of natural realists since the time of Reid, Sir W. Hamilton is the most distinguished.

Origin of Representative Idealism.—The doctrine of representative perception doubtless originated in the difficulty of conceiving how a purely spiritual existence, the human mind, can, by any possibility, take cognizance of, or be affected by, a purely material substance, the external world. The soul seated in its presence-chamber, the brain, can cognize nothing beyond and without, for nothing can get except where it is present. It must be, then, said the philosophers, that in order to the mind's perceiving any thing of that which lies beyond and without its own immediate locality, there must come to the mind from that outer world certain little images bearing some resemblance to the things without, and representing to the soul that external world. These images—more refined than matter, less spiritual than mind itself, of an intermediate nature between the two—they termed ideas.

Tendency of Representative to Absolute Idealism.—It is easy to see how such a doctrine would lead almost inevitably to absolute idealism. If we do not in perception take cognizance directly of matter external, but only of certain images or ideas in our own minds, then how do we know that these images correctly represent the external reality, which we have never cognized, and never shall? How do we know, in fact, that there is any such external reality? What evidence have we, in a word, of the existence of any thing beyond and without our own minds? This was the actual result to which Berkley and Hume drove the then prevalent philosophy of Europe, as to a legitimate and inevitable result.

Relation of Dr. Reid to this Controversy.—To Dr. Reid belongs the credit of rescuing philosophy from this dangerous extreme, by showing the utter falsity of the ideal theory. He took the ground that the existence of any such representative images in the mind is wholly without proof, nay more, is inconceivable; that while we can conceive of an image of form or figure, we cannot conceive of an image of sound, or of taste or smell. The hypothesis is wholly without foundation. But even if it were conceivable and established by sufficient evidence, still it would explain nothing as to the manner in which the mind perceives external objects. It relieves no difficulty. If the representative image be itself material, how can the mind take cognizance of it? If not material, how can it represent matter, and how can the mind know that it does represent correctly the external object?

State of the Matter since Reid.—Since the time of Dr. Reid, this theory of representative perception, at least in this non-egoistic form, has been for the most part abandoned, and philosophers have been content to take the ground indicated by consciousness, and the common sense of mankind, that in perception we take direct cognizance of the external object.

Position of Hamilton.—It remained for Sir W. Hamilton to complete the work which Dr. Reid began, by showing that the representative theory, in its finer or egoistic form, as held by Dr. Brown and others, is equally untenable or unsound; that it makes little difference whether we regard the image or idea, which we take to represent the external object, as something distinct from the mind itself, or whether we view it as a mere modification or state of the mind, so long as we make any thing of the sort the direct object of perception instead of the real external thing. Idealism is the result in either case, and philosophical skepticism the goal. In place of any and all such views, Hamilton maintains, with great power and earnestness, the doctrine of natural realism—that in perception we are cognizant immediately and directly of the external object.

As no other writer has so fully elaborated this department of science, it may be of service to present in this connection the chief points of his theory.

Chief Points of Hamilton's Theory of Perception.—All perception is immediate cognition; we perceive only what we apprehend as now and here existent; and hence what we perceive is either in our own organism, viewed as material, extended, etc., or else is in immediate correlation to it. The organism is, in perception, viewed as not-me; in sensation, as of the me.

What is given in Perception proper.—What we apprehend in perception proper is: 1. The primary qualities of body as pertaining to our own organism; 2. The secundo-primary qualities of bodies in correlation to it. (See Hamilton's division of qualities of bodies, as above.)

Primary Qualities of external Objects, how known.—The primary qualities of things external to our organism we do not perceive immediately, but only infer, from the effects produced on us by them. Neither in perception nor sensation do we apprehend immediately, or in itself, the external cause of our affection or sensation. That is always unknown to consciousness, known only by inference or conjecture.

External Existence, how learned.—The existence of the world without is apprehended not in a perception of the primary qualities of things external, but of the secundo-primary—i. e., in the consciousness that our movements are resisted by something external to our organism. This involves the consciousness of something external, resisting. The two things are conjunctly apprehended.

This presupposes what.—This experience presupposes the notion of space, and motion in space. These are inherent, instinctive native elements of thought, and it is idle to inquire how we come by them. Every perception of sensations out of, and distinct from, other sensations gives occasion for conceiving the idea of space. Outness involves it.

Points of Difference between this Theory and Reid's.—The system, as thus stated, differs in some respects materially from the doctrine of perception advanced by Dr. Reid, and generally adopted since his time by the English and Scotch philosophers. According to Hamilton, perception is not, as held by Reid and others, the conception of an object suggested by sensation, but the direct cognition of something. We do not merely conceive of the object as existing, and believe it to exist, we know it and perceive it to exist. Nor does sensation precede, and perception follow, as generally stated, but the two are, in time, conjunct, coËxistent. Nor do we perceive the secondary qualities of bodies, as such, but only infer them from our sensations. Neither do we perceive distant objects through a medium, as usually held, but what we perceive is either the organism itself, as affected thus and thus, or what is directly in contact with it, as affecting and resisting it. Extension and externality, again, are not first learned by touch, as Reid holds, and most subsequent writers, both English and American, but in other ways; the former, by the perception of the primary qualities of our own organism, as the seat of sensations distinct from other sensations elsewhere localized; the latter, by the resistance which we experience to our own locomotive force. Finally, sensation proper is not, as with Reid and others, an affection purely of the mind, but of mind and body as complex. Its subject is as much one as the other.

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