and his followers, while the New Theory of Vision obtained the general
consent of the Scottish metaphysicians. Adam Smith refers to it in his
_Essays_ (published in 1795) as “one of the finest examples of
philosophical analysis that is to be found either in our own or in any
other language.” Dugald Stewart characterises it in his _Elements_ as “one
of the most beautiful, and at the same time one of the most important
theories of modern philosophy.” “The solid additions,” he afterwards
remarks in his _Dissertation_, “made by Berkeley to the stock of human
knowledge, were important and brilliant. Among these the first place is
unquestionably due to his _New Theory of Vision_, a work abounding with
ideas so different from those commonly received, and at the same time so
profound and refined, that it was regarded by all but a few accustomed to
deep metaphysical reflection, rather in the light of a philosophical
romance than of a sober inquiry after truth. Such, however, has since been
the progress and diffusion of this sort of knowledge, that the leading and
most abstracted doctrines contained in it form now an essential part of
every elementary treatise on optics, and are adopted by the most
superficial smatterers in science as fundamental articles of their faith.”
The _New Theory_ is accepted by Thomas Brown, who proposes (_Lectures_,
29) to extend the scope of its reasonings. With regard to perceptions of
sight, Young, in his _Lectures on Intellectual Philosophy_ (p. 102), says
that “it has been universally admitted, at least since the days of
Berkeley, that many of those which appear to us at present to be
instantaneous and primitive, can yet be shewn to be acquired; that most of
the adult perceptions of sight are founded on the previous information of
touch; that colour can give us no conception originally of those qualities
of bodies which produce it in us; and that primary vision gives us no
notion of distance, and, as I believe, no notion of magnitude.” Sir James
Mackintosh, in his _Dissertation_, characterises the _New Theory of
Vision_ as “a great discovery in Mental Philosophy.” “Nothing in the
compass of inductive reasoning,” remarks Sir William Hamilton (Reid’s
_Works_, p. 182, note), “appears more satisfactory than Berkeley’s
demonstration of the necessity and manner of our learning, by a slow
process of observation and comparison alone, the connexion between the
perceptions of vision and touch, and, in general, all that relates to the
distance and magnitude of external things(281).”
The New Theory of Vision has in short been generally accepted, so far as
it was understood, alike by the followers of Hartley and by the associates
and successors of Reid. Among British psychologists, it has recommended
itself to rationalists and sensationalists, to the advocates of innate
principles, and to those who would explain by accidental association what
their opponents attribute to reason originally latent in man. But this
wide conscious assent is I think chiefly confined to the proposition that
distance is invisible, and hardly reaches the deeper implicates of the
theory, on its extension to all the senses, leading to a perception of the
final unity of the natural and the supernatural, and the ultimate
spirituality of the universe(282).
Dedication
TO THE RT. HON. SIR JOHN PERCIVALE, BART.(283),
ONE OF HER MAJESTY’S MOST HONOURABLE PRIVY COUNCIL
IN THE KINGDOM OF IRELAND.
Sir,
I could not, without doing violence to myself, forbear upon this occasion
to give some public testimony of the great and well-grounded esteem I have
conceived for you, ever since I had the honour and happiness of your
acquaintance. The outward advantages of fortune, and the early honours
with which you are adorned, together with the reputation you are known to
have amongst the best and most considerable men, may well imprint
veneration and esteem on the minds of those who behold you from a
distance. But these are not the chief motives that inspire me with the
respect I bear you. A nearer approach has given me the view of something
in your person infinitely beyond the external ornaments of honour and
estate. I mean, an intrinsic stock of virtue and good sense, a true
concern for religion, and disinterested love of your country. Add to these
an uncommon proficiency in the best and most useful parts of knowledge;
together with (what in my mind is a perfection of the first rank) a
surpassing goodness of nature. All which I have collected, not from the
uncertain reports of fame, but from my own experience. Within these few
months that I have the honour to be known unto you, the many delightful
hours I have passed in your agreeable and improving conversation have
afforded me the opportunity of discovering in you many excellent
qualities, which at once fill me with admiration and esteem. That one at
those years, and in those circumstances of wealth and greatness, should
continue proof against the charms of luxury and those criminal pleasures
so fashionable and predominant in the age we live in; that he should
preserve a sweet and modest behaviour, free from that insolent and
assuming air so familiar to those who are placed above the ordinary rank
of men; that he should manage a great fortune with that prudence and
inspection, and at the same time expend it with that generosity and
nobleness of mind, as to shew himself equally remote from a sordid
parsimony and a lavish inconsiderate profusion of the good things he is
intrusted with—this, surely, were admirable and praiseworthy. But, that he
should, moreover, by an impartial exercise of his reason, and constant
perusal of the sacred Scriptures, endeavour to attain a right notion of
the principles of natural and revealed religion; that he should with the
concern of a true patriot have the interest of the public at heart, and
omit no means of informing himself what may be prejudicial or advantageous
to his country, in order to prevent the one and promote the other; in
fine, that, by a constant application to the most severe and useful
studies, by a strict observation of the rules of honour and virtue, by
frequent and serious reflections on the mistaken measures of the world,
and the true end and happiness of mankind, he should in all respects
qualify himself bravely to run the race that is set before him, to deserve
the character of great and good in this life, and be ever happy
hereafter—this were amazing and almost incredible. Yet all this, and more
than this, SIR, might I justly say of you, did either your modesty permit,
or your character stand in need of it. I know it might deservedly be
thought a vanity in me to imagine that anything coming from so obscure a
hand as mine could add a lustre to your reputation. But, I am withal
sensible how far I advance the interest of my own, by laying hold on this
opportunity to make it known that I am admitted into some degree of
intimacy with a person of your exquisite judgment. And, with that view, I
have ventured to make you an address of this nature, which the goodness I
have ever experienced in you inclines me to hope will meet with a
favourable reception at your hands. Though I must own I have your pardon
to ask, for touching on what may possibly be offensive to a virtue you are
possessed of in a very distinguishing degree. Excuse me, SIR, if it was
out of my power to mention the name of SIR JOHN PERCIVALE without paying
some tribute to that extraordinary and surprising merit whereof I have so
clear and affecting an idea, and which, I am sure, cannot be exposed in
too full a light for the imitation of others,
Of late I have been agreeably employed in considering the most noble,
pleasant, and comprehensive of all the senses(284). The fruit of that
(labour shall I call it or) diversion is what I now present you with, in
hopes it may give some entertainment to one who, in the midst of business
and vulgar enjoyments, preserves a relish for the more refined pleasures
of thought and reflexion. My thoughts concerning Vision have led me into
some notions so far out of the common road(285) that it had been improper
to address them to one of a narrow and contracted genius. But, you, SIR,
being master of a large and free understanding, raised above the power of
those prejudices that enslave the far greater part of mankind, may
deservedly be thought a proper patron for an attempt of this kind. Add to
this, that you are no less disposed to forgive than qualified to discern
whatever faults may occur in it. Nor do I think you defective in any one
point necessary to form an exact judgment on the most abstract and
difficult things, so much as in a just confidence of your own abilities.
And, in this one instance, give me leave to say, you shew a manifest
weakness of judgment. With relation to the following _Essay_, I shall only
add that I beg your pardon for laying a trifle of that nature in your way,
at a time when you are engaged in the important affairs of the nation, and
desire you to think that I am, with all sincerity and respect,
SIR,
Your most faithful and most humble servant,
GEORGE BERKELEY.
An Essay Towards A New Theory Of Vision
1. My design is to shew the manner wherein we perceive by Sight the
Distance, Magnitude, and Situation of objects: also to consider the
difference there is betwixt the ideas of Sight and Touch, and whether
there be any idea common to both senses(286).
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2. It is, I think, agreed by all that Distance, of itself and immediately,
cannot be seen(287). For, distance(288) being a line directed endwise to
the eye, it projects only one point in the fund of the eye, which point
remains invariably the same, whether the distance be longer or
shorter(289).
3. I find it also acknowledged that the estimate we make of the distance
of objects considerably remote is rather an act of judgment grounded on
experience than of sense. For example, when I perceive a great number of
intermediate objects, such as houses, fields, rivers, and the like, which
I have experienced to take up a considerable space, I thence form a
judgment or conclusion, that the object I see beyond them is at a great
distance. Again, when an object appears faint and small which at a near
distance I have experienced to make a vigorous and large appearance, I
instantly conclude it to be far off(290). And this, it is evident, is the
result of experience; without which, from the faintness and littleness, I
should not have inferred anything concerning the distance of objects.
4. But, when an object is placed at so near a distance as that the
interval between the eyes bears any sensible proportion to it(291), the
opinion of speculative men is, that the two optic axes (the fancy that we
see only with one eye at once being exploded), concurring at the object,
do there make an angle, by means of which, according as it is greater or
lesser, the object is perceived to be nearer or farther off(292).
5. Betwixt which and the foregoing manner of estimating distance there is
this remarkable difference:—that, whereas there was no apparent
_necessary_ connexion between small distance and a large and strong
appearance, or between great distance and a little and faint appearance,
there appears a very _necessary_ connexion between an obtuse angle and
near distance, and an acute angle and farther distance. It does not in the
least depend upon experience, but may be evidently known by any one before
he had experienced it, that the nearer the concurrence of the optic axes
the greater the angle, and the remoter their concurrence is, the lesser
will be the angle comprehended by them.
6. There is another way, mentioned by optic writers, whereby they will
have us judge of those distances in respect of which the breadth of the
pupil hath any sensible bigness. And that is the greater or lesser
divergency of the rays which, issuing from the visible point, do fall on
the pupil—that point being judged nearest which is seen by most diverging
rays, and that remoter which is seen by less diverging rays, and so on;
the apparent distance still increasing, as the divergency of the rays
decreases, till at length it becomes infinite, when the rays that fall on
the pupil are to sense parallel. And after this manner it is said we
perceive distance when we look only with one eye.
7. In this case also it is plain we are not beholden to experience: it
being a certain necessary truth that, the nearer the direct rays falling
on the eye approach to a parallelism, the farther off is the point of
their intersection, or the visible point from whence they flow.
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8. (293)Now, though the accounts here given of perceiving _near_ distance
by sight are received for true, and accordingly made use of in determining
the apparent places of objects, they do nevertheless seem to me very
unsatisfactory, and that for these following reasons:—
9. [_First_(294),] It is evident that, when the mind perceives any idea
not immediately and of itself, it must be by the means of some other idea.
Thus, for instance, the passions which are in the mind of another are of
themselves to me invisible. I may nevertheless perceive them by sight;
though not immediately, yet by means of the colours they produce in the
countenance. We often see shame or fear in the looks of a man, by
perceiving the changes of his countenance to red or pale.
10. Moreover, it is evident that no idea which is not itself perceived can
be to me the means of perceiving any other idea. If I do not perceive the
redness or paleness of a man’s face themselves, it is impossible I should
perceive by them the passions which are in his mind.
11. Now, from sect. ii., it is plain that distance is in its own nature
imperceptible, and yet it is perceived by sight(295). It remains,
therefore, that it be brought into view by means of some other idea, that
is itself immediately perceived in the act of vision.
12. But those lines and angles, by means whereof some men(296) pretend to
explain the perception(297) of distance, are themselves not at all
perceived; nor are they in truth ever thought of by those unskilful in
optics. I appeal to any one’s experience, whether, upon sight of an
object, he computes its distance by the bigness of the angle made by the
meeting of the two optic axes? or whether he ever thinks of the greater or
lesser divergency of the rays which arrive from any point to his pupil?
nay, whether it be not perfectly impossible for him to perceive by sense
the various angles wherewith the rays, according to their greater or
lesser divergence, do fall on the eye? Every one is himself the best judge
of what he perceives, and what not. In vain shall any man(298) tell me,
that I perceive certain lines and angles, which introduce into my mind the
various ideas of distance, so long as I myself am conscious of no such
thing.
13. Since therefore those angles and lines are not themselves perceived by
sight, it follows, from sect. x., that the mind does not by them judge of
the distance of objects.
14. [_Secondly_(299),] The truth of this assertion will be yet farther
evident to any one that considers those lines and angles have no real
existence in nature, being only an hypothesis framed by the
mathematicians, and by them introduced into optics, that they might treat
of that science in a geometrical way.
15. The [_third_ and(300)] last reason I shall give for rejecting that
doctrine is, that though we should grant the real existence of those optic
angles, &c., and that it was possible for the mind to perceive them, yet
these principles would not be found sufficient to explain the phenomena of
distance, as shall be shewn hereafter.
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16. Now it being already shewn(301) that distance is _suggested_(302) to
the mind, by the mediation of some other idea which is itself perceived in
the act of seeing, it remains that we inquire, what ideas or sensations
there be that attend vision, unto which we may suppose the ideas of
distance are connected, and by which they are introduced into the mind.
And, _first_, it is certain by experience, that when we look at a near
object with both eyes, according as it approaches or recedes from us, we
alter the disposition of our eyes, by lessening or widening the interval
between the pupils. This disposition or turn of the eyes is attended with
a sensation(303), which seems to me to be that which in this case brings
the idea of greater or lesser distance into the mind.
17. Not that there is any natural or necessary(304) connexion between the
sensation we perceive by the turn of the eyes and greater or lesser
distance. But—because the mind has, by constant experience, found the
different sensations corresponding to the different dispositions of the
eyes to be attended each with a different degree of distance in the
object—there has grown an habitual or customary connexion between those
two sorts of ideas: so that the mind no sooner perceives the sensation
arising from the different turn it gives the eyes, in order to bring the
pupils nearer or farther asunder, but it withal perceives the different
idea of distance which was wont to be connected with that sensation. Just
as, upon hearing a certain sound, the idea is immediately suggested to the
understanding which custom had united with it(305).
18. Nor do I see how I can easily be mistaken in this matter. I know
evidently that distance is not perceived of itself(306); that, by
consequence, it must be perceived by means of some other idea, which is
immediately perceived, and varies with the different degrees of distance.
I know also that the sensation arising from the turn of the eyes is of
itself immediately perceived; and various degrees thereof are connected
with different distances, which never fail to accompany them into my mind,
when I view an object distinctly with both eyes whose distance is so small
that in respect of it the interval between the eyes has any considerable
magnitude.
19. I know it is a received opinion that, by altering the disposition of
the eyes, the mind perceives whether the angle of the optic axes, or the
lateral angles comprehended between the interval of the eyes or the optic
axes, are made greater or lesser; and that, accordingly, by a kind of
natural geometry, it judges the point of their intersection to be nearer
or farther off. But that this is not true I am convinced by my own
experience; since I am not conscious that I make any such use of the
perception I have by the turn of my eyes. And for me to make those
judgments, and draw those conclusions from it, without knowing that I do
so, seems altogether incomprehensible(307).
20. From all which it follows, that the judgment we make of the distance
of an object viewed with both eyes is entirely the result of experience.
If we had not constantly found certain sensations, arising from the
various disposition of the eyes, attended with certain degrees of
distance, we should never make those sudden judgments from them concerning
the distance of objects; no more than we would pretend to judge of a man’s
thoughts by his pronouncing words we had never heard before.
21. _Secondly_, an object placed at a certain distance from the eye, to
which the breadth of the pupil bears a considerable proportion, being made
to approach, is seen more confusedly(308). And the nearer it is brought
the more confused appearance it makes. And this being found constantly to
be so, there arises in the mind an habitual connexion between the several
degrees of confusion and distance; the greater confusion still implying
the lesser distance, and the lesser confusion the greater distance of the
object.
22. This confused appearance of the object doth therefore seem to be the
medium whereby the mind judges of distance, in those cases wherein the
most approved writers of optics will have it judge by the different
divergency with which the rays flowing from the radiating point fall on
the pupil(309). No man, I believe, will pretend to see or feel those
imaginary angles that the rays are supposed to form, according to their
various inclinations on his eye. But he cannot choose seeing whether the
object appear more or less confused. It is therefore a manifest
consequence from what has been demonstrated that, instead of the greater
or lesser divergency of the rays, the mind makes use of the greater or
lesser confusedness of the appearance, thereby to determine the apparent
place of an object.
23. Nor doth it avail to say there is not any necessary connexion between
confused vision and distance great or small. For I ask any man what
necessary connexion he sees between the redness of a blush and shame? And
yet no sooner shall he behold that colour to arise in the face of another
but it brings into his mind the idea of that passion which hath been
observed to accompany it.
24. What seems to have misled the writers of optics in this matter is,
that they imagine men judge of distance as they do of a conclusion in
mathematics; betwixt which and the premises it is indeed absolutely
requisite there be an apparent necessary connexion. But it is far
otherwise in the sudden judgments men make of distance. We are not to
think that brutes and children, or even grown reasonable men, whenever
they perceive an object to approach or depart from them, do it by virtue
of geometry and demonstration.
25. That one idea may suggest another to the mind, it will suffice that
they have been observed to go together, without any demonstration of the
_necessity_ of their coexistence, or without so much as knowing what it is
that makes them so to coexist. Of this there are innumerable instances, of
which no one can be ignorant(310).
26. Thus, greater confusion having been constantly attended with nearer
distance, no sooner is the former idea perceived but it suggests the
latter to our thoughts. And, if it had been the ordinary course of nature
that the farther off an object were placed the more confused it should
appear, it is certain the very same perception that now makes us think an
object approaches would then have made us to imagine it went farther off;
that perception, abstracting from custom and experience, being equally
fitted to produce the idea of great distance, or small distance, or no
distance at all.
27. _Thirdly_, an object being placed at the distance above specified, and
brought nearer to the eye, we may nevertheless prevent, at least for some
time, the appearance’s growing more confused, by straining the eye(311).
In which case that sensation supplies the place of confused vision, in
aiding the mind to judge of the distance of the object; it being esteemed
so much the nearer by how much the effort or straining of the eye in order
to distinct vision is greater.
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28. I have here(312) set down those sensations or ideas(313) that seem to
be the constant and general occasions of introducing into the mind the
different ideas of near distance. It is true, in most cases, that divers
other circumstances contribute to frame our idea of distance, viz. the
particular number, size, kind, &c. of the things seen. Concerning which,
as well as all other the forementioned occasions which suggest distance, I
shall only observe, they have none of them, in their own nature, any
relation or connexion with it: nor is it possible they should ever signify
the various degrees thereof, otherwise than as by experience they have
been found to be connected with them.
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29. I shall proceed upon these principles to account for a phenomenon
which has hitherto strangely puzzled the writers of optics, and is so far
from being accounted for by any of their theories of vision, that it is,
by their own confession, plainly repugnant to them; and of consequence, if
nothing else could be objected, were alone sufficient to bring their
credit in question. The whole difficulty I shall lay before you in the
words of the learned Doctor Barrow, with which he concludes his _Optic
Lectures_(314):—
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