Front Page Titles (by Subject) CHAPTER I.: THE NATURE OF INTELLIGENCE. - The Principles of Psychology
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CHAPTER I.: THE NATURE OF INTELLIGENCE. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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THE NATURE OF INTELLIGENCE.
§ 168. The two great classes of vital phenomena which Physiology and Psychology respectively embrace, are broadly distinguished in this; that while the one class includes both simultaneous and successive changes, the other includes successive changes only. While the phenomena forming the subject-matter of Physiology, exhibit themselves as an immense number of different series bound up together; those forming the subject-matter of Psychology, exhibit themselves as but a single series. The briefest consideration of the many continuous actions constituting the life of the body at large, suffices to show that they are synchronous—that digestion, circulation, respiration, excretion, secretion, &c., in all their many subdivisions, are going on at one time, in mutual dependence. And the briefest introspection serves to make it clear, that the actions constituting thought, occur, not together, but one after another. Should a rigorous criticism demand qualifications of this statement, they cannot be such as to diminish its general truth. Life being the definite combination of heterogeneous changes, both simultaneous and successive, in correspondence with external coexistences and sequences; the two great divisions of life must ever be distinguished as, the one a correspondence that is both simultaneous and successive, and the other a correspondence that is successive only.
At first sight, this may be supposed to constitute an impassable distinction between the two. Such, however, is by no means the fact. Even were the highest psychical life thus absolutely distinguished from physical life, which we shall presently see reason to doubt, it would still be true that psychical life, in its earlier and lower phases, is not thus distinguished; but that the distinction arises, only in the course of that progression by which life in general attains to its more perfect forms. That gradual differentiation and integration, seen alike in the evolution of organic structures, and in the evolution of the correspondence between their actions and those in the environment, is also seen in the separation of that correspondence into its two great orders. At the same time that through it have resulted the various subordinate divisions of the correspondence, through it also, has resulted this fundamental division. Originally, the particular kinds of change forming the germ of psychical life, were, like those out of which physical life arises, both simultaneous and successive; and it is but by slow steps that they have come to be distinguishable as successive only. Let us glance at a few of the facts.
Passing over the creatures moved by cilia, in which the independence of the constituent irritations and motions simultaneously going on, is manifest—passing over the zoophytes, in which each part of the organism is capable, in a greater or less degree, of stimulations and contractions apart from the rest, which may at the same moment be responding to other stimuli—passing over these lowest creatures, in which the absence, or rudimentary character, of the nervous system, forbids anything like community of impressions throughout the mass; let us consider what happens even when the nervous system has attained some development. In the higher Radiata, as, for example, the star-fish, each of the several like divisions of which the body consists, “is connected with a ganglionic centre, that seems to be subservient to the functions of its own division alone, and to have little communication with, or dependence upon, the remainder.”∗ The result is, that the sensory and motor actions going on in each ray of a star-fish, are, in the main, independent of those going on in the others. Such elementary psychical changes as the creature manifests, take place simultaneously in different parts of its body; each part separately responding to the impressions made upon it. And hence the fact, that for a length of time after being divided from each other, the rays severally continue to exhibit their ordinary actions. Though in the Mollusca, there is no such repetition of like parts having similar endowments; yet it is held, that the ganglia distributed through the body, are in great measure independent in their actions, or have these actions but very imperfectly co-ordinated into any general psychical life.∗ In the Articulata, whose structure specially fits them for the experiment, this dispersion of the psychical life may be very clearly shown. “The Mantis religiosa customarily places itself in a curious position, especially when threatened or attacked, resting upon its two posterior pairs of legs, and elevating its thorax with the anterior pair, which are armed with powerful claws: now if the anterior segment of the thorax, with its attached members, be removed, the posterior part of the body will still remain balanced upon the four legs which belong to it, resisting any attempts to overthrow it, recovering its position when disturbed, and performing the same agitated movements of the wings and elytra as when the unmutilated insect is irritated; on the other hand, the detached portion of the thorax, which contains a ganglion, will, when separated from the head, set in motion its long arms, and impress their hooks on the fingers which hold it.—If the head of a Centipede be cut off, whilst it is in motion, the body will continue to move onwards by the action of the legs; and the same will take place in the separate parts, if the body be divided into several distinct portions. ∗ ∗ ∗ ∗ If the body be opposed in its progress by an obstacle of not more than half of its own height, it mounts over it, and moves directly onwards, as in its natural state; but if the obstacle be equal to its own height, its progress is arrested, and the cut extremity of the body remains forced up against the opposing substance, the legs still continuing to move.—If, again, the nervous cord of a Centipede be divided in the middle of the trunk, so that the hinder legs are cut off from connection with the cephalia ganglia, they will continue to move, but not in harmony with those of the fore part of the body; being completely paralyzed so far as the animal's controlling power is concerned; though still capable of performing reflex movements by the influence of their own ganglia, which may thus continue to propel the body in opposition to the determinations of the animal itself.”∗ From all which facts we see, that in one of these articulated creatures, the actions which pertain to the psychical division of the life, are in great measure performed independently and simultaneously by the several segments. Just as, in the structure, is provided a separate ganglion to each segment; so, in the function, each segment exhibits a more or less distinct nervous activity. The impression made upon each leg by the surface touched, is conveyed to the special ganglion of that leg, and thence reflected upon a muscle moving in the leg; and only in its power of setting agoing or arresting this automatic action, has the creature's chief nervous centre any participation in the process. So that, even in animals of this comparatively advanced organization, both orders of vital changes are simultaneous and successive: the differentiation of the psychical from the physical life is but slight. Even in the Vertebrata this differentiation is by no means complete. A large part of the actions that appear voluntary, are in a great degree automatic, and may be performed without consciousness. “Infants are sometimes born without any Cerebrum or Cerebellum; and such have existed for several hours or even days, breathing; crying, sucking, and performing various other movements. The Cerebrum and Cerebellum have been experimentally removed from Birds and young Mammalia, thus reducing these beings to a similar condition; and all their vital operations have, nevertheless, been so regularly performed as to enable them to live for weeks, or even months.”† The ordinary experiments on decapitated frogs, clearly show the reflex origin of many muscular actions. “It is certain that, in Birds, the movements of flight may be performed after the removal of the Cerebrum.”∗ Nay, even in the adult human being, there are many actions belonging to the psychical division, which either may or may not enter into the current of consciousness. The motion of the legs is necessarily accompanied with various muscular and tactual changes. These, together with the state of feeling constituting volition, may be distinctly present to consciousness—may be thought of as by a child learning to walk; or they may, as in ordinary walking, be wholly left out of consciousness. The various impressions received by the feet; the various feelings of muscular tension; the various combinations of sensations and contractions by which the equilibrium is maintained; may be all going on while consciousness is entirely absorbed in some interesting train of thought—may form an independent series of changes parallel to those going on in consciousness—may form, as it were, a kind of secondary consciousness, subordinate to the primary one. The processes we perform while eating display a very similar relation. The several acts by which each morsel is selected, cut, prepared, and carried to the mouth, may perhaps be held to enter into the current of our thoughts; though in general, and especially during conversation, they seem next to unconscious. But many of the impressions and motions involved are certainly unconscious. The sensations which the knife-handle gives; the contractions by which it is grasped; and the muscular changes which the arms are every moment undergoing, scarcely ever, if at all, occupy the attention. That is to say:—Out of a great number of psychical actions going on in the organism, only a part are woven into the thread of consciousness; while the others form one or more distinct strands, which, as it were, occasionally inosculate with the thread of consciousness, but do not permanently unite with it. The like is manifestly to a great extent true in speaking and writing. And the reader can, doubtless, call to mind occasions on which some habitually performed process, even of considerable complexity, was performed quite unthinkingly, and while—to use the common phrase—he “did not know what he was about.”
Contemplating, then, these typical facts, it will be manifest that the differentiation by virtue of which the changes constituting psychical life, have become successive only, instead of simultaneous and successive, has arisen by degrees, and has not even now become complete. In the lowest animal types, each part of the organism, while it performs by and for itself all other vital functions, also responds by and for itself to external stimuli; and the psychical changes, or what stand for them, are both simultaneous and successive to almost as great an extent as the physical ones. Gradually as a nervous system makes its appearance, these psychical changes become slightly co-ordinated—have their various strands connected. Gradually as the nervous system becomes more and more integrated, the twisting of these various strands of changes into one thread of changes grows more complete. But to the last their union never becomes entire. The vital actions constituting the subject-matter of Psychology, while distinguished from other vital actions by their tendency to assume the form of a single series, never absolutely attain that form.
§ 169. The gradual rise of this distinction between the psychical and the physical life, will be most clearly understood, if we consider the mode in which it first appears, and the leading stages of its progress.
Throughout the homogeneous tissue of which the lowest creatures consist, there is complete community of actions. Each part does what the other parts do. The several vital processes are going on simultaneously in many places alike. These primordial organisms, if organisms they can be called, exhibit no differentiation of either structure or function. And thus, the two great divisions of life, as well as the various subdivisions of each, are, in the beginning, one.
The first great differentiation established, is that between the inner and outer tissues—the mass, and its limiting membrane—the substance of the body, and its skin. The parts of the originally uniform jelly, are subject to but one marked contrast of conditions—that between contact with each other, and contact with the environment. The external portions are bathed by the surrounding medium: the internal portions are not. And in response to this primary contrast of conditions, there eventually arises a contrast of structure and function. That which is permanently outermost, takes on the modified form of vital action which its circumstances demand: that which is permanently innermost, similarly assumes a more specialized order of activity. And with this differentiation of function there goes on a simultaneous differentiation of structure.
Primarily, the division of labour thus commenced may be considered as physiological only. In virtue of its position, the surface may be regarded as necessarily assuming the duties of absorption—the taking in of water, and nutriment, and oxygen. And when, by the involution of the surface, a stomach comes to be formed, the change may be understood as a further separation of duties, such that nutrition is chiefly confined to one part of the limiting membrane and aeration to another. But the advance is not solely an advance in the physiological division of labour: it is at the same time an advance towards the separation of psychical actions from physical ones; and is even a first step towards bringing the psychical actions into a serial order. As a necessary result of its position, the skin not only permanently assumes the office of taking in the matters by which the processes of integration and disintegration may be maintained, and of excreting the effete products; but it also permanently assumes the office of receiving all those impressions which form the raw material of intelligence. The mechanical and other actions going on in the environment, can be responded to by the organism, only when it is affected by them; and any effect they produce upon it must be proximately experienced by its surface. The skin, then, being the part immediately subject to the various kinds of external stimuli, necessarily becomes the part in which psychical changes are originated. That adjustment of inner to outer relations in which intelligence of all degrees consists, must in every case be initiated by the actions of things upon the outside of the organism. Any consequent movement of the organism entails further actions of things upon its outside. And hence, as contrasted with the contained substance, the skin comes to be more especially concerned in such psychical changes as arise; and more and more definitely so, as the differentiation becomes more complete. But now mark the implication. The changes constituting the physical life, continue, as before, to go on simultaneously throughout the entire mass. Those which foreshadow the psychical life, are, in an increasing degree, localized in its outer surface—belong to the outer surface primarily, and affect some other parts secondarily. Though, as soon as there is any rudiment of a nervous system, impressions received by the skin are followed by specific changes elsewhere; yet, as these specific changes elsewhere, would not have occurred without the impressions on the skin, we must consider these as fundamental. So that, contemplating the facts under their general aspect, we may say that while the physical changes pervade a solid, the psychical ones, or rather those out of which psychical ones arise, tend to be confined to a surface. And as the changes that can be simultaneously going on throughout a solid, are infinitely greater in number than those to which a surface can be subject; it results that, even by this primary differentiation, the incipient psychical life comes to be distinguished from the purely physical life, by the diminished quantity of simultaneous changes that it may include.
At succeeding stages in the progression, further differentiations, having like natures and results, are clearly traceable. At first, this sensitiveness, which forms the basis of the psychical life, is diffused more or less equably over the whole surface; but it presently becomes in some degree concentrated. Though, in general, all parts of the skin remain impressible by touch; yet certain parts, which are by their positions more especially liable to receive tactual impressions, become more highly susceptible than the rest; and in these parts the great majority of the sensorial changes are localized. That is to say, the changes forming the raw material of intelligence, by being in a great measure restricted in the area of their occurrence, have the characteristic of simultaneity still further limited; and the more highly developed the tactual apparatus, the more marked is the limitation.
Still more decisive is this limitation rendered by the development of the special senses. The olfactory and gustatory sensations are localized in smaller tracts than the sensation of touch; and each of these tracts is little, if at all, capable of undergoing more than one change at one time. Visual and aural impressions are receivable only within yet narrower areas; and even the two areas susceptible of each, become functionally one. The ears are simultaneously affected by the same sounds; and in the higher creatures the eyes, being so placed as to converge their axes on the same object, are occupied with almost identical images, and yield to consciousness what seems to be one impression. Nay, even of the sensations occurring within the narrow space of each retina, a further concentration is manifest. The highest sensitiveness of the retina is confined to a very minute spot; and the changes to which that spot is subject, so dominate over the others as greatly to obscure them. If we further call to mind that when the most advanced intelligence is reached, the sensational changes that arise in the nose and the palate are but occasional; and that those proceeding from the eyes and ears are by far the most frequent; it will be seen to what extremely small portions of the organism the changes which form the greater part of the raw material of intelligence, are ultimately confined.
This continued process of differentiation and integration—by which the changes forming the substance of psychical life, are first gradually concentrated upon the surface of the organism; afterwards upon certain regions of that surface; afterwards upon those most specialized parts of it constituting the organs of the higher senses; and in the most perfect of these are even more or less localized in minute centres; will clearly show how the psychical life grows distinct from the physical life, by the increasing tendency of its changes to assume the serial arrangement. We have nothing to do with the progressive development of the nervous system, and the actions that are carried on throughout its mass. All these actions originate in the senses. The internal changes are consequent upon the external ones. And just in proportion as the external ones tend towards the serial form, the consequent internal ones must do the same. Evidently, then, this distinction is involved in the very progress of the sensitive organization.
§ 170. But now, from our present point of view, the matter will be more fully comprehended on observing, that the advance of the correspondence of itself necessitates a growing seriality in the psychical changes; or in other words—that the advance of the correspondence, the development of consciousness, and the increasing tendency towards a linear order in the psychical changes, are different aspects of the same progression.
For how only can the constituent changes involved in any complex correspondence be co-ordinated? Those abilities which an intelligent creature possesses, of recognizing a variety of external objects of different structures, and of adjusting its actions to composite phenomena of many kinds, imply a power of combining many separate impressions. These separate impressions are received by the senses—by different parts of the body. If they go no further than the points at which they are made, they are useless. Or if only some of them are brought into relation with each other, they are useless. That an adjustment may be effected, they must be all brought into relation with each other. But for them all to be brought into relation with each other, implies some centre of communication common to them all. They cannot possibly be co-ordinated without this. This centre of communication common to all the impressions, must be one through which they severally pass; and as they cannot pass through it simultaneously, they must necessarily pass through it in succession. Just in proportion as the external phenomena responded to become greater in number, and more complicated in kind, must the variety and rapidity of the changes to which this common centre of communication is subject, increase—just in this proportion must there result an unbroken series of these changes—just in this proportion must there arise a consciousness.
Hence then it is manifest, that the progress of the correspondence between the organism and its environment, inevitably involves a more and more complete reduction of the sensorial changes to a succession; and by so doing inevitably involves the evolution of a consciousness—a consciousness that becomes higher and higher as the succession becomes more rapid and the correspondence more complete.
§ 171. This doctrine, that mental phenomena constitute a series, is one of very old standing; and one the general truth of which none call in question. As we have seen, however, it requires to be understood in a somewhat qualified sense. Where, as above, the facts are contemplated objectively, it becomes manifest that though the changes constituting intelligence approach more or less nearly to a single succession, they do not absolutely form one—that there are constantly being performed actions of an intelligent kind which are not present to consciousness—and that, through the many gradations between the completely conscious actions and the completely unconscious ones, the psychical changes merge into those which we distinguish as physical, and the boundaries of the series are blurred. When we go on to consider the facts subjectively—when we interrogate consciousness, we still find that though the seriality of the changes becomes yet more clearly manifest, there are nevertheless certain experiences which make us hesitate to assert this seriality in any very rigorous sense.
Thus, the visual impressions which we are every moment receiving, though ordinarily regarded as single states, are yet in reality compound ones; and it becomes a perplexing question whether each of these compound states can, strictly speaking, be a member of a linear series of changes. It is not simply that the various distances, solidities, structures, &c., which appear to be immediately given in each impression, are really known by inference, and severally imply many changes; but it is that the various objects included within the visual field, are simultaneously present to consciousness with various degrees of distinctness—produce what may in some sense be called simultaneous changes in consciousness. Besides the particular thing to which the eyes are directed, many other things are seen more or less clearly; and no lines of demarcation can be drawn between either the degrees of perfection with which they are impressed upon the retina, or those with which they are presented to consciousness. Only one particular point of the object looked at, is perceived with perfect distinctness. Yet it cannot be said that consciousness is wholly occupied with this one point; for the object itself becomes known by the single glance directed to the one point. Obviously the degree of consciousness which we have of things within the visible area, becomes insensibly less as they become more remote from the centre to which the axes of the eyes converge. Obviously there is no particular distance from it at which we can say that consciousness ceases. And thus there would seem to be a great number of nascent consciousnesses, of different intensities, existing at the same moment. Still more manifest will become the difficulty of regarding this visually-produced consciousness as single, when it is remembered that each of these nascent consciousnesses is really the result of a distinct change, or group of changes, in the retina. The immense number of separate sensitive agents of which the retina consists, being severally capable of independent stimulation, it results that when a cluster of images is cast upon them, they are one and all affected in various modes and degrees. They simultaneously undergo a variety of changes, which are more or less distinctly presented to consciousness. Evidently, then, it is only by a certain license that the internal change produced by any visual impression can be called single. It is in reality a multitude of simultaneous changes bound together. The thread of consciousness is made up of an immense number of separate strands; and it is only in the sense that these separate strands are more or less united, that consciousness can be said to consist of a succession of changes.
Nevertheless, the truth of the general doctrine that the psychical life is distinguished from the physical life by presenting successive changes only, instead of successive and simultaneous changes, may be even further shown from the very facts here cited. For though, when subject to a visual impression, we become nascently conscious of many things; yet, there is always some one thing of which we are conscious in a higher degree than the rest. And beyond this, it is observable that when we so direct our attention to any one thing as to perceive it in the true sense of the word—to know it as such or such, we are almost exclusively occupied with that one thing, or some particular part of that one thing. Though the images of other objects are all the while being impressed upon the retina, and are producing changes there; yet these appear to produce extremely little internal effect—are scarcely more than physical changes—do not undergo that co-ordination with others which is required to constitute them psychical changes. And this fact, that in proportion as any object, or part of an object, seen, is distinctly thought of, the other objects within view cease to be thought of, shows very clearly how consciousness becomes more definitely serial as it rises to a higher form. So that, reverting to the metaphor before used, we may say that while the outer strands of changes which constitute the thread of consciousness, are indefinite and loosely adherent, there is always an internal closely-twisted series of changes, forming what we may consider as consciousness proper.
Thus, though a critical examination of the facts, shows that the seriality of psychical changes can be asserted only in a qualified sense, it shows that, if not absolutely so distinguished from physical changes, they are relatively so distinguished; and it shows, that in proportion as the psychical changes assume that more perfect form constituting consciousness proper, they become so distinctly serial, as to originate what we recognize to be a single succession of states. Though these may be physiologically composite, and were once psychologically so; yet, to the extent that they have become consolidated elements of thought, they may rightly be regarded as severally simple.
And here indeed, where the question is considered in relation to the human consciousness only, it is resolvable by the briefest introspection. No controversies respecting the nature of our mental states, can alter our inward perception that consciousness cannot be in two states at one time—that any one state of consciousness necessarily excludes any other. However difficult it may be to say where one state of consciousness ends and another begins—however difficult it may be to say respecting certain states of consciousness, whether they are simple or complex; the fact remains the same, that the states of consciousness are serial. If any state, commonly regarded as one, is asserted to be made up of many states; then, those many occur in succession. If they do not occur in succession, they must occur together; and must so form one state. These are the only alternatives. And whichever be chosen, it remains equally manifest that, subjectively considered, the changes in consciousness constitute a linear series.
§ 172. Concerning the nature of Intelligence, therefore, we reach the conclusion, that it consists of a certain order of changes, which are distinguished from that lower order of changes constituting bodily life, by the peculiarity, that, instead of being both simultaneous and successive, they are successive only. Step by step differentiated from the lower order of changes with which they are originally one; they assume a more completely serial arrangement in proportion as intelligence advances. Though this serial arrangement never becomes in all respects absolute; yet, in the human consciousness, it becomes almost so: and the highest processes of this consciousness are possible on no other condition. The simple fact that every distinct proposition expresses a relation, and that every relation subsists between two terms, of itself proves that distinct thought cannot exist except as a single succession of states. And hence, the seriality of its changes must be regarded as that especial characteristic of intelligence, which approaches to absoluteness as the intelligence approaches to perfection.
A continued series of changes being thus the subject-matter of Psychology, it is the business of Psychology to determine the law of their succession. That they do not occur at random, is manifest. That they follow one another in a particular way, the existence of Intelligence itself testifies. The problem then, is, to explain their order.
[∗]Carpenter's “Principles of Comparative Physiology.” Fourth edition, p. 654.
[∗]Carpenter's “Principles of Comparative Physiology,” p. 658.
[∗]Carpenter's “Principles of Comparative Physiology,” p. 665.
[†]Ditto, p. 686.
[∗]Carpenter's “Principles of Comparative Physiology,” p. 689.