Fundamental Philosophy, Vol. I (of 2)

66. So hostile was Condillac to the sense of sight that he was unwilling to allow it even the faculty of perceiving extension in surfaces; but as he is of all philosophers the one who has most contributed to the propagation and establishment of this opinion, we will examine his doctrine and its fundamental reasons. We have only to read the chapters in which he explains it, to see that he was not himself very confident of its truth, but that he felt himself contradicted by both experience and reason.

In his Traité des Sensations,36 where he examines the ideas of a man limited to the sense of sight, he says that colors are distinguished by the sight because they seem to form a surface of which the eyes occupy a part, and then asks: "Will our statue, judging itself to be at one time many colors, perceive itself as a sort of colored surface?" We must bear in mind that, according to Condillac, the statue confined to one sense will believe itself the sensation, that is, it will think that it is the odor, the sound, or the taste, according as the sense of smell, hearing, or taste, is the sense in exercise; for which reason, if a surface enter into the sensation of sight, the statue ought to believe itself a colored surface. I shall not examine the correctness of these observations, but shall confine myself to the main point, which is the relation of sight to a surface.

67. According to Condillac, the statue will never believe itself a colored surface, that is, although it may perceive the color, it will not perceive the surface. Let the philosopher himself speak, for his own words will suffice to condemn his opinion, and to show the uncertainty with which he advanced it, or else the obscurity under which it labors: "The idea of extension supposes the perception of many things, some distinct from others. This perception we cannot deny to the statue, for it feels that it is repeated outside of itself as many times as there are colors modifying it. When it is the red, it feels itself outside of the green; when the green, it feels itself outside of the red, and so with other colors." Some may imagine that, conformably to these principles, Condillac goes on to establish that sight gives us the idea of extension, since it makes us perceive things, some outside of others, in which, according to him, the idea of extension exactly consists. But he does not; far from following the true road, he miserably loses his way; he not only violates the principle he has just laid down, but notably changes the state of the question. He continues: "But in order to have a distinct and precise idea of magnitude, it is necessary to see how the things perceived, some outside of others, are connected, how they mutually terminate, and how they are all enclosed in the limits which bound them." This, I repeat, is to change the state of the question; we are not now treating of a distinct and precise idea, but simply of an idea. How far the idea of extension given by sight is perfect, is another question; although it is manifest that if sight can give us an idea of extension, it will come by continual exercise to render this idea more perfect.

68. The statue, in Condillac's opinion, could not perceive itself to be circumscribed by any limit, because it could know nothing beyond itself; but did he not just now tell us that the statue would believe itself different colors; that some of these were outside of others; and that when it would be one, it would perceive itself outside of the others? Does this not imply not only one but many limits?

This difficulty did not altogether escape Condillac; for after having asked if the me of the statue, when modified by a blue surface, bordered with white, would not believe itself a limited blue color, he says: "At first sight we were inclined to believe that it would; but the contrary opinion is much more probable." But why? "The statue cannot perceive itself extended by this surface, save inasmuch as each part modifies it in the same way; each part should produce the sensation of blue color; but if it is alike modified by a foot of this surface and by an inch, it cannot perceive itself, in this modification, to be one magnitude rather than another. Therefore it does not perceive itself as magnitude; therefore the sensation of color does not involve the idea of extension." It is easy to see that Condillac either supposes what is in debate, or else says nothing to the point. According to him, the statue is alike modified by a foot of colored surface and by an inch. If by this he means that the two modifications are identical under all aspects, he supposes the very thing he ought to have proved; for this is precisely the point in dispute, whether surfaces differing in magnitude do, or do not, produce different sensations. If he means, as his words seem to indicate, that the sensation as color, and solely as color, is the same in a foot of colored surface as in an inch, he utters, indeed, an incontestable truth, but one not at all to his purpose. Undoubtedly, the sensation of blue, as blue, is the same in different magnitudes, and no one ever thought of denying it. But this is not the question: it is whether, the color remaining one and the same, the sensation of sight is modified differently, according to the variety of magnitude of the colored surface. Condillac denies it, but in an uncertain and hesitating way. We believe his negation to be so groundless that the direct contrary may be proved.

69. I would ask Condillac if he can have color without surface; if an object without extension can be painted upon the retina; if we can even conceive a color without extension. No one of these is possible, sight is therefore necessarily accompanied by extension.

70. Condillac places the idea of extension in some things being presented to us outside of others. This, as he him self confesses, is verified in the sensation of color; therefore the sight of what is colored must produce the idea of extension. Condillac's subterfuge here is an exceedingly weak one. He pretends that it is necessary, in order to have the idea of extension, to have that of its limits. But first of all, we have shown from his own doctrine that these limits are perceived by the senses; besides it is a very strange pretension to attribute to sight the faculty of giving us the idea of unlimited extension, and to deny to it that of producing the idea of limitation; as if there did not by the very fact of our seeing what is extended, rise within us the idea of limitation, if from no other cause, from the very limitation of our organ; or as if an unlimited were not more inconceivable than a limited sensation.

But suppose the limits not be perceived by the senses, does unlimited extension therefore cease to be extension? Is it not rather extension of the highest order? Does the idea of space without end, because unlimited, cease to be an idea of extension?

71. Two colored circles, one an inch, and the other a yard in diameter, are placed before our eyes; will the effect produced upon the retina be the same in both, abstraction made from all sensation of touch? Evidently not; experience shows the contrary, and the reason is founded on the laws of the reflection of light, and on mathematical principles. If the impressions are different, the difference will be perceived; therefore the difference of magnitude can be appreciated.

We will now suppose some one in spite of reason and experience to persist in maintaining that the sensation of the two circles will be the same in order to make the extravagance, even the ridiculousness of this opinion palpable. Let us imagine the two circles to be of a red color, and terminated by a blue line; and now placing the less upon the greater circle so as to bring their centres together, we ask, will not the eye cast upon the figure see the less within the greater circle? Will not the blue line that terminates the circle of an inch in diameter be sure to be contained within the blue line that terminates the other circle of a yard in diameter? But what else is the perception of extension than the perception of some parts beyond others? Is it not to perceive the difference of magnitude, to perceive some greater than others, and containing them? Evidently it is. The sight therefore perceives magnitude; therefore it perceives extension.

72. We may still further confirm this truth. Experience teaches, and did it not exist, reason would still teach that there must be a limit to the field of sight, according to our distance from the object. Thus, when we fix our sight upon a wall of great extent we do not see it all, but only a part. Now suppose an object of given magnitude to be within the range of sight, but not so great as to cover the surface embraced by the eye. According to Condillac's system, there can be no difference in the perception, provided the color be the same; whence, it will follow, that the sensation will be just the same, whether the object occupy the whole, or only an exceedingly minute part, of the visual field. It will likewise follow, that, if this visual field be, for example, a great white curtain a hundred yards square, and the object a piece of blue cloth a yard square, the sensation will be just the same whether the blue cloth be one inch or ninety yards square.

73. These arguments, which must have occurred at least confusedly to Condillac, made him hesitate in his expressions, and even use contradictory language. We may have already observed this in the passages cited, but we shall see it yet more clearly in the following: – "We have no term to express with exactness the sentiment that the statue modified by many colors at one time has of itself; but in fine, it knows that it exists in many ways, and perceives itself in a certain mode as a colored point beyond which are others, in which it turns to find itself; and under this point of view, it may be said, that it perceives itself extended." He had before said, that color did not seem extended to the statue, until, sight being instructed by touch, the eye became accustomed to refer the one simple sensation to all the points of the surface: and in the very next line, as we have just seen, he asserts the contrary; the statue now perceives itself to be extended, and the ideologist discovers no way of avoiding the contradiction, but to warn us that the sentiment of extension will be vague because it wants limits. This is a contradiction which we have already made evident. But whence this want of limits? If various figures of different colors, green, red, etc., be supposed to be upon a visual field of a hundred yards square of white surface, the sight will, as is evident, perceive the limits of these figures; where, then, did Condillac discover that illimitation of which he talks?

74. Although it is very true that even if the sensation of color were to involve that of extension, it would not therefore follow that it would produce it in us, because we do not take from sensations all the ideas they contain, but those only which we know. This does not at all affect the present question. We do not treat of what we can take from the sensation, but of what is in it. If Condillac maintains that we may take the idea of extension from the sensation of touch, by what right does he deny the same faculty with respect to sight, supposing the idea of extension to be contained in both sensations?

If I mistake not, this is a tacit confession of the falseness of his opinion. The idea of extension is in the sensation of sight, but we cannot take it thence. Why not? Because it is vague. But then what is to prevent exercise, involving comparison and reflection, from rendering it distinct? The difficulty consists in acquiring it in one way or another; to perfect it is the work of time.

Undoubtedly the first sensations of sight will not have that exactness which they have after much exercise; but the same is true of the sense of touch. This sense is perfected like the others; it like them needs to be educated, so to speak; and those born blind, who, by force of concentration and labor, come to possess it to an astonishing degree of delicacy, offer us a manifest proof of this truth.

CHAPTER XIII.

CHESELDEN'S BLIND MAN

75. Cheselden's blind man, of whom Condillac spoke, in confirmation of his opinions, presents no phenomenon upon which they can rest. This blind person was a youth of thirteen or fourteen years of age, upon whom Cheselden, a distinguished London surgeon, performed the operation of removing cataracts, first from one eye, then from the other. He could before the operation tell day and night, and in a very strong light distinguish, white, black, and red. This is an important circumstance, and merits attention. The phenomena the most remarkable, and having the most relation to the question now before us, were the following:

I. When he began to see, he believed that objects touched the external surface of his eye. This would seem to show that sight alone cannot enable us to judge of distances; but, after close examination, we shall clearly see that the argument is not conclusive. No one will pretend that sight, in the first moment of its exercise, can communicate equally clear and distinct ideas to us, as when experience has accustomed us to compare its different impressions. This is the same with touch as with sight. A blind person, from his frequent custom of guiding himself, in many of his movements by sensations of touch alone, comes to know the position and distances of objects with wonderful precision. If we suppose a man deprived of the sense of touch suddenly to acquire it, neither will he at first judge with the same certainty the objects of this sense as after having exercised it. Experience teaches that the sense of touch is capable of a high degree of perfection. We see it in blind persons at its highest point; and probably the lowest point of its perfection, in the first moments of its exercise, would greatly resemble that of sight at the instant of being freed from the cataracts; objects would be presented to it likewise in confusion; and the subject experiencing them could not well appreciate their differences until practice had taught him how to distinguish and classify.

With respect to distance, it is to be observed, that this blind person of Cheselden, so far from having the habit of appreciating it, had false ideas upon it. As he was not totally blind, the light, which he perceived through the cataracts, was sufficient to even enable him to distinguish between white, black, and red, which seemed to him to touch his eye. We may form some idea of this by observing what happens to us if we close our eyes in a very strong light. Hence he ought, when he gained his sight, to have imagined that the new sight was the same as the old, and, consequently, that nothing had happened but a simple change of object. A person totally blind would have better shown the power of sight to appreciate distances; for he would have had no habit either favorable or unfavorable to their knowledge.

II. It cost him much trouble to conceive that there were other objects beyond those he saw; he could not distinguish limits; every thing seemed to him immense. Although he knew by experience that his chamber was smaller than the whole house, he could not conceive how he could see this.

From these facts Condillac draws a confirmation of his system. We are astonished that he should pretend to found an entire philosophy upon such data. We submit the following considerations to the reader:

76. The subject is here a youth of thirteen or fourteen years, and consequently without any habit of observation. He would naturally express very confusedly the impressions he received in so new and strange a situation.

The organ of sight must, when exercised for the first time, be exceedingly weak, and consequently perform its sensitive functions only in a very imperfect way. We ourselves repeatedly experience that we cannot, if we suddenly pass from darkness to light, especially if it be a very strong light, distinguish objects, but we see every thing in great confusion; what then would happen to a poor child, when at the age of thirteen years, he for the first time opens his eyes to the light?

According to Cheselden's own account, objects were presented to him in such confusion that he could not distinguish them, no matter what their size or shape. This confirms what we have just said, that the partial, if not the sole cause of the confusion, was that the organ did not produce impressions well, because if these had been properly produced, he would have been able to distinguish the limits of the different colors; for, in simple sensation, to see is to distinguish.

We are also told that he could not recognize by sight the objects which he knew by touch. But this only proves that not having been able to compare the two orders of sensations, he could not know what corresponded in one to the impressions of the other. By touch he would have known a spherical body; but as he was still ignorant of the impression which a globe makes on the eye, it is clear that if any one should show him a ball which he had handled a thousand times, he would not even have suspected that the object seen was the same which he had touched. This leads me to another observation which I consider very important.

77. The child on whom these experiments were made was obliged to express his sensations in the visual order, in a language which he did not understand. For any one who is deprived of one of the senses must be absolutely ignorant of all the ideas which have their origin in that sensation. Hence it follows that he knows nothing of the language relating to that sense, and the ideas which he joins to the words are entirely different from what those who possess that sense mean to express. The blind man will speak of colors and the impressions produced by sight, because he hears others speak of these things; but for him the word to see does not mean to see, light is not light, nor color color, as we understand them, but they express different ideas which he has formed according to the circumstances, in conformity with the explanations he has heard. What importance then should we attach to what a child may say who, besides the thoughtlessness natural to his age, is placed in a situation new to him, and required to express his ideas in a language which he does not know? He is asked, for example, if he can distinguish a greater object from another which is smaller, without considering that the words greater and smaller as he understood them, inasmuch as they expressed abstract ideas, or were referred to the sensations of touch, were altogether new to him when applied to objects seen, since he had no means of knowing what was meant when referred to a sensation which he experienced for the first time. If within a circle, a number of smaller circles of a different color were described, he would see the smaller circles within the circumference of the greater; but if asked if one appeared greater than the rest, or if he could distinguish the limits which, separated the smaller circles from each other, he could not but give very absurd answers, which the observers might perhaps take as the expression of curious phenomena. They speak to him of figures, lines, extremities, size, position, and distances in relation to sight, and as he is ignorant of this language, yet knows not that he is ignorant of it, he must necessarily talk in a very strange manner. A more attentive and profound observer would have perceived the same misunderstanding as when a deaf man disputes without hearing what was said.

These remarks are further confirmed by the contradiction in the account of Cheselden. The oculist tells us that the child could not distinguish the objects, even those which differed most in form and size: but that he found those most agreeable which were the most regular. He must then have distinguished them; for otherwise, the sensation could not have been more or less pleasing. And here in choosing an alternative in this contradiction, we must hold that he distinguished the objects, since there is a strong argument in its favor. When two objects, the one regular, the other irregular, were presented to him, and he was questioned as to their resemblance and difference, he must have answered so absurdly as to create the suspicion that he could not distinguish them. The reason of this is, that besides the confusion of sensations, to which he was always more or less subject, he was also ignorant of the language, and although he distinguished the objects plainly, still he could not understand what he was asked, nor express what he felt. But when examined as to the nature of the impression and whether it was pleasing or otherwise, he found himself on a field common to all sensations, the ideas of pleasure and displeasure were not new to him, and he could say without confusion, this pleases me; that is displeasing to me.

To sum up what I have said, I believe that the phenomena of Cheselden's blind man, only prove that sight, like all the other senses, needs a certain education, that its first impressions are necessarily confused, that the organ acquires the proper strength and precision only after long practice, and finally, that the judgments formed in consequence, must be very incorrect until comparison, joined with reflection, has taught how to rectify inaccuracies.37

CHAPTER XIV.

CAN SIGHT GIVE US THE IDEA OF A SOLID?

78. It has been asserted that sight can not give us the idea of size or of a solid, but that this can be obtained only by the help of touch. I believe the contrary may be proved with convincing certainty.

What is a solid? It is the union of three dimensions. If sight can give us the idea of surfaces which consist of two, why not also of solids which consist of three dimensions? This one reflection is enough to show that it has been denied without reason; but I shall not stop with this, but shall prove, by the most rigorous observation, and the analysis of its phenomena, that sight can give us the idea of a solid.

79. I willingly agree, that if we suppose a man deprived of all the other senses, to have his eyes immovably fixed on an immovable object, he would never be able to distinguish between what is solid and what is merely perspective in the object; or, in other words, that all the objects permanently painted on the retina will appear to be projected on a plane. The reason of this is founded on the very laws of the organ of this sense, and of the transmission of its impressions to the brain.

The soul refers the sensation to the extremity of the visual ray; and since in the present instance it has been unable to make any comparisons, it can have no motive for placing these extremities at unequal distances, which constitutes the third dimension.

In order to understand this better, let us suppose the object to be a cube placed so that three of its sides are seen. It is evident that although the three surfaces are equal, they will not appear so to the eye, because their respective positions do not permit them to send their rays equally to it. But as the soul has not had occasion to compare this sensation with any other, it can not calculate the difference produced by the different positions and distances, but must refer all the points to the same plane, regarding the sides of the cube as unequal; though, in reality, they are not so.

Sight, in this case, presents the whole object on a perspective plane; and as it could have no means of calculating the distance of the object from the eye, it would probably believe it joined to the eye, or, more strictly speaking, the sensation would represent only a simple phenomenon, the relations and cause of which we could not explain.

80. It is likewise probable, that if, while the eye remained fixed, we could open and shut the lids, we might form the idea that the object seen was outside of us; so that by this motion alone, we should obtain a point of comparison, by the succession of the alternate disappearance and reproduction of the sensation of the object by the interposition or non-interposition of an obstacle. Then the idea of a greater or less distance would arise, and as this would be in the direction perpendicular to the plane of the object, we should already have the idea of a solid.

Fortunately, nature has been more beneficent to us, and we are not obliged to limit ourselves to a supposition which thus curtails our means of acquiring ideas. Still it will not be useless to have examined the phenomenon on this supposition; for, from this examination, we shall gain light to understand what I propose to demonstrate.