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 though their objects had no intercourse, no manner of relation to one
another, in point of distance or position(402).
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, &c., 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 linages 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(403) objects are painted on the bottom of the eye. It has been
shewn there is no resemblance between the ideas of sight and things
tangible. It hath likewise been demonstrated(404), 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 any one consult his own thoughts, and then tell me, 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(405), but the larger pictures(406) 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 the business in hand, 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 shewn to exist only in the mind(407); which, perceiving
its own ideas, and comparing them together, does call some pictures in
respect to others. What hath been said, being rightly comprehended and
laid together, does, 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(408) as much as possible, consider
the bare notions themselves, and then judge whether they are agreeable to
truth and his own experience or no.
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121. We have shewn the way wherein the mind, by mediation of visible
ideas(409), doth perceive or apprehend the distance, magnitude, and
situation of tangible objects(410). I 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(411). From what we have at large set forth and
demonstrated in the foregoing parts of this treatise, it is plain there is
no one self-same 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 very 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 or 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?
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122. But, before I come more particularly to discuss this matter, I find
it proper to take into my thoughts extension in abstract(412). 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(413) 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(414); 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 anywise 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, &c.; nor long,
nor short, nor rough, nor smooth, nor square, nor round, &c. 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(415); but we have shewn 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 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 shew 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 efforts and pangs of thought(416) to apprehend the
general idea of a triangle(417), I have found it altogether
incomprehensible. And surely, if any one were able to let that idea into
my mind, it must be the author(418) 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(419) describes the general
or [which is the same thing, the(420)] abstract idea of a triangle. “It
must be,” says he, “neither oblique nor rectangle, 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
Human Understanding_, B. iv. ch. 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. [Sure I am, if this be the
case, it is impossible for me to attain to know even the first elements of
geometry: since I have not the faculty to frame in my mind such an idea as
is here described(421).] 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. ch. 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 [of such a clear
understanding(422)], who thought so much and so well, and 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 [of abstract figures and
extension (423)] 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 vast and comprehensive to be insisted on in this place(424).
[I shall only observe that your metaphysicians and men of speculation seem
to have faculties distinct from those of ordinary men, when they talk of
general or abstracted triangles and circles, &c., and so peremptorily
declare them to be the subject of all the eternal, immutable, universal
truths in geometry(425).] And so much for extension in abstract.
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126. Some, perhaps, may think pure space, vacuum, or trine dimension, to
be equally the object of sight and touch(426). 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 demonstrated 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(427).
127. It having been shewn 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(428), 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_(429)_ 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. [_First_(430),] 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(431) 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. [And surely the
judgment of such an unprejudiced person is more to be relied on in this
case than the sentiments of the generality of men; who, in this as in
almost everything else, suffer themselves to be guided by custom, and the
erroneous suggestions of prejudice, rather than reason and sedate
reflection(432).]
129. _Secondly_, Light and colours are allowed by all to constitute a sort
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(433). 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. [The excellent(434)] 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 Understanding_, B. iii. ch. 9. s. 9.) Space or
distance(435), we have shewn, is no otherwise the object of sight than of
hearing. (Vid. sect. 46.) And, as for figure and extension, I leave it to
any one that shall calmly attend to his own clear and distinct ideas to
decide whether he has any idea intromitted immediately and properly by
sight save only light and colours: or, whether it be 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. I know
very well that, 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, indeed, that, by the mediation of light and colours,
other far different ideas are suggested to my mind. But so they are by
hearing(436). But then, upon this score, I see no reason why the sight
should be thought more comprehensive than the 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 them for that reason esteemed entirely disparate and heterogeneous.
Now let any one 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. [I
acknowledge myself to be of the latter sort(437).] 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 reflection 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_(438): 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 of
the same bigness, so as to tell when he felt one and the other, which is
the cube, and which the sphere. Suppose then the cube and sphere placed on
a table, and the blind man made to see: Quære, 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. ch. 9. s. 8.)
133. Now, if a square surface perceived by touch be of the same sort with
a square surface perceived by sight, it is certain the blind man here
mentioned might know a square surface as soon as he saw it. It is no more
but introducing into his mind, by a new inlet, an idea he has been already
well acquainted with. Since therefore he is supposed to have known by his
touch that a cube is a body terminated by square surfaces; and that a
sphere is not terminated by square surfaces—upon the supposition that a
visible and tangible square differ only _in numero_, it follows that he
might know, by the unerring mark of the square surfaces, which was the
cube, and which not, while he only saw them. We must therefore allow,
either that visible extension and figures are specifically distinct from
tangible extension and figures, or else, that the solution of this
problem, given by those two [very(439)] thoughtful and ingenious men, is
wrong.
134. Much more might be laid together in proof of the proposition I have
advanced. But, what has been said is, if I mistake not, sufficient to
convince any one that shall yield a reasonable attention. And, as for
those that will not be at the pains of a little thought, no multiplication
of words will ever suffice to make them understand the truth, or rightly
conceive my meaning(440).
135. I cannot let go the above-mentioned problem without some reflection
on it. It hath been made evident that a man blind from his birth would
not, at first sight, denominate anything he saw, by the names he had been
used to appropriate to ideas of touch. (Vid. sect. 106.) Cube, sphere,
table are words he has known applied to things perceivable by touch, but
to things perfectly intangible he never knew them applied. Those words, in
their wonted application, always marked out to his mind bodies or solid
things which were perceived by the resistance they gave. But there is no
solidity, no resistance or protrusion, perceived by sight. In short, the
ideas of sight are all new perceptions, to which there be no names annexed
in his mind; he cannot therefore understand what is said to him concerning
them. And, to ask of the two bodies he saw placed on the table, which was
the sphere, which the cube, were to him a question downright bantering and
unintelligible; nothing he sees being able to suggest to his thoughts the
idea of body, distance, or, in general, of anything he had already known.
136. It is a mistake to think the same(441) thing affects both sight and
touch. If the same angle or square which is the object of touch be also
the object of vision, what should hinder the blind man, at first sight,
from knowing it? For, though the manner wherein it affects the sight be
different from that wherein it affected his touch, yet, there being,
beside this manner or circumstance, which is new and unknown, the angle or
figure, which is old and known, he cannot choose but discern it.
137. Visible figure and extension having been demonstrated to be of a
nature entirely different and heterogeneous from tangible figure and
extension, it remains that we inquire concerning motion. Now, that visible
motion is not of the same sort with tangible motion seems to need no
farther proof; it being an evident corollary from what we have shewn
concerning the difference there is betwixt visible and tangible extension.
But, for a more full and express proof hereof, we need only observe that
one who had not yet experienced vision would not at first sight know
motion(442). Whence it clearly follows that motion perceivable by sight is
of a sort distinct from motion perceivable by touch. The antecedent I
prove thus—By touch he could not perceive any motion but what was up or
down, to the right or left, nearer or farther from him; besides these, and
their several varieties or complications, it is impossible he should have
any idea of motion. He would not therefore think anything to be motion, or
give the name motion to any idea, which he could not range under some or
other of those particular kinds thereof. But, from sect. 95, it is plain
that, by the mere act of vision, he could not know motion upwards or
downwards, to the right or left, or in any other possible direction. From
which I conclude, he would not know motion at all at first sight. As for
the idea of motion in abstract, I shall not waste paper about it, but
leave it to my reader to make the best he can of it. To me it is perfectly
unintelligible(443).