An elementary treatise on sense-perception

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AN ELEMENTARY TREATISE

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CHAPTER I. Preliminary

§ 1. It is unnecessary at the beginning of this Treatise, to say more of the nature of the human soul than that every man consciously. possesses the power to know, to feel and to choose. The human soul is that entity to which these powers belong. The existence of these powers and of this entity admits of no question. If we cannot know this, we cannot know anything. Inquiry is meaningless and science impossible.

It is equally unquestionable, that, at the beginning of human life, we are in the profoundest ignorance of everything. It will also appear more and more in the progress of this Treatise, that all knowledge is acquired through the activities of a rational soul, exerting its own powers through the bodily organism with which it is connected. It is the design of the Treatise now undertaken to point out the conditions under which and the processes by which the soul so exerts these activities, as to find its way out of the ignorance in which it begins to be, into a clear knowledge of itself and of the mate- 1 rial universe. Itself it must know, as a condition of knowing anything else ; for the beginning of all knowledge is self-knowledge. "Know thyself" is not only a rule of wisdom, but of necessity.

§ 2. In the construction of a Treatise on any science, the meaning of certain words must be assumed without any definition. The knowledge of their meaning cannot be communicated from one mind to another by a definition, but must spring up in each mind through its own experience independently of the action of any other mind. If there is not in any mind such an independent experience, the meaning of the word which expresses that experience can in no manner be known. Many minds all having the same idea derived from experience, or occasioned by it, can agree together upon a word by which that idea shall be expressed.

Such a word is " knowledge." Its meaning can only be understood by an experience of knowing. In the progress of this Treatise, we must often employ words of which the same is true. All men use such words, not only in science, but in all human intercourse. The use of such words always assumes and implies the independent mental activity both of him who employs them and of those to whom they are addressed. Human intercourse itself thus assumes the individual personality of all human beings, that is, that every individual possesses or rather is a rational soul.

We can make no progress in the inquiries upon which we are entering without assuming the fundamental facts of human consciousness. It is therefore necessary to define that word.

Definition.— Consciousness is the knowledge or the power of knowing one's own mental states and activities.

In consciousness therefore all knowledge begins. It is in consciousness, the conscious experience of joy or sorrow, of desire, gratification or purpose, that the fact of our own existence is originally revealed to us. It is by the experiences of which we are conscious, that all those activities are excited and stimulated by which knowledge is acquired and a human life rendered possible. It is unnecessary to our present purpose to enter into any of those inquiries respecting the nature of consciousness which have attracted the attention of the curious. It is quite enough to recognize the fact that the human soul has the power of knowing its own thoughts, its own experiences of pain or pleasure, its own activities and purposes. This power we call consciousness.

§ 3. It is necessary in this place to say a few words respecting those bodily organs which are the instruments employed by the soul in the various processes of sense-perception. Every portion of the bodily organism is, in greater or less degree, subsidiary to these processes. It is, however, important to our purpose, to call special attention to three distinct systems of the bodily organism, — the muscles, the nerves, and the special senses. All these sustain an intimate relation to our subject.

The muscles are those parts of the bodily organism by the contraction and relaxation of which all the motions of the body are produced. Without them we shall see as we proceed, the whole arrangement of nerves and special senses would be powerless to convey to the mind any knowledge of the material universe. This fact it is important to our purpose distinctly to recognize. Beyond this it is unnecessary to go further in the examination of the muscular system. For such an examination the student must be referred to the anatomists.

Important as the nervous system confessedly is to our subject, it is unnecessary for us to enter upon its examination, more than simply to recognize two of its functions. Those functions are voluntary motion and sensibility. To each of these functions certain nerves are distinctly appropriated. Every muscle of the body is furnished with its own appropriate nerve through which it communicates with the brain, and without the healthful action of which the power of the muscle cannot be exerted. Some of these nerves are called into action only by the will, and always obey its behests. These are the nerves of voluntary motion. Other nerves act spontaneously, without the action of the will, and maintain in perpetuity the vital movements of the heart, the lungs and other vital organs. These are nerves of involuntary and spontaneous motion. They begin to act with the very beginning of life and cease their activity only at death.

§ 4. The other function of the nervous system is that of sensibility or feeling. The nerves which are appropriate to this function originate, like those already described, in the brain, and are distributed, in greater or less degree, to every portion or tissue of the living organism. On the presence of these nerves, the sensibility of the whole body depends. Their function is twofold, general sensibility and special sensation. The former of these functions is present in every portion of the body with the exception of the hair and finger and toe nails. It is found even in the hardest bones. At this point the two functions of general sensibility and motion are very intimately united. To every muscle of the body, a nerve of sensibility and a nerve of motion are conveyed enclosed in the same sheath. Along the one any sensation experienced is reported at the nervous center, to which the nerve of motion spontaneously responds by exciting such muscular action as the exigency requires. Thus if the light admitted to the eye is painful to the optic nerve, a reflex muscular action takes place, by which the pupil is contracted, so as to admit less light to the eye. A similar relation between nerves of sensibility and nerves of motion pervades the living organism. Motion so produced must however be sharply distinguished from voluntary motion. The latter is very intimately, the former not at all, related to sense-perception.

§ 5. The nervous system, as the source of the sensibility of the living organism, must be viewed in a threefold aspect.

1. The general sensibility. This, as already stated, pervades the whole living organism. It responds to the slightest touch of the surface of the body by any material substance, to the change of temperature of any portion of the body whether internal or superficial, and to all irritations or lesions from whatever causes originated. It is connected in greater or less degree with the spontaneous action of all the vital organs. When, however, the vital organs are in normal condition, and their functions are healthfully performed, their action is attended by little or no sensibility. A man in perfect health scarcely knows that he has a bodily organization. But when they are deranged by disease, their action is often attended with most distressing and painful sensibility.

2. Another aspect in which the nervous system as related to sensibility must be viewed is, the muscular sensibility. In this aspect of it, we find the first step which the mind takes towards a knowledge of the external universe. The action of every voluntary muscle of the body is attended by its own peculiar sensibility. It is by the experience of that sensibility, that the soul learns what muscle must be brought into action to produce any given motion, and what muscle is in action when a given motion is produced. It is by observing the sensibility of each muscle that the soul acquires the power of voluntary motion. The almost incessant motions of the limbs of a new-born infant are neither guided by the intelligence nor controlled by the will. The first problem which the rational soul has to solve is? to gain the control of the motions of the body and the limbs. It is only by the muscular sensibility that the solution of this problem is rendered possible. We shall learn as we proceed that it is here that the soul acquires its first idea of an extended and external universe.

3. The remaining aspect in which the nervous system is to be viewed, has reference to the action of the special senses. These are commonly said to be five in number, viz : touch, sight, hearing, taste, smell. From this statement it seems necessary to dissent. What is called touch cannot with propriety be regarded as one of the special senses. The reasons for this dissent, however, cannot be fully stated in this place, but will be rendered apparent as we proceed. One reason however is here apparent. The special senses have each a special organ, by which only the function of the sense can be performed. Touch has no such organ, but is found in greater or less degree in all parts of the surface of the living body. This alone is a full justification for classifying it as a part of the general sensibility and not as a special sense.

We cannot, however, regard this enumeration of the special senses as exhaustive. Sex appears to be entitled to be ranked with the special senses. It however performs so small a function in the soul's knowledge of the external universe, that a consideration of the indelicacy of the subject seems to justify its omission in a treatise on sense-perception. Its function is very closely analogous to that of taste, sustaining the same relation to the perpetuation of the species that taste does to the life and health of the individual.

CHAPTER II. Three Fundamental Questions Considered

§ 6. Every student of the human mind must necessarily meet, almost at the outset of his enquiries, three questions, which underlie the whole subject.

I. What is the origin of the idea of duration ?

II. How does the mind acquire the idea of an extended surface or body ?

III. How does the mind acquire the idea of externality or outness ?

I. These questions are to be considered in the order in which they have been propounded. We here encounter one of the words which admit of no definition. He who has not derived from his own mental activities and experiences the idea expressed by the word duration can never get that idea from a definition. Two persons both of whom have it may agree upon the name by which it shall be called ; but we must account for its origin in every mind by its own independent action.

The soul knows itself to exist as a permanent entity by its experiences of pleasure or pain, activity or rest.* From the beginning of our existence these experiences occur in almost unceasing succession. We now experience pleasure, next we suffer pain, next we are active, next we have ceased to act and are at rest. We know these changes as successive one to the other. One goes before, another follows after. This necessarily gives the idea of duration, now and then, longer and shorter. Since one event, many soul experiences have occurred, since another, very few. Thus every being that exists and is capable of knowledge, and is conscious of existing in a succession of mental states, must know events as involving duration. If a soul could exist having no knowledge of things external, but only of himself, that soul would not lack the idea of duration. He would know himself as existing in a perpetual succession of changes.

§ 1. II. How then originates the idea of extension ?f This word is also incapable of definition. It stands in this respect on precisely the same footing as duration. We all have the idea which the word expresses, and cannot divest ourselves of it. We conceive of all bodies as having length, breadth and thickness. But like duration this idea has come to us not by any definition, but by the activity of our own minds. How then does this idea arise in the mind by occasion of the experiences to which it has been subjected ?

It is obvious that this question is far more complicated than the question of the origin of duration. That involves nothing but a succession of soul-experiences ; but this involves the soul's use and control of the bodily

* "Reid's Collected Writings, pp. 342, 343.

fReid's Collected Writings, pp. 123-126. 142-144, 528.

organism. It is only through the organs of the body, that the mind deals with material things.

It seems to me that few persons will be disposed to deny the proposition, that if the body and all its organs were incapable of motion, the mind could never so mal^e use of the senses as to acquire the notion of extension. To a soul so limited in its powers, there could be no here and no there, as there could be no now and no then to a soul that experiences no changes.

We have yet made but little progress in our task; yet by this assertion we are brought into direct conflict with writers of the highest authority. This assertion however we shall endeavor fully to substantiate as we proceed. It must here be taken, not as a proposition which we claim to have proved, but as one which we expect to establish.*

In our judgment, the only answer which can be given to the question, what the origin of the idea of extension is, that it springs up of necessity with the earliest exercise of the soul's power of controlling the motions of the body. How different the development of the human infant, from that of the young of brute animals ! The latter are for the most part able to control their limbs, and to use them for their own help and preservation, from the moment of birth, and must depend upon them or perish, and where this is not true of all their bodily organs, as in the case of the young bird in the nest, it is still true of certain organs. The young bird must stretch up its neck and open wide its mouth, to receive the food which the parent bird drops into it, or it will starve to death. In the case of the human infant, the source of its food must be placed within its lips, and the action of obtaining its food is as spontaneous and unintelligent as the beating of its heart. At this point, human and brutal life are on the same level. Beyond this the infant's preservation and well-being must depend alone on intelligence. Over the motions of its limbs and head the new-born infant has no control. It is utterly helpless, and must perish very speedily unless its wants are supplied by the intervention of an intelligence not its own.

From this condition of utter helplessness, the human infant can only escape by learning, in the use of its own rational powers, to control and guide the motions of the limbs and organs of the body. The hands and feet of an infant are often in motion ; but those motions are at first controlled by no intelligence or will power. They are aimless, and useless for the supply of the wants of the child. The first lesson of infancy is to learn to control and guide these motions ; and in the process by which this acquisition is made, the idea of extension begins to manifest itself. The notion of place, here and there, is necessarily suggested by all motion voluntarily and consciously begun, continued and terminated. The child voluntarily moves his own hand. The beginning of that motion is here, the end of it is there, and the continuance of it suggests the extension that separates them. The distinction between the ego and the non-ego may not yet have been thought of; but the position of that something which I voluntarily move must be recognized as changed, here and there must be distinguished, and the intervening distance. This is the idea of extension in its most rudimentary form, and it must spring up in the mind with the first exercise of the power of voluntary motion. The child that has learned intentionally to move his hand, or to open and shut it, or to turn his eyes from side to side, or to turn his head on the joint of his neck, must have learned the distinction between here and there, and that distance separates them.

It is not claimed that this is the fully developed idea of extension in its three dimensions, or even of an extended surface. In order to acquire the full conception of an extended surface, the notion of body must have been gained, and the ego must have been distinguished from the non-ego.

§ 8. III. Our next inquiry is, how is this acquisition made ? Perhaps the gravest difficulty we must encounter in our enquiries into the genesis of human knowledge is here. How does the soul pass from the knowledge of itself to the knowledge of that outer universe which is not itself ?

Before, however, proceeding to answer this question, it seems necessary to define two terms which we can hardly avoid using in the discussion. They are the two correlative terms "subjective" and "objective." In using these two terms, we regard them as an exhaustive division of all the knowable. All the objects in the universe are comprehended either in myself or in the universe outside of myself. All then which I know of myself, my own thoughts, feelings, joys, sorrows, acts, intentions, is subjective knowledge. All which I know of the universe outside of myself is objective knowledge.

At the threshold of this inquiry we meet the stubborn, indisputable fact, that at the beginning of the soul's activity, all its knowledge is purely subjective. It is true from the very first, that most of our experiences are caused by impressions which the universe outside of ourselves makes upon us. But these impressions are purely subjective.* The new-born infant knows nothing of the causes which produce them. For example, a loud noise is made near an infant's ear. He experiences the sensation, and is startled and distressed by it ; but he knows nothing of its cause. It is to him only a subjective feeling, and suggests no idea of anything external to himself. The same is true of all the impressions which are made upon him through any of his senses. All the impressions which are made upon the inexperienced infant, through the eye, the ear, the taste, the smell, are mere subjective sensations. This statement will be called in question by some and will be more fully discussed further on.

We shall however at this point sufficiently anticipate the subsequent discussion to illustrate it by a single example. Let us suppose that a man of good natural understanding had been, up to a certain time of his mature life, quite destitute of the sense of smell, and had never been informed that other people had such a sense. At last, while he is quite alone in his room, he is suddenly endowed with that sense in full acuteness. At the same moment his room happens to be filled with some intense and disgusting odor, say of assafcetida ; I affirm that the new sensation would be purely subjective, and he would probably think himself attacked with disease, and perhaps hastily call a physician. Sitting still in his chair, the offending substance probably being in some remote part of the room, he would not even have the power of referring the new sensation to that part of the nostril where the nerve of smell is situated. We do not make such a reference of a sensation of smell to that nerve, even after years of experience. We have learned indeed that the nostril is the place of the sensation, by finding that the odorous object must be applied to the nostril in order that the sensation may be most intense ; but we do not know, till we have studied the matter anatomically, in what particular part of the nostril that nerve is situated, or how extensively the nostril is pervaded by it. In such a case as we have supposed, the man would have no power of locating the sensation in the nostril even. The same will hereafter be proved to be true of all the special sensations. They are all subjective experiences, which the soul has no original power of referring either to their external causes, or to the part of the body where they are produced.

§ 9. Our question then is narrowed down to a point : how does the soul acquire the power of referring the impressions that are made upon it by the outside universe to the causes by which they are produced ? How does it pass from the knowledge of subjective impression to a knowledge of objective causation ? One thing must here be conceded by all. By the mere experience of subjective sensation, the mind never can acquire a knowledge of an external objective cause. For example, a hard substance touches the surface of one's body. It is purely a subjective sensation, and no repetition of it can give any more idea of the objective cause than the first experience of it.

We shall find no answer to our question till we go back to the same cause which conducted us to the first idea of extension. Here we shall find the solution. Let us suppose that the infant had at last subjected his muscles and the limbs which those muscles move, to the control of his intelligence and his will. He is perfectly conscious of a power to move his hand in any direction at pleasure. But on a certain occasion, he finds a motion of the hand which he is perfectly conscious of being able to make, resisted and effectually stopped. Here then is the ego conscious of power to do a given thing, standing face to face with a resisting non-ego, that is, a power 3 resisting and hindering his own power in action. Nor let us suppose that the infant mind stops here. It is true that it is chiefly employed in the problems of sense-perception ; but all the faculties cooperate from the first. We shall show further on, and in doing so be sustained by the highest authority, that infancy does use inductive reasoning* in the solution of some of the simplest problems of sense-perception. It is just as reasonable to believe that it employs in like cases the intuition of cause and effect as -the law of induction. What difficulty then in admitting that in resistance experienced it sees a resisting cause? Indeed the whole problem of sense-perception necessarily involves the notion of causation. To perceive is to refer our sensations to their appropriate causes. If the infant has not the power of passing from a known effect to a knowledge of its cause, it has no power of sense-perception, for this is sense-perception. He does not infer an objective cause from a subjective sensation, but the existence of a resisting agent from an experience of his own activity resisted.

President Porter claims that the non-ego which is known in sense-perception is " the bodily organism itself or that part of the sensorium which is excited to action." To this it may be replied, that in the proper place it has been abundantly shown, that in many cases of sense-perception, if not indeed in most cases, we never do refer the sensation to the part of the organism in which it is produced. We see perfectly without referring the sensation of vision to the retina of the eye, or knowing that we have any retina. The same thing holds in respect to all the senses. The non-ego which is discerned is not our own organism but that which resists our will power. It is by such resistance alone that we learn the existence of the non-ego.f

* Porter's Elements, Sec. 109. f Porter's Elements, Sec. 86.

It is important to be noticed, that in acquiring such a notion of a resisting non-ego, the mind does not necessarily employ the aid of either of the special senses. In the act of voluntary motion and in the cognition of the resistance experienced to it, the mind employs only its muscular power and muscular sensibility. Even in recognizing the existence of a resisting power, the mind does not necessarily call into exercise what is commonly called the sense of touch. The muscular sensibility alone conveys to the mind the consciousness of the act of voluntary motion and the experience of its resistance and arrest.

§ 10. This notion of externality is only rudimentary, sustaining nearly the same relation to the fully developed idea that the notion of extension which is implied in all voluntary motion, does to the completed conception of an extended surface. Perhaps, however, it will not be found difficult at this point of the discussion, to indicate the manner in which the development of both these ideas is completed. At this stage of the process, the mind will soon perceive that this resistance is experienced only within certain boundaries. Nothing hinders but that these boundaries should be definitely ascertained, and ascertained on all sides. In this process the mind has become master of all the conditions of the full development of the idea of a straight line and of a resisting extended surface. With this latter also the idea of hardness is inseparably linked. Indeed the two ideas are identical.

This, however, only accounts for the origin of the idea of extension in the two dimensions of length and breadth. The question still remains, how does the mind pass to the third dimension of space, or to the knowledge of solid bodies ? In order to answer this question, it is not necessary to introduce into the discussion anyother factor than voluntary motion and muscular sensibility. The mind is capable of cognizing the fact of a change of direction in that motion, and of continued resistance in that changed direction, when the resistance is interrupted in a straight line. This is sufficient to reveal two resisting surfaces standing at an angle to each other. This process is capable of being extended to all the plane surfaces by which a solid body is bounded. In a similar manner the lines in which the several planes bounding a body meet may be traced, its solid angles may be discovered and a conception of its outline completed. In tracing the bounding lines of the several planes, the general sensibility to contact will render important aid. It is also easy to see, that when the dimensions of the body are not greater than can be grasped by one hand or by the two hands, the muscular power of one hand may be exerted in the direction opposite to that of the other, and thus it will become obvious to the mind that the body has two surfaces separated from each other by its third dimension. In no part of the process does the mind require any other aid than voluntary motion and muscular sensibility.

In all these processes doubtless the action of what is commonly called the sense of touch and the sense of sight, will be present and consciously active, but their activity will not be necessary to the processes we have been describing. It will, however, be readily admitted that the general sensibility of the surface of the body greatly facilitates the process by which we pass from a knowledge of the extended surface to that of the solid body ; yet it cannot be admitted that it is indispensable.

§ 11. It does not fall in with the plan of this treatise to enter upon any extended discussion of the intuitive faculty of the soul ; but it is necessary at this point to assume the existence of such a faculty, and its activity in these earliest processes of the mind. A rational soul cannot act in such a manner as to acquire knowledge, without recognizing the relation of cause and effect. It may be objected to the foregoing argument, that in these earliest processes of the infant mind, it has as yet no notion of this relation. But why not ? It is a condition of the very first step toward any knowledge of the external, that the soul should know itself as a cause, that it should be conscious of power in action. It is in this very consciousness, that the notion of cause and effect originates in the soul. He that knows himself as a doer, knows a cause, knows the thing done as an effect, and is fully prepared to know that which resists his causative power as another cause distinguished from and set over against the cause which is resisted. This conclusion cannot be set aside otherwise than by denying that the infant has a rational soul, and to deny this is to deny that it has any power of acquiring knowledge.