1.2: The Theory of Vision Vindicated and Explained (1733)

A. Letter from an anonymous critic

[We have the critic’s letter, which was published in a journal, but it won’t be given here. Considered as criticism of Berkeley’s work it is boring and worthless; its writer was at best a fourth-rate thinker.]

B. A warning against creeping atheism

v1. [Berkeley opens with remarks about the kind of critic ‘who contradicts himself and misrepresents me’, and doesn’t deserve to be answered. Then he continues:] But argument, I allow, has a right to be considered, and where it doesn’t convince it has a right to be opposed with reason. Being convinced that the Theory of Vision published with Alciphron provides thinking men with a new and unanswerable proof of the existence and immediate operation of God, and the constant condescending [see Glossary] care of his providence, I think I ought to defend and explain it as well as I can at a time when atheism has made more progress than some are willing to admit and than others are willing to believe.

v2. Anyone who •considers that the present open enemies of Christianity began their attacks against it under the specious pretext of defending the Christian church and its rights, and •observes the same men pleading for natural religion, will be tempted to suspect their views and to judge their sincerity in one case from what they have shown in the other. Certainly the notion of a watchful, active, intelligent, free Spirit who has dealings with us and in whom we ‘live and move and have our being’ [Acts 17:28] is not the most prominent topic in the books and conversation even of the so-called deists! [see Glossary] Besides, as their schemes take effect we can plainly see moral virtue and the religion of nature fading away, and can see—both from reason and from experience—that destroying the revealed religion must end in atheism or idolatry. Admittedly, many minute [see Glossary] philosophers would not like at present to be accounted atheists. But twenty years ago how many would have been offended to be thought infidels but would now be much more offended to be thought Christians! It would be unjust to charge with atheism people who are not really tainted with it; but it would be very uncharitable and imprudent to overlook it in those who are, and allow such men under specious pretexts to spread their principles and eventually play the same game with natural religion that they have done with revealed religion.

v3. [The ‘admired writer’ referred to here is Shaftesbury, who is the primary target of Berkeley’s long and sometimes bitter attack Alciphron, or The Minute Philosopher. That work can be found on the website that houses this version of the vision works.] Some innocent admirers of a certain plausible pretender to deism and natural religion would doubtless be shocked if someone told them that that admired writer’s works show strong signs of atheism and irreligion—lack of natural religion as well as of revealed religion. But

• to introduce taste instead of duty ·as the basis for morality·,
• to make man a necessary ·rather than a free· agent, and
• to make fun of the day of judgment

seem to all intents and purposes atheistic, i.e. subversive of all religion. And every attentive reader can clearly discover those to be his principles, although it isn’t always easy to fix a determinate sense on such a loose and incoherent writer. There seems to be a certain way of writing—whether good or bad, tinsel or sterling, sense or nonsense—that is suited to the size of understanding that qualifies its owners for the minute philosophy, and impresses and dazzles those clever men who are led by it, they don’t know how and they don’t know where to. The atheist with the best chance of spreading his principles is the one who gilds them and insinuates them and at the same time disclaims them. He may in the cause of virtue and natural religion acknowledge the strongest traces of wisdom and power throughout the structure of the universe; but what good is that if this wisdom isn’t employed to observe our actions and the power isn’t used to reward or punish them, i.e. if we don’t believe •that we are accountable or •that God is our judge?

v4. Everything that is said ·by deists· about

• a vital principle, or order, harmony, and proportion,
• the natural rightness and fitness of things,
• taste and enthusiasm,

can hang together and be supported without

• any religion, even natural religion,
• any notion of law or duty,
• any belief in a lord or judge, or
• any religious sense of a God.

Contemplating the ideas of beauty, virtue, order, and fitness is one thing; a sense of religion is another. So long as we admit no source of good actions but natural affection, no reward but natural consequences; so long as we apprehend no judgment, harbour no fears, and cherish no hopes of a future state, but laugh at all these things with the author of the Characteristics [Shaftesbury] and those he admires as the liberal and polished part of mankind, how can we be said to be religious in any sense? What is here that an atheist can’t provide for in his account in as well as a theist? On this view of things, couldn’t •fate or •nature serve the same moral purpose as a •deity? And isn’t this what all those charming pretences ultimately add up to?

v5. Atheistic men who accept no principles of any religion, natural or revealed, are increasing in number, including people of high rank in society; this has long since been explicitly acknowledged by this same plausible pretender to deism and enthusiasm—who’ll be agreed to be a good judge!. . . .

v6. That atheistic principles have taken deeper root, and are further spread, than most people are apt to imagine, will be obvious to anyone who considers that •pantheism, materialism, and fatalism are nothing but slightly disguised atheism; that •the notions of Hobbes, Spinoza, Leibniz and Bayle are relished and applauded; that •just as those who deny the freedom and immortality of the soul are in effect denying its existence, so also those who deny that God is an observer, judge, and rewarder of human actions are in effect denying his existence; and that •the course of arguing pursued by infidels leads to atheism as well as infidelity. . . .

If •I see it in their writings, if •they admit it in their conversation, if •their ideas imply it, if •their goals require them to suppose it, if •their leading author has claimed to demonstrate atheism but thought fit to conceal his demonstration from the public, if •this was known in their clubs and yet that author had followers and was represented to the world as believing in natural religion—if these things are so (and I know them to be so), surely what the supporters of their schemes want to tone down is what others have a duty to display and refute.

v7. To men of plain sense and common understanding the characters of divinity are large and legible throughout the whole creation; but there are others whom we have to convert, adversaries we have to oppose—men committed to false systems and proof against the common arguments, who must be dealt with on a different basis. Conceited, metaphysical, disputing men must be paid in another coin; we must show that truth and reason in all shapes are equally against them. . . .

v8. Meanwhile this much is evident: good men who don’t care to employ their thoughts on this Theory of Vision have no reason to find fault. They are just where they were, in full possession of all the other arguments for a God, none of which are weakened by this one. As for those who take the trouble to examine and consider this subject, I hope they’ll be pleased to find, at a time when so many schemes of atheism are restored or invented, a new and unique argument in proof of the immediate care and providence of a God who present to our minds and directs our actions. These considerations convince me that I can’t employ myself more usefully than in contributing to awaken and possess men with a thorough sense of the Deity inspecting, concerning, and interesting itself in human actions and affairs, so I hope it won’t be disagreeable to you [he is addressing the critic] if for this purpose I make my appeal to reason from your remarks on what I have written about vision. Men who differ about the means may yet agree about the goal, both with open honesty and love of truth.

C. Reply to the critic: preliminaries

[The next ten paragraphs give a beginner’s lesson, for the critic, who clearly needed it! It is included here, as being of some general interest.]

v9. By a ‘sensible object’ I mean something that is properly perceived by sense. Things properly perceived by sense are immediately perceived. There may also be other things suggested to the mind by means of those proper and immediate objects; things suggested in this way are not objects of that sense, because they are really only objects of the imagination that originally belonged to some other sense or faculty. Thus, sounds are the proper objects of hearing, being properly and immediately perceived by that sense and by no other. By the mediation of sounds or words, other things can be suggested to the mind, but those things aren’t thought of as objects of hearing.

v10. The objects of each sense, though truly or strictly perceived only by that sense, can be suggested to the imagination by some other sense. So the objects of all the senses can become objects of imagination, a faculty that represents all sensible things. A colour, which is truly perceived by sight alone, may upon hearing the words ‘blue’ or ‘red’ be apprehended by the imagination. It is in a primary and unique manner an object of sight; in a secondary manner it is an object of imagination; but it can’t properly be supposed to be an object of hearing.

v11. The objects of sense, being things immediately perceived, are otherwise called ‘ideas’. The cause of these ideas, i.e. the power of producing them, is not the object of sense because it isn’t itself perceived but only inferred by reason from its effects—namely the objects or ideas that are perceived by sense. From our ideas of sense we are entitled to make inferences to power, cause, agent. But we’re not to infer that our ideas are like this power, cause, or active being. On the contrary, it seems evident that the only thing an idea can be like is another idea, and that our ideas or immediate objects of sense don’t include anything involving power, causality, or agency.

v12. It follows that the power or cause of ideas is an object not of sense but of reason. Our knowledge of the cause is measured by the effect; of the power, by our idea. We have nothing to say about the absolute nature of external causes or powers; they aren’t objects of our sense or perception. So the only definite intelligible sense for the phrase ‘sensible object’ is as referring not to •the absolutely existing external cause or power but to •the ideas themselves produced by it.

v13. When two ideas are observed to be inter-connected, the man in the street sees this as involving the relation of •cause to effect, whereas in strict and philosophic truth they are only related as •sign to thing signified. We know our ideas, so we know that one idea can’t be the cause of another. We know that our ideas of sense are not the causes of themselves. We know also that we don’t cause them. Hence we know they must have some efficient cause distinct from any ideas and distinct from us.

v14. My purpose in treating vision was to consider •the effects and appearances, •the objects perceived by my senses, •the ideas of sight as connected with those of touch; to inquire how one idea comes to suggest another belonging to a different sense, how things visible suggest things tangible, how present things suggest distant and future things, whether by likeness, by necessary connection, by geometrical inference, or by arbitrary institution [= ‘or through systems set up by men’].

v15. It has indeed been a prevailing opinion—an undoubted principle—among mathematicians and philosophers that there are certain ideas common to both senses; from which arose the distinction between primary and secondary qualities. But I think I have demonstrated that there is no such thing as a common object, an idea or kind of idea perceived both by sight and touch.

v16. To talk about the nature of vision with due exactness, the first thing needed is precision in what we say about our own ideas:

• to distinguish where there is a difference;
• to call things by their right names;
• to define terms, and not confuse ourselves and others by using them ambiguously.

Failure in those respects has often produced mistakes: talking as if one idea was the efficient cause of another; mistaking inferences of reason for perceptions of sense; confusing the power residing in something external with the proper object of sense, which is in truth no more than our own idea.

v17. When we have well understood and considered the nature of vision we may, by reasoning from that be better able to acquire some knowledge of the external unseen cause of our ideas—whether it is one or many, thinking or non-thinking, active or inert, body or spirit. But the most promising way to get an intelligible theory of vision in the first place, and to learn its true principles, is not by attending to unknown substances, external causes, agents or powers; and not by drawing conclusions about things that are obscure, unperceived, and altogether unknown—or by drawing conclusions from such things.

v18. . . . .It follows that if someone is planning to treat of the nature of vision it would be wrong if instead of attending to visible ideas he defined the object of sight to be that obscure cause, that invisible power or agent, which produced visible ideas in our minds. Such a cause or power doesn’t seem to be the object of the visual sense or of the science of vision, because anything we know about it we know only from its effects. I now proceed to consider the principles laid down in your letter, which I shall take in order you gave them.

D. Reply to the critic

[Berkeley now devotes sixteen paragraphs to picking apart the critic’s letter. The letter is so bad that Berkeley’s patient dealings with it are neither instructive nor interesting to the rest of us. Only the final two paragraphs are given here.]

v33. We impose not only on others but often on ourselves when we use terms in an unsteady or ambiguous way. One would imagine that an ‘object’ is something that is perceived; and when that word is used in a different sense [as it is by the critic], I’m at a loss for its meaning and consequently can’t understand any arguments or conclusions in which it occurs. My treatise on vision may be difficult for a casual reader, perhaps through •some inaccuracy [see Glossary] in my writing and also •the special nature of the subject, which isn’t always easy to explain or to conceive. But to anyone who attends properly and makes my words stimulus to his own thinking, I think the whole work will be very intelligible, and when it is rightly understood I hardly doubt that it will be assented to. One thing at least I can affirm: if I am mistaken, I can’t blame that on haste or carelessness, because I have taken true pains and much thought about it.

v34. If you, Sir, had thought it worthwhile to deal with the subject in more detail, to point out individual passages in my treatise, to answer any of my objections to currently accepted notions, to refute any of my arguments on behalf of mine, or made a particular application of your own—then I might well have profited by your reflections. But it seems to me that either we have been considering different things, or we have been considering the same things in such different views that neither can cast any light on the other. But I shall take this opportunity to make a review of my theory, in order to make it more easy and clear; especially because in all my work on this subject it has become familiar to me, and in expounding things that are familiar to ourselves we’re too apt to think them familiar to others.

E. A review of the theory

v35. It seemed proper, if not unavoidable, to begin in the usual style of writers on optics by admitting as true various things that are not strictly true but only accepted by the vulgar [see Glossary] and regarded as true. There has been a long and close connection in our minds between the ideas of sight and of touch. So they are considered as one thing, a prejudice which fits well enough with the purpose of life, and language is also fitted to this prejudice. The work of science and speculation [see Glossary] is to unravel our prejudices and mistakes, •untwisting the closest connections, •distinguishing things that are different, •giving us distinct views instead of confused or perplexed ones, •gradually correcting our judgment, and reducing it to a philosophical exactness. But this takes time and is done gradually, so that it is extremely difficult—if not impossible—to escape the snares of everyday language and avoid being betrayed by it into saying things that aren’t strictly true or even consistent. This makes thought and candour more especially necessary in the reader. Because language is fitted to men’s •prenotions [see Glossary] and •everyday doings, it is difficult to use it to express the precise truth of things, which is so distant from those doings and so contrary to our prenotions.

v36. In the design of vision as of other things, the wisdom of providence seems to have had a concern for man’s operations rather than his theoretical understanding. The very features that are so admirably fitted to practical convenience often perplex the understanding. These immediate suggestions and constant connections are useful to direct our actions; but distinguishing things that get run together is no less necessary for speculation and knowledge of truth.

v37. The knowledge of these connections, relations, and differences of visible things and tangible things—their nature, force, and significance—has not been duly considered by previous writers on optics, and seems to have been the great desideratum in that science, which has been confused and imperfect because of the lack of it. So the understanding of vision has needed

• a treatise of this philosophical kind

at least as much as it has needed

• the physical consideration of the eye, nerve, coats, humours, refractions, bodily nature, and motion of light; or
• the geometrical application of lines and angles for practise or theory, in dioptric glasses and mirrors, for computing and reducing to some rule and measure our judgments so far as they are proportional to the objects of geometry.

For a complete theory of optics, vision should be considered in all these three ways.

v38. In developing my theory of vision I followed a certain known method in which men often arrive at truth by starting from false and popular suppositions. There is also a way of delivering science or truth that has already been found, in which the order is reversed: we start from the conclusions that we reached by the other method. I shall therefore now begin with the conclusion that vision is the language of the Author of nature, deducing from that theorems and solutions of phenomena, and explaining the nature of visible things and the visual faculty.

v39. Ideas that are observed to be connected with other ideas come to be considered as signs by means of which things that aren’t actually perceived by sense are signified or suggested to the imagination, whose objects they are and which alone perceives them. And just as sounds suggest other things, so characters—·e.g. letters of the alphabet·—suggest other sounds; and quite generally all signs suggest the things signified; there’s no idea that can’t offer to the mind another idea that has frequently been joined with it. In certain cases a sign may suggest its correlate as an image [= ‘as something like it’], in others as an effect, in others as a cause. But even when there’s no such similarity or causality, and no necessary connection whatsoever,

• one thing can suggest or signify another merely through their coexistence; and
• one idea can suggest or signify another merely through their being perceived together.

In these cases, the connection between them is arbitrary [see Glossary], but all that’s needed for this ‘suggest or signify’ relation is that there be this connection—·it doesn’t matter that its source is·.

v40. A great number of arbitrary signs, varied and appropriate, constitute a language. If the arbitrary connections are instituted by men it is an artificial language; if by the Author of nature it is a natural language. There’s no limit to the different kinds of light and sound there can be, enabling each to supply an endless variety of signs; which is why each has been employed to form languages—one by the arbitrary appointment of mankind, the other by that of God himself. A connection established by the Author of nature in the ordinary course of things can surely be called ‘natural’, as that made by men will be named ‘artificial’; but they are equally arbitrary. There is no more similarity or necessary connection between •tangible things and •the modifications of light than there is in ·artificial· languages between •the meanings and •the sounds. When you understand how various tones and articulations of voice are connected with their respective meanings, that is also how the various modes of light are connected with their respective correlates—i.e. how the ideas of sight are connected with the ideas of touch.

v41. As for light and its various modes or colours, all thinking men are agreed that they are ideas only of sight; they aren’t ideas of touch and they aren’t like any ideas that are perceived by that sense. But herein lies the mistake ·that even thinking men make·, of supposing that there are also other ideas that are common to both senses, being equally perceived by sight and by touch, such as

• extension,
• size,
• shape, and
• motion

But I have proved in my New Theory of Vision that there are in reality no such common ideas, and that the objects of sight marked by those ·four· words are entirely different and dissimilar from whatever is the object of touch and marked by the same names. [He adds some scolding words addressed to the writer of the critical letter.]

v42. To perceive is one thing; to judge is another. Similarly, to be suggested is one thing and to be inferred is another. Things are suggested and perceived by sense. We make judgments and inferences by the understanding. What we immediately and properly perceive by sight is its primary object, light and colours. What is suggested, or perceived by mediation of these, are tangible ideas, which may be considered as secondary and improper objects of sight. We infer causes from effects, effects from causes, and properties from one another when they are necessarily connected. But how does it happen that we apprehend by the ideas of sight certain other ideas that

• don’t resemble them,
• don’t cause them,
• aren’t caused by them, and
• have no necessary connection with them?

The solution of this problem, in its full extent, takes in the whole New Theory of Vision. This way of stating the situation puts it on a new footing, and throws a different light on it from all preceding theories.

v43. (i) To explain how the mind or soul of man simply sees is one thing, and belongs to philosophy. (ii) To consider particles as moving in certain lines, rays of light as refracted or reflected or crossing and making angles, is quite another thing and belongs to geometry. (iii) To account for the visual sense by the mechanism of the eye is a third thing, which belongs to anatomy and experiments. Of these, (ii) and (iii) are of use in practice, to make good the defects of sight and remedy its illnesses in accordance with the natural laws contained in this world of ours. But (i) is what makes us understand the true nature of vision considered as a faculty of the soul. And the whole of this, as I have already said, comes down to this simple question:

How does it happen that a set of ideas that are altogether different from tangible ideas nevertheless suggest them to us, when there’s no necessary connection between them?

To which the proper answer is that this is done in virtue of an arbitrary connection set up by the Author of nature.

v44. The proper and immediate object of vision is light in all its modes and variations—

• colours that vary in kind, in degree, in quantity;
• some colours lively and others faint;
• more of some colours and less of others;
• colours that vary in their boundaries or limits;
• colours that vary in their order and situation.

A blind man when first made to see might perceive these objects in which there is an endless variety; but he wouldn’t perceive—and wouldn’t even imagine—resemblance or connection between these •visible objects and •the ones perceived by touch. Lights, shades, and colours would suggest nothing to him about bodies, hard or soft, rough or smooth; nor would their quantities, limits, or order suggest to him geometrical figures, or extension, or situation, which they must do according to the generally accepted supposition that these objects are common to sight and touch.

v45. All the various sorts, combinations, quantities, degrees, and dispositions of light and colours would when first perceived be considered in themselves only as a new set of sensations and ideas. To a man born blind they would be wholly new and unknown, so he wouldn’t at first sight give them the names of things he already knew and perceived by his sense touch. But after some experience he would perceive their connection with tangible things, and would therefore •consider them as signs, and •give them (as is usual in other cases) the same names as the things signified.

v46. More and less, greater and smaller, extent, proportion, interval are all found in time as in space; but it doesn’t follow that these are homogeneous quantities. Similarly, from the attribution of common names across two senses it doesn’t follow that that visible ideas are homogeneous with those of touch. It’s true that terms denoting tangible extension, figure, location, motion, and the like are also applied to denote the quantity, relation, and order of the ideas of sight, but this comes only from experience and analogy. There is a higher and lower in the notes of music; men speak in a high or a low key. This is obviously no more than metaphor or analogy. Likewise, to express the order of visible ideas the words ‘situation’, ‘high’ and ‘low’, ‘up’ and ‘down’ are used, and their meaning when so used is analogical.

v47. But in the case of vision we don’t rest on a supposed analogy between different and heterogeneous natures. We suppose an identity of nature, i.e. one and the same object common to both senses. What leads us into this mistake is the following. The various motions of the head—upward and downward, to the right and to the left—are accompanied by a diversity in the visible ideas ·that are perceived·; so those motions and situations of the head, which in fact are tangible, confer their own attributes and labels on the visible ideas they are connected with. Thus visible ideas come to be termed ‘high’ and ‘low’, ‘right’ and ‘left’, and to be marked by other names indicating the modes of position. Before the experienced connection these words wouldn’t have been attributed to visual ideas, at least not in the primary and literal sense.

v48. This shows us how the mind is enabled to discern by sight the situation of distant objects. Those immediate ·visual· objects whose mutual relations and order come to be expressed by words concerning tangible place because they are connected with the real objects of touch, what we say and judge concerning the one we say and judge concerning the other, transferring our thought. . . .from the signs to the things signified. It is like what happens when we are hearing or reading a discourse: we overlook the sounds or letters, and instantly pass on to the meaning.

v49. But there is a great difficulty concerning the orientation of objects, as perceived by sight. The pencils of light-rays coming from any luminous object, after passing through the pupil and being refracted by the lens, delineate inverted pictures in the retina—pictures that are taken to be the immediate proper objects of sight. So how does it come about that the objects the pictures are of seem erect [see Glossary] and in their natural orientation when the pictures are inverted? The objects are perceived only by their pictures, so when the pictures are inverted it should follow that the objects seem to be inverted too. This difficulty is inexplicable on all the generally accepted principles and theories, but it has a most natural solution if we bear in mind that

• the retina,
• lens,
• pupil, and
• light-rays crossing when refracted ·by the lens· and reunited in distinct images similar to the external objects

are all things of an entirely tangible nature.

v50. The so-called pictures formed by the packets of rays after their crossing and refraction are not so truly pictures as images, or figures, or projections—tangible figures projected by tangible rays on a tangible retina, which are so far from being the proper objects of sight that they are not perceived by sight at all, being by nature altogether of the tangible kind and apprehended only by the imagination when we suppose them actually taken in by the eye. These tangible images on the retina have some resemblance to the tangible objects from which the rays are sent, and relative to those objects they are indeed inverted. But they are not and cannot be the proper immediate objects of sight. The writers of optics vulgarly suppose that they are; but this is a vulgar error, and when it is removed the difficulty I have mentioned is removed with it; it admits a just and full solution, being shown to arise from a mistake.

v51. So ‘pictures’ can be understood in a twofold sense, i.e. as referring to two quite dissimilar and heterogeneous kinds of item:

• pictures properly so-called, consisting of light, shade, and colours;
• items that are not properly pictures, but images projected on the retina.

Pictures are visible, and are the special objects of sight. Images are so far from this that a man blind from birth can perfectly imagine, understand, and comprehend them. And perhaps I should point out here that shapes and motions that we can’t actually feel but only imagine can nevertheless be regarded as tangible ideas because •they are of the same kind as objects of touch and •the imagination drew them from that sense.

v52. Throughout this whole affair the mind •is wonderfully apt to be deluded by the sudden suggestions of fancy [= ‘imagination’], which it confuses with the perceptions of sense, and •is prone to mistake a close and habitual connection between things that are utterly unalike for an identity of nature. The solution of this knot about inverted images seems to be the principal point in the whole optic theory; the hardest to comprehend, perhaps, but the most deserving of our attention, and when rightly understood the surest way to lead the mind into a thorough knowledge of the true nature of vision.

v53. Although these inverted images on the retina are altogether different in kind from the proper objects of sight, i.e. pictures, they can nevertheless be proportional to them. Indeed, the most different and heterogeneous things in nature can have analogy and be proportional each to other. For any given distance an image should be large or small in proportion as the radiating surface is large or small; so that the picture is large or small in proportion to the size of the radiating surface, i.e. the tangible real size of the thing; but it doesn’t follow that in common sight we perceive or judge concerning those tangible real sizes simply by the visible sizes of the pictures; because in common sight the distance is not given, tangible objects being placed at various distances; and the diameters of the images to which the pictures are proportional are inversely proportional to those distances, which •are not immediately perceived by sight. And even if they •were, it is certain that the mind does not compute the sizes of tangible objects of sight by means of the inverse proportion of the distances, and the direct proportion of the pictures. Your own experience will tell you that no such inference or reasoning accompanies the common act of seeing!

v54. To know how we perceive or apprehend by sight the real size of tangible objects, we must consider the properties of the immediate visible objects, namely the pictures. Some of these pictures are more lively, others more faint. Some are higher, others are lower in their own order or location; and although their order is quite distinct and altogether different from the order of tangible objects, it has a relation and connection with it and thus comes to be signified by the same terms—‘high’, ‘low’, and so forth. Now, by the size of the pictures, their faintness and their situation, we perceive the size of tangible objects. . . .

v55. To explain this point further, let us suppose. . . . [and then he launches into something that is quite straightforward, but his presentation of it gets off to a bad start. The basic idea is as follows. You are standing looking out at a landscape which stretches horizontally from you to the horizon. (Berkeley will be referring to this as ‘the horizontal plane’.) Suppose you are looking at this through a vertical transparent plane that is close to your eye and divided into small equal squares. What you see through the lowest squares of the vertical plane will be the bits of landscape closest to you; as your eye moves up to higher squares, you are looking at things that are further away; and because they are further away they will, Berkeley says:] appear vastly bigger than those seen through the lower squares, though occupying as many or even more of those equal squares in the vertical transparent plane.

v56. Rays coming from every point of each item in the horizontal plane, reaching the eye through the vertical transparent plane, exhibit to the imagination an image of the horizontal plane and all its parts, delineated in the transparent plane and occupying its squares up to a certain height marked out by a straight line reaching from the eye to the horizon—I call this the ‘reflection’. Every square contains an image of some corresponding part of the horizontal plane. We can call this entire image the ‘horizontal image’, and the picture corresponding to it the ‘horizontal picture’. In this representation the upper images suggest much greater sizes than the lower ones; and these upper images are also fainter. So •faintness and •situation co-operate with •visible size to suggest tangible size. For the truth of all this I appeal to the experience and attention of the reader who will add his own reflection to what I have written.

v57. It is true this transparent plane and the images supposed to be projected onto it are of a purely tangible nature. But then there are pictures corresponding to those images; those pictures have an order among themselves corresponding to the order among the images, and they (the pictures) are said to be ‘higher’ and ‘lower’ in terms of their order. These pictures also are more or less faint; and it’s really they and not the images that are the visible objects. So what I have said about the images must be thought of as said about the corresponding pictures, whose •faintness, •situation, and •size—all immediately perceived by sight—concur in suggesting the size of tangible objects, doing this only by an experienced connection.

v58. You might think that the size of the picture has a necessary connection with the size of the tangible object, or. . . .at least to be the sole means of suggesting it. But this is so far from being true that of two equally large visible pictures, one that is fainter and higher will suggest a tangible size a hundred times greater than the other suggests. . . .

v59. As well as the size, situation, and faintness of the pictures, our prenotions [see Glossary] concerning the kind, size, shape, and nature of things also contribute to the suggestion of tangible sizes. A picture in the shape of a •man will suggest a smaller size than it would in the shape of a •tower, even if size, faintness and situation were the same in both cases.

v60. Where the kind, faintness, and situation of the horizontal pictures are given, the suggested tangible size will be proportional to the visible size. . . . As an object gradually ascends from the horizon towards being overhead, our judgment concerning its tangible size gradually comes to depend more entirely on its visible size. The faintness is lessened as the quantity of intervening air and vapours is reduced. And as the object rises in the sky the eye of the spectator is also raised above the horizon, so that •faintness and •horizontal situation [see Glossary] cease to influence the suggestion of tangible size, and this suggestion (or judgment) moves towards being the effect solely of the visible size and the prenotions. But obviously if faintness, situation, and visible size concur to enlarge an idea, as some of those things are gradually omitted the idea will be gradually lessened. That is what happens with the moon, when it rises above the horizon and gradually lessens its apparent size as its altitude increases.

v61. It is natural for mathematicians to regard the visual angle and the apparent size as the sole or principal means of our apprehending the tangible size of objects. But what I have been saying makes it clear that our apprehension is much influenced by other things that have no similarity or necessary connection with tangible size.

v62. And these means that suggest tangible things’ size also suggest their distance; and in the same way, i.e. by experience alone and not by any necessary connection or geometrical inference. So the true medium by which we apprehend tangible distances are

• faintness/vividness,
• upper/lower situations,
• the visible size of the pictures, and
• our prenotions concerning tangible objects’ shape and kind.

This. . . .will be evident to anyone who bears in mind that visual angles etc. are not perceived by sight or by experience of any other sense. Whereas it is certain that the pictures—with their sizes, situations, and degrees of faintness—are proper objects of sight, and indeed the only ones; so that whatever is perceived by sight must be perceived by means of them. And this perception is partly produced by the prenotions that are gained by experience of touch or sight and touch conjointly.

v63. We need only to reflect on what we see to be assured that the smaller the pictures are, the fainter they are, and the higher they are (provided they are beneath the horizontal line [see v56 ] or its picture), the greater the distance will seem to be. . . . Obviously none of these things has in its own nature any necessary connection with the various distances. It will also appear, upon a little reflection, that various circumstances of shape, colour, and kind influence our judgments or apprehensions of distance; all of which follows from our prenotions, which are merely the effect of experience.

v64. It is natural for mathematicians to reduce things to the rule and measure of geometry, which makes them apt to suppose that apparent size has a greater share than it really does in forming our judgments concerning the distance of things from the eye. No doubt it would be an easy and ready rule to determine the apparent place of an object if we could say that its distance is inversely proportional to the diameter of its apparent size, and judge by this alone without bringing in any other circumstance. But this wouldn’t be a true rule, because in certain cases of vision by refracted or reflected light the lessening of the apparent size is accompanied by an apparent lessening of the distance [see 31].

v65. To satisfy us further that our judgments or apprehensions of size or distance don’t depend on the apparent size and nothing else, we need only ask the first painter we meet. He, considering nature rather than geometry, and knows well that several other circumstances contribute also; and . . . .we need only observe pieces of perspective and landscapes to be able to judge concerning this.

v66. When the object is so near that the distance between the pupils is a significant proportion of the distance to the object, the eyes turn or strain inward so as to unite the two optic axes; and the sensation that accompanies this is to be considered as one means of our perceiving distance. Admittedly this sensation belongs properly to the sense of feeling; but because it has a regular connection with distinct vision of near distance (the shorter the distance the greater the sensation), it’s natural that it should become a sign of distance and suggest it to the mind. That it actually does so can be seen from the known experiment of hanging up a ring edge-wise to the eyes, and then trying with one eye shut to insert a stick into it by a lateral motion. This turns out to be harder to do than with both eyes open, because with one eye closed one doesn’t have this means of judging by the sensation that accompanies the nearer meeting or crossing of the two optic axes.

v67. The mind of man is pleased to observe in nature rules or methods that are simple, uniform, general, and reducible to mathematics, as a means of rendering its knowledge at once easy and extensive. But we mustn’t •let our liking for uniformities or analogies take us away from truth and fact, or •imagine that the apparent place or distance of an object must be suggested by the same means in all cases. Indeed it squares with the purpose of vision to suppose that the mind has certain additional means or helps for judging more accurately the distance from us of the objects that are the nearest, and that consequently most concern us.

v68. When the distance is so small that the breadth of the pupil bears a considerable proportion to it, the object appears confused. This confusion is constantly observed in looking at such near objects, and it increases as the object comes closer, so this is a means of suggesting the place of an object. One idea is qualified to suggest another merely by being often perceived with it. And if one increases either directly or inversely in proportion to increases of the other, various degrees of the former will suggest various degrees of the latter by virtue of such habitual connection and proportional increase or diminution. Thus the gradual changing confusedness of an object may contribute to our apprehension of closeness when we look only with one eye. And this alone may explain Dr Barrow’s difficulty over the case he presented in 29, because that involved only one visible point. When several points are considered, i.e. the image is an extended surface, its increasing confusedness will co-operate with the increasing size to diminish its ·apparent· distance, which will be inversely proportional to both.

v69. Our experience in vision comes through the naked eye. We apprehend or judge from this same experience when we look through glasses. But we can’t in all cases conclude from the one to the other; because certain circumstances added or excluded by the use of glasses may sometimes alter our judgments, particularly as they depend upon prenotions.

v70. What I have written here may serve as a commentary on my Essay towards a New Theory of Vision; and I believe it will make it plain to thinking men. At a time when we hear so much about thinking and reasoning, it may seem needless to remark how useful and necessary it is to think if one is to

• obtain just and accurate notions,
• distinguish things that are different,
• speak consistently,
• know even one’s own meaning.

And yet for lack of thinking we may see many, even in these days, run into perpetual blunders and paralogisms. So no friend to truth and knowledge would restrain or discourage thinking. There are, it must be admitted, certain general maxims—the result of ages and of the collected sense of thinking persons—which serve instead of thinking as a guide or rule for the multitude; because the multitude don’t care to think for themselves, it is appropriate for them to be led by the thoughts of others. But those who depart from the public rule and set up for themselves,. . . .if they don’t think, what will men think of them? I don’t claim to have made any discoveries that couldn’t have been made by someone else who thought it worth the trouble; to which I add that without trouble and thought no man will ever understand the true nature of vision, or understand what I have written concerning it.

v71. Before I conclude, it may not be amiss to add this extract from the Philosophical Transactions concerning a man blind from his infancy and then as an adult made to see:

‘When he first saw, he was so far from making any judgment about distances that he thought all objects whatever touched his eyes (as he expressed it) as what he felt did his skin, and thought no objects so agreeable as those which were smooth and regular, though he could form no judgment of their shape, or guess what it was in any object that was pleasing to him. He didn’t know the shape of anything, and couldn’t tell one thing from another, however different in shape or size. But when he was told what things were, whose shape he before knew from feeling, he would carefully observe them so as to know them again; but having too many objects to learn at once, he forgot many of them; and (as he said) at first he learned to know and then forgot a thousand things in a day. Several weeks after the operation that restored his sight, being deceived by pictures, he asked which was the lying sense, feeling or seeing? He was never able to imagine any lines beyond the bounds he saw. The room he was in, he said, he knew to be part of the house, but he couldn’t conceive that the whole house could look bigger. He said that every new object was a new delight, and the pleasure was so great that he was at a loss for words to express it.’

Thus, by fact and experiment, those points of the theory that seem the most remote from common apprehension were considerably confirmed many years after I had been led to the discovery of them by reasoning.