An Essay Towards a New Theory of Vision
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George Berkeley >> An Essay Towards a New Theory of Vision
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108. In order to get clear of this seeming difficulty we need only
observe that diversity of visible objects doth not necessarily infer
diversity of tangible objects corresponding to them. A picture painted
with great variety of colours affects the touch in one uniform manner; it
is therefore evident that I do not by any necessary consecution,
independent of experience, judge of the number of things tangible from
the number of things visible. I should not, therefore, at first opening
my eyes conclude that because I see two I shall feel two. How, therefore,
can I, before experience teaches me, know that the visible legs, because
two, are connected with the tangible legs, or the visible head, because
one, is connected with the tangible head? The truth is, the things I see
are so very different and heterogeneous from the things I feel that the
perception of the one would never have suggested the other to my
thoughts, or enabled me to pass the least judgment thereon, until I had
experienced their connexion.
109. But for a fuller illustration of this matter it ought to be
considered that number (however some may reckon it amongst the primary
qualities) is nothing fixed and settled, really existing in things
themselves. It is entirely the creature of the mind, considering either
an idea by itself, or any combination of ideas to which it gives one
name, and so makes it pass for an unit. According as the mind variously
combines its ideas the unit varies: and as the unit, so the number, which
is only a collection of units, doth also vary. We call a window one, a
chimney one, and yet a house in which there are many windows and many
chimneys hath an equal right to be called one, and many houses go to the
making of the city. In these and the like, instances it is evident the
unit constantly relates to the particular draughts the mind makes of its
ideas, to which it affixes names, and wherein it includes more or less as
best suits its own ends and purposes. Whatever, therefore, the mind
considers as one, that is an unit. Every combination of ideas is
considered as one thing by the mind, and in token thereof is marked by
one name. Now, this naming and combining together of ideas is perfectly
arbitrary, and done by the mind in such sort as experience shows it to be
most convenient: without which our ideas had never been collected into
such sundry distinct combinations as they now are.
110. Hence it follows that a man born blind and afterwards, when grown
up, made to see, would not in the first act of vision parcel out the
ideas of sight into the same distinct collections that others do, who
have experienced which do regularly coexist and are proper to be bundled
up together under one name. He would not, for example, make into one
complex idea, and thereby esteem an unit, all those particular ideas
which constitute the visible head or foot. For there can be no reason
assigned why he should do so, barely upon his seeing a man stand upright
before him. There crowd into his mind the ideas which compose the visible
man, in company with all the other ideas of sight perceived at the same
time: but all these ideas offered at once to his view, he would not
distribute into sundry distinct combinations till such time as by
observing the motion of the parts of the man and other experiences he
comes to know which are to be separated and which to be collected
together.
111. From what hath been premised it is plain the objects of sight and
touch make, if I may so say, two sets of ideas which are widely different
from each other. To objects of either kind we indifferently attribute the
terms high and low, right and left, and suchlike, denoting the position
or situation of things: but then we must well observe that the position
of any object is determined with respect only to objects of the same
sense. We say any object of touch is high or low, according as it is more
or less distant from the tangible earth: and in like manner we denominate
any object of sight high or low in proportion as it is more or less
distant from the visible earth: but to define the situation of visible
things with relation to the distance they bear from any tangible thing,
or VICE VERSA, this were absurd and perfectly unintelligible. For all
visible things are equally in the mind, and take up no part of the
external space: and consequently are equidistant from any tangible thing
which exists without the mind.
112. Or rather, to speak truly, the proper objects of sight are at no
distance, neither near nor far, from any tangible thing. For if we
inquire narrowly into the matter we shall find that those things only are
compared together in respect of distance which exist after the same
manner, or appertain unto the same sense. For by the distance between any
two points nothing more is meant than the number of intermediate points:
if the given points are visible the distance between them is marked out
by the number of the interjacent visible points: if they are tangible,
the distance between them is a line consisting of tangible points; but if
they are one tangible and the other visible, the distance between them
doth neither consist of points perceivable by sight nor by touch, i.e. it
is utterly inconceivable. This, perhaps, will not find an easy admission
into all men's understanding: however, I should gladly be informed
whether it be not true by anyone who will be at the pains to reflect a
little and apply it home to his thoughts.
113. The not observing what has been delivered in the two last sections
seems to have occasioned no small part of the difficulty that occurs in
the business of erect appearances. The head, which is painted nearest the
earth, seems to be farthest from it: and on the other hand the feet,
which are painted farthest from the earth, are thought nearest to it.
Herein lies the difficulty, which vanishes if we express the thing more
clearly and free from ambiguity, thus: how comes it that to the eye the
visible head which is nearest the tangible earth seems farthest from the
earth, and the visible feet, which are farthest from the tangible earth
seem nearest the earth? The question being thus proposed, who sees not
the difficulty is founded on a supposition that the eye, or visive
faculty, or rather the soul by means thereof, should judge of the
situation of visible objects with reference to their distance from the
tangible earth? Whereas it is evident the tangible earth is not perceived
by sight: and it hath been shown in the two last preceding sections that
the location of visible objects is determined only by the distance they
bear from one another; and that it is nonsense to talk of distance, far
or near, between a visible and tangible thing.
114. If we confine our thoughts to the proper objects of sight, the whole
is plain and easy. The head is painted farthest from, and the feet
nearest to, the visible earth; and so they appear to be. What is there
strange or unaccountable in this? Let us suppose the pictures in the fund
of the eye to be the immediate objects of the sight. The consequence is
that things should appear in the same posture they are painted in; and is
it not so? The head which is seen seems farthest from the earth which is
seen; and the feet which are seen seem nearest to the earth, which is
seen; and just so they are painted.
115. But, say you, the picture of the man is inverted, and yet the
appearance is erect: I ask, what mean you by the picture of the man, or,
which is the same thing, the visible man's being inverted? You tell me it
is inverted, because the heels are uppermost and the head undermost?
Explain me this. You say that by the head's being undermost you mean that
it is nearest to the earth; and by the heels being uppermost that they
are farthest from the earth. I ask again what earth you mean? You cannot
mean the earth that is painted on the eye, or the visible earth: for the
picture of the head is farthest from the picture of the earth, and the
picture of the feet nearest to the picture of the earth; and accordingly
the visible head is farthest from the visible earth, and the visible feet
nearest to it. It remains, therefore, that you mean the tangible earth,
and so determine the situation of visible things with respect to tangible
things; contrary to what hath been demonstrated in sect. 111 and 112. The
two distinct provinces of sight and touch should be considered apart, and
as if their objects had no intercourse, no manner of relation one to
another, in point of distance or position.
116. Farther, what greatly contributes to make us mistake in this matter
is that when we think of the pictures in the fund of the eye, we imagine
ourselves looking on the fund of another's eye, or another looking on the
fund of our own eye, and beholding the pictures painted thereon. Suppose
two eyes A and B: A from some distance looking on the pictures in B sees
them inverted, and for that reason concludes they are inverted in B: but
this is wrong. There are projected in little on the bottom of A the
images of the pictures of, suppose, man, earth, etc., which are painted
on B. And besides these the eye B itself, and the objects which environ
it, together with another earth, are projected in a larger size on A.
Now, by the eye A these larger images are deemed the true objects, and
the lesser only pictures in miniature. And it is with respect to those
greater images that it determines the situation of the smaller images: so
that comparing the little man with the great earth, A judges him
inverted, or that the feet are farthest from and the head nearest to the
great earth. Whereas, if A compare the little man with the little earth,
then he will appear erect, i.e. his head shall seem farthest from, and
his feet nearest to, the little earth. But we must consider that B does
not see two earths as A does: it sees only what is represented by the
little pictures in A, and consequently shall judge the man erect. For, in
truth, the man in B is not inverted, for there the feet are next the
earth; but it is the representation of it in A which is inverted, for
there the head of the representation of the picture of the man in B is
next the earth, and the feet farthest from the earth, meaning the earth
which is without the representation of the pictures in B. For if you take
the little images of the pictures in B, and consider them by themselves,
and with respect only to one another, they are all erect and in their
natural posture.
117. Farther, there lies a mistake in our imagining that the pictures of
external objects are painted on the bottom of the eye. It hath been shown
there is no resemblance BETWEEN the ideas of sight and things tangible.
It hath likewise been demonstrated that the proper objects of sight do
not exist without the mind. Whence it clearly follows that the pictures
painted on the bottom of the eye are not the pictures of external
objects. Let anyone consult his own thoughts, and then say what affinity,
what likeness there is between that certain variety and disposition of
colours which constitute the visible man, or picture of a man, and that
other combination of far different ideas, sensible by touch, which
compose the tangible man. But if this be the case, how come they to be
accounted pictures or images, since that supposes them to copy or
represent some originals or other?
118. To which I answer: in the forementioned instance the eye A takes the
little images, included within the representation of the other eye B, to
be pictures or copies, whereof the archetypes are not things existing
without, but the larger pictures projected on its own fund: and which by
A are not thought pictures, but the originals, or true things themselves.
Though if we suppose a third eye C from a due distance to behold the fund
of A, then indeed the things projected thereon shall, to C, seem pictures
or images in the same sense that those projected on B do to A.
119. Rightly to conceive this point we must carefully distinguish between
the ideas of sight and touch, between the visible and tangible eye; for
certainly on the tangible eye nothing either is or seems to be painted.
Again, the visible eye, as well as all other visible objects, hath been
shown to exist only in the mind, which perceiving its own ideas, and
comparing them together, calls some PICTURES in respect of others. What
hath been said, being rightly comprehended and laid together, doth, I
think, afford a full and genuine explication of the erect appearance of
objects; which phenomenon, I must confess, I do not see how it can be
explained by any theories of vision hitherto made public.
120. In treating of these things the use of language is apt to occasion
some obscurity and confusion, and create in us wrong ideas; for language
being accommodated to the common notions and prejudices of men, it is
scarce possible to deliver the naked and precise truth without great
circumlocution, impropriety, and (to an unwary reader) seeming
contradictions; I do therefore once for all desire whoever shall think it
worth his while to understand what I have written concerning vision, that
he would not stick in this or that phrase, or manner of expression, but
candidly collect my meaning from the whole sum and tenor of my discourse,
and laying aside the words as much as possible, consider the bare notions
themselves, and then judge whether they are agreeable to truth and his
own experience, or no.
121. We have shown the way wherein the mind by mediation of visible ideas
doth perceive or apprehend the distance, magnitude and situation of
tangible objects. We come now to inquire more particularly concerning the
difference between the ideas of sight and touch, which are called by the
same names, and see whether there be any idea common to both senses. From
what we have at large set forth and demonstrated in the foregoing parts
of this treatise, it is plain there is no one selfsame numerical
extension perceived both by sight and touch; but that the particular
figures and extensions perceived by sight, however they may be called by
the same names and reputed the same things with those perceived by touch,
are nevertheless different, and have an existence distinct and separate
from them: so that the question is not now concerning the same numerical
ideas, but whether there be any one and the same sort of species of ideas
equally perceivable to both senses; or, in other words, whether
extension, figure, and motion perceived by sight are not specifically
distinct from extension, figure, and motion perceived by touch.
122. But before I come more particularly to discuss this matter, I find
it proper to consider extension in abstract: for of this there is much
talk, and I am apt to think that when men speak of extension as being an
idea common to two senses, it is with a secret supposition that we can
single out extension from all other tangible and visible qualities, and
form thereof an abstract idea, which idea they will have common both to
sight and touch. We are therefore to understand by extension in abstract
an idea of extension, for instance, a line or surface entirely stripped
of all other sensible qualities and circumstances that might determine it
to any particular existence; it is neither black nor white, nor red, nor
hath it any colour at all, or any tangible quality whatsoever and
consequently it is of no finite determinate magnitude: for that which
bounds or distinguishes one extension from another is some quality or
circumstance wherein they disagree.
123. Now I do not find that I can perceive, imagine, or any wise frame in
my mind such an abstract idea as is here spoken of. A line or surface
which is neither black, nor white, nor blue, nor yellow, etc., nor long,
nor short, nor rough, nor smooth, nor square, nor round, etc., is
perfectly incomprehensible. This I am sure of as to myself: how far the
faculties of other men may reach they best can tell.
124. It is commonly said that the object of geometry is abstract
extension: but geometry contemplates figures: now, figure is the
termination of magnitude: but we have shown that extension in abstract
hath no finite determinate magnitude. Whence it clearly follows that it
can have no figure, and consequently is not the object of geometry. It is
indeed a tenet as well of the modern as of the ancient philosophers that
all general truths are concerning universal abstract ideas; without
which, we are told, there could be no science, no demonstration of any
general proposition in geometry. But it were no hard matter, did I think
it necessary to my present purpose, to show that propositions and
demonstrations in geometry might be universal, though they who make them
never think of abstract general ideas of triangles or circles.
125. After reiterated endeavours to apprehend the general idea a
triangle, I have found it altogether incomprehensible. And surely if
anyone were able to introduce that idea into my mind, it must be the
author of the ESSAY CONCERNING HUMAN UNDERSTANDING; he who has so far
distinguished himself from the generality of writers by the clearness
and significancy of what he says. Let us therefore see how this
celebrated author describes the general or abstract idea of a triangle.
'It must be (says he) neither oblique nor rectangular, neither
equilateral, equicrural, nor scalenum; but all and none of these at once.
In effect, it is somewhat imperfect that cannot exist; an idea, wherein
some parts of several different and inconsistent ideas are put together'
ESSAY ON HUM. UNDERSTAND. B. iv. C. 7. S.9. This is the idea which he
thinks needful for the enlargement of knowledge, which is the subject of
mathematical demonstration, and without which we could never come to know
any general proposition concerning triangles. That author acknowledges it
doth 'require some pains and skill to form this general idea of a
triangle.' IBID. But had he called to mind what he says in another place,
to wit, 'That ideas of mixed modes wherein any inconsistent ideas are put
together cannot so much as exist in the mind, i.e. be conceived.' VID. B.
iii. C. 10. S. 33. IBID. I say, had this occurred to his thoughts, it is
not improbable he would have owned it above all the pains and skill he
was master of to form the above-mentioned idea of a triangle, which is
made up of manifest, staring contradictions. That a man who laid so great
a stress on clear and determinate ideas should nevertheless talk at this
rate seems very surprising. But the wonder will lessen if it be
considered that the source whence this opinion flows is the prolific womb
which has brought forth innumerable errors and difficulties in all parts
of philosophy and in all the sciences: but this matter, taken in its full
extent, were a subject too comprehensive to be insisted on in this place.
And so much for extension in abstract.
126. Some, perhaps, may think pure space, VACUUM, or trine dimension to
be equally the object of sight and touch: but though we have a very great
propension to think the ideas of outness and space to be the immediate
object of sight, yet, if I mistake not, in the foregoing parts of this
essay that hath been clearly demonstated to be a mere delusion, arising
from the quick and sudden suggestion of fancy, which so closely connects
the idea of distance with those of sight, that we are apt to think it is
itself a proper and immediate object of that sense till reason corrects
the mistake.
127. It having been shown that there are no abstract ideas of figure, and
that it is impossible for us by any precision of thought to frame an idea
of extension separate from all other visible and tangible qualities which
shall be common both to sight and touch: the question now remaining is,
whether the particular extensions, figures, and motions perceived by
sight be of the same kind with the particular extensions, figures, and
motions perceived by touch? In answer to which I shall venture to lay
down the following proposition: THE EXTENSION, FIGURES, AND MOTIONS
PERCEIVED BY SIGHT ARE SPECIFICALLY DISTINCT FROM THE IDEAS OF TOUCH
CALLED BY THE SAME NAMES, NOR is THERE ANY SUCH THING as ONE IDEA OR KIND
OF IDEA COMMON TO BOTH SENSES. This proposition may without much
difficulty be collected from what hath been said in several places of
this essay. But because it seems so remote from, and contrary to, the
received notions and settled opinion of mankind, I shall attempt to
demonstrate it more particularly and at large by the following arguments.
128. When upon perception of an idea I range it under this or that sort,
it is because it is perceived after the same manner, or because it has a
likeness or conformity with, or affects me in the same way as, the ideas
of the sort I rank it under. In short, it must not be entirely new, but
have something in it old and already perceived by me. It must, I say,
have so much at least in common with the ideas I have before known and
named as to make me give it the same name with them. But it has been, if
I mistake not, clearly made out that a man born blind would not at first
reception of his sight think the things he saw were of the same nature
with the objects of touch, or had anything in common with them; but that
they were a new set of ideas, perceived in a new manner, and entirely
different from all he had ever perceived before: so that he would not
call them by the same name, nor repute them to be of the same sort with
anything he had hitherto known.
129. SECONDLY, light and colours are allowed by all to constitute a son
or species entirely different from the ideas of touch: nor will any man,
I presume, say they can make themselves perceived by that sense: but
there is no other immediate object of sight besides light and colours. It
is therefore a direct consequence that there is no idea common to both
senses.
130. It is a prevailing opinion, even amongst those who have thought and
writ most accurately concerning our ideas and the ways whereby they enter
into the understanding, that something more is perceived by sight than
barely light and colours with their variations. Mr. Locke termeth sight,
'The most comprehensive of all our senses, conveying to our minds the
ideas of light and colours, which are peculiar only to that sense; and
also the far different ideas of space, figure, and motion. ESSAY ON HUMAN
UNDERSTAND. B. ii. C. 9. S. 9. Space or distance, we have shown, is not
otherwise the object of sight than of hearing. VID. sect. 46. And as for
figure and extension, I leave it to anyone that shall calmly attend to
his own clear and distinct ideas to decide whether he had any idea
intromitted immediately and properly by sight save only light and
colours: or whether it De possible for him to frame in his mind a
distinct abstract idea of visible extension or figure exclusive of all
colour: and on the other hand, whether he can conceive colour without
visible extension? For my own part, I must confess I am not able to
attain so great a nicety of abstraction: in a strict sense, I see nothing
but light and colours, with their several shades and variations. He who
beside these doth also perceive by sight ideas far different and distinct
from them hath that faculty in a degree more perfect and comprehensive
than I can pretend to. It must be owned that by the mediation of light
and colours other far different ideas are suggested to my mind: but so
they are by hearing, which beside sounds which are peculiar to that
sense, doth by their mediation suggest not only space, figure, and
motion, but also all other ideas whatsoever that can be signified by
words.
131. THIRDLY, it is, I think, an axiom universally received that
quantities of the same kind may be added together and make one entire
sum. Mathematicians add lines together: but they do not add a line to a
solid, or conceive it as making one sum with a surface: these three kinds
of quantity being thought incapable of any such mutual addition, and
consequently of being compared together in the several ways of
proportion, are by then esteemed entirely disparate and heterogeneous.
Now let anyone try in his thoughts to add a visible line or surface to a
tangible line or surface, so as to conceive them making one continued sum
or whole. He that can do this may think them homogeneous: but he that
cannot, must by the foregoing axiom think them heterogeneous. A blue and
a red line I can conceive added together into one sum and making one
continued line: but to make in my thoughts one continued line of a
visible and tangible line added together is, I find, a task far more
difficult, and even insurmountable: and I leave it to the reflexion and
experience of every particular person to determine for himself.
132. A farther confirmation of our tenet may be drawn from the solution
of Mr. Molyneux's problem, published by Mr. Locke in his ESSAY: which I
shall set down as it there lies, together with Mr. Locke's opinion of it,
'"Suppose a man born blind, and now adult, and taught by his touch to
distinguish between a cube and a sphere of the same metal, and nighly
[SIC] of the same bigness, so as to tell, when he felt one and t'other,
which is the cube and which the sphere. Suppose then the cube and sphere
placed on a table, and the blind man to be made to see: QUAERE, whether
by his sight, before he touched them, he could now distinguish and tell
which is the globe, which the cube?" To which the acute and judicious
proposer answers: "Not. For though he has obtained the experience of how
a globe, how a cube, affects his touch, yet he has not yet attained the
experience that what affects his touch so or so must affect his sight so
or so: or that a protuberant angle in the cube that pressed his hand
unequally shall appear to his eye as it doth in the cube." I agree with
this thinking gentleman, whom I am proud to call my friend, in his answer
to this his problem; and am of opinion that the blind man at first sight
would not be able with certainty to say which was the globe, which the
cube, whilst he only saw them.' (ESSAY ON HUMAN UNDERSTANDING, B. ii. C.
9. S. 8.)
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