1732, collated with the two preceding and with the posthumous ones. The Appendix is reprinted from the second edition.

The ascertainment by reflection of the contents and relations of purely visual consciousness is one of three problems professedly solved in Berkeley's metaphysical account of the material world. That visible objects are a system of arbitrary signs of tangible matter, is the conclusion of this Essay; that objects visible and tangible are a system of sensible signs of absent objects of sense, is the conclusion of the Principles of Human Knowledge, and especially of the Dialogues of Hylas and Philonous; and that this arbitrary system of signs, which cannot exist without a percipient, is a sensible expression of the Divine ideas, presence, and providence, is the conclusion common to all the three treatises. This last comprehensive conclusion is illustrated and applied in the New Theory of Vision Vindicated, and in Berkeley's other philosophical and theological works. We trace it in his old age throughout the contemplative and mystical philosophy of Siris.

A due appreciation of Berkeley's New Theory of Vision, and of its relative place in his metaphysics, thus requires a study not merely of this tentative and juvenile Essay, but also of its development and applications in his more matured works. This has been commonly forgotten, alike by the hostile critics and by the professed disciples of the Theory.

Various circumstances contribute to make this Essay more perplexing to the reader than perhaps any of Berkeley's other works.

Its occasion and design, and its relation to his conception of matter, are to some extent explained in the 43rd and 44th sections of the Principles of Human Knowledge. These sections are so far a key to the Essay. They inform us that in this earlier work Berkeley intentionally used language which seems to imply the absolute or independent existence of tangible objects,-it being 'beside his purpose' to 'examine and refute' that 'vulgar error' in 'a work on vision.' This reticence of his metaphysical conception of matter, in reasonings on vision which are fully explained only under that conception, is a chief occasion of the comparative obscurity of the Essay.

Another circumstance adds to our embarrassment. The earlier English writers in metaphysics were often careless in the employment of equivocal words. Even Berkeley was no exception. We are now accustomed to greater precision in the use of metaphysical language, and that language has itself undergone many changes. Some of the principal terms in the Essay are equivocal. It is enough to refer to the words perception, sensation, sight, external, and distance, with their

conjugates. Others, for example idea and touch, have had their meaning modified, and it is difficult for the modern reader habitually to return to that with which they were associated in Berkeley's mind (cf. sect. 120).

6

The interchange of the terms 'outward,' 'outness,' externality,' 'without the mind,' and 'without the eye' is confusing, if we forget that Berkeley in this treatise adopts language which implies that mind is locally and literally diffused over our organism, and coextensive with it, so that being absent or at a distance from the organism is being absent or at a distance from mind. I have tried in the annota→ tions to obviate some of these ambiguities.

The Essay abounds in repetition, while its logical structure, its train of thought, and even its leading generalization are not to be apprehended without a careful study and collation of passages. This, with the active exercise of thought, and exact use of words, which the nature of the subject requires, as Berkeley himself repeatedly reminds us, has enveloped the treatise in a cloud of misconceptions, which the author's subsequent Vindication has not removed.

I shall endeavour in what follows to present in an orderly way the principal propositions of the Essay, and to indicate the nature of the evidence by which they are sustained.

The reader must remember that the Essay is a professed appeal to pure consciousness. It is an analysis, immediately of what we are conscious in seeing, and by suggestion of what we are conscious in touch. It takes no observation of mere optical or physiological phenomena (cf. Theory of Vision Vindicated, sect. 43), in its exclusive attention to the facts of consciousness which underlie them; and it is only after what we are conscious of in seeing has been ascertained, that the result is incidentally, or now and then by way of verification, applied to solve some celebrated optical or physiological puzzle. The treatise is in short a professed account of the facts, the whole facts, and nothing but the facts of which we are visually conscious, as distinguished from pretended facts and metaphysical abstractions, which confused thought, an irregular exercise of imagination, or an abuse of words had substituted for them. It is a contribution to the psychological analysis of the fact of vision, and not a deduction from merely physical experiments in optics or the physiology of the eye.

The Essay contains some preliminary analyses, which gradually conduct to the constructive principle that properly constitutes the New Theory.

These preliminary inquiries enforce the antithesis of the two worlds of visible objects and tangible objects, as regards—

1. Distance, i. e. externality in space relatively to our organism;

2. Magnitude or size, i. e. occupancy of a larger or smaller quantity

of space;

3. Situation, or position relatively to one another in space.

The constructive principle, or New Theory proper, is the explanation of the synthesis in which, notwithstanding this radical antithesis of their constituents, we are accustomed to blend in imagination what we see and what we touch, as common properties of 'the same thing.'

From the beginning of the second section onwards, the Essay may be broadly divided into six Parts, devoted in succession to a proof of the six following theses, regarding the relation of Sight to Extension in its three dimensions::

I. (Sect. 2-51.) Distance, or the fact of an interval between two points in the line of vision, in other words externality in space, in itself invisible, is, in all cases in which we appear to see it, only suggested to our imagination by certain visible phenomena and visual sensations, which are its arbitrary signs.

II. (Sect. 52-87.) Magnitude, or the external space that objects occupy, is absolutely invisible: all that we can see is merely a greater or less quantity of colour, and our apparently visual perceptions of real magnitude are interpretations of the tactual meaning of colours and other sensations in the visual organ.

III. (Sect. 88-120.) The Situation of objects, or their relation to one another in space, is invisible: all that we can see is variety in the relations of quantities of colour to one another, our supposed pure vision of actual locality being an interpretation of visual signs.

IV. (Sect. 121-146.) There is no sensible object common to sight and touch space or extension, which has the best claim to this character, and which is nominally the object of both, is specifically as well as numerically different in each,-externality in space, or distance, being absolutely invisible, while size and situation, as visible, have nothing in common with size and situation as tangible.

V. (Sect. 147–148.) The explanation of the unity which we attribute

In his two scientific expositions of his New Theory of Vision Berkeley reverses his order of procedure. In this Essay he ascends from the preliminary analyses of consciousness, which enforce the antithesis of the visual and tactual, to the summary generalisation or theory of their union;

in the Vindication he descends synthetically from the Theory to those inferences regarding Situation, Magnitude, and Distance, which it involves. (See Essay, sect. I; and cf. Theory of Vision Vindicated, &c., sect. 38.)

to sensible things, as complements of visible and tangible qualities of one and the same substance, is contained in the Theory that visible ideas and visual sensations, arbitrary signs in a Divine Language, are significant of distances, and of the real sizes and situations of distant things; while the constant association in nature of the two worlds of vision and touch, has so associated them in our thoughts, that visible and tangible extension are habitually regarded by us as specifically and even numerically one.

VI. (Sect. 149-160.) The proper object of geometry is the kind of Extension given in our tactual experience, and not the kind of Extension given in our visual experience; and neither real solids nor real planes can be seen-real Extension in all its phases being invisible, and colour in its modifications of quantity being the only proper object of sight, while colour, being a pure sensation, cannot exist extraorganically in space.

It is curious that the doctrine of the invisibility of distance is popularly regarded as Berkeley's New Theory of Vision. In reality this is the assumption with which the Essay sets out (sect. 2). The part of the treatise (sect. 2-51) which especially treats of Distance does not profess to prove its invisibility, but, taking this for granted, to show that near distances as well as the more remote are suggested in seeing by certain arbitrary signs. That the relation between the signs and distances signified is, whether the distance be remote or near, a purely arbitrary relation, discoverable only by experience, is the burden of sect. 2-40. The previously recognised arbitrary signs of considerably remote' distanceslinear and aerial perspective-are mentioned (sect. 3). But distances less remote were then commonly supposed to be necessarily inferred, by a sort of visual geometry, and not to be merely suggested in imagination by experience. The determination of the true visual signs of near distances is the professed discovery of Berkeley regarding distance.

According to the Essay there are three sorts of arbitrary signs of near distances

1. The peculiar organic sensation which accompanies the adjustment of the eye to what is presented to it (sect. 16–20);

2. The degree of confusion in the visible object (sect. 21-26);

3. The organic sensation of straining (sect. 27).

Berkeley endeavours so far to verify this, by applying the second sort of sign to explain an optical phenomenon which Dr. Barrow and others had given up as inexplicable (sect. 29-40).

This generalization of the arbitrary signs of distance, visible and

organic, is followed (sect. 43) by a reference to the purely sensational nature of colour-the 'proper and immediate object of sight,' from which it is inferred that visible extension, as a quality of colour, must also be in the eye or rather in the mind.' We are thus led on, from the account given of the arbitrary signs of distances, to a proof that visible objects are not external to the animated organism, and that, inasmuch as they are sensations, they cannot exist without a mind. Berkeley's account of the manner in which distances are suggested in seeing, is his introduction to the doctrine that everything properly visible consists of, or is dependent on, the sensation of colour.

It is next argued (sect. 44) that this ideal world of visible objects bears no resemblance even to 'things placed at a distance' from us. Then the tangible nature of all things that are entitled to be called 'real' is enforced (sect. 45). Here, for the first time in the Essay, Touch and our tactual experience are mentioned. Tactual and locomotive experience is needed, we are virtually told, to infuse meaning into the term 'distance.' The notion cannot, it is alleged, be derived from seeing any more than from hearing (sect. 46). We can indeed both see and hear what suggests it, in consequence of our previous experience of the connexion of visible or audible signs with the tactual and locomotive meaning which they now signify. What we see is also apter, from its more frequent previous association, to suggest an ambient space, and objects existing at a distance in it, than audible objects are (sect. 47). Notwithstanding, it is as impossible to see and feel the same thing as it is to hear and feel the same thing. Visible objects and organic sensations-the arbitrary signs of distances, and of things placed at a distance-are, to all intents and purposes, a language; and they are one in which the signs are so blended with their significations that a life devoted to reflective analysis is not able fully to disentangle them (sect. 51).

Sections 43, 44, and 45 are in some respects the most important in the Essay. They represent visible extension as based upon sensation— the sensation of colour; they recognise, as real or external, only that extension which is derived from tactual and locomotive experience. If sensations, in their varieties of quality and quantity, are the only objects we see, it follows that the visible world cannot be without the mind.' The problem of the Essay is, to explain how sensations or ideas of colour, a consciousness of which constitutes vision, can inform us about tangible objects, which they do not in the least resemble, and with which they have no necessary connexion in thought. That certain visible ideas, and certain organic sensations which accompany vision (sect. 3, 16, 21, 27, 56,