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 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.
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.)
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 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 anyone 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.
135. I cannot let go the above-mentioned problem without some reflexion
on it. It hath been 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 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 his 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. 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 shown concerning
the difference there is between 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. 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.
138. The consideration of motion may furnish a new field for inquiry: but
since the manner wherein the mind apprehends by sight the motion of
tangible objects, with the various degrees thereof, may be easily
collected from what hath been said concerning the manner wherein that
sense doth suggest their various distances, magnitudes, and situations, I
shall not enlarge any farther on this subject, but proceed to consider
what may be alleged, with greatest appearance of reason, against the
proposition we have shown to be true. For where there is so much
prejudice to be encountered, a bare and naked demonstration of the truth
will scarce suffice. We must also satisfy the scruples that men may raise
in favour of their preconceived notions, show whence the mistake arises,
how it came to spread, and carefully disclose and root out those false
persuasions that an early prejudice might have implanted in the mind.
139. FIRST, therefore, it will be demanded how visible extension and
figures come to be called by the same name with tangible extension and
figures, if they are not of the same kind with them? It must be something
more than humour or accident that could occasion a custom so constant and
universal as this, which has obtained in all ages and nations of the
world, and amongst all ranks of men, the learned as well as the
illiterate.
140. To which I answer, we can no more argue a visible and tangible
square to be of the same species from their being called by the same
name, than we can that a tangible square and the monosyllable consisting
of six letters whereby it is marked are of the same species because they
are both called by the same name. It is customary to call written words
and the things they signify by the same name: for words not being
regarded in their own nature, or otherwise than as they are marks of
things, it had been superfluous, and beside the design of language, to
have given them names distinct from those of the things marked by them.
The same reason holds here also. Visible figures are the marks of
tangible figures, and from sect. 59 it is plain that in themselves they
are little regarded, or upon any other score than for their connexion
with tangible figures, which by nature they are ordained to signify. And
because this language of nature doth not vary in different ages or
nations, hence it is that in all times and places visible figures are
called by the same names as the respective tangible figures suggested by
them, and not because they are alike or of the same sort with them.
141. But, say you, surely a tangible square is liker to a visible square
than to a visible circle: it has four angles and as many sides: so also
has the visible square: but the visible circle has no such thing, being
bounded by one uniform curve without right lines or angles, which makes
it unfit to represent the tangible square but very fit to represent the
tangible circle. Whence it clearly follows that visible figures are
patterns of, or of the same species with, the respective tangible figures
represented by them: that they are like unto them, and of their own
nature fitted to represent them, as being of the same sort: and that they
are in no respect arbitrary signs, as words.
142. I answer, it must be acknowledged the visible square is fitter than
the visible circle to represent the tangible square, but then it is not
because it is liker, or more of a species with it, but because the
visible square contains in it several distinct parts, whereby to mark the
several distinct corresponding parts of a tangible square, whereas the
visible circle doth not. The square perceived by touch hath four
distinct, equal sides, so also hath it four distinct equal angles. It is
therefore necessary that the visible figure which shall be most proper to
mark it contain four distinct equal parts corresponding to the four sides
of the tangible square, as likewise four other distinct and equal parts
whereby to denote the four equal angles of the tangible square. And
accordingly we see the visible figures contain in them distinct visible
parts, answering to the distinct tangible parts of the figures signified
or suggested by them.
143. But it will not hence follow that any visible figure is like unto,
or of the same species with, its corresponding tangible figure, unless it
be also shown that not only the number but also the kind of the parts be
the same in both. To illustrate this, I observe that visible figures
represent tangible figures much after the same manner that written words
do sounds. Now, in this respect words are not arbitrary, it not being
indifferent what written word stands for any sound: but it is requisite
that each word contain in it so many distinct characters as there are
variations in the sound it stands for. Thus the single letter A is proper
to mark one simple uniform sound; and the word ADULTERY is accommodated
to represent the sound annexed to it, in the formation whereof there
being eight different collisions or modifications of the air by the
organs of speech, each of which produces a difference of sound, it was
fit the word representing it should consist of as many distinct
characters, thereby to mark each particular difference or part of the
whole sound. And yet nobody, I presume, will say the single letter a, or
the word ADULTERY, are like unto, or of the same species with, the
respective sounds by them represented. It is indeed arbitrary that, in
general, letters of any language represent sounds at all: but when that
is once agreed, it is not arbitrary what combination of letters shall
represent this or that particular sound. I leave this with the reader to
pursue, and apply it in his own thoughts.
144. It must be confessed that we are not so apt to confound other signs
with the things signified, or to think them of the same species, as we
are visible and tangible ideas. But a little consideration will show us
how this may be without our supposing them of a like nature. These signs
are constant and universal, their connexion with tangible ideas has been
learnt at our first entrance into the world; and ever since, almost every
moment of our lives, it has been occurring to our thoughts, and fastening
and striking deeper on our minds. When we observe that signs are
variable, and of human institution; when we remember there was a time
they were not connected in our minds with those things they now so
readily suggest; but that their signification was learned by the slow
steps of experience: this preserves us from confounding them. But when we
find the same signs suggest the same things all over the world; when we
know they are not of human institution, and cannot remember that we ever
learned their signification, but think that at first sight they would
have suggested to us the same things they do now: all this persuades us
they are of the same species as the things respectively represented by
them, and that it is by a natural resemblance they suggest them to our
minds.
145. Add to this that whenever we make a nice survey of any object,
successively directing the optic axis to each point thereof, there are
certain lines and figures described by the motion of the head or eye,
which being in truth perceived by feeling, do nevertheless so mix
themselves, as it were, with the ideas of sight, that we can scarce think
but they appertain to that sense. Again, the ideas of sight enter into
the mind several at once, more distinct and unmingled than is usual in
the other senses beside the touch. Sounds, for example, perceived at the
same instant, are apt to coalesce, if I may so say, into one sound: but
we can perceive at the same time great variety of visible objects, very
separate and distinct from each other. Now tangible extension being made
up of several distinct coexistent parts, we may hence gather another
reason that may dispose us to imagine a likeness or an analogy between
the immediate objects of sight and touch. But nothing, certainly, doth
more contribute to blend and confound them together than the strict and
close connexion they have with each other. We cannot open our eyes but
the ideas of distance, bodies, and tangible figures are suggested by
them. So swift and sudden and unperceived is the transition from visible
to tangible ideas that we can scarce forbear thinking them equally the
immediate object of vision.