Critiques and Addresses by Thomas Henry Huxley

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Not only does every _visibile_ appear to be remote, but it has a
position in external space, just as a _tangibile_ appears to be
superficial and to have a determinate position on the surface of
the body. Every _visibile_, in fact, appears (approximately) to be
situated upon a line drawn from it to the point of the retina on which
its image falls. It is referred outwards, in the general direction of
the pencil of light by which it is rendered visible, just as, in the
experiment with the stick, the _tangibile_ is referred outwards to the
end of the stick.

It is for this reason that an object, viewed with both eyes, is seen
single and not double. Two distinct images are formed, but each image
is referred to that point at which the two optic axes intersect;
consequently, the two images exactly cover one another, and appear as
completely one as any other two exactly similar superimposed images
would be. And it is for the same reason, that, if the ball of the
eye is pressed upon at any point, a spot of light appears apparently
outside the eye, and in a region exactly opposite to that in which the
pressure is made.

But while it seems to me that there is no reason to doubt that the
extradition of sensation is more complete in the case of the eye than
in that of the skin, and that corporeal distinctness, and hence space,
are directly suggested by vision, it is another, and a much more
difficult question, whether the notion of geometrical solidity is
attainable by pure vision; that is to say, by a single eye, all the
parts of which are immoveable. However this may be, for an absolutely
fixed eye, I conceive there can be no doubt in the case of an eye that
is moveable and capable of adjustment. For, with the moveable eye,
the muscular sense comes into play in exactly the same way as with the
moveable hand; and the notion of change of place, _plus_ the sense of
effort, gives rise to a conception of visual space, which runs exactly
parallel with that of tangible space. When two moveable eyes are
present, the notion of space of three dimensions is obtained in the
same way as it is by the two hands, but with, much greater precision.

And if, to take a case similar to one already assumed, we suppose a
man deprived of every sense except vision, and of all motion except
that of his eyes, it surely cannot be doubted that he would have a
perfect conception of space; and indeed a much more perfect conception
than he who possessed touch alone without vision. But of course our
touchless man would be devoid of any notion of resistance; and hence
space, for him, would be altogether geometrical and devoid of body.

And here another curious consideration arises, what likeness, if
any, would there be between the visual space of the one man, and the
tangible space of the other?

Berkeley, as we have seen (in the eighth proposition), declares that
there is no likeness between the ideas given by sight and those given
by touch; and one cannot but agree with him, so long as the term ideas
is restricted to mere sensations. Obviously, there is no more likeness
between the feel of a surface and the colour of it, than there is
between its colour and its smell. All simple sensations, derived
from different senses, are incommensurable with one another, and only
gradations of their own intensity are comparable. And thus so far as
the primary facts of sensation go, visual figure and tactile figure,
visual magnitude and tactile magnitude, visual motion and tactile
motion, are truly unlike, and have no common term. But when Berkeley
goes further than this, and declares that there are no "ideas" common
to the "ideas" of touch and those of sight, it appears to me that he
has fallen into a great error, and one which is the chief source of
his paradoxes about geometry.

Berkeley in fact employs the word "idea" in this instance to denote
two totally different classes of feelings, or states of consciousness.
For these may be divided into two groups: the primary feelings,
which exist in themselves and without relation to any other, such as
pleasure and pain, desire, and the simple sensations obtained through
the sensory organs; and the secondary feelings, which express those
relations of primary feelings which are perceived by the mind; and the
existence of which, therefore, implies the pre-existence of at least
two of the primary feelings. Such are likeness and unlikeness in
quality, quantity, or form; succession and contemporaneity; contiguity
and distance; cause and effect; motion and rest.

Now it is quite true that there is no likeness between the primary
feelings which are grouped under sight and touch; but it appears to me
wholly untrue, and indeed absurd, to affirm that there is no likeness
between the secondary feelings which express the relations of the
primary ones.

The relation of succession perceived between the visible taps of
a hammer, is, to my mind, exactly like the relation of succession
between the tangible taps; the unlikeness between red and blue is a
mental phenomenon of the same order as the unlikeness between rough
and smooth. Two points visibly distant are so, because one or more
units of visible length _(minima visibilia_) are interposed between
them; and as two points tangibly distant are so, because one or more
units of tangible length _(minima tangibilia_) are interposed between
them, it is clear that the notion of interposition of units of
sensibility, or _minima sensibilia_, is an idea common to the two. And
whether I see a point move across the field of vision towards another
point, or feel the like motion, the idea of the gradual diminution of
the number of sensible units between the two points appears to me to
be common to both kinds of motion.

Hence, I conceive, that though it be true that there is no likeness
between the primary feelings given by sight and those given by touch,
yet there is a complete likeness between the secondary feelings
aroused by each sense.

Indeed, if it were not so, how could Logic, which deals with those
forms of thought which are applicable to every kind of subject-matter,
be possible? How could numerical proportion be as true of _visibilia_,
as of _tangibilia_, unless there were some ideas common to the two?
And to come directly to the heart of the matter, is there any more
difference between the relations between tangible sensations which we
call place and direction, and those between visible sensations which
go by the same name, than there is between those relations of tangible
and visible sensations which we call succession? And if there be
none, why is Geometry not just as much a matter of _visibilia_ as of
_tangibilia_?

Moreover, as a matter of fact, it is certain that the muscular sense
is so closely connected with both the visual and the tactile senses,
that, by the ordinary laws of association, the ideas which it suggests
must needs be common to both.

From what has been said it will follow that the ninth proposition
falls to the ground; and that vision, combined with the muscular
sensations produced by the movement of the eyes, gives us as complete
a notion of corporeal separation and of distance in the third
dimension of space, as touch, combined with the muscular sensations
produced by the movements of the hand, does. The tenth proposition
seems to contain a perfectly true statement, but it is only half
the truth. It is no doubt true that our visual ideas are a kind of
language by which we are informed of the tactile ideas which may or
will arise in us; but this is true, more or less, of every sense in
regard to every other. If I put my hand in my pocket, the tactile
ideas which I receive prophesy quite accurately what I shall
see--whether a bunch of keys or half-a-crown--when I pull it out
again; and the tactile ideas are, in this case, the language which
informs me of the visual ideas which will arise. So with the other
senses: olfactory ideas tell me I shall find the tactile and visual
phenomena called violets, if I look for them; taste tells me that
what I am tasting will, if I look at it, have the form of a clove; and
hearing warns me of what I shall, or may, see and touch every minute
of my life.

But while the "New Theory of Vision" cannot be considered to possess
much value in relation to the immediate object its author had in view,
it had a vastly important influence in directing attention to the real
complexity of many of those phenomena of sensation, which appear at
first to be simple. And even if Berkeley was, as I imagine he was,
quite wrong in supposing that we do not see space, the contrary
doctrine makes quite as strongly for his general view, that space can
be conceived only as something thought by a mind.

The last of Locke's "primary qualities" which remain to be considered
is mechanical solidity, or impenetrability. But our conception of this
is derived from the sense of resistance to our own effort, or active
force, which we meet with in association with sundry tactile or visual
phenomena; and, undoubtedly, active force is inconceivable except as a
state of consciousness. This may sound paradoxical; but let anyone try
to realize what he means by the mutual attraction of two particles,
and I think he will find, either, that he conceives them simply as
moving towards one another at a certain rate, in which case he only
pictures motion to himself, and leaves force aside; or, that he
conceives each particle to be animated by something like his own
volition, and to be pulling as he would pull. And I suppose that this
difficulty of thinking of force except as something comparable to
volition, lies at the bottom of Leibnitz's doctrine of monads, to say
nothing of Schopenhauer's "Welt als Wille und Vorstellung;" while the
opposite difficulty of conceiving force to be anything like volition,
drives another school of thinkers into the denial of any connection,
save that of succession, between cause and effect.

* * * * *

To sum up. If the materialist affirms that the universe and all its
phenomena are resolvable into matter and motion, Berkeley replies,
True; but what you call matter and motion are known to us only as
forms of consciousness; their being is to be conceived or known; and
the existence of a state of consciousness, apart from a thinking mind,
is a contradiction in terms.

I conceive that this reasoning is irrefragable. And therefore, if
I were obliged to choose between absolute materialism and absolute
idealism, I should feel compelled to accept the latter alternative.
Indeed, upon this point Locke does, practically, go as far in the
direction of idealism, as Berkeley, when he admits that "the simple
ideas we receive from sensation and reflection are the boundaries of
our thoughts, beyond which the mind, whatever efforts it would make,
is not able to advance one jot."--Book II. chap, xxiii. Sec. 29.

But Locke adds, "Nor can it make any discoveries when it would pry
into the nature and hidden causes of these ideas."

Now, from this proposition, the thorough materialists dissent as much,
on the one hand, as Berkeley does, upon the other hand.

The thorough materialist asserts that there is a something which he
calls the "substance" of matter; that this something is the cause of
all phenomena, whether material or mental; that it is self-existent
and eternal, and so forth.

Berkeley, on the contrary, asserts with equal confidence that there is
no substance of matter, but only a substance of mind, which he terms
spirit; that there are two kinds of spiritual substance, the one
eternal and uncreated, the substance of the Deity, the other created,
and, once created, naturally eternal; that the universe, as known
to created spirits, has no being in itself, but is the result of
the action of the substance of the Deity on the substance of those
spirits.

In contradiction to which bold assertion, Locke affirms that we simply
know nothing about substance of any kind.[1]

[Footnote 1: Berkeley virtually makes the same confession of
ignorance, when he admits that we can have no idea or notion of a
spirit ("Principles of Human Knowledge," Sec. 138); and the way in which
he tries to escape the consequences of this admission, is a splendid
example of the floundering of a mired logician.]

"So that if anyone will examine himself concerning his notion
of pure substance in general, he will find he has no other
idea of it at all, but only a supposition of he knows not
what support of such qualities, which are capable of producing
simple ideas in us, which qualities are commonly called
accidents.

"If anyone should be asked, what is the subject wherein colour
or weight inheres? he would have nothing to say but the
solid extended parts; and if he were demanded what is it that
solidity and extension inhere in? he would not be in much
better case than the Indian before mentioned, who, urging that
the world was supported by a great elephant, was asked what
the elephant rested on? to which his answer was, a great
tortoise. But being again pressed to know what gave support
to the broad-backed tortoise I replied, something, he knew not
what. And thus here, as in all other cases when we use
words without having clear and distinct ideas, we talk like
children, who, being questioned what such a thing is, readily
give this satisfactory answer, that it is something; which in
truth signifies no more when so used, either by children or
men, but that they know not what, and that the thing they
pretend to talk and know of is what they have no distinct idea
of at all, and are, so, perfectly ignorant of it and in the
dark. The idea, then, we have, to which we give the general
name substance, being nothing but the supposed but unknown
support of those qualities we find existing, which we imagine
cannot exist _sine re substante_, without something to support
them, we call that support _substantia_, which, according to
the true import of the word, is, in plain English, standing
under or upholding."[1]

[Footnote 1: Locke, "Human Understanding," Book II. chap, xiii. Sec. 2.]

I cannot but believe that the judgment of Locke is that which
Philosophy will accept as her final decision.

Suppose that a piano were conscious of sound, and of nothing else. It
would become acquainted with a system of nature entirely composed
of sounds, and the laws of nature would be the laws of melody and of
harmony. It might acquire endless ideas of likeness and unlikeness, of
succession, of similarity and dissimilarity, but it could attain to no
conception of space, of distance, or of resistance; or of figure, or
of motion.

The piano might then reason thus: All my knowledge consists of sounds
and the perception of the relations of sounds; now the being of sound
is to be heard; and it is inconceivable that the existence of the
sounds I know, should depend upon any other existence than that of the
mind of a hearing being.

This would be quite as good reasoning as Berkeley's, and very sound
and useful, so far as it defines the limits of the piano's faculties.
But for all that, pianos have an existence quite apart from sounds,
and the auditory consciousness of our speculative piano would be
dependent, in the first place, on the existence of a "substance" of
brass, wood, and iron, and, in the second, on that of a musician. But
of neither of these conditions of the existence of his consciousness
would the phenomena of that consciousness afford him the slightest
hint.

So that while it is the summit of human wisdom to learn the limit of
our faculties, it may be wise to recollect that we have no more right
to make denials, than to put forth affirmatives, about what lies
beyond that limit. Whether either mind, or matter, has a "substance"
or not, is a problem which we are incompetent to discuss; and it is
just as likely that the common notions upon the subject should be
correct as any others. Indeed, Berkeley himself makes Philonous wind
up his discussions with Hylas, in a couple of sentences which aptly
express this conclusion:--

"You see, Hylas, the water of yonder fountain, how it is
forced upwards in a round column to a certain height, at which
it breaks and falls back into the basin from whence it rose;
its ascent as well as its descent proceeding from the same
uniform law or principle of gravitation. Just so, the same
principles which, at first view, lead to scepticism, pursued
to a certain point, bring men back to common sense."

THE END.

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