Part 14

The reader must remember that this _Essay on Vision_ is professedly an introspective appeal to human consciousness. It is an analysis of what human beings are conscious of when they see, the results being here and there applied, partly by way of verification, to solve some famous optical or physiological puzzle. The aim is to present the facts, the whole facts, and nothing but the facts of our internal visual experience, as distinguished from supposed facts and empty abstractions, which an irregular exercise of imagination, or abuse of words, had put in their place. The investigation, moreover, is not concerned with Space in its metaphysical infinity, but with finite sections of Space and their relations, which concern the sciences, physical and mathematical, and with real or tangible Distance, Magnitude, and Place, in their relation to seeing.

From the second section onwards the _Essay_ naturally falls into six Parts, devoted successively to the proof of the six following theses regarding the relation of Sight to finite spaces and to things extended:—

I. (Sect. 2-51.) Distance, or outness from the eye in the line of vision, is not seen: it is only suggested to the mind by visible phenomena and by sensations felt in the eye, all which are somehow its arbitrarily constituted and non-resembling Signs.

II. (Sect. 52-87.) Magnitude, or the amount of space that objects of sense occupy, is really invisible: we only see a greater or less quantity of colour, and colour depends upon percipient mind: our supposed visual perceptions of real magnitude are only our own interpretations of the tactual meaning of the colours we see, and of sensations felt in the eye, which are its Signs.

III. (Sect. 88-120.) Situation of objects of sense, or their real relation to one another in ambient space, is invisible: what we see is variety in the relations of colours to one another: our supposed vision of real tangible locality is only our interpretation of its visual non-resembling Signs.

IV. (Sect. 121-46.) There is no object that is presented in common to Sight and Touch: space or extension, which has the best claim to be their common object, is specifically as well as numerically different in Sight and in Touch.

V. (Sect. 147-48.) The explanation of the tactual significance of the visible and visual Signs, upon which human experience proceeds, is offered in the Theory that all visible phenomena are arbitrary signs in what is virtually the Language of Nature, addressed by God to the senses and intelligence of Man.

VI. (Sect. 149-60.) The true object studied in Geometry is the kind of Extension given in Touch, not that given in Sight: real Extension in all its phases is tangible, not visible: colour is the only immediate object of Sight, and colour being mind-dependent sensation, cannot be realised without percipient mind. These concluding sections are supplementary to the main argument.

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The fact that distance or outness is invisible is sometimes regarded as Berkeley’s contribution to the theory of seeing. It is rather the assumption on which the _Essay_ proceeds (sect. 2). The _Essay_ does not prove this invisibility, but seeks to shew how, notwithstanding, we learn to find outness through seeing. That the relation between the visual signs of outness, on the one hand, and the real distance which they signify, on the other, is in all cases arbitrary, and discovered through experience, is the burden of sect. 2-40. The previously recognised signs of “considerably remote” distances, are mentioned (sect. 3). But _near_ distance was supposed to be inferred by a visual geometry—and to be “suggested,” not signified by arbitrary signs. The determination of the visual signs which suggest outness, near and remote, is Berkeley’s professed discovery regarding vision.

An induction of the visual signs which “suggest” distance, is followed (sect. 43) by an assertion of the wholly sensuous reality of _colour_, which is acknowledged to be the only immediate object of sight. Hence _visible_ extension, consisting in colour, must be dependent for its realisation upon sentient or percipient mind. It is then argued (sect. 44) that this mind-dependent visible outness has no resemblance to the tangible reality (sect. 45). This is the first passage in the _Essay_ in which Touch and its data are formally brought into view. Tactual or locomotive experience, it is implied, is needed to infuse true reality into our conceptions of distance or outness. This cannot be got from seeing any more than from hearing, or tasting, or smelling. It is as impossible to see and touch the same object as it is to hear and touch the same object. Visible objects and ocular sensations can only be _ideal signs_ of _real things_.

The sections in which Touch is thus introduced are among the most important in the _Essay_. They represent the outness given in hearing as wholly sensuous, ideal, or mind-dependent: they recognise as more truly real that got by contact and locomotion. But if this is all that man can see, it follows that his _visible_ world, at any rate, becomes real only in and through percipient mind. The problem of an _Essay on Vision_ is thus, to explain _how_ the visible world of extended colour can inform us of tangible realities, which it does not in the least resemble, and with which it has no _necessary_ connexion. That visible phenomena, or else certain organic sensations involved in seeing (sect. 3, 16, 21, 27), gradually _suggest_ the real or tangible outness with which they are connected in the divinely constituted system of nature, is the explanation which now begins to dawn upon us.

Here an ambiguity in the _Essay_ appears. It concludes that the _visible_ world cannot be real without percipient realising mind, i.e. not otherwise than ideally: yet the argument seems to take for granted that we are percipient of a _tangible_ world that is independent of percipient realising mind. The reader is apt to say that the tangible world must be as dependent on percipient mind for its reality as the visible world is concluded to be, and for the same reason. This difficulty was soon afterwards encountered in the book of _Principles_, where the worlds of sight and touch are put on the same level; and the possibility of unperceived reality in both cases is denied; on the ground that a material world cannot be realised in the total absence of Spirit—human and divine. The term “external” may still be applied to tactual and locomotive phenomena alone, if men choose; but this not because of the ideal character of what is seen, and the unideal reality of what is touched, but only because tactual perceptions are found to be more firm and steady than visual. Berkeley preferred in this way to _insinuate_ his new conception of the material world by degrees, at the risk of exposing this juvenile and tentative _Essay on Vision_ to a charge of incoherence.

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The way in which visual ideas or phenomena “suggest” the outness or distance of things from the organ of sight having been thus explained, in what I call the First Part of the _Essay_, the Second and Third Parts (sect. 52-120) argue for the invisibility of real extension in two other relations, viz. magnitude and locality or situation. An induction of the visual signs of tangible size and situation is given in those sections. The result is applied to solve two problems then notable in optics, viz. (1) the reason for the greater visible size of the horizontal moon than of the moon in its meridian (sect. 67-87); and (2) the fact that objects are placed erect in vision only on condition that their images on the retina are inverted (sect. 88-120). Here the antithesis between the ideal world of coloured extension, and the real world of resistant extension is pressed with vigour. The “high” and “low” of the visible world is not the “high” and “low” of the tangible world (sect. 91-106). There is no resemblance and no necessary relation, between those two so-called extensions; not even when the number of visible objects happen to coincide with the number of tangible objects of which they are the visual signs, e.g. the visible and tangible fingers on the hand: for the born-blind, on first receiving sight, could not parcel out the visible phenomena in correspondence with the tangible.

The next Part of the _Essay_ (sect. 121-45) argues for a specific as well as a numerical difference between the original data of sight and the data of touch and locomotion. Sight and touch perceive nothing in common. Extension in its various relations differs in sight from extension in touch. Coloured extension, which alone is visible, is found to be different in kind from resistant extension, which alone is tangible. And if actually perceived or concrete extensions differ thus, the question is determined. For all extension with which man can be concerned must be concrete (sect. 23). Extension in the abstract is meaningless (sect. 124-25). What remains is to marshal the scattered evidence, and to guard the foregoing conclusions against objections. This is attempted in sections 128-46.

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The enunciation of the summary generalisation, which forms the “New Theory of Vision” (sect. 147-8), may be taken as the Fifth and culminating Part of the _Essay_.

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The closing sections (149-60), as I have said, are supplementary, and profess to determine the sort of extension—visible or tangible—with which Geometry is concerned. In concluding that it is tangible, he tries to picture the mental state of Idominians, or unbodied spirits, endowed with visual perceptions _only_, and asks what _their_ conception of outness and solid extension must be. Here further refinements in the interpretation of visual perception, and its organic conditions, which have not escaped the attention of latter psychologists and biologists, are hinted at.

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Whether the data of sight consist of non-resembling arbitrary Signs of the tactual distances, sizes, and situations of things, is a question which some might prefer to deal with experimentally—by trial of the experience of persons in circumstances fitted to supply an answer. Of this sort would be the experience of the born-blind, immediately after their sight has been restored; the conception of extension and its relations found in persons who continue from birth unable to see; the experience (if it could be got) of persons always destitute of all tactual and locomotive perceptions, but familiar with vision; and the facts of seeing observed in infants of the human species, and in the lower animals.

Berkeley did not try to verify his conclusions in this way. Here and there (sect. 41, 42, 79, 92-99, 103, 106, 110, 128, 132-37), he conjectures what the first visual experience of those rescued from born-blindness is likely to be; he also speculates, as we have seen, about the experience of unbodied spirits supposed to be able to see, but unable to touch or move (sect. 153-59); and in the Appendix he refers, in confirmation of his New Theory, to a reported case of one born blind who had obtained sight. But he forms his Theory independently of those delicate and difficult investigations. His testing facts were sought introspectively. Indeed those physiologists and mental philosophers who have since tried to determine what vision in its purity is, by cases either of communicated sight or of continued born-blindness, have illustrated the truth of Diderot’s remark—“préparer et interroger un aveugle-né n’eût point été une occupation indigne des talens réunis de Newton, Des Cartes, Locke, et Leibniz(275).”

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Berkeley’s _New Theory_ has been quoted as a signal example of discovery in metaphysics. The subtle analysis which distinguishes _seeing_ strictly so called, from judgments about extended things, suggested by what we see, appears to have been imperfectly known to the ancient philosophers. Aristotle, indeed, speaks of colour as the only proper object of sight; but, in passages of the _De Anima_(276) where he names properties peculiar to particular senses, he enumerates others, such as motion, figure, and magnitude, which belong to all the senses in common. His distinction of Proper and Common Sensibles appears at first to contradict Berkeley’s doctrine of the heterogeneity of the ideal visible and the real tangible worlds. Aristotle, however, seems to question the immediate perceptibility of Common Sensibles, and to regard them as realised through the activity of intelligence(277).

Some writers in Optics, in mediaeval times, and in early modern philosophy, advanced beyond Aristotle, in explaining the relation of our matured notion of distance to what we originally perceive in seeing, and in the fifteenth century it was discovered by Maurolyco that the rays of light from the object converge to a focus in the eye; but I have not been able to trace even the germ of the _New Theory_ in these speculations.

Excepting some hints by Descartes, Malebranche was among the first dimly to anticipate Berkeley, in resolving our supposed power of seeing outness into an interpretation of visual signs which we learn by experience to understand. The most important part of Malebranche’s account of seeing is contained in the _Recherche de la Vérité_ (Liv. I. ch. 9), in one of those chapters in which he discusses the frequent fallaciousness of the senses, and in particular of our visual perceptions of extension. He accounts for their inevitable uncertainty by assigning them not to sense but to misinterpretation of what is seen. He also enumerates various visual signs of distance.

That the _Recherche_ of Malebranche, published more than thirty years before the _Essay_, was familiar to Berkeley before the publication of his _New Theory_, is proved by internal evidence, and by his juvenile _Commonplace Book_. I am not able to discover signs of a similar connexion between the _New Theory_ and the chapter on the mystery of sensation in Glanvill’s _Scepsis Scientifica_ (ch. 5), published some years before the _Recherche_ of Malebranche, where Glanvill refers to “a secret deduction,” through which—from motions, &c., of which we are immediately percipient—we “spell out” figures, distances, magnitudes, and colours, which have no resemblance to them.

An approach to the _New Theory_ is found in a passage which first appeared in the second edition of Locke’s _Essay_, published in 1694, to which Berkeley refers in his own _Essay_ (sect. 132-35), and which, on account of its relative importance, I shall here transcribe at length:—

“We are further to consider concerning Perception that the ideas we receive by sensation are often, in grown people, altered by the judgment, without our taking notice of it. When we set before our eyes a round globe of any uniform colour, e.g. gold, alabaster, or jet, it is certain that the idea thereby imprinted in our mind is of a flat circle, variously shadowed, with several degrees of light and brightness coming to our eyes. But, we having by use been accustomed to perceive what kind of appearance convex bodies are wont to make in us, what alterations are made in the reflection of light by the difference in the sensible figures of bodies—the judgment presently, by an habitual custom, alters the appearances into their causes; so that, from that which is truly variety of shadow or colour, collecting the figure, it makes it pass for a mark of figure, and frames to itself the perception of a convex figure and an uniform colour, when the idea we receive from them is only a plane variously coloured, as is evident in painting.

“To which purpose I shall here insert a problem of that very ingenious and studious promoter of real knowledge, the learned and worthy Mr. Molyneux, which he was pleased to send me in a letter some months since, and it is this:—Suppose a man born blind, and now adult, and taught by his touch to distinguish between a cube and a sphere of the same metal, and nighly of the same bigness, so as to tell, when he felt the one and the other, which is the cube and which the sphere. Suppose then the cube and the sphere placed on a table, and the blind man be made to see: quere, whether, by his sight, before he touched them, he could not distinguish and tell, which is the globe and which the cube? To which the acute and judicious proposer answers: ‘Not.’ For, though he has obtained the experience of how a globe, how a cube affects his touch; yet he has not obtained the experience that what affects his touch so and so, must affect his sight so and so; so that a protuberant angle in the cube, that pressed his hand unequally, shall appear to his eye as it does in the cube.—I agree with this thinking gentleman, whom I am proud to call my friend, in his answer to this his problem, and am of opinion that the blind man, at first sight, would not be able to say with certainty which was the globe and which the cube, whilst he only saw them; though he would unerringly name them by his touch, and certainly distinguish them by the difference in their figures felt.

“This I have set down, and leave with my reader, as an occasion for him to consider how much he may be beholden to experience, improvement, and acquired notions, where he thinks he had not the least use of, or help from them: and the rather because this observing gentleman further adds that, having, upon the occasion of my book, proposed this problem to divers very ingenious men, he hardly ever met with one that at first gave the answer to it which he thinks true, till by hearing his reasons they were convinced.

“But this is not I think usual in any of our ideas but those received by sight: because sight, the most comprehensive of the senses, conveying to our minds the ideas of light and colours, which are peculiar only to that sense; and also the far different ideas of space, figure, and motion, the several varieties of which change the appearance of its proper object, i.e. light and colours; we bring ourselves by use to judge of the one by the other. This, in many cases, by a settled habit, in things whereof we have frequent experience, is performed so constantly and so quick, that we take that for the perception of our sensation, which is an idea formed by our judgment; so that one, i.e. that of sensation, serves only to excite the other, and is scarce taken notice of itself; as a man who reads or hears with attention and understanding takes little notice of the character or sounds, but of the ideas that are excited in him by them.

“Nor need we wonder that this is done with so little notice, if we consider how very quick the actions of the mind are performed; for, as itself is thought to take up no space, to have no extension, so its actions seem to require no time, but many of them seem to be crowded into an instant. I speak this in comparison of the actions of the body.... Secondly, we shall not be much surprised that this is done with us in so little notice, if we consider how the facility we get of doing things, by a custom of doing, makes them often pass in us without notice. Habits, especially such as are begun very early, come at last to produce actions in us which often escape our observation.... And therefore it is not so strange that our mind should often change the idea of its sensation into that of its judgment, and make the one serve only to excite the other, without our taking notice of it.” (_Essay concerning Human Understanding_, Book II. ch. 9. § 8.)

This remarkable passage anticipates by implication the view of an interpretation of materials originally given in the visual sense, which, under the name of “suggestion,” is the ruling factor in the _New Theory of Vision_.

The following sentences relative to the invisibility of distances, contained in the _Treatise of Dioptrics_ (published in 1690) of Locke’s friend and correspondent William Molyneux, whose son was Berkeley’s pupil, illustrate Locke’s statements, and may be compared with the opening sections of the _Essay on Vision_:—

“In plain vision the estimate we make of the distance of objects (especially when so far removed that the interval between our two eyes bears no sensible proportion thereto, or when looked upon with one eye only) is rather the act of our judgment than of sense; and acquired by exercise, and a faculty of comparing, rather than natural. For, distance of itself is not to be perceived; for, ’tis a line (or a length) presented to our eye with its end toward us, which must therefore be only a point, and that is invisible. Wherefore distance is chiefly perceived by means of interjacent bodies, as by the earth, mountains, hills, fields, trees, houses, &c. Or by the estimate we make of the comparative magnitude of bodies, or of their faint colours, &c. These I say are the chief means of apprehending the distance of objects that are considerably remote. But as to nigh objects—to whose distance the interval of the eyes bears a sensible proportion—their distance is perceived by the turn of the eyes, or by the angle of the optic axes (_Gregorii Opt. Promot._ prop. 28). This was the opinion of the ancients, Alhazen, Vitellio, &c. And though the ingenious Jesuit Tacquet (_Opt. Lib. I._ prop. 2) disapprove thereof, and objects against it a new notion of Gassendus (of a man’s seeing only with one eye at a time one and the same object), yet this notion of Gassendus being absolutely false (as I could demonstrate were it not beside my present purpose), it makes nothing against this opinion.

“Wherefore, distance being only a line and not of itself perceivable, if an object were conveyed to the eye by one single ray only, there were no other means of judging of its distance but by some of those hinted before. Therefore when we estimate the distance of nigh objects, either we take the help of both eyes; or else we consider the pupil of one eye as having breadth, and receiving a parcel of rays from each radiating point. And, according to the various inclinations of the rays from one point on the various parts of the pupil, we make our estimate of the distance of the object. And therefore (as is said before), by one single eye we can only judge of the distance of such objects to whose distance the breadth of the pupil has a sensible proportion.... For, it is observed before (prop. 29, sec. 2, see also _Gregorii Opt. Promot._ prop. 29) that for viewing objects remote and nigh, there are requisite various conformations of the eye—the rays from nigh objects that fall on the eye diverging more than those from more remote objects.” (_Treatise of Dioptrics_, Part I. prop. 31.)

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All this helps to shew the state of science regarding vision about the time Berkeley’s _Essay_ appeared, especially among those with whose works he was familiar(278). I shall next refer to illustrations of the change which the _Essay_ produced.

The _New Theory_ has occasioned some interesting criticism since its appearance in 1709. At first it drew little attention. For twenty years after its publication the allusions to it were few. The account of Cheselden’s experiment upon one born blind, published in 1728, in the _Philosophical Transactions_, which seemed to bring the Theory to the test of scientific experiment, recalled attention to Berkeley’s reasonings. The state of religious thought about the same time confirmed the tendency to discuss a doctrine which represented human vision as interpretation of a natural yet divine language, thus suggesting Omnipresent Mind.

Occasional discussions of the _New Theory_ may be found in the _Gentleman’s Magazine_, from 1732 till Berkeley’s death in 1753. Some criticisms may also be found in Smith’s _Optics_, published in 1738.