Front Page Titles (by Subject) CHAPTER XI.: THE PERCEPTION OF BODY AS PRESENTING STATICO-DYNAMICAL AND STATICAL ATTRIBUTES. - The Principles of Psychology
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CHAPTER XI.: THE PERCEPTION OF BODY AS PRESENTING STATICO-DYNAMICAL AND STATICAL ATTRIBUTES. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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THE PERCEPTION OF BODY AS PRESENTING STATICO-DYNAMICAL AND STATICAL ATTRIBUTES.
§ 53. If we imagine a human being without sight, hearing, taste, smell, or the sense of temperature, and having no channels through which to receive impressions of the outer world, save the tactile and muscular senses; then the only attributes of body cognizable by him, will be the statico-dynamical and the statical. All the knowledge which he can gain of things, by touching, pressing, pulling, and rubbing them, and by moving his limbs or body, or both, in contact with them, comes under these heads: the one comprehending that knowledge gained by an activity on his part, and a reactivity on the part of the things; the other comprehending that knowledge gained by his independent internal activity in putting together certain of the impressions he has received,—knowledge in respect of which the things themselves are altogether passive.
These statico-dynamical and statical attributes of body are usually presented to consciousness closely united. When in the dark any object is examined by the hands, more or less definite perceptions of its softness, smoothness, elasticity, &c., are joined with more or less definite perceptions of its position, size, and form. These two classes of perceptions may accompany each other with various degrees of incompleteness: but some connection between them is invariable. As will hereafter be shown, it is questionable whether primordially they are perceived in this relation; but without doubt by the adult human consciousness, all tactile resistances are unconditionally known as coexistent with some extension; and all tactile extensions are unconditionally known as coexistent with some resistance.
In pursuance of the method hitherto followed, we have now to analyze one of these complex tactile perceptions in its totality. And as in the last chapter we directed our attention mainly to a certain contingent class of attributes, and their relations to these essential ones, with a view of subsequently leaving them out of consideration; so here, it will be best to treat more especially of the resistance-attributes, so that having examined the mode in which we perceive them and their relations to the extension-attributes, we may proceed to deal with the extension-attributes by themselves.
§ 54. Observe in the first place, why these resistance-attributes which have been termed secundo-primary, may be more appropriately termed statico-dynamical. They are all of them known as manifestations of mechanical force. They are all, considered in themselves, the results of attraction, or repulsion, or that property of body in virtue of which its reaction upon a disturbing agent varies as the quantity of motion which that disturbing agent impresses upon it.∗ They are the attributes of body involved alike in its standing and in its acting. That capacity which matter has of passively retaining, while undisturbed, its size, figure, and position, may rightly be regarded as statical; while that capacity which it has of opposing a counteracting force to any force brought to bear upon it, must be considered as dynamical; and the fact that these capacities cannot be dissociated, but are two sides of the same capacity, is expressed by uniting the descriptive terms. The duality of aspect demands duality of name. Add to this, that if we class those attributes in respect of which the object is active while the subject is passive, as dynamical; and if we class as statical, those in respect of which the subject is active while the object is passive; then we must class as statico-dynamical, those in respect of which subject and object are both active.
These attributes that have for their common element some manifestation of mechanical force, and that are severally known to us through impressions of which resistance is the essential element, are more numerous than would be supposed. The opposition which objects offer to force tending to raise them—their weight—originates only the attributes of Heavy and Light; which simply indicate certain relative amounts of gravitative force. But the opposition which objects offer to compression or extension, is distinguishable, not only in its relative amounts, but in its kinds. Of bodies that resist in different modes as well as in different degrees, we have the Hard and Soft; the Firm and Fluid; the Viscid and Friable; the Tough and Brittle; the Rigid and Flexible; the Fissile and Infissile; the Ductile and Inductile; the Retractile and Irretractile; the Compressible and Incompressible; the Resilient and Irresilient; and (combined with figure) the Rough and Smooth.∗ Of these pairs of attributed qualities, several are purely relative—are simply degrees of the same. This is manifestly the case with Hard and Soft, Firm and Fluid, Compressible and Irrecompressible. But there are some, as Ductile and Inductile, which are not united by insensible gradations.
To determine the modes in which we perceive these attributes, it is requisite that we should first consider the several distinct sensations resulting from the direct action of body upon us; together with those which accompany our direct action upon body. There are two in respect of which body is active, and we are passive; and two in respect of which we are active and body is passive. Those which we may class as of objective origin, are the sensations of touch and pressure: those which originate subjectively are the sensations of muscular tension and muscular motion. Let us consider them seriatim.
When one of the fingers is brought very gently in contact with anything; or when a fly settles upon the forehead, or a hair gets into the mouth; we have the sensation of touch proper. This sensation is undecomposable—is not accompanied by any sensation of pressure; and though we always ascribe it to some object capable of exercising more or less resistance, we cannot properly say that the resistance is given in the sensation. Though we know the sensation to be caused by mechanical force, it is not immediately, but mediately, that we know this. Mechanical force is immediately knowable to us only as that which opposes our muscular action; and as, in this case, muscular action is not called forth, mechanical force can only be inferred.
If the hand be opened out upon the table, and a weight be placed on one of the fingers, there results the sensation of pressure, which is clearly distinguishable from the last. In most of our tactile impressions, the two are so mixed as to be with difficulty discriminated. But if we compare the feeling caused by a fly on the forehead, with that caused by a weight on the finger, we shall perceive that no increase in the intensity of either will produce the other. And that the two differ not in degree but in kind, will be yet more clearly seen on remembering that the sensation of tickling, which a continuity of touch proper produces, is the strongest when the touch is extremely light; and that when the touch becomes heavier, the sensation of tickling wholly ceases, and is replaced by another. Contrasting them physiologically, we may presume that the sensation of touch proper results from a stimulation of the nerves of the skin, while that of pressure results from a stimulation of nerves in the subjacent tissues; that hence, by very gentle contact the nerves of the skin are alone affected, while by a rougher contact the nerves of both are affected; that consequently, in passing from gentle to rough contact by degrees, the single feeling at first experienced becomes masked by another feeling that arises by insensible gradations; and that thus results the habitual confusion of the two. It remains to be noticed that the sensation of pressure, though often associated with that of muscular tension, often exists apart from it; as in the example above given, and as in our ever-present experience of the reactive pressure of the surface supporting our bodies.
The sensation of muscular tension also, is capable of existing separately from the others. On raising the arm to a horizontal position and keeping it so, and still more on dealing similarly with the leg, a sensation is felt, which, tolerably strong as it is at the outset, presently becomes unbearable. If the limb be uncovered, and be not brought against anything, this sensation is associated with no other, either of touch or pressure.
Allied to the sensation accompanying tension of the muscles, is that accompanying the act of contracting them—the sensation of muscular motion. Concerning the state of consciousness induced by muscular motion, and concerning the ideas of Space and Time which are connected with it in adult minds, something will be said hereafter. For present purposes it will suffice to notice, that while, from the muscles of a limb at rest no sensation arises; while from the muscles of a limb in a state of continuous strain, there arises a continuous sensation which remains uniform for a considerable time; from the muscle of a limb in motion, there arises a sensation which is ever undergoing increase or decrease or change of composition.
The several sensations thus distinguished, and more particularly the last three, are those which, by their combination in various degrees and relations, constitute our perceptions of the statico-dynamical attributes of body. Let us consider some of these perceptions as thus constituted.
§ 55. When we express our immediate experiences of a body by saying that it is hard, what are the experiences implied? First, a sensation of pressure of considerable intensity is implied; and if, as in most cases, this sensation of pressure is given to a finger voluntarily thrust against the object, then there is simultaneously felt a correspondingly strong sensation of muscular tension. But this is not all: for feelings of pressure and muscular tension may be given by bodies which we call soft, provided the compressing finger follows the surface as fast as it gives way. In what then consists the difference between the perceptions? In this; that whereas when a soft body is pressed with increasing force, the synchronous sensations of increasing pressure and increasing muscular tension are accompanied by sensations of muscular movement; when a hard body is pressed with increasing force, these sensations of increasing pressure and tension are not accompanied by sensations of muscular movement. Considered by itself then, the perception of softness may be defined as the establishment in consciousness of a relation of simultaneity between three series of sensations—a series of increasing sensations of pressure; a series of increasing sensations of tension; and a series of sensations of motion. And the perception of hardness is the same with omission of the last series. As, however, hardness and softness are names for different degrees of the same attribute, these definitions must be understood in a relative sense.
Take again the attribute of resilience, as displayed in such a body as indian rubber. The perception of it manifestly includes as one component, the perception of softness; but it includes something more. While, when the finger is thrust against some soft but irresilient body, as wet clay, the three simultaneous series of sensations of pressure, tension, and motion, are followed (on the withdrawal of the finger) by sensations of motion only; when it is thrust against a piece of indian rubber, these three simultaneous series of sensations are followed by three other series in the reverse order. Following the retiring finger, the indian rubber gives a decreasing series of sensations of pressure, and a decreasing series of sensations of tension. Thus the perception of resilience is definable as the establishment in consciousness, of a relation of sequence between the group of co-ordinated sensations constituting the perception of softness, and a certain other group of co-ordinated sensations similar in kind but opposite in order.
The perceptions of roughness and smoothness, referring as they do, not to the degree or kind of cohesion subsisting among the particles of a body, but to the quality of its surface, have little in common with the foregoing. The motion by which either of them is gained, is not in the line of pressure; but at right angles to it. The accompanying sensations of pressure, or of touch proper, do not form either an increasing or a decreasing series; but are either uniform (as when smoothness is perceived) or irregularly varied (as when roughness is perceived). The perception of smoothness, then, consists in the establishment in consciousness of a relation of simultaneity between a special series of sensations of motion, and a uniform sensation of touch proper, or pressure, or both. While in the perception of roughness, the like sensations of motion are known as simultaneous with a broken series of sensations of touch, or pressure, or both.
It is as unnecessary as it would be tiresome, thus to analyze our perceptions of all the statico-dynamical attributes above enumerated. What has been said renders it sufficiently manifest, that they severally consist in the establishment of relations of simultaneity and sequence among our sensations of touch, pressure, tension and motion; experienced as increasing, decreasing or uniform; and combined in various modes and degrees: and this is all which it here concerns us to know.
§ 56. Passing from these preliminary analyses to the general subject of the chapter—the perception of body as presenting statico-dynamical and statical attributes, or in other words—the perception of body obtained through the tactile and motor organs alone; we find that it is made up of the following elements. The relations between subject and object, of coexistence in time and adjacency in space; the combined impressions which make up our ideas of a more or less specific size and a more or less specific shape; the further impressions included in our notions of surface; those included in our notions of texture; and those many others signified by the terms ductility, elasticity, flexibility, &c.—all of them referred to one place in time and space. Not to dwell upon these several constituents of the perception, which were to some extent incidentally described in the last chapter, it now remains to specify more definitely than before, the kind of union subsisting among them. When in the dark the presence of some object is revealed to us by accidental collision, we have, along with certain unexpected sensations of pressure and muscular tension, a more or less vague conception of a something extended; and, as previously explained, this relation of coexistence between resistance and extension is unconditional—is independent alike of the will of the subject and the quality of the object. But if the nature of the object is to be ascertained, its reactions must be called forth by certain appropriate actions of the subject. The sensations it gives us must become known as sequent to certain sensations we give ourselves. There must be particular kinds of volition and the particular changes of internal state that follow them, before the changes resulting from external impressions can be received. It is true that some of the resistance-attributes, as hardness and softness, usually become involuntarily known in the act of collision; though this is not necessary, seeing that when moving with outstretched hands, the gentlest touch suffices to prove to us that there is something, before yet we can know aught of its nature. But to determine whether the body is rough or smooth, flexible or rigid, ductile or inductile, &c. manifestly presupposes subjective activities of a complicated kind: and the modifications of consciousness accompanying these, must become essential elements of the perceptions. Hence, a statico-dynamical attribute is perceived through a union of internally-determined impressions with externally-determined impressions; which combined group of impressions is known as the consequent of those internally-determined impressions constituting volition.
Defined in its totality then, the perception of body as presenting statico-dynamical and statical attributes, is a composite state of consciousness, having for its primary elements the impressions of resistance and extension unconditionally united with each other and the subject in relations of coincidence in time and adjacency in space; having for its secondary elements the impressions of touch, pressure, tension, and motion, variously united with each other in relations of simultaneity and sequence that are severally conditional on the nature of the object and the acts of the subject, and all of them conditionally united with the primary elements by relations of sequence; and having for its further secondary elements certain yet undefined relations (constituting the cognitions of size and form, hereafter to be analyzed), which are also conditionally united alike with the primary elements and the other secondary elements.
Such being the constituents of the perception, it only requires to remind the reader that, as shown at length in the last chapter, the act of perception consists in the classing these constituents, each with others of its own order. No one of them can be known for what it is, without being assimilated to the before-known ones which it resembles. And from the classing of each impression with like remembered impressions; each relation with like remembered relations; and each condition with like remembered conditions; results that classing of the object in its totality which is synonymous with a perception of it.
[∗]I use this awkward circumlocution to avoid an inaccuracy. Among the sources, physically considered, of the secundo-primary attributes, Sir William Hamilton enumerates inertia. But inertia is not a force: it is simply the negation of activity. It is not a positive attribute: it is a purely negative one. There is a very general belief that matter offers some absolute opposition to anything tending to displace it. This is not the fact. Take away all extrinsic hindrance—all friction, all resisting medium—and an infinitesimal force will produce motion; only the motion will be infinitesimal, in consequence of the law that the velocity varies as the momentum (or force impressed) divided by the mass. Were inertia a force, all the calculations of astronomers respecting planetary perturbations and the like, would be erroneous. The term vis inertiœ is a misnomer.
[∗]With some exceptions this is Sir William Hamilton's classification. I do not, however, separate, as he attempts to do, the atributes which (physically considered) imply atomic attraction (as the Retractile) from those which imply atomic repulsion (as the Resilient); because, in reality, all of them imply both. As there is a balance of the molecular attractions and repulsions in an undisturbed body, so, a body cannot have any of its atoms disturbed by an external force, without both the attractive and repulsive forces coming into active opposition. On examining the fracture of a piece of wood broken transversely, part of the area will be seen to exhibit marks of tension, and part of compression (in wood about 3/8 and 5/8 respectively); and the line dividing these areas is called the “neutral axis.” A body cannot exhibit ductility or retractility without being partially thrown into a state of compression; seeing that, until parts are compressed, the extending force cannot be applied to the body.