either directly or inversely as the other, various degrees of the former will suggest various degrees of the latter, by virtue of such habitual connexion, and proportional increase or diminution. And thus the gradual changing confusedness of an object may concur to form our apprehension of near distance, when we look only with one eye. And this alone may explain Dr. Barrow's difficulty, the case as proposed by him regarding only one visible point 84. And when several points are considered, or the image supposed an extended surface, its increasing confusedness will, in that case, concur with the increasing magnitude to diminish its distance, which will be inversely as both.

69. Our experience in Vision is got by the naked eye. We apprehend or judge from this same experience, when we look through glasses. We may not, nevertheless, in all cases, conclude from the one to the other; because that certain circumstances, either excluded or added, by the help of glasses, may sometimes alter our judgments, particularly as they depend upon prænotions.

70. What I have here written may serve as a commentary on my Essay towards a New Theory of Vision; ard, I believe, will make it plain to thinking men. In an age wherein we hear so much of thinking and reasoning, it may seem needless to observe, how useful and necessary it is to think, in order to obtain just and accurate notions, to distinguish things that are different, to speak consistently, to know even our own meaning. And yet, for want of this, we may see many, even in these days, run into perpetual blunders and paralogisms. No friend, therefore, to truth and knowledge would lay any restraint or discouragement on thinking. There are, it must be owned, certain general maxims, the result of ages, and the collected sense of thinking persons, which serve instead of thinking, for a guide or rule to the multitude, who, not caring to think for themselves, it is fit they should be conducted by the thoughts of others. But those who set up for themselves, those who depart from the public rule, or those who would reduce them to it, if they do not think, what will men think of them? As I pretend not to make any discoveries which another might not as well have made, who should have thought it worth his pains: so I must needs say that without pains and thought

84 [Theory of Vision, sect. 29]-AUTHOR.

400 The Theory of Vision Vindicated and Explained.

no man will ever understand the true nature of Vision, or comprehend what I have wrote concerning it.

71. 85 Before I conclude, it may not be amiss to add the following extract from the Philosophical Transactions, relating to a person blind from his infancy, and long after 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 knew not the shape of anything, nor any one thing from another, however different in shape or magnitude: but upon being told what things were, whose form he before knew from Feeling, he would carefully observe them that he might 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 again forgot, a thousand things in a day. Several weeks after he was couched, 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, yet he could not conceive that the whole house could look bigger. He said every new object was a new delight, and the pleasure was so great that he wanted ways to express it 6.' -Thus, by fact and experiment, those points of the theory which seem the most remote from common apprehension were not a little confirmed, many years after I had been led into the discovery of them by reasoning.

85 Sect. 71 contains Berkeley's principal reference to external observation and experiment, as distinguished from reflection upon what we are conscious of-in verification of the New Theory, and especially in verification of the principle that our power of interpreting the real or tangible meaning of visual signs is due, not to an original

instinct, but to the suggestion of custom.

86

[Philosophical Transactions, No. 402] -AUTHOR. This is Berkeley's only allusion to the famous experiment of Cheselden, recorded in the Philosophical Transactions for 1728. This original record is given at full length in a supplementary note at the end of this volume.

H

FINIS.

A Letter from an Anonymous Writer to the Author of the Minute

Philosopher.

REVEREND SIR,

I have read over your treatise called Alciphron, in which the Free-thinkers of the present age, in their various shifted tenets, are pleasantly, elegantly, and solidly confuted. The style is easy, the language plain, and the arguments are nervous. But upon the Treatise annexed thereto2, and upon that part where you seem to intimate that Vision is the sole Language of God, I beg leave to make these few observations, and offer them to your's and your readers' consideration.

1. Whatever it is without that is the cause of any idea within, I call the object of sense; the sensations arising from such objects, I call ideas. The objects, therefore, that cause such sensations are without us, and the ideas within.

2. Had we but one sense, we might be apt to conclude that there were no objects at all without us, but that the whole scene of ideas which passed through the mind arose from its internal operations; but since the same object is the cause of ideas by different senses, thence we infer its existence. But, though the object be one and the same, the ideas that it produces in different senses have no manner of similitude with one another. Because,

3. Whatever connexion there is betwixt the idea of one sense and the dea of another, produced by the same object, arises only from experience. To explain this a little familiarly, let us suppose a man to have such an exquisite sense of feeling given him that he could perceive plainly and distinctly the inequality of the surface of two objects, which, by its reflecting and refracting the rays of light, produces

1 This 'Letter' appeared in the Daily Post-Boy, September 9, 1732. The first edition of Alciphron, or The Minute Philosopher, was published in Dublin six months before, and the Theory of Vision Vindicated and Explained four months after its appearance. The Letter 'is appended to the latter. VOL. I.

.D d

2 The Essay towards a New Theory of Vision-which was annexed to Alciphron, on account of its connexion with the Fourth Dialogue.

3

e. g. Essay, sect. 147; with which cf. Alcipbron, Dial. IV. sect. 7-15.

the ideas of colours. At first, in the dark, though he plainly perceived a difference by his touch, yet he could not possibly tell which was red and which was white, whereas a little experience would make him feel a colour in the dark, as well as see it in the light.

4. The same word in languages stands very often for the object without, and the ideas it produces within, in the several senses. When

it stands for any object without, it is the representative of no manner of idea; neither can we possibly have any idea of what is solely without us. Because,

5. Ideas within have no other connexion with the objects without than from the frame and make of our bodies, which is by the arbitrary appointment of God; and, though we cannot well help imagining that the objects without are something like our ideas within, yet a new set of senses, or the alteration of the old ones, would soon convince us of our mistake; and, though our ideas would then be never so different, yet the objects might be the same.

6. However, in the present situation of affairs, there is an infallible certain connexion betwixt the idea and the object; and, therefore, when an object produces an idea in one sense, we know, but from experience only, what idea it will produce in another sense.

7. The alteration of an object may produce a different idea in one sense from what it did before, which may not be distinguished by another sense. But, where the alteration occasions different ideas in different senses, we may, from our infallible experience, argue from the idea of one sense to that of the other; so that, if a different idea arises in two senses from the alteration of an object, either in situation or distance, or any other way, when we have the idea in one sense, we know from use what idea the object so situated will produce in the other.

8. Hence, as the operations of Nature are always regular and uniform, where the same alteration of the object occasions a smaller difference in the ideas of one sense, and a greater in the other, a curious observer may argue as well from exact observations as if the difference in the ideas was equal; since experience plainly teaches us that a just proportion is observed in the alteration of the ideas of each sense, from the alteration of the object. Within this sphere is confined all the judicious observations and knowledge of mankind.

Now, from these observations, rightly understood and considered, your New Theory of Vision must in a great measure fall to the ground, and the laws of Optics will be found to stand upon the old unshaken bottom. For, though our ideas of magnitude and distance in one sense

are entirely different from our ideas of magnitude and distance in another, yet we may justly argue from one to the other, as they have one common cause without, of which, as without, we cannot possibly have the faintest idea. The ideas I have of distance and magnitude by feeling are widely different from the ideas I have of them by seeing; but that something without which is the cause of all the variety of the ideas within, in one sense, is the cause also of the variety in the other; and, as they have a necessary connexion with it, we may very justly demonstrate from our ideas of feeling of the same object what will be our ideas in seeing. And, though to talk of seeing by tangible angles and tangible lines be, I agree with you, direct nonsense, yet to demonstrate from angles and lines in feelings, to the ideas in seeing that arise from the same common object, is very good sense, and so vice versa.

From these observations, thus hastily laid together, and a thorough digestion thereof, a great many useful corollaries in all philosophical disputes might be collected.

I am,

Your humble servant, &c.