impulse of a ray of light on the upper part of the eye, considers this ray
as coming in a direct line from the lower part of the object; and, in like
manner, tracing the ray that strikes on the lower part of the eye, it is
directed to the upper part of the object. Thus, in the adjacent figure,
_C_, the lower point of the object _ABC_, is projected on _c_ the upper
part of the eye. So likewise, the highest point _A_ is projected on _a_
the lowest part of the eye; which makes the representation _cba_ inverted.
But the mind—considering the stroke that is made on _c_ as coming in the
straight line _Cc_ from the lower end of the object; and the stroke or
impulse on _a_, as coming in the line _Aa_ from the upper end of the
object—is directed to make a right judgment of the situation of the object
_ABC_, notwithstanding the picture of it be inverted. Moreover, this is
illustrated by conceiving a blind man, who, holding in his hands two
sticks that cross each other, doth with them touch the extremities of an
object, placed in a perpendicular situation(381). It is certain this man
will judge that to be the upper part of the object which he touches with
the stick held in the undermost hand, and that to be the lower part of the
object which he touches with the stick in his uppermost hand. This is the
common explication of the erect appearance of objects, which is generally
received and acquiesced in, being (as Mr. Molyneux tells us, _Diopt._ part
ii. ch. vii. p. 289) “allowed by all men as satisfactory.”
90. But this account to me does not seem in any degree true. Did I
perceive those impulses, decussations, and directions of the rays of
light, in like manner as hath been set forth, then, indeed, it would not
at first view be altogether void of probability. And there might be some
pretence for the comparison of the blind man and his cross sticks. But the
case is far otherwise. I know very well that I perceive no such thing.
And, of consequence, I cannot thereby make an estimate of the situation of
objects. Moreover, I appeal to any one’s experience, whether he be
conscious to himself that he thinks on the intersection made by the radius
pencils, or pursues the impulses they give in right lines, whenever he
perceives by sight the position of any object? To me it seems evident that
crossing and tracing of the rays, &c. is never thought on by children,
idiots, or, in truth, by any other, save only those who have applied
themselves to the study of optics. And for the mind to judge of the
situation of objects by those things without perceiving them, or to
perceive them without knowing it(382), take which you please, it is
perfectly beyond my comprehension. Add to this, that the explaining the
manner of vision by the example of cross sticks, and hunting for the
object along the axes of the radius pencils, doth suppose the proper
objects of sight to be perceived at a distance from us, contrary to what
hath been demonstrated(383). [We may therefore venture to pronounce this
opinion, concerning the way wherein the mind perceives the erect
appearance of objects, to be of a piece with those other tenets of writers
in optics, which in the foregoing parts of this treatise we have had
occasion to examine and refute(384).]
91. It remains, therefore, that we look for some other explication of this
difficulty. And I believe it not impossible to find one, provided we
examine it to the bottom, and carefully distinguish between the ideas of
sight and touch; which cannot be too oft inculcated in treating of
vision(385). But, more especially throughout the consideration of this
affair, we ought to carry that distinction in our thoughts; for that from
want of a right understanding thereof, the difficulty of explaining erect
vision seems chiefly to arise.
92. In order to disentangle our minds from whatever prejudices we may
entertain with relation to the subject in hand, nothing seems more
apposite than the taking into our thoughts the case of one born blind, and
afterwards, when grown up, made to see. And—though perhaps it may not be a
task altogether easy and familiar to us, to divest ourselves entirely of
the experiences received from sight, so as to be able to put our thoughts
exactly in the posture of such a one’s—we must, nevertheless, as far as
possible, endeavour to frame true conceptions of what might reasonably be
supposed to pass in his mind(386).
93. It is certain that a man actually blind, and who had continued so from
his birth, would, by the sense of feeling, attain to have ideas of upper
and lower. By the motion of his hand, he might discern the situation of
any tangible object placed within his reach. That part on which he felt
himself supported, or towards which he perceived his body to gravitate, he
would term _lower_, and the contrary to this _upper_; and accordingly
denominate whatsoever objects he touched.
94. But then, whatever judgments he makes concerning the situation of
objects are confined to those only that are perceivable by touch. All
those things that are intangible, and of a spiritual nature—his thoughts
and desires, his passions, and in general all the modifications of his
soul—to these he would never apply the terms upper and lower, except only
in a metaphorical sense. He may perhaps, by way of allusion, speak of high
or low thoughts: but those terms, in their proper signification, would
never be applied to anything that was not conceived to exist without the
mind. For, a man born blind, and remaining in the same state, could mean
nothing else by the words higher and lower than a greater or lesser
distance from the earth; which distance he would measure by the motion or
application of his hand, or some other part of his body. It is, therefore,
evident that all those things which, in respect of each other, would by
him be thought higher or lower, must be such as were conceived to exist
without his mind, in the ambient space(387).
95. Whence it plainly follows, that such a one, if we suppose him made to
see, would not at first sight think that anything he saw was high or low,
erect or inverted. For, it hath been already demonstrated, in sect. 41,
that he would not think the things he perceived by sight to be at any
distance from him, or without his mind. The objects to which he had
hitherto been used to apply the terms up and down, high and low, were such
only as affected, or were some way perceived by his touch. But the proper
objects of vision make a new set of ideas, perfectly distinct and
different from the former, and which can in no sort make themselves
perceived by touch. There is, therefore, nothing at all that could induce
him to think those terms applicable to them. Nor would he ever think it,
till such time as he had observed their connexion with tangible objects,
and the same prejudice(388) began to insinuate itself into his
understanding, which, from their infancy, had grown up in the
understandings of other men.
96. To set this matter in a clearer light, I shall make use of an example.
Suppose the above-mentioned blind person, by his touch, perceives a man to
stand erect. Let us inquire into the manner of this. By the application of
his hand to the several parts of a human body, he had perceived different
tangible ideas; which being collected into sundry complex ones(389) have
distinct names annexed to them. Thus, one combination of a certain
tangible figure, bulk, and consistency of parts is called the head;
another the hand; a third the foot, and so of the rest—all which complex
ideas could, in his understanding, be made up only of ideas perceivable by
touch. He had also, by his touch, obtained an idea of earth or ground,
towards which he perceives the parts of his body to have a natural
tendency. Now—by _erect_ nothing more being meant than that perpendicular
position of a man wherein his feet are nearest to the earth—if the blind
person, by moving his hand over the parts of the man who stands before
him, do perceive the tangible ideas that compose the head to be farthest
from, and those that compose the feet to be nearest to, that other
combination of tangible ideas which he calls earth, he will denominate
that man erect. But, if we suppose him on a sudden to receive his sight,
and that he behold a man standing before him, it is evident, in that case,
he would neither judge the man he sees to be erect nor inverted; for he,
never having known those terms applied to any other save tangible things,
or which existed in the space without him, and what he sees neither being
tangible, nor perceived as existing without, he could not know that, in
propriety of language, they were applicable to it.
97. Afterwards, when, upon turning his head or eyes up and down to the
right and left, he shall observe the visible objects to change, and shall
also attain to know that they are called by the same names, and connected
with the objects perceived by touch; then, indeed, he will come to speak
of them and their situation in the same terms that he has been used to
apply to tangible things: and those that he perceives by turning up his
eyes he will call upper, and those that by turning down his eyes he will
call lower.
98. And this seems to me the true reason why he should think those objects
uppermost that are painted on the lower part of his eye. For, by turning
the eye up they shall be distinctly seen; as likewise they that are
painted on the highest part of the eye shall be distinctly seen by turning
the eye down, and are for that reason esteemed lowest. For we have shewn
that to the immediate objects of sight, considered in themselves, he would
not attribute the terms high and low. It must therefore be on account of
some circumstances which are observed to attend them. And these, it is
plain, are the actions of turning the eye up and down, which suggest a
very obvious reason why the mind should denominate the objects of sight
accordingly high or low. And, without this motion of the eye—this turning
it up and down in order to discern different objects—doubtless _erect_,
_inverse_, and other the like terms relating to the position of tangible
objects, would never have been transferred, or in any degree apprehended
to belong to the ideas of sight, the mere act of seeing including nothing
in it to that purpose; whereas the different situations of the eye
naturally direct the mind to make a suitable judgment of the situation of
objects intromitted by it(390).
99. Farther, when he has by experience learned the connexion there is
between the several ideas of sight and touch, he will be able, by the
perception he has of the situation of visible things in respect of one
another, to make a sudden and true estimate of the situation of outward,
tangible things corresponding to them. And thus it is he shall
perceive(391) by sight the situation of external(392) objects, which do
not properly fall under that sense.
100. I know we are very prone to think that, if just made to see, we
should judge of the situation of visible things as we do now. But, we are
also as prone to think that, at first sight, we should in the same way
apprehend the distance and magnitude of objects, as we do now; which hath
been shewn to be a false and groundless persuasion. And, for the like
reasons, the same censure may be passed on the positive assurance that
most men, before they have thought sufficiently of the matter, might have
of their being able to determine by the eye, at first view, whether
objects were erect or inverse.
101. It will perhaps be objected to our opinion, that a man, for instance,
being thought erect when his feet are next the earth, and inverted when
his head is next the earth, it doth hence follow that, by the mere act of
vision, without any experience or altering the situation of the eye, we
should have determined whether he were erect or inverted. For both the
earth itself, and the limbs of the man who stands thereon, being equally
perceived by sight, one cannot choose seeing what part of the man is
nearest the earth, and what part farthest from it, i.e. whether he be
erect or inverted.
102. To which I answer, the ideas which constitute the tangible earth and
man are entirely different from those which constitute the visible earth
and man. Nor was it possible, by virtue of the visive faculty alone,
without superadding any experience of touch, or altering the position of
the eye, ever to have known, or so much as suspected, there had been any
relation or connexion between them. Hence, a man at first view would not
denominate anything he saw, _earth_, or _head_, or _foot_; and
consequently, he could not tell, by the mere act of vision, whether the
head or feet were nearest the earth. Nor, indeed, would we have thereby
any thought of earth or man, erect or inverse, at all—which will be made
yet more evident, if we nicely observe, and make a particular comparison
between, the ideas of both senses.
103. That which I see is only variety of light and colours. That which I
feel is hard or soft, hot or cold, rough or smooth. What similitude, what
connexion, have those ideas with these? Or, how is it possible that any
one should see reason to give one and the same name(393) to combinations
of ideas so very different, before he had experienced their co-existence?
We do not find there is any necessary connexion betwixt this or that
tangible quality, and any colour whatsoever. And we may sometimes perceive
colours, where there is nothing to be felt. All which doth make it
manifest that no man, at first receiving of his sight(394), would know
there was any agreement between this or that particular object of his
sight and any object of touch he had been already acquainted with. The
colours therefore of the head would to him no more suggest the idea of
head(395) than they would the idea of feet.
104. Farther, we have at large shewn (vid. sect. 63 and 64) there is no
discoverable necessary connexion between any given visible magnitude and
any one particular tangible magnitude; but that it is entirely the result
of custom and experience, and depends on foreign and accidental
circumstances, that we can, by the perception of visible extension, inform
ourselves what may be the extension of any tangible object connected with
it. Hence, it is certain, that neither the visible magnitude of head or
foot would bring along with them into the mind, at first opening of the
eyes, the respective tangible magnitudes of those parts.
105. By the foregoing section, it is plain the visible figure of any part
of the body hath no necessary connexion with the tangible figure thereof,
so as at first sight to suggest it to the mind. For, figure is the
termination of magnitude. Whence it follows that no visible magnitude
having in its own nature an aptness to suggest any one particular tangible
magnitude, so neither can any visible figure be inseparably connected with
its corresponding tangible figure, so as of itself, and in a way prior to
experience, it might suggest it to the understanding. This will be farther
evident, if we consider that what seems smooth and round to the touch may
to sight, if viewed through a microscope, seem quite otherwise.
106. From all which, laid together and duly considered, we may clearly
deduce this inference:—In the first act of vision, no idea entering by the
eye would have a perceivable connexion with the ideas to which the names
earth, man, head, foot, &c. were annexed in the understanding of a person
blind from his birth; so as in any sort to introduce them into his mind,
or make themselves be called by the same names, and reputed the same
things with them, as afterwards they come to be.
107. There doth, nevertheless, remain one difficulty, which to some may
seem to press hard on our opinion, and deserve not to be passed over. For,
though it be granted that neither the colour, size, nor figure of the
visible feet have any necessary connexion with the ideas that compose the
tangible feet, so as to bring them at first sight into my mind, or make me
in danger of confounding them, before I had been used to and for some time
experienced their connexion; yet thus much seems undeniable, namely, that
the number of the visible feet being the same with that of the tangible
feet, I may from hence, without any experience of sight, reasonably
conclude that they represent or are connected with the feet rather than
the head. I say, it seems the idea of two visible feet will sooner suggest
to the mind the idea of two tangible feet than of one head—so that the
blind man, upon first reception of the visive faculty, might know which
were the feet or two, and which the head or one.
108. In order to get clear of this seeming difficulty, we need only
observe that diversity of visible objects does 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(396).
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(397)) is nothing fixed and settled, really existing in things
themselves. It is entirely the creature of the mind, considering either a
simple idea by itself, or any combination of simple ideas to which it
gives one name, and so makes it pass for a 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, has an equal right to be called one; and many
houses go to the making of one 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 shews
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 co-exist and are proper to be bundled up
together under one name. He would not, for example, make into one complex
idea, and thereby esteem and unite 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(398).
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 such like, 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(399).
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(400). 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 any one 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 direct 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 shewn, 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 sight(401). 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.