ND   Jacques Maritain Center : Psychology / by Michael Maher, S.J.



Growth of Knowledge. -- The true account of our cognition of the external world is that which maintains the doctrine of immediate perception -- that in some of its acts the mind directly apprehends a material reality other than itself; but there is no incompatibility between this theory and the admission that in the percipient acts of mature life there are involved many results gathered by association, and numerous mediate inferences of a more or less complicated nature. The advocate of immediate perception is not committed to the doctrine that the eye of itself immediately apprehends something presented to its view as a solid brick house situated at a hundred yards distance, nor that touch from the beginning makes known a particular sensation of pressure as due to a squeeze of the foot. The apparently simple cognitions which succeed each other from moment to moment in mature life, contain certain primary data which have been immediately presented to the senses; but a large fraction of the whole is, in most cases, built up out of contributions furnished by imagination and memory. The variety of the elements involved, and the plurality of the stages comprised in these brief acts of knowledge, have been dwelt on at copious length by many modern psychologists, and elaborate descriptions of the gradual development of apprehension by the "aggregation," "segregation," and "integration" of sensuous "ingredients" into the final product, the perceived thing, are very familiar to the reader of English philosophical literature.

Intellect usually ignored. -- In spite, however, of the seeming exhaustiveness of these analyses one all-important factor is almost invariably omitted. Intellect, in its old and proper signification, as a higher rational activity superior to sense, awakened, indeed, to exercise by the latter, but transcending its range -- Intellect, thus understood, is ignored. Yet it is precisely this faculty which makes intelligible the stream of change disclosed in sensation. The formal object of sense is the concrete quality of the individual thing, and it is percipient of successive changes and co-existing accidents; but it cannot apprehend the being or essence of things; it is blind to the causality of agents, and to the substantiality of objects; and of those numerous relations of identity, similarity, unlikeness, dependence, and the rest, which form the universal frame-work, the rational tissue, of our knowledge, it can give no account. A creature endowed merely with sensibility conld never come to know itself as a person, to apprehend itself as an abiding ego, and to set itself in contrast and opposition to an objective world. Nor could it come to truly cognize any portion of the external universe, any more than itself as a being. Now in normal perception these sensuous and intellectual elements are closely interwoven, and it may require careful attention and reflexion to separate them; but none the less are they radically different in kind. As, however, the plan of our work requires us to treat of intellectual activity by itself, we will in the present chapter devote ourselves mainly to the exposition of the development of the sentient factor in the process, although, of course, in man's actual experience sense and intellect are not thus isolated.

Complexity of perceptional process. -- Before beginning, an example may be useful to show the reader unfamiliar with psychological analysis, that seemingly simple perceptions are really complex. Walking in a field, I become suddenly conscious of a familiar sound, and exclaim, "I hear my big, white dog barking in the road on my right about eighty yards away." But a little reflexion will convince me that the sense of hearing contributes only a small share to such a percipient act. Of the distance, direction, size, and colour of the agent which has caused the noise, my ear of itself can tell me nothing. It merely presents to me an auditory sensation of a particular quality, and of greater or less intensity; the remaining elements of the cognition are reproductions of past experiences. Similarly in other cases, unnoticed inferences, and faint associations furnished by the rest of the senses, attaching to the direct testimony of each particular faculty, simulate after a time the character of immediate revelations of the latter. These indirect or inferential cognitions may be styled the acquired perceptions of the sense in question. It is the office of the psychologist carefully to analyze these into their primitive elements, to ascertain what are the ultimate data afforded by each sense, and to trace the chief steps in the process by which the elaborate result is reached.

Development of Tactual Perception. -- Although in describing the general features of the different senses viewed as mental powers, the order of treatment adopted was unimportant, here in tracing the development of perception it is a matter of great moment to follow as closely as possible the natural order in which de facto the several faculties come to offer their contributions.{1} Accordingly we will commence with the sense of touch, including under it tactual sensations proper, feelings of pressure, and muscular sensations, whether of resistance or of movement. It seems to us a mistake in this connexion to endeavour to separate the consciousness of pressure from that of mere contact. The isolation is purely ideal. The difference between them is one of degree, and in the actual experience of the child sensations of touch, so far as they are of any psychological significance, involve feelings of pressure. The consciousness of resistance to active effort put forth, indeed, implies a new element, and facilitates the apprehension of something other than self given in the recipient sensation of passive pressure, but even this latter state makes us directly cognizant of extra-mental reality. Starting then with the sense of touch, naturally the first question which meets us is: How do we come to know the spatial relations of the several parts of our own person?

Localization of Sensations. -- In mature life we instantaneously localize an impression in the point of the body{2} irritated; and some writers maintain that the affirmation of consciousness is of such a character that his reference of a feeling to the part excited must be a natural endowment possessed from the beginning. But what precisely is meant by saying, "I feel a pain in my foot"? The statement at once calls up a visual image of the member affected; and it further presents this image at about five feet in a nearly vertical line from my eyes. However, as distance cannot be directly apprehended by the eye, but is known primarily through muscular sensations of movement, and as the visual image of my foot is certainly not given in the painful feeling of pressure, the first consciousness of such a sensation could not have been similar to this. We are not born with an innate idea or representation of our person. Aristotle, long ago, taught that all knowledge starts from experience, and the topography of our own body is no exception to the rule. By observation and experiment, and not through any a priori endowment, we have come to learn the shape and appearance of our organism, and to know the definite locality on the visual map to which a particular tactual stimulation is to be referred.{3}

Tactual Cognition of the Organism. -- Although the extreme "nativistic" theory is thus erroneous, exaggerated empiricism rushes into an equally false opinion when it refuses to admit the presence of any element of a local character, or any presentation of extension in our primitive sensations of contact. The true doctrine, as usual, lies between the extreme views. Impressions of extended objects are given from the beginning as extended, and bearing a local reference, but of an extremely vague and indefinite character. From the apprehension of purely unextended sensations the notion of extended matter cannot be formed, and in this respect the cognition of the spatial character of our own body stands in the same situation as the rest of the material world. The extended nature of the organ is given simultaneously with that of the extended surface pressing upon it, but as we have said, this primitive presentation is very ill-defined.{4}

Local Signs. -- Of the shape or quantity of the surface covered our knowledge is at first almost infinitesimal, whilst of the local relations between the point affected and the rest of our person we necessarily as yet know nothing. Nevertheless the character of an impression is largely dependent on its situation; the pressure, for instance, of the same object across the fingers, the palm, the fore-arm, on the head, and on the calf of the leg possesses in each case a certain distinctive feature. Further, this variation in the aspect of the mental state is in proportion, though not in a constant proportion, to variation in locality. Thus, if the same stimulus be applied to two points on the arm, separated by a short interval, the sensations aroused will contain a certain difference of character, which will increase if the intermediate distance be increased; similarly with impressions on the fingers, though here change in the sensation is more rapid in proportion to variation of locality. Assuming the faculty of apprehending extended impressions over the surface of the body, and this "local colouring," which marks the sensibility of the different parts affected, if an object is moved along the skin from one locality to another, the capacity of the intermediate region for tactual sensations is discovered.

The terms, local sign, and local colour, have been used by Lotze to designate a purely subjective quality varying with the part of the organism affected, and attached to the purely subjective non-spatial presentations of sense. These local signs become symbols of the muscular sensations of movement required to pass from one sensitive point to another, and by their means out of mental states, individually revealing no element of extension, the notion of space is alleged to be built up: Lotze thus advanced beyond the empiricism advocated by Dr. Bain, Mill, and other English sensationalists, in admitting the necessity of more than mere tactual and muscular sensations. But the local signs cannot generate, though they may be of great value in defining our notion of space. A direct presentation of extension must be somehow afforded as material to work upon,

Sensations of Double-Contact. -- It is probably, however, the experience of double-contact, which contributes most to the definition of the relative situation of the several parts of the organism. If a child lays his right hand upon his left there is awakened a double tactual feeling of extension. If he then moves the right palm along the left arm up to the elbow or shoulder be becomes conscious of a series of muscular sensations in the right arm, and also of a series of extended tactual impressions both in the right hand and along the left arm, which vary in character as they depart farther from the original sensation in the left hand. This movement may be then reversed and the tactual sensations gone through in the opposite direction; and finally by laying the left arm along a flat surface, or vice versa, the series of tactual impressions, formerly given in succession, will now be presented as co-existing outside of each other in space. When these or kindred experiments have been executed a few times, the difference in character of the tactual impressions on two points of the arm awaken by association a representation of the number of tactual sensations and of the duration of the series of muscular sensations required to span the interval, and their relative situations are so far defined. In this way a blind child would rapidly gather by experience a tolerably accurate knowledge of the configuration of its body, and of the relative positions of its varying forms of tactual sensibility. The localization of impressions would become more definite in the parts capable of being easily explored by means of sensations of double contact, while the outlying districts would be known in a less perfect way.

Combination of Touch and Sight. -- Still, it is sight which, normally speaking, presents to us the rich realities of space. Apprehending in a simultaneous act a large space of the surface of the body, the eye far surpasses in efficiency the consciousness of double contact, while it supplements the latter experience as a third witness in a multitude of observations. As our education advances the visual image of the point of the organism stimulated becomes more intimately associated with the local colouring of the tactual sensibility of that point, and the map of the sense of touch is translated into that of sight.

Tactual Cognition of other Extended Objects. -- Together with progress in our knowledge of our own body proceeds our education as regards the material world outside; every increment of information in the one department is a corresponding gain in the other. Abstracting again from vision, when the child lays his hand flat on some object before him, suppose a book, he becomes conscious of an extended impression. By moving his hand he experiences two concomitant series of tactual and motor sensations. When he reaches the edge of the surface the tactual sensations cease, and then reversing the operation he may reproduce them in opposite order. After a few such experiments, he would come to know in a rough way the number of units of tactual or motor sensations necessary to pass from the first to the last impression of contact, and he would thus have a measure of the length or breadth of the book. Suppose he then takes the volume between his two hands or fingers, he will discover that it presents several resisting surfaces, and some further experiments in the way of tactual and muscular feelings define his knowledge of its solidity and weight.

Here, again, as before, to the normally endowed being, the visual images presented by sight of the objects touched and handled enormously facilitate progress, and gradually enable him to infer the temperature, magnitude, solidity, and weignt of things at a distance. This mode of education is going on in one shape or another every movement of his waking existence, and consequently his perception of the objects in his immediate vicinity very soon becomes tolerably accurate.

Permanent existence of Material Objects. -- The several members and parts of his own body permanently present as the centre of his pleasures and pains, and the subject of his sensations of double contact, are known to be very different from all other objects. These latter by their repeated recurrence to his notice in like circumstances, by the frequently confirmed experience that he can renew his acquaintance with them at will, and by their regularity in producing their effects, whether observed or unobserved, first evoke a dim belief, and then a rational conviction as to their abiding existence when beyond his view. Consequently, at a very early stage in his existence he becomes alive to the fact that his nurse, his bed, his food, and other objects of interest are not annihilated every time he closes his eyes.

Inferential knowledge of other Minds. -- Among external objects a class particularly interesting for the child are organisms like in shape to his own. These bodies, moreover, react by movement in response to stimuli just as he himself does. But in his own case his consciousness assures him that mental states are the effects of similar stimulation and the causes of similar movements. Consequently, by analogy he infers that mental existences like his own are present in other human bodies. Language is indeed the strongest evidence for the reality of other human minds, but even when it is absent, as in the case of the lower animals, the argument is felt to be irresistible.

These other human minds can now in turn afford valuable corroboratory evidence concerning the objective existence and permanence of material objects when doubts as to the possibility of illusion are awakened.

Secondary acquisitions. -- We have spoken so far of the essential capabilities of touch: a word may he of interest now on the special or accidental acquirements of this percipient faculty. The degree to which the sense of touch can be cultivated, and the fineness of the capacity of both muscular and tactual sensations for being discriminated appear truly amazing when thoughtfully considered. The miller can by the sense of feeling distinguish variations in the quality of flour utterly invisible to the eye. The clothier can recognize subtile differences in the texture of silk, linen, or velvet, of an equally minute character. In such universal attainments as those of speaking, reading, writing, playing the piano, shaving, and indeed in all mechanical arts, the most delicate sensibility is exhibited. These actions involve a complicated series of movements under the guidance of muscular and tactual sensations which are distinguishable by differences so faint that we are fairly lost in astonishment at the infinitesimal forces governing thus infallibly the seemingly easy process.

It is in the blind, however, that this sense reaches its proper perfection. By them space is known and remembered solely in terms of tactual and motor experience. Their attention is concentrated on this field of cognition, and their powers of memory devoted to its service. The increased exercise and cultivation of the remaining senses when sight is in abeyance, has the effect of developing these faculties in an extraordinary manner, and none of them more so than that of touch. The blind, for instance, who have been taught to read, can decipher the contents by passing their fingers rapidIy over type not much larger than the print of the present work, with a facility that seems incredible to their more fortunate brethren who make the attempt. Dr. Carpenter relates of Laura Bridgman, the well-known deaf and dumb mute, that she unhesitatingly recognized his brother "after the lapse of a year from his previous interview by the 'feel' of his hand."{5} She estimates the age and frame of mind of her visitors by feeling the wrinkles of their face, and it is said that she can even perceive variation in intensity and pitch of voice by feeling the throat.{6} John Metcalf, the celebrated blind road-maker, was deemed an excellent judge of horses. When a lad he was a favourite guide through the lanes and marshes of his native county. As a young man he followed the hounds on horseback across country, and on one occasion won a three mile race round a circular course. These latter feats, however, were performed rather by the sense of hearing than of touch. To guide him in the race, he placed a man with a bell at each post; and in the hunting-field the cry of the hounds, the intelligence of his horse, and his knowledge of the country enabled him to keep a leading place.{7}

Visual Perception. -- As the formal object of sight is merely coloured surface, the eye cannot originally inform us of distance. This faculty, even more than that of touch, has constituted a battleground for the "nativistic" and "empirical" theories. The more thoroughgoing nativists have held that the eye, or rather the visual organ consisting of both eyes, has from the beginning the power of immediately or intuitively apprehending the distance and relative situation of objects, just as well as the ability of perceiving differences of colour. Empiricists, on the other hand, deny to the eye all native capacity of cognizing extension in any form. According to their view, it is only by experience and association that ocular sensations, which in themselves bear no more reference to space than feelings of sound or smell, are gradually construed into extended solid objects. Here again, as before, it will be found that truth lies in the mean. The primary perception of the eye is simply coloured surface; neither distance, solidity, nor absolute magnitude is originally presented to us by this sense. These are secondary or acquired perceptions, gained by associating in experience various shades of colour, and degrees of tension in the ocular muscles, with different motor and tactual experiences. But surface space is originally perceived directly.

The original presentation of superficial extension is very vague. The central point of the retina is most sensitive, and the shape of an external surface, e.g., of a triangle, is defined by moving the line of direct vision round its outline. The relative situation of the parts subtending different points on the retina, and the intervals of space between them, vaguely presented by the quantity of intermediate distinct sentient points, similarly receive accurate determination by means of the muscular sensations involved in bringing the central axis of the eye to bear on them. In sight, as in touch, Lotze amends the empirical doctrine by the hypothesis of "local signs." Though the sensations of different points of the retina are qualitatively different, he holds that there is originally no presentation of extension. By association the qualitative mark of any spot awakens a representation of the quantity of muscular sensation requisite to direct the central point towards the object subtended by that spot, and this, he teaches, is all that spatial distance means. Greater or less space is, in fact, merely the possibility of more or fewer muscular feelings. (Cf. Metaphysic, Book III. c. iv.)

Here again, as in the development of tactual perception the hypothesis of "local signs" may be accepted as a means of explaining the determination of the relative positions and comparative magnitudes of objects within the extended field of vision, but it cannot account for the original presentation of extension itself.

Immediate Perception of Surface Extension. -- The argument used to establish the direct perception of extension by D'Alembert, Hamilton, and others, has never been really answered. We will adopt Dr. Porter's enunciation of the proof: "If two more bands of colour were present to the infant which had never exercised touch or movement, it must see them both at once; and if it sees them both, it must see them as expanded or extended; otherwise it could not see them at all, nor the line of transition or separation between them. Or if a disc of red were presented in the midst of and surrounded by a field of yellow or blue, or if a bright band of red were painted so as to return as a circle upon itself, on a field of black, the band could not be traced by the eye without requiring that the eye should contemplate as an extended percept the included surface or disc of red."{8}

Experimental evidence. -- This demonstration is reinforccd by the direct evidence of a number of experiments tried on persons who had late in life been couched for cataract. The testimony from this line of investigation is unhappily not yet in as satisfactory a condition as could be desired. it is a significant comment on the lofty claims of some physiological psychologists to find that the experiments on Cheselden's patient still receive a leading place among the most recent text-books. In spite of the supposed enormous and fruitful advances of physiological psychology, that venerable and oft-recounted incident, now nearly one hundred and seventy years old, and claimed by both sides, is still amongst the least unsatisfactory cases we possess. The best experiment, however, on the whole, seems to be that of Dr. Franz, of Leipzig (1840). In the operations of both Franz and Cheselden the subjects were intelligent boys of seventeen and eighteen years of age. When, after the cataract had been removed, the eyes of the patients were sufficiently healed to be exposed to the light, a series of observations and experiments were instituted in order to ascertain exactly how much they could directly perceive by their newly-received faculty. The points of importance best established were: (1) that the newly-acquired sense presented to the mind a field of colour extended in two dimensions of space; (2) that it did not afford a perception of the relative distances of objects, all being apprehended in a confused manner as in close proximity to the eye; (3) and that, consequently, no information was given as to the absolute magnitude of things. (4) In Franz's case, where the investigation was more skilfully conducted than on the earlier occasion, the patient recognized the identity between horizontal and perpendicular lines now seen by the eye and those formerly known by tonch. He could similarly recognize square and round figures, though he could not distinguish these from solid cubes and spheres.{9}

Analogical argument. -- The force of the evidence in favour of the immediate apprehension of space of at least two dimensions by the human infant is still further increased by the fact that several of the lower animals are now proved to possess a perfect appreciation of even three dimensions of space at birth. Mr. Spalding established intuitive perceptions in the case of chickens by covering their eyes with hoods as soon as they left the shell, and so preventing all visual experiences until they were strong enough for various experiments. When the hoods were removed they immediately showed their appreciation of spatial relations. "Often at the end of two minutes," says Mr. Spalding, "they followed with their eyes the movements of crawling insects, turning their head with all the precision of an old fowl. In from two to fifteen minutes they pecked at some speck or insect, showing not merely an instinctive perception of distance, but an original ability to judge, to measure distance, with something like infallible accuracy. . . . They never nsissed by more than a hair's breadth, and that too, when the specks aimed at were no bigger, and less visible, than the small dot of an i."{10} He shows a similar power of intuitive perception to be possessed by young pigs and some other animals physically well developed at birth. This evidence of some sort of intuitive apprehension of space of three dimensions demonstrates in a striking manner the absurdity of the implicit assumption in associationist accounts of the subject that immediate vision even of surface extension is impossible.

Mediate perception of Distance and Magnitude. -- That the human eye has not originally the capacity of estimating distance is shown by such experiments as those just cited; and by the fact that in mature life in unusual circumstances, as for instance, at sea, we feel at a great loss when we attempt to judge the length of considerable intervals of space. The simple experiment of closing one eye, especially when entering an unfamiliar room, also shows how imperfect is our purely visual appreciation of distance. And the various illusions of painting, of the diorama, and of the stereoscope, all go to prove the truth that the apparently immediate apprehension of the third dimension of space by sight is really an acquired perception, which involves a rapid process of inference from numerous visual signs.

In developed perception there are engaged many factors whose presence and action are commonly ignored. Starting from an originally indefinite apprehension of extended coloured surface, we find that different perspective appearances, shades of colour, and degrees of tension in the ocular muscles are associated with longer or shorter distances to be moved through in order to touch the coloured object. After a sufficient number of experiences the visual appearance suggests the appropriate amount of movement, and the former becomes the symbol of the latter. The chief elements in the process seem to be the following:

1. Focal adjustment.{11} -- The single eye is subject to different muscular sensations according to the varying distance of the object up to an interval of twenty feet. This is due to the self-regulating action of the ciliary muscle, which increases or decreases the convexity of the crystalline lens so as to adjust the focus to a shorter or longer range.

2. Axial adjustment. -- The muscular sensations awakened by converging the axes of both eyes to meet in a point, vary according as the object is nearer or farther within a space of two hundred yards.

3. Mathematical perspective. -- The size of the retinal image and the apparent size of an object change with the distance of the latter; consequently, if its real magnitude is already known, we have the means of determining how remote it is. It is for this purpose the painter is accustomed to introduce the figure of a man or of some well-known animal into the foreground of his pictures.

4. Aerial perspective. -- Finally, changes of colour, and the greater or less haziness in the outlines of objects becomes by experience the signs of a longer or shorter interval between them and us.

Our visual perception of the magnitude of an object is an inference from its apparent size and presumed distance, and most of the steps just given may enter into the estimate. Thus, in judging the dimensions of an unfamiliar object, such as a rock, or a mound of earth afar off, we are led to form an idea of the length of space, intervening by the number and apparent magnitude of known objects between us and the point in question, by the apparent size of other known figures, such as those of men or animals situated in its vicinity, and by the clearness or mistiness of the outlines of the object and of its neighbours. Having thus estimated the distance we infer the real from the apparent magnitude of the object.

Mutual aid of Sight and Touch. -- The education of the sense of sight proceeds concomitantly with that of the faculty of tactual and motor sensations. Mutually aiding each other their progress is very rapid. The advantages gained by touch through the consciousness of double-contact are now largely increased by the addition of a power which can apprehend in an instant the entire contour of the body, and the situation of the various agents acting upon it. The length of the sweep of the arm or leg are known not merely in the dim terms of subjective motor feelings, but through the fine visual perceptions of space. The wide range of the eye, and those other numerous excellences which have been detailed in describing this sense, confer upon its acts the power of arousing with marvellous facility and speed the representation of associated tactual and muscular sensations. By this singularly perfect appropriation of the acquisitions of touch, vision is enabled tp inform us in an easy, rapid, and admirable manner of a multitude of the tangible properties of things which we could never, or but by an incredible amount of labour, ascertain through actual contact. At the same time, the control of the organ of sight is secured by the ciliary muscles; and while we watch the movement of the arm, the muscular sensations of the eye reveal the quantity of change in its own direction, the degree of convergence of the optic axes, and the increase or decrease in the convexity of the crystalline lens. In this way by the mutual co-operation of the two faculties our knowledge of the most important attributes of matter is elaborated.

Vision, unlike touch, taste, and smell, does not seem to be capable of much advance in range or refinement beyond what it normally reaches. The skill with which the Indian can follow a trail and the sailor recognize an object at sea seem among the most remarkable effects of special education of this sense. Unlike the other faculties, sight is normally developed almost up to its full maximum efficiency.

Binocular Vision. -- A large district of the spatial scene apprehended by sight is common to both eyes, but the outskirts on either side extend beyond the binocular field of vision, and can be reached only by a single organ. In the perception of distant objects within the common field there is ordinarily formed on each of the retinas a similar picture, but things seen in our immediate neighbourhood offer a different appearance to the right and to the left eye. This fact has given rise to the problem of single vision. Why with two eyes do we not see two objects instead of one? Various explanations have been suggested. One view supposes that we originally saw double, but by experience have learned to assign the two images to a single cause. Another maintains that the two eyes form really but one organ. There are, it is held, "identical or corresponding points" on the two retinas, and pairs of nerves running from these to the brain coalesce, so that the two stimuli are fused into a single final excitation awakening but one sensation. Other writers have asserted that although the two eyes see different pictures yet, at any given time, we attend only to one.

As regards the last hypothesis it is undoubtedly true that one eye is commonly more active than the other, and most people will find that the right is more efficient than the left; still it is going beyond the evidence to assume that our attention is normally so concentrated upon the activity of one eye that the other may be thrown out of account. In favour of the second view may be urged the authority of several distinguished German physiologists starting with Muller fifty years ago, who consider the anatomical evidence to be on the whole in support of the physical explanation. It is also maintained that if the two retinas were really subjects of two distinct sensations, careful reflexion and examination of our consciousness ought to enable us to distinguish them. Finally, it is held that the analogy in the case of young animals constitutes a forcible argument. If the two eyes are co-ordinated so as to originate a single perception from the beginning in these latter, as is undoubtedly the case, it is reasonable to suppose, where there in no positive evidence to the contrary, that the same holds for the young infant.

On the other side it is argued: (a) That more accurate knowledge of anatomy does not hear out the nativistic position. (b) That points physiologically not "corresponding" sometimes give rise to a single perception, whilst on other occasions points that ought to correspond excite double vision. In abnormal conditions, such as squinting, where the derangement is permanent, vision is single, in spite of the non-correspondence of identical points, and when the irregularity has been removed by surgical means, so that the two axes get into a normal position, double vision arises for a time, but by continued experience passes again into single vision. (c) Some writers contend that the "conflict or rivalry of the retinas," which takes place when the two eyes are made to contemplate different colours, is in favour of the empirical theory. If there was a real physical fusion of the nerve currents from the retinas to the brain, then we ought to have a sensation of an intermediate character and not, as is the case at present, an alternative struggling sensation of each. A modification of this experiment, however, is held by others to support the nativistic theory.{12} (d) It is also urged that the illusion produced by the stereoscope, where two dissimilar pictures presented to the different eyes give rise to the perception of a single object, confirms the empirical theory.{13}

On the whole that view seems to us to be nearest to the truth which, while admitting a certain degree of natural harmony in the structure of the two instruments, yet assigns to experience the development and perfection of binocular vision.{14}

The importance of binocular vision in the perception of solidity and distance is very great. The muscular tension involved in the convergence of the axes of the two eyes, and the dissimilarity in the two retinal impressions, confer an immense advantage on the double organ. Somewhat analogously to the case of the two hands in the sense of touch and to the two ears in hearing, the twin members of the visual faculty, by means of their different standpoints, are enabled to bring forward valuable contributions of a new character. Moreover, though double-contact aids us by two distinct and separable experiences, while ordinarily in sight but one sensation is consciously realized, yet the effect of the second visual organ, whether due to experience or connate aptitude, is such that we obtain an instantaneous perception of the third dimension of space.

Erect Vision. -- In addition to binocular vision, a second "anomaly" of sight is found in the perception of objects as erect while the image on the retina is inverted. Some writers refuse to admit the existence of any special difficulty. We do not, they point out, see the retinal image but the object, and it is simply a law of our nature that an inverted image awakens the perception of an erect object. Others accentuate the fact that during the transmission of the retinal impression to the brain in the form of a neural tremor, the original spatial relations of the parts must be lost, and so there is no reason why the resulting mental state should redistribute them in their old position. The erection of the object will then be due either to innate disposition or acquired habit. Dr. Carpenter holds that "one of the most elementary of our visual cognitions is the sense of direction, whereby we recognize the relations of the points from which the rays issue and thus see the objects erect, though their pictures on the retina are inverted."{15} By this "extradition," rays of light falling from above or below will be referred back to their source. He appeals to the operations for cataract as confirming his view. The question is, howevei of no great philosophical significance.

Auditory Perception. -- The ear gives us originally no knowledge of the spatial relations of the external world, nor even of the nature of the objective cause of the sensations of sound. Of the acquired perceptions of this faculty the most remarkable are the sense of the direction of a sounding body, and the sense of its distance. Both are due to association, and neither of them reach in man a very high degree of perfection. If while our eyes are closed a noise is produced near us by the concussion of two objects, such as keys, we shall find is almost impossible to localize the sound, especially when the experiment is performed above our head or near our feet. In mature life we estimate the distance of a familiar sound by means of its intensity. If it is of a rare character, such as that of thunder or of the explosion of gunpowder, we feel completely at a loss. The discrimination of direction is dependent on the difference in the effects produced in the two ears, and also on the variation in the character or intensity of the sound brought about by moving the head. An object on the right side makes a stronger impression on the right than on the left ear, and the sound is intensified by bringing the head or body to that side, or by setting the ear in a more direct line with the sonorous object. Hares and other animals endowed with large movable ears far surpass man in this respect. Careful cultivation may extend considerably the power of distinguishing faint sounds, and we find certain uncivilized tribes, as well as some species of the lower animals, in which this sense has been developed to a surprising degree as a means of ascertaining the advent of their foes or their prey. Its imperfection as an informant regarding space is partially redeemed by the fineness of its appreciation of time lengths, and to this quality its value not merely as the musical faculty, but as the instrument of social communication is largely due.

Gustatory and Olfactory Perception. -- Neither the sense of taste nor that of smell afforded us originally an immediate perception of external reality. If we make the experiment of tasting a liquid of moderately sweet or sour flavour, which is at the same temperature as the organ, we shall find that even in mature life the resulting sensation is of a vague ill-defined character, and contains little more direct reference to the external world than a headache, or a general feeling of depression. In experience, however, special tastes have been found to be invariably excited by objects possessing particular tactual and visual qualities, and therefore the three classes of sensation come to be associated so that either may recall the others. By cultivation this faculty can be developed in a very surprising degree, and the expert can detect variations in the flavour of tea, wine, and other articles so faint as to be utterly imperceptible to the ordinary mortal. The first odours which assailed our nostrils probably awoke us up to an indefinite pleasurable or painful feeling, and to nothing more. But after a time we grew to associate certain smells with particular objects known by touch and sight, and as the higher activities of the mind unfolded themselves we began to apprehend the former as the cause of the latter. To the circumstance that this sense is stimulated by effluvia of distant bodies, much of its superiority to taste, both in point of refinement and of cognitional importance, is due. As revealing future gustatory experiences, and giving timely warning of poisonous or unwholesome food, olfactory perception becomes an instrument of considerable value. This faculty, like that of taste, is susceptible of a high degree of cultivation, and in the absence of some of the other senses it has reached a remarkable degree of acuteness.

Objections solved. -- The account we have just given of the gradual growth of perception obviates various difficulties urged against the doctrine of Natural Realism. Mr. Bain, for instance, objects against Hamilton that the terms "external," "independent," and "reality" "are not simple and ultimate notions, but complex and derived," and consequently that "it is inadmissible to regard any proposition involving them as an ultimate fact of consciousness."{16} Undoubtedly these terms in ordinary language imply a variety of elements which it would be absurd to assert are all given in the "primitive unanalyzable dictum of consciousness." Accordingly, to maintain that the first sensation of pressure or sight revealed to the infant a material world as external, independent, and real, to the full significance of these words, would be as unjustifiable as to hold that the first glance at a triangle or circle presents to us all its geometrical properties. Starting from impressions of sight and touch which vaguely present to us extended reality other than our perceiving mind, our present well-defined knowledge of our own sentient organism, and of objects external to it, became gradually elaborated. The continuous existence of these realities when unperceived, which especially establishes their independence of the Ego, is guaranteed by memory, reflexion, and inference, and not by direct intuition. Finally, through the same means we learn to distinguish between the illusions of the imagination and the genuine deliverances of the external senses, and so come to comprehend the full meaning of reality.

The objection that we cannot have an immediate knowledge of an "external reality," that "it is impossible to understand how the mind can be cognizant of a thing detached from itself,"{17} is equally futile. It is at least fully as impossible to understand how the mind can be cognizant of itself. How mind and body are united, how either can act upon the other, or indeed how any one thing can move another, are to our present faculties insoluble questions; but the fact that there is interaction cannot be denied any more than the growth of plants or the existence of gravitation merely because we cannot imagine how such an event is possible. If the living body is informed and animated throughout its whole being by a spiritual soul, why should not the sentient organism so constituted be capable of responding to a material stimulus by an immediately percipient act? A priori dogmas as to what is or is not impossible are here out of place, especially in the hands of empiricists. To experience we must appeal, and this testifies that in sensations of pressure and sight we are immediately percipient of something other than our own mental states, whilst observation of many of the lower animals proves that they can accurately appreciate spatial relations from birth.

Co-operation of External Senses, Internal Sense, and Intellect. -- We have endeavoured, in the present chapter, to trace the growth of each of the external senses separately, and we have tried to confine ourselves to the development of the sensuous factor in apprehension. But in real life there is no such isolation. The external senses are all connected with the same brain, and they are all faculties of the same mind. Their several activities are accordingly unified in the same interior sensuous consciousness. In human beings, as well as in the lower animals, the operations of the senses are synthesized by internal sentiency, and apart from all higher rational activity, the sensations of the different senses are obscurely felt as similar or dissimilar.

But in man, during mature life, even the simplest acts of perception usually involve intelletual activity, and it is virtually as impossible to assign the exact date of the first awakening of rational cognition as it is to point to the birth of the primitive free volition. In both departments lower grades of consciousness, sentiency and spontaneity, precede as necessary conditions the higher forms of mental life; and to the child during the years of early infancy the existence of the external world is given as an instinctive and indestructible belief, and its reality is for him little more than that of sensations and possibilities of sensations.

Dr. Porter very aptly remarks: "It is quite conceivable, as has been already suggested, that before those percepts (peceived things) and sensations (qualities apprehended by sensations) are connected under the relation of substance and attribute, they should be known as constant attendants, co-existent or successive, and that, simply as conjoined, the presence or the thought (i.e. sensuous image) of the one should, under the laws of association, suggest the thought of the other. It is under this relation that things and properties are known to the animal. It is obvious that the animal cannot and does not distinguish the relation of conjunction from that of causation. If he has experienced one sensation or sense-percept in connection with another, the repetition of the one brings up the image of the other, and the pain and pleasure, the hope and fear, which are appropriate to it. The dog connects with the whip in the hand of his master the thought (image) of chastisement and pain; with the sight of his gun or his walking-stick, the excitement of a ramble or sport."{18}

Intelligent Cognition not mere Instinctive Belief. -- It is through a confusion between the spontaneous faith embodied in the primitive percipient act and the rational conviction evoked in the developed consciousness by intellectual perception, that Reid and others were misled into describing our assurance of external reality as an instinctive belief irresistibly suggested by the sensation. Instinctive belief stands opposed to intelligent cognition as being blind and irrational. No grounds can be assigned for its existence and no cogent reason can be adduced for its validity. The mere fact that a mental state of this character is indestructible does not alone afford it a sufficient philosophical guarantee, while the appearance of idealist philosophers would seem to imply that such a faith can at all events suffer temporary eclipse. But our knowledge of material objects is not of this kind. However blind and unintelligent may be the trust of the infant or the brute in an external world, developed cognition in man is essentially other than impulsive faith; and his certainty of a material universe, an assurance in which rational intuition, abstraction, reflexion, and inference are involved, and which is based on reasons as solid as those we have already advanced, is most erroneously described as an instinctive belief.

Mental and Cerebral development. -- Mental development is marked by growth in power, enlargement in range and variety, and increase in the complexity of our mental activities. Much industry has been recently devoted to the systematic observation of the working of the faculties of the mind from earliest childhood, and although the psychologist's interpretations of the infant's mental states may remain of doubtful value, careful study of facts must ultimately prove fruitful in the interests of truth. Among the results, partly physiological, partly psychological, claimed to be established are the following.

The weight of the human brain at birth is about one-sixth of that of the whole body. The brain more than doubles its size during the first year, after which its increase is much less rapid, and although it continues to grow very slowly to middle life, it has nearly reached its full size by the end of the seventh year. At maturity it averages between one-fortieth and one-fiftieth of the weight of the body, reaching in normal adult Europeans from about forty-six to fifty-two ounces. Whilst during infancy it thus grows rapidly in bulk, it also exhibits increasing distinctness and perfection in its several parts, and its convolutions become deeper and more marked. The sense-organs also, though very imperfect at first, develop still more speedily, and within a few weeks, or at most a few months, they attain maturity. Experiments go to show that the newly-born child is deaf, probably owing to the presence of a fluid in the internal cavity of the ear, which is only gradually replaced by air. At first, sound produces merely a vague shock. The muscular control over the eyes is imperfect, and according to some observers during the first days of its life the infant merely distinguishes light from darkness, whilst the capacity to discriminate colours remains very feeble for some weeks.{19} The child seems to be unable to distinguish different distances, by means of sight. Although, as we have already observed, this aptitude is enjoyed from the beginning in a completely developed condition by some of the lower animals. Sensations of contact are of a similarly indefinite character. On the whole it is probable that the consciousness of the infant during the first weeks of its life is of a vague, indefinite, drowsy character, in which there is little or no awareness of the various qualities of sensations which will become so widely differentiated later on.{20}

With varied and contrasted experiences, however, the sensibility to different stimuli rapidly improves, and the monotony of the earlier somnolency is more and more broken up. Each stimulation leaves a certain residual effect in the faculty, and repetition of an impression, while strengthening the power exercised, also tends to awaken a faint curiosity and interest, and the infant begins to compare in a semiconscious way different experiences, and also to recognize them on their recurrence. As definiteness of impressions is increased memory improves, and conscious attention is called more and more into play, and intellect proper begins to exert itself. The primary tendency of all mental activity is objective -- self-consciousness coming later. The course and the range of development is determined in part by inherited temperament, in part by surrounding circumstances, physical, intellectual, and moral.

Periods. -- The periods of development are variously divided by different writers, but in general the following are recognized as distinct epochs. Infancy, reaching to nearly the end of the second year, during which the several faculties of sense-perception reach maturity, the power of locomotion is imperfectly acquired, and the first efforts at speech are made. Childhood comes next, reaching to the seventh year. Memory and imagination show considerable progress. Curiosity frequently manifests itself, and the so-called "play-impulse" or tendency to spontaneous, random movement is active. A full self-conscious knowledge of his own personality is reached early in this period, although the general tendency of the mind is objective; and the power of voluntary self-control and reflective obedience to rule is ordinarily sufficiently developed before the eighth year to constitute the child responsible for his acts where temptation does not exceed a moderate degree of strength. For this reason moral theologians have fixed on the seventh year as the date about which the "use of reason" is commonly reached.

The next seven years mark the period of boyhood, during which the faculty of memory increases in strength and intellectual abstraction comes more into play. Self-control too grows in power, and individual peculiarities reveal themselves. This is especially the plastic period when the found ations of those moral and intellectual habits are to be laid which will in great part determine the quality of the boy's future career. If habits in conflict with truthfulness, generosity, obedience, or purity are in possession at the age of fifteen, it is extremely difficult to dislodge them afterwards.

The period of youth, covering the next seven years, marks the final "setting" of the character in various directions. Whilst the memory and imagination continue active, the intellectual faculty of abstract conception, judgment, and reasoning rapidly expands, and the power of introspection also increases. The emotions and passions come into prominence. This is especially the season for building up ideals. It is the age of enthusiasm, of poetry, and of fancy, but it is also the epoch during which our most important intellectual convictions and moral habits crystallize and determine for good or ill the course of our whole future life.

Primary and Secondary Qualities of Matter. -- Our knowledge of the smell, sound, taste, or temperature of objects differs widely in character from our cognition of their extension, figure, or number. The latter are called primary, the former secondary qualities of matter. The significance of this difference has played a prominent part in the history of the Philosophy of Perception in modern times, especially in England, but the distinction was clearly grasped in its most essential bearings by Aristotle and St. Thomas. Aristotle distinguished between "common" and "proper sensibles," and further between the latter in a state of formal actuality or energy (en energeia, in actu), and in a dormant or potential condition{21} (en dunamei, in potentia). The "proper sensibles" are the qualities in bodies which correspond to the specific energies of the several senses -- colour, sound, odour, taste, temperature, and other special Tactual qualities. Under the "common sensibles" were included extension, figure, motion, rest, and number. They are perceived through, but simultaneously with, the sensibilia propria, and by more senses than one. Moreover, the sensibilia propria do not exist in a state of actuality except when perceived, but only virtually as dormant powers of matter. To this latter most profoundly important distinction, erroneously imagined to be a discovery of modern philosophy, we will return again. Aristotle's doctrine on both points was adopted by St. Thomas,{22} who reduced the various forms of common sensibles to that of quantity. This was conceived to be the most fundamental attribute of matter, and the various qualities which give rise to the special sensations were looked upon as properties inhering in it. From this to the modern division into primary and secondary qualities the transition is obvious.

Descartes, between whom and Locke the credit of the discovery of the ancient distinction has been supposed to lie, taught that the attributes, Magnitude Figure, Motion, Situation, Duration, and the like, are clearly perceived. We have an idea of them as they may be in the object. On the other hand, Colour, Pain, Odour, Taste, et cetera, are not thus apprehended. We have only a confused and obscure knowledge of something or other in the external body which causes these sensations in us.

Locke, who borrowed from Galileo the terms Primary or Real and Secondary Qualities to mark the old distinction between the common and proper sensibles, gives solidity, extension or bulk, figure, motion or rest, and number, as included in the first class. These attributes we cannot conceive as separable from matter, and, moreover, they are like the ideas by which we represent them. The secondary or imputed qualities, colours, sounds, tastes, smells, and the rest, are not essential to the idea of matter. Where present in bodies they exist merely as powers to produce sensations, properties emerging out of occult modifications of the primary attributes, and capable of awakening in us feelings in no way like themselves.

Berkeley and Hume, proceeding from Locke's most fundamental doctrine that we can only know our own ideas, quickly demolished the distinction. Hume even demonstrated that, on Locke's principles, the primary qualities, extension, and the rest, are less real and objective than the secondary, for the former are merely complex subjective products elaborated out of the latter, and so the purest of mental fictions. In the Kantian philosophy, although the subject is not explicitly treated, the objective significance of the two groups is similarly reversed. As Space is an exclusively subjective form, while the sensations of smell, sound, et cetera, haye some sort of an external correlate, however remote from them in kinship, the latter would seem to be of a less purely ideal character.

Sir W. Hamilton from a psychological point of view distinguishes three classes: (1) Primary or objective. (2) Secundo-primary or subjectivo-objective, and (3) Secondary or subjective qualities.{23} The primary qualities include all the relations of matter to space whether as container or contained. These are (1) Extension, (2) Divisibility, (3) Size, (4) Density, (5) Figure, (6) Absolute Incompressibility, (7) Mobility, (8) Situation. These attributes are completely objective. They are percepts proper, implying no reference to sensation in their meaning, though involving sensation in their first apprehension. They are, he holds, absolutely essential to body; deprived of them matter is inconceivable. The secundo-primary qualities comprehend gravity, cohesion, repulsion, and inertia. Viewed as objective they are forces resisting our locomotive faculty or muscular energy. As subjective they are revealed through the varying affections of pressure in the sentient organism. Involving in their meaning these subjective sensations, they do not possess the objective independence of the primary qualities. They are, moreover, not essential to matter. The secondary qualities are not in propriety qualities of bodies at all. As apprehended they are only sensations which lead us to infer objective properties in the external thing. They are experienced as idiopathic affections of our organism, indefinite in number, and producible by a variety of stimuli. Besides the sensations of the special senses, Hamilton includes in this class a number of other feelings, such as shuddering, titillation, and sneezing. They are of course in no way essential to matter.{24}

Criticism. -- The recognition of the distinction in kind between the primary and the secondary qualities, or between the common and proper sensibles, is justified metaphysically by the more and less fundamental character of the two classes respectively, and psychologically by the numerous differences in the mode of their apprehension. Among these latter enough attention has not been directed to the ancient distinction based on the fact that secondary and secundo-primary qualities are disclosed only through a single sense, while the primary attributes are revealed through a plurality of independent sources. This circumstance, as well as their more intelligible nature, makes our cognition of them clearer, more convincing, and more comprehensive. The perfect identity of ratios subsisting between parts of space, e.g., the relation of the side to the diagonal of the square, known through visual and tactual sensations, the mathematical power of the blind, and the recognition of circular and square figures by those just receiving sight for the first time, present an irresistible testimony to the reality of what is affirmed by such diverse witnesses. In addition to this, the manifestation of extension in the two different experiences of colour and pressure enables us to detach in a singularly perfect manner the common element, and so to form an abstract idea of extension, far surpassing in clearness those derived from any single sensuous channel.

The Relativity of Knowledge. -- This expression has been used in a great variety of meanings. (1) The phrase Relativity of Knowledge, or rather the Law or Principle of Relativity, has been used to signify a leading tenet of Bain and Wundt -- that knowledge and feeling are possible only in transition, that we can know anything only by knowing it as distinguished from something else, that in fact all consciousness is of difference. We have discussed the subject at the end of chapter v. This doctrine, however, is not that ordinarily intended when we speak of the Relativity of Knowledge.

(2) The Relativity of Knowledge in its most important sense refers not to the nature of the relations between one known object and another, but to that between the known object and the knowing mind. All systems of philosophy which reject the doctrine of immediate perception of extended reality must maintain that our knowledge is relative to the mind in the sense that we can never know anything but our own subjective states. Among these the most consistent thinkers, as we have argued, are the idealists proper. They logically maintain that if we have no knowledge of anything beyond consciousness, it is unphilosophical to suppose that anything else exists. This thoroughgoing view is represented by Hume, and by Mill at times. The great majority of modern philosophers, however, shrinking back from this extreme, have adopted some intermediate position akin to that of Kant or Mr. Spencer. They maintain that while all our knowledge is relative to our own mental states, and in no way represents or reflects reality, yet there is de facto some sort of reality outside of our minds. Our imaginary cognitions of spaces time, and causality are universal subjective illusions either inherited or elaborated by the mind; consequently, since these fictitious elements mould or blend with all our experience, we can have no knowledge of things in themselves, of noumena, of the absolute. But notwithstanding this, and in spite of the fact that the principle of causality has no more real validity than a continuous hallucination, these philosophers are curiously found to maintain the existence of a cause, and even of an external, non-mental cause of our sensations.

(3) True doctrine. -- Another, and what we maintain to be the true expression of the Relativity of Knowledge, and one which is in harmony with the theory of immediate or pre. sentative perception, holds -- (A) that we can only know as much as our faculties, limited in number and range, can reveal to us; (B) that these faculties can inform us of objects only so far, and according as the latter manifest themselves; (C) that accordingly (a) there may remain always an indefinite number of qualities which we do not know, and (b) what is known must be set in relation to the mind, and can only be known in such relation.{25}

So much relativity is necessarily involved in the very nature of knowledge, but it in no way destroys the worth of that knowledge. If knowledge is defined to imply a relation between the mind and the known object, and if the noumenon or thing-in-itself is defined to signify some real element of an object which never stands in any relation to our cognitive powers, then a knowledge of noumena or things-in-themselves is obviously an absurdity.{26} But i by noumena are understood, as Kant on the one side, and sensationalists like Mr. Spencer on the other seem to mean, hypothetical external causes of our sensations, which yet somehow do not in any way reveal their character through these sensations, then we must, in the first place, deny the assumption that we can only know our own conscious states, and, in the second, we must point out the fundamental contradiction common to both schools of disputing the objective or real validity of the principle of causality, whilst in virtue of a surreptitious use of this rejected principle they affirm the reality of an unknowable noumenal cause.

Cognition of Primary and Secondary qualities compared. -- Admitting all knowledge to be relative in the third sense defined, there yet remain grades in the comparative perfection of cognitions gained through diverse channels; and here the distinctions both between sense and intellect, and between the primary and secondary qualities of matter, assume great importance. The doctrine that colours, sounds, and the other secondary qualities do not exist in objects as they are in the mind has heen often cited as a modern psychological discovery. This, however, is a complete mistake. The wide difference which separates the objective or material conditions of sound, colour, and the rest from the corresponding subjective consciousness, was as clearly and as firmly grasped by Aristotle and St. Thomas, as by Locke, Hume, Kant, or Herbert Spencer. The acute minds of the sensationalists and sceptics of Ancient Greece had, in fact, raised in one form or another all the most forcible difficulties now urged by their modern representatives, and the Stagirite was necessarily led to answer them. He did this by pointing out the distinction between the potential condition and the completed realization of the secondary properties. Sound and colour in apprehension he describes as having reached their full perfection, actuality, or energy, whilst when unperceived they exist in the object merely in a potential or virtual state. In this stage he recognized them simply as powers capable of arousing sensation. He even called attention to the ambiguity arising from the frequent use of the same word -- e.g., "sound" or "taste," to designate both the physical property and the mental state; and he employs the two terms, sonation and audition, to bring out the difference. He thus successfully opposed the scepticism of the ancient empiricists, who denied all reality or differences of colours, sounds, and the rest apart from perception, by admitting their contention as regards the full realization of the qualities of matter, while refusing to allow its truth in reference to the potential conditions of these qualities. Neither light, nor sounds, nor odours would exist in their proper signification as actualities if all sentient beings were withdrawn from the universe; but they would still remain as potencies ready to emerge into life when the recipient faculty appeared. Aristotle's treatment of the subject was adopted and elucidated by St. Thomas, and we deem the matter of such importance that we cite a number of passages from both the Greek philosopher and his scholastic commentator below.{27}

Sensuous and Intellectual cognitions compared. -- Through its secondary qualities, then, an object is known by any sense only as something capable of producing a particular sensation in me. The primary attributes are, however, of such a kind, and presented to us in such a manner, that our knowledge of them, even when limited to the range of the sensuous faculties, is of far superior importance to that which we possess of the sensibilia propria. In themselves the primary attributes consist of extensional determinations universal to matter, and independent of the nature of the sentient faculty. In relation to us the fact of their being revealed through the several channels of ocular, motor, and tactual sensations, gives our sensuous perception of them a clearness and distinctness far surpassing that of the proper sensibles.

But it is as affording material for intellectual knowledge that their true value is to be estimated. Disclosed through distinct channels the common presentation is instinctively detached by the higher abstractive activity of the mind; and since it is thus given to us unobscured by any subjective affections of sensibility, it is perceived in a very perfect and comprehensive manner. Owing to this fact our simplest intellectual cognitions of spatial relations are enabled to image with distinctness and lucidity the most fundamental laws of the physical world.

Finally, by observation, reasoning, and abstraction we come to discern in these primary attributes universal extensional relations conditioning the mutual connexion and interdependence of material objects apart from their perception by the knowing spirit. We are assured that, although the realization of the secondary qualities requires the presence of the sentient faculty, yet the most important part of the meaning of the primary attributes holds in its absence: we see that while perception is essential to the one, it is accidental to the other. Remote and complicated deductions from a few primary luminous intuitions of space and number, together with certain assumptions as to the action of real force, are found to describe accurately the future conduct of the universe. Astronomy and Physics, the Law of Gravitation as well as the Undulatory Theory of light, imply the extra-mental validity of our notions of space, motion, and real energies, and assume their existence and action apart from observation. The verification which subsequently observed results afford to our reasoned deductions must, consequently, be held to establish that these conceptions are neither "integrations" of purely subjective feelings, nor mental "forms," which in no way represent the hypothetical, unknowahle, external noumenon, but true cognitions which mirror in a veracious manner the genuine conditions of real or ontological being. Our knowledge, then, of the primary attributes does not relate exclusively to our own mental states, as is asserted in the prevalent creed of relativity. Still in the case of these, as well as of the secondary qualities, we can never know the object unless in so far as it reveals itself directly or indirectly to our faculties, and in the simplest creature there will always remain beyond our ken an indefinite number of secrets which a higher intelligence might scrutinize, so that the perfection, range, and penetration of knowledge is, in truth, ever relative to the knowing mind.

Readings -- On immediate perception, cf. Farges, L'Objectivité de la Perception, pp. 17-36, 83-99, 155-181; also J. Mark Baldwin, Senses and Intellect, c. viii.; Dr. Porter, The Human Intellect, Pt. I cc. iii.-vi.; Balmez, Fundamental Philosophy, Vol. I. pp. 267-324, 339-360. On the localization of sensations, cf. Gutberlet, op. cit. pp. 59-84; Mercier, Psychologie, pp. 132-147; On the Primary and Secondary Qualities of Matter, cf. St. Thomas, De Anima, II. l. 13; Hamilton, Metaph. II. 108-115; Notes on Reid, pp. 825, seq.; On Relativity of Knowledge, St. Thomas, De Anima, III. l. 2; Martineau, A Study of Religion, Bk. I. c. iv.; M'Cosh, Exam. of Mill, c. x. and Intuitions of Mind, pp. 340, seq. (2nd Edit.); Dr. Mivart, On Truth, c. x.; Mark Baldwin, op. cit. 58-63.

{1} To start with perception by taste, smell, or hearing, or at all events to take any of these as the true type of external perception, is a complete inversion of what is actually given in nature, and may lead into serious philosophical error. These are precisely the faculties by which originally we do not obtain any direct perception of matter. They are wanting in the most important feature of that species of cognition which they are supposed to exemplify. They are originally of an almost purely subjective character, and are therefore but little better suited than imagination or memory to illustrate the manner in which we come to know the material universe. Hearing, employed not for the illustration of indirect or acquired perceptions, but as a typical representation of the perceptual process in general, as is often done by psychologists, misleads the reader into the belief that since by far the greater part of the information yielded by this faculty is of a mediate and inferential character, testifying only to possibilities of other forms of sensation, therefore all modes of perception are of a similarly subjective character, and no percipient faculty gives us a direct immediate presentation of extended matter. Hearing and smell exhibit abundantly the force of associated or acquired perceptions, but direct perception they do not illustrate.

{2} This seems true in the case of sensations of surface pressure, not so, however, as regards the organic sensations, or those of the other special senses. We project or externalize the cause of the auditory or visual sensation, but unless the impression is markedly painful we do not in mature life advert to the point of the organism affected by the stimuli of these senses. It is in fact the organic or tactual element involved in these sensations which enables us to localize them in our own body.

{3} Dr. Gutberlet, who maintains the doctrine that an original reference of a very vague character is attached to sensations of contact, summarizes the arguments against the extreme "nativistic" or a priori view: (1) We appear to localize impressions in parts of the body demonstrably incapable of sensations, e.g., in our bones, teeth, hair, &c. (2) We also misinterpret the locus of known impressions, assigning them to wrong places, e.g., pressure of the elbow is felt in the fingers, irritation of the brain is referred to the extremities. (3) Irritation of the stump of an amputated leg causes us to assign the sensation to the locality originally occupied by the lost limb. (4) We sometimes project sensations outside of the body, e.g., the feeling of pressure to the end of a walking-stick or a pen. (5) The definiteness of localization varies considerably in different parts of the body, and decreases in proportion as the part affected is beyond the range of the eye and of the hand, e.g., irritation in the back and within the organism. (Die Psychologie, pp. 60, 61.)

{4} There is an element of voluminousness . . . discernible in each and every sensation, though more developed in some than in others, and this is the original sensation of space, out of which all the exact knowledge we afterwards come to have is woven by processes of discrimination, association, and selection." (James, Vol. II., p. 135:) Similarly, J. Mark Baldwin: "No purely empirical explanation is sufficient to account for the extensive form of sensation. . . . The power to perceive space is as native as the power to perceive anything else; but this does not mean that space is native to the mind any more than trees are or music. Objects are given to us in space, and space is given to us with objects." (Senses and Intellect, p. 122.) The empiricism of the associationists on this question is falling more and more into disrepute.

{5} Mental Physiology, § 127.

{6} "Pressing thus on the throat of several persons successively, she sometimes sportively attempts to imitate their voice with her own in a way which shows that she does distinguish differences of both loudness and pitch (paradoxical as the language may be) without any conception or sensation whatever of sound." (Cf. Mind, 1879, pp. 166-167.)

{7} Smiles, Lives of Engineers, Vol. I. p 2IO

{8} The Human Intellect, p. 155 Cf. also Balmez, Fundamental Philosophy, Book II. c. xii., and Hamilton, Metaph. Vol. II. pp. 165, 172. This argument is restated in an effective manner by Mr. Mahaffy, The Critical Philosophy, pp. 115-121. It is no reply to say that the extent of colour perceived by a motionless eye is very small and its outline vague, This is true, though not to the extent that Mill and Dr. Bain would make out. It is conceded by them that the retina is extended, and that a small circle of colour can be originally apprehended by sight alone. This admits at once the leading contention of the intuitive school. A circle of the one-tenth of an inch in diameter is as truly extended as the orbit of a planet, while no microscope can reveal space in a sound or an odour, and no summation of these latter sensations can result in a surface or a solid. {9} These two cases, and others of less value during the interval, are reported in the Phil. Trans. of the Royal Society. Dr. Carpenter, Mental Philosophy, §§ 161 and 167, alludes to some other instances, and others again are cited by Helmholtz, but the two given above are among the best. A large portion of the account of Franz's case is transcribed from the Phil. Trans. 1841, into Mr. Mahaffy's Critical Philosophy, pp. 122-133, and in briefer form into Dr. M'Cosh's Exam. of Mill, pp. 163-165. Hamilton's Metaph. Vol. II. pp. 177-179, contains the Cheselden case at length. The best summary, however, of all these cases is given in Preyer's Development of the Intellect (1896), pp. 286-317. The fact that the most recent case recorded there is that of Franz, already fifty-six years old, is instructive.

{19} Cf. Macmillan's Magazine, February, 1873 James, Vol. II. pp. 394-400; and Preyer, The Senses and the Will, pp. 66, 235-241.

{11} Cf. Le Conte, Sight, Part II. c.v.

{12} Cf. Wyld, Physics and Philosophy of the Senses, pp. 226, 227.

{13} The stereoscope is an instrument, invented by Wheatstone, and improved by Brewster, in which slightly dissimilar pictures, such as would be presented to the right and left retinas by a neighbouring solid object, are simultaneously set separately each hefore the appropriate eye. The result is an irresistible conviction of a single solid object. The empirical school hold this fact to establish that single vision is really an interpretation of two mental images attained by experience. Their opponents, however, would argue that though illusory in the present case, the single apprehension is due to native disposition and not merely to association. {14} The reader interested in the question will find the empirical doctrine supported by Carpenter, op. cit. §§ 168-171, and Bernstein, The Five Senses, pp. 128, seq. On the other side, cf. R. S. Wyld, op. cit. pp. 221-227. P. Salis Sewis, Della Conoscenza Sensitiva, pp. 483-486, opposes the physiological explanation which he traces back to Galen. La Psychologie Allemande Costemporaine pp. 118-145, by M. Ribot, gives an account of the dispute between Nativists and Empiricists in Germany. However, this book, which is written entirely from an empiricist standpoint, is very unreliable. {15} Mental Physiology, § 165. {16} Mental Science, p. 120.

{17} Mental Science, p. 209.

{18} The Human Intellect, § 166.

{19} Cf. Preyer, The Mind of the Child, Part I. pp. 180-183. Some of his conclusions, however, seem very hazardous and scarcely warranted by the evidence. Their uncertainty illustrates clearly the grave difficulties inherent in the objective method as employed in Comparative Psychology.

{20} "The baby assailed by eyes, ears, nose, skin, and entrails at once, feels it all as one great, blooming, buzzing confusion." (James, Vol. I. p.488.) J.Ward ("Psychology," Encyc. Brit., 9th Edit.) similarly insists that the primitive consciousness must be a sensory continuum, a homogeneous mass, as it were of feeling in which the separate elements have to be gradually discriminated and differentiated by subsequent experiences. This is a striking reversal of the old associationist "atomistic" view which conceived mental development as mainly a process of fusion or "chemical combination" of originally distinct impressions.

{21} There was also another distinction recognized by the peripatetic school, that of sensibile per se and sensibile per accidens. That is sensibile per accidens which is apprehended indirectly through being accidentally conjoined with something which is sensibile per se; and in this signification individual corporeal substances were said to be sensibile per accidens, "ut si dicimus quod Diarus vel Socrates est sensibile per accidens, quia accidit ei esse album." (St. Thomas, De Anima, Lib. II. l. 13.) Both sensibilia propria and sensibilia communia were held to be sensibilia per se; the former, however, being classed as per se primo vel proprie, the latter as per se secundo. The several "proper sessibles" (per se primo) were defined to be the formal object, or appropriate stimulus of the different special senses. The "common sensibles" (sensibilia per se sed non proprie), extension, figure, &c., manifest themselves through, but simultaneously with, the sensibilia propria. They are thus not mediate acquisitions derived from the former, but forms of reality directly revealed through them.

{22} Cf. Sum. i. q. 78. a. 3. ad 2. and iii. q. 77. a. 2.

{23} These groups have been also styled the geometrical, mechanical, and pysiological properties, and Mr. Herbert Spencer (Principles of Psychology, Pt. VI. cc. xi.-xiii.) still further enriches our already exuberantly wealthy terminology by the invention of the terms, statical, statico-dynamical, and dynamical, to mark substantially the same distinctions. In the dynamical or secondary attributes the external body is active, the mind is wholly passive. These qualities are objectively occult properties in virtue of which matter modifies the forces brought to bear on it, so as through these forces to awaken sensations. With the exception of taste, they act across a distance; they are accidents cognizable apart from the body, and manifested only incidentally. In experiences of the statico-dynamical kind, both subject and object are simultaneously agent and patient. These attributes are known through some objective re-activity evoked by subjective activity. "In respect of its space (statical) attributes, body is altogether passive and the perception of it is wholly due to certain mental operations." Unlike the other attributes "extension is cognizable through a wholly internal co-ordination of impressions a process in which the extended object has no share." Some distinctive features of the different groups previously recognized are here pointed out, but there are also some errors. The mind is never purely passive, even in sensations like those of colour, taste, et cet., the mental reaction is as real as the physical stimulation. Consequently the distinction between the dynamical and statico-dynamical fails. Mr. Spencer is right in holding that the primary are not the direct object of the special senses in the same manner as the secondary qualities. In the words of St. Thomas the sensibilia communia do not constitute formal objects of individual senses. Still they are not, as Mr. Spencer's exposition implies, purely subjective products, but forms of reality revealed through, yet concomitantly with, certain of the proper sensibles. Surface extension as such does not of course stimulate the retina or the nerves of touch; it is made known in experiences of pressure and colour. Still it is not a mediate inference from the latter, nor a complex integration of unextended feelings of any kind. Cognition of the third dimension of space results, as we have already described, from a reapplication of the same faculties in a new direction.

{24} As regards Hamilton's treatment of the subject: (1) There is no warrant either metaphysical or psychological for the intermediate class. On both grounds it belongs to the third. (2) It is absurd to speak of secondary qualities of matter as not being properties of matter at all, but merely conscious states. Hamilton, moreover, is peculiarly inconsistent in this respect, since he elsewhere holds that all our senses make us immediately cognizant of the non-ego.

{25} What is given in one or more relations may necessarily implicate other relations, and the e may subsist not merely between the mind and other objects, but between the several objects themselves. Still, mediate cognitions of this sort are knowledge only in so far as they are rationally connected with what is immediately given. Our knowledge of the mutual dynamical influence of two invisible planets, which faithfully reflects their reciprocal relations, is but an elaborate evolution of what is apprehended by sense and intellect in experiences where subject and object stand in immediate relations

{26} "To speak of 'knowing,' 'things in themselves,' or 'things as they are,' is to talk of not simply an impossibility, but a contradiction; for these phrases are invented to denote what is in the sphere of being and not is the sphere of thought; and to suppose them known is ipso facto to take away this character. The relativity of cognition (i.e., in the sense defined) imposes on us no forfeiture of privilege, no humiliation of pride; there is not any conceivable form of apprehension from which it excludes us." (Cf. Martineau, A Study of Religion, Vol. I. p. 119.)

{27} 'Sensibilis autem actus et sensus idem est, et unus; esse autem ipsorum non idem. Dico autem ut sonus secundum actum, et auditus secundum actum. Contingit enim auditum habentia non audire, et habens sonum non semper sonat. Cum autem operetur potens (id quod potest) audire, et sonet potens sonare, tunc secundum actum auditus simul fit, et secundum actum sonus. Quorum dicet aliquis hoc quidem auditionem esse, hoc verum sonationem." (Aristotle, De Anima, Lib. III. Lect. 2.) ' Sonativi (rei sonorae) igitur actus, aut sonus aut sonatio est. Auditivi autem, ant auditus ant auditio est. Dupliciter enim auditus, et dupliciter sonus. Eadem autem ratio est et is aliis sensibus et sensibilibus . . . sed in quibusdam nomina quoque sunt posita, ut sonatio ac auditio; in quibundam caret alterum nomine; visio enim dicitur actus visus, at coloris (actus) nomine vacat, et gustativi gustatio est, at saporis nomen non habet." (id. ib.) "Necesse est quod auditus dictus secundum actum, et sonus dictus secundum actum, simul salventur et corrumpantur; et similiter est de sapore et gustu, et aliis sensibilibus et sensibus. Sed si dicantur secundum potentiam, non necesse est quod simul corrumpantur et salventur. Ex hac autem ratione (Aristoteles) excludit opinionem antiquorum naturalium . . . dicens, quod priores naturales non bene dicebant in hoc, quia opinabuntur nihil esse album, aut nigrum, nisi quando videtur; neque saporem esse, nisi quando gustatur; et similiter de aliis sensibilibus et sensibus. Et quia non credebant esse alia entia, nisi sensibilia, neque aliam virtutem cognoscitivam, nisi sensum, credebant quod totum esse et veritas rerum esset in apparere. Et ex hoc deducebantur ad credendum contradictoria simul esse vera, propter hoc quod diversi contradictoria opinantur. Dicebant autem quodammodo recte et quodammodo non. Cum enim dupliciter dicatur sensus et sensibile, scilicet secundum potentiam et secundum actum, de sensu et sensibili secundum actum accedit quod ipsi dicebant quod non est sensibile sine sensu. Non autem hoc verum est de sensu et sensibili secundum potentiam. Sed ipsi loquebantur simpliciter, id est sine distinctione, de his quae dicuntur multipliciter." (St. Thomas, Comm. de Anima, Lib. III. l. 2, ad finem). Cf. Hamilton, Notes on Reid, pp. 826-830.

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