distance of things from the organ of sight having been thus explained, in
what I call the First Part of the _Essay_, the Second and Third Parts
(sect. 52-120) argue for the invisibility of real extension in two other
relations, viz. magnitude and locality or situation. An induction of the
visual signs of tangible size and situation is given in those sections.
The result is applied to solve two problems then notable in optics, viz.
(1) the reason for the greater visible size of the horizontal moon than of
the moon in its meridian (sect. 67-87); and (2) the fact that objects are
placed erect in vision only on condition that their images on the retina
are inverted (sect. 88-120). Here the antithesis between the ideal world
of coloured extension, and the real world of resistant extension is
pressed with vigour. The “high” and “low” of the visible world is not the
“high” and “low” of the tangible world (sect. 91-106). There is no
resemblance and no necessary relation, between those two so-called
extensions; not even when the number of visible objects happen to coincide
with the number of tangible objects of which they are the visual signs,
e.g. the visible and tangible fingers on the hand: for the born-blind, on
first receiving sight, could not parcel out the visible phenomena in
correspondence with the tangible.
The next Part of the _Essay_ (sect. 121-45) argues for a specific as well
as a numerical difference between the original data of sight and the data
of touch and locomotion. Sight and touch perceive nothing in common.
Extension in its various relations differs in sight from extension in
touch. Coloured extension, which alone is visible, is found to be
different in kind from resistant extension, which alone is tangible. And
if actually perceived or concrete extensions differ thus, the question is
determined. For all extension with which man can be concerned must be
concrete (sect. 23). Extension in the abstract is meaningless (sect.
124-25). What remains is to marshal the scattered evidence, and to guard
the foregoing conclusions against objections. This is attempted in
sections 128-46.
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The enunciation of the summary generalisation, which forms the “New Theory
of Vision” (sect. 147-8), may be taken as the Fifth and culminating Part
of the _Essay_.
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The closing sections (149-60), as I have said, are supplementary, and
profess to determine the sort of extension—visible or tangible—with which
Geometry is concerned. In concluding that it is tangible, he tries to
picture the mental state of Idominians, or unbodied spirits, endowed with
visual perceptions _only_, and asks what _their_ conception of outness and
solid extension must be. Here further refinements in the interpretation of
visual perception, and its organic conditions, which have not escaped the
attention of latter psychologists and biologists, are hinted at.
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Whether the data of sight consist of non-resembling arbitrary Signs of the
tactual distances, sizes, and situations of things, is a question which
some might prefer to deal with experimentally—by trial of the experience
of persons in circumstances fitted to supply an answer. Of this sort would
be the experience of the born-blind, immediately after their sight has
been restored; the conception of extension and its relations found in
persons who continue from birth unable to see; the experience (if it could
be got) of persons always destitute of all tactual and locomotive
perceptions, but familiar with vision; and the facts of seeing observed in
infants of the human species, and in the lower animals.
Berkeley did not try to verify his conclusions in this way. Here and there
(sect. 41, 42, 79, 92-99, 103, 106, 110, 128, 132-37), he conjectures what
the first visual experience of those rescued from born-blindness is likely
to be; he also speculates, as we have seen, about the experience of
unbodied spirits supposed to be able to see, but unable to touch or move
(sect. 153-59); and in the Appendix he refers, in confirmation of his New
Theory, to a reported case of one born blind who had obtained sight. But
he forms his Theory independently of those delicate and difficult
investigations. His testing facts were sought introspectively. Indeed
those physiologists and mental philosophers who have since tried to
determine what vision in its purity is, by cases either of communicated
sight or of continued born-blindness, have illustrated the truth of
Diderot’s remark—“préparer et interroger un aveugle-né n’eût point été une
occupation indigne des talens réunis de Newton, Des Cartes, Locke, et
Leibniz(275).”
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Berkeley’s _New Theory_ has been quoted as a signal example of discovery
in metaphysics. The subtle analysis which distinguishes _seeing_ strictly
so called, from judgments about extended things, suggested by what we see,
appears to have been imperfectly known to the ancient philosophers.
Aristotle, indeed, speaks of colour as the only proper object of sight;
but, in passages of the _De Anima_(276) where he names properties peculiar
to particular senses, he enumerates others, such as motion, figure, and
magnitude, which belong to all the senses in common. His distinction of
Proper and Common Sensibles appears at first to contradict Berkeley’s
doctrine of the heterogeneity of the ideal visible and the real tangible
worlds. Aristotle, however, seems to question the immediate perceptibility
of Common Sensibles, and to regard them as realised through the activity
of intelligence(277).
Some writers in Optics, in mediaeval times, and in early modern
philosophy, advanced beyond Aristotle, in explaining the relation of our
matured notion of distance to what we originally perceive in seeing, and
in the fifteenth century it was discovered by Maurolyco that the rays of
light from the object converge to a focus in the eye; but I have not been
able to trace even the germ of the _New Theory_ in these speculations.
Excepting some hints by Descartes, Malebranche was among the first dimly
to anticipate Berkeley, in resolving our supposed power of seeing outness
into an interpretation of visual signs which we learn by experience to
understand. The most important part of Malebranche’s account of seeing is
contained in the _Recherche de la Vérité_ (Liv. I. ch. 9), in one of those
chapters in which he discusses the frequent fallaciousness of the senses,
and in particular of our visual perceptions of extension. He accounts for
their inevitable uncertainty by assigning them not to sense but to
misinterpretation of what is seen. He also enumerates various visual signs
of distance.
That the _Recherche_ of Malebranche, published more than thirty years
before the _Essay_, was familiar to Berkeley before the publication of his
_New Theory_, is proved by internal evidence, and by his juvenile
_Commonplace Book_. I am not able to discover signs of a similar connexion
between the _New Theory_ and the chapter on the mystery of sensation in
Glanvill’s _Scepsis Scientifica_ (ch. 5), published some years before the
_Recherche_ of Malebranche, where Glanvill refers to “a secret deduction,”
through which—from motions, &c., of which we are immediately percipient—we
“spell out” figures, distances, magnitudes, and colours, which have no
resemblance to them.
An approach to the _New Theory_ is found in a passage which first appeared
in the second edition of Locke’s _Essay_, published in 1694, to which
Berkeley refers in his own _Essay_ (sect. 132-35), and which, on account
of its relative importance, I shall here transcribe at length:—
“We are further to consider concerning Perception that the ideas we
receive by sensation are often, in grown people, altered by the judgment,
without our taking notice of it. When we set before our eyes a round globe
of any uniform colour, e.g. gold, alabaster, or jet, it is certain that
the idea thereby imprinted in our mind is of a flat circle, variously
shadowed, with several degrees of light and brightness coming to our eyes.
But, we having by use been accustomed to perceive what kind of appearance
convex bodies are wont to make in us, what alterations are made in the
reflection of light by the difference in the sensible figures of
bodies—the judgment presently, by an habitual custom, alters the
appearances into their causes; so that, from that which is truly variety
of shadow or colour, collecting the figure, it makes it pass for a mark of
figure, and frames to itself the perception of a convex figure and an
uniform colour, when the idea we receive from them is only a plane
variously coloured, as is evident in painting.
“To which purpose I shall here insert a problem of that very ingenious and
studious promoter of real knowledge, the learned and worthy Mr. Molyneux,
which he was pleased to send me in a letter some months since, and it is
this:—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 the one and the other, which
is the cube and which the sphere. Suppose then the cube and the sphere
placed on a table, and the blind man be made to see: quere, whether, by
his sight, before he touched them, he could not distinguish and tell,
which is the globe and 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 obtained the
experience that what affects his touch so and so, must affect his sight so
and so; so that a protuberant angle in the cube, that pressed his hand
unequally, shall appear to his eye as it does 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 to say with certainty which was the globe and which the
cube, whilst he only saw them; though he would unerringly name them by his
touch, and certainly distinguish them by the difference in their figures
felt.
“This I have set down, and leave with my reader, as an occasion for him to
consider how much he may be beholden to experience, improvement, and
acquired notions, where he thinks he had not the least use of, or help
from them: and the rather because this observing gentleman further adds
that, having, upon the occasion of my book, proposed this problem to
divers very ingenious men, he hardly ever met with one that at first gave
the answer to it which he thinks true, till by hearing his reasons they
were convinced.
“But this is not I think usual in any of our ideas but those received by
sight: because sight, the most comprehensive of the 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, the
several varieties of which change the appearance of its proper object,
i.e. light and colours; we bring ourselves by use to judge of the one by
the other. This, in many cases, by a settled habit, in things whereof we
have frequent experience, is performed so constantly and so quick, that we
take that for the perception of our sensation, which is an idea formed by
our judgment; so that one, i.e. that of sensation, serves only to excite
the other, and is scarce taken notice of itself; as a man who reads or
hears with attention and understanding takes little notice of the
character or sounds, but of the ideas that are excited in him by them.
“Nor need we wonder that this is done with so little notice, if we
consider how very quick the actions of the mind are performed; for, as
itself is thought to take up no space, to have no extension, so its
actions seem to require no time, but many of them seem to be crowded into
an instant. I speak this in comparison of the actions of the body....
Secondly, we shall not be much surprised that this is done with us in so
little notice, if we consider how the facility we get of doing things, by
a custom of doing, makes them often pass in us without notice. Habits,
especially such as are begun very early, come at last to produce actions
in us which often escape our observation.... And therefore it is not so
strange that our mind should often change the idea of its sensation into
that of its judgment, and make the one serve only to excite the other,
without our taking notice of it.” (_Essay concerning Human Understanding_,
Book II. ch. 9. § 8.)
This remarkable passage anticipates by implication the view of an
interpretation of materials originally given in the visual sense, which,
under the name of “suggestion,” is the ruling factor in the _New Theory of
Vision_.
The following sentences relative to the invisibility of distances,
contained in the _Treatise of Dioptrics_ (published in 1690) of Locke’s
friend and correspondent William Molyneux, whose son was Berkeley’s pupil,
illustrate Locke’s statements, and may be compared with the opening
sections of the _Essay on Vision_:—
“In plain vision the estimate we make of the distance of objects
(especially when so far removed that the interval between our two eyes
bears no sensible proportion thereto, or when looked upon with one eye
only) is rather the act of our judgment than of sense; and acquired by
exercise, and a faculty of comparing, rather than natural. For, distance
of itself is not to be perceived; for, ’tis a line (or a length) presented
to our eye with its end toward us, which must therefore be only a point,
and that is invisible. Wherefore distance is chiefly perceived by means of
interjacent bodies, as by the earth, mountains, hills, fields, trees,
houses, &c. Or by the estimate we make of the comparative magnitude of
bodies, or of their faint colours, &c. These I say are the chief means of
apprehending the distance of objects that are considerably remote. But as
to nigh objects—to whose distance the interval of the eyes bears a
sensible proportion—their distance is perceived by the turn of the eyes,
or by the angle of the optic axes (_Gregorii Opt. Promot._ prop. 28). This
was the opinion of the ancients, Alhazen, Vitellio, &c. And though the
ingenious Jesuit Tacquet (_Opt. Lib. I._ prop. 2) disapprove thereof, and
objects against it a new notion of Gassendus (of a man’s seeing only with
one eye at a time one and the same object), yet this notion of Gassendus
being absolutely false (as I could demonstrate were it not beside my
present purpose), it makes nothing against this opinion.
“Wherefore, distance being only a line and not of itself perceivable, if
an object were conveyed to the eye by one single ray only, there were no
other means of judging of its distance but by some of those hinted before.
Therefore when we estimate the distance of nigh objects, either we take
the help of both eyes; or else we consider the pupil of one eye as having
breadth, and receiving a parcel of rays from each radiating point. And,
according to the various inclinations of the rays from one point on the
various parts of the pupil, we make our estimate of the distance of the
object. And therefore (as is said before), by one single eye we can only
judge of the distance of such objects to whose distance the breadth of the
pupil has a sensible proportion.... For, it is observed before (prop. 29,
sec. 2, see also _Gregorii Opt. Promot._ prop. 29) that for viewing
objects remote and nigh, there are requisite various conformations of the
eye—the rays from nigh objects that fall on the eye diverging more than
those from more remote objects.” (_Treatise of Dioptrics_, Part I. prop.
31.)
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All this helps to shew the state of science regarding vision about the
time Berkeley’s _Essay_ appeared, especially among those with whose works
he was familiar(278). I shall next refer to illustrations of the change
which the _Essay_ produced.
The _New Theory_ has occasioned some interesting criticism since its
appearance in 1709. At first it drew little attention. For twenty years
after its publication the allusions to it were few. The account of
Cheselden’s experiment upon one born blind, published in 1728, in the
_Philosophical Transactions_, which seemed to bring the Theory to the test
of scientific experiment, recalled attention to Berkeley’s reasonings. The
state of religious thought about the same time confirmed the tendency to
discuss a doctrine which represented human vision as interpretation of a
natural yet divine language, thus suggesting Omnipresent Mind.
Occasional discussions of the _New Theory_ may be found in the
_Gentleman’s Magazine_, from 1732 till Berkeley’s death in 1753. Some
criticisms may also be found in Smith’s _Optics_, published in 1738.
Essential parts of Berkeley’s analysis are explained by Voltaire, in his
_Élémens de la Philosophie de Newton_. The following from that work is
here given on its own account, and also as a prominent recognition of the
new doctrine in France, within thirty years from its first promulgation:—
“Il faut absolument conclure de tout ceci, que les distances, les
grandeurs, les situations, ne sont pas, à proprement parler, des
choses visibles, c’est-à-dire, ne sont pas les objets propres et
immédiats de la vue. L’objet propre et immédiat de la vue n’est
autre chose que la lumière colorée: tout le reste, nous ne le
sentons qu’à la longue et par expérience. Nous apprenons à voir
précisément comme nous apprenons à parler et à lire. La différence
est, que l’art de voir est plus facile, et que la nature est
également à tous notre maître.
“Les jugements soudains, presque uniformes, que toutes nos âmes, à
un certain âge, portent des distances, des grandeurs, des
situations, nous font penser qu’il n’y a qu’à ouvrir les yeux pour
voir la manière dont nous voyons. On se trompe; il y faut le
secours des autres sens. Si les hommes n’avaient que le sens de la
vue, ils n’auraient aucun moyen pour connaître l’étendue en
longueur, largeur et profondeur; et un pur esprit ne la
connaîtrait pas peutêtre, à moins que Dieu ne la lui révélât. Il
est très difficile de séparer dans notre entendement l’extension
d’un objet d’avec les couleurs de cet objet. Nous ne voyons jamais
rien que d’étendu, et de là nous sommes tous portés à croire que
nous voyons en effet l’étendue.” (_Élémens de la Philos. de
Newton_, Seconde Partie, ch. 7.)
Condillac, in his _Essais sur l’Origine des Connaissances Humaines_ (Part
I. sect. 6), published in 1746, combats Berkeley’s _New Theory_, and
maintains that an extension exterior to the eye is immediately discernible
by sight; the eye being naturally capable of judging at once of figures,
magnitudes, situations, and distances. His reasonings in support of this
“prejudice,” as he afterwards allowed it to be, may be found in the
section entitled “De quelques jugemens qu’on a attribués à l’âme sans
fondement, ou solution d’un problème de métaphysique.” Here Locke,
Molyneux, Berkeley, and Voltaire are criticised, and Cheselden’s
experiment is referred to. Condillac’s subsequent recantation is contained
in his _Traité des Sensations_, published in 1754, and in his _L’Art de
Penser_. In the _Traité des Sensations_ (Troisième Partie, ch. 3, 4, 5, 6,
7, 8, &c.) the whole question is discussed at length, and Condillac
vindicates what he allows must appear a marvellous paradox to the
uninitiated—that we only gradually learn to see, hear, smell, taste, and
touch. He argues in particular that the eye cannot originally perceive an
extension that is beyond itself, and that perception of trinal space is
due to what we experience in touch.
Voltaire and Condillac gave currency to the _New Theory_ in France, and it
soon became a commonplace with D’Alembert, Diderot, Buffon, and other
French philosophers. In Germany we have allusions to it in the Berlin
Memoirs and elsewhere; but, although known by name, if not in its
distinctive principle and latent idealism, it has not obtained the
consideration which its author’s developed theory of the material as well
as the visible world has received. The Kantian _a priori_ criticism of our
cognition of Space, and of our mathematical notions, subsequently
indisposed the German mind to the _a posteriori_ reasoning of Berkeley’s
_Essay_.
Its influence is apparent in British philosophy. The following passages in
Hartley’s _Observations on Man_, published in 1749, illustrate the extent
to which some of the distinctive parts of the new doctrine were at that
time received by an eminent English psychologist:—
“Distance is judged of by the quantity of motion, and figure by the
relative quantity of distance.... And, as the sense of sight is much more
extensive and expedite than feeling, we judge of tangible qualities
chiefly by sight, which therefore may be considered, agreeably to Bishop
Berkeley’s remark, as a philosophical language for the ideas of feeling;
being, for the most part, an adequate representative of them, and a
language common to all mankind, and in which they all agree very nearly,
after a moderate degree of experience.
“However, if the informations from touch and sight disagree at any time,
we are always to depend upon touch, as that which, according to the usual
ways of speaking upon these subjects, is the true representation of the
essential properties, i.e. as the earnest and presage of what other
tangible impressions the body under consideration will make upon our
feeling in other circumstances; also what changes it will produce in other
bodies; of which again we are to determine by our feeling, if the visual
language should not happen to correspond to it exactly. And it is from
this difference that we call the touch the reality, light the
representative—also that a person born blind may foretell with certainty,
from his present tangible impressions, what others would follow upon
varying the circumstances; whereas, if we could suppose a person to be
born without feeling, and to arrive at man’s estate, he could not, from
his present visible impressions, judge what others would follow upon
varying the circumstances. Thus the picture of a knife, drawn so well as
to deceive his eye, would not, when applied to another body, produce the
same change of visible impressions as a real knife does, when it separates
the parts of the body through which it passes. But the touch is not liable
to these deceptions. As it is therefore the fundamental source of
information in respect of the essential properties of matter, it may be
considered as our first and principal key to the knowledge of the external
world.” (Prop. 30.)
In other parts of Hartley’s book (e.g. Prop. 58) the relation of our
visual judgments of magnitude, figure, motion, distance, and position to
the laws of association is explained, and the associating circumstances by
which these judgments are formed are enumerated in detail.
Dr. Porterfield of Edinburgh, in his _Treatise on the Eye, or the Manner
and Phenomena of Vision_ (Edinburgh, 1759), is an exception to the consent
which the doctrine had then widely secured. He maintains, in opposition to
Berkeley, that “the judgments we form of the situation and distance of
visible objects, depend not on custom and experience, but on original
instinct, to which mind is subject in our embodied state(279).”
Berkeley’s Theory of Vision, in so far as it resolves our visual
perceptions of distance into interpretation of arbitrary signs, received
the qualified approbation of Reid, in his _Inquiry into the Human Mind on
the Principles of Common Sense_ (1764). He criticises it in the _Inquiry_,
where the doctrine of visual signs, of which Berkeley’s whole philosophy
is a development, is accepted, and to some extent applied. With Reid it is
divorced, however, from the Berkeleian conception of the material world,
although the Theory of Vision was the seminal principle of Berkeley’s
Theory of Matter(280).