THE NATURE OF MATTER
In the preceding chapter we agreed, though without being able to find
demonstrative reasons, that it is rational to believe that our
sense-data--for example, those which we regard as associated with my
table--are really signs of the existence of something independent of
us and our perceptions. That is to say, over and above the sensations
of colour, hardness, noise, and so on, which make up the appearance of
the table to me, I assume that there is something else, of which these
things are appearances. The colour ceases to exist if I shut my eyes,
the sensation of hardness ceases to exist if I remove my arm from
contact with the table, the sound ceases to exist if I cease to rap
the table with my knuckles. But I do not believe that when all these
things cease the table ceases. On the contrary, I believe that it is
because the table exists continuously that all these sense-data will
reappear when I open my eyes, replace my arm, and begin again to rap
with my knuckles. The question we have to consider in this chapter
is: What is the nature of this real table, which persists
independently of my perception of it?
To this question physical science gives an answer, somewhat incomplete
it is true, and in part still very hypothetical, but yet deserving of
respect so far as it goes. Physical science, more or less
unconsciously, has drifted into the view that all natural phenomena
ought to be reduced to motions. Light and heat and sound are all due
to wave-motions, which travel from the body emitting them to the
person who sees light or feels heat or hears sound. That which has
the wave-motion is either aether or 'gross matter', but in either case
is what the philosopher would call matter. The only properties which
science assigns to it are position in space, and the power of motion
according to the laws of motion. Science does not deny that it _may_
have other properties; but if so, such other properties are not useful
to the man of science, and in no way assist him in explaining the
phenomena.
It is sometimes said that 'light _is_ a form of wave-motion', but this
is misleading, for the light which we immediately see, which we know
directly by means of our senses, is _not_ a form of wave-motion, but
something quite different--something which we all know if we are not
blind, though we cannot describe it so as to convey our knowledge to a
man who is blind. A wave-motion, on the contrary, could quite well be
described to a blind man, since he can acquire a knowledge of space by
the sense of touch; and he can experience a wave-motion by a sea
voyage almost as well as we can. But this, which a blind man can
understand, is not what we mean by _light_: we mean by _light_ just
that which a blind man can never understand, and which we can never
describe to him.
Now this something, which all of us who are not blind know, is not,
according to science, really to be found in the outer world: it is
something caused by the action of certain waves upon the eyes and
nerves and brain of the person who sees the light. When it is said
that light _is_ waves, what is really meant is that waves are the
physical cause of our sensations of light. But light itself, the
thing which seeing people experience and blind people do not, is not
supposed by science to form any part of the world that is independent
of us and our senses. And very similar remarks would apply to other
kinds of sensations.
It is not only colours and sounds and so on that are absent from the
scientific world of matter, but also _space_ as we get it through
sight or touch. It is essential to science that its matter should be
in _a_ space, but the space in which it is cannot be exactly the space
we see or feel. To begin with, space as we see it is not the same as
space as we get it by the sense of touch; it is only by experience in
infancy that we learn how to touch things we see, or how to get a
sight of things which we feel touching us. But the space of science
is neutral as between touch and sight; thus it cannot be either the
space of touch or the space of sight.
Again, different people see the same object as of different shapes,
according to their point of view. A circular coin, for example,
though we should always _judge_ it to be circular, will _look_ oval
unless we are straight in front of it. When we judge that it _is_
circular, we are judging that it has a real shape which is not its
apparent shape, but belongs to it intrinsically apart from its
appearance. But this real shape, which is what concerns science, must
be in a real space, not the same as anybody's _apparent_ space. The
real space is public, the apparent space is private to the percipient.
In different people's _private_ spaces the same object seems to have
different shapes; thus the real space, in which it has its real shape,
must be different from the private spaces. The space of science,
therefore, though _connected_ with the spaces we see and feel, is not
identical with them, and the manner of its connexion requires
investigation.
We agreed provisionally that physical objects cannot be quite like our
sense-data, but may be regarded as _causing_ our sensations. These
physical objects are in the space of science, which we may call
'physical' space. It is important to notice that, if our sensations
are to be caused by physical objects, there must be a physical space
containing these objects and our sense-organs and nerves and brain.
We get a sensation of touch from an object when we are in contact with
it; that is to say, when some part of our body occupies a place in
physical space quite close to the space occupied by the object. We
see an object (roughly speaking) when no opaque body is between the
object and our eyes in physical space. Similarly, we only hear or
smell or taste an object when we are sufficiently near to it, or when
it touches the tongue, or has some suitable position in physical space
relatively to our body. We cannot begin to state what different
sensations we shall derive from a given object under different
circumstances unless we regard the object and our body as both in one
physical space, for it is mainly the relative positions of the object
and our body that determine what sensations we shall derive from the
object.
Now our sense-data are situated in our private spaces, either the
space of sight or the space of touch or such vaguer spaces as other
senses may give us. If, as science and common sense assume, there is
one public all-embracing physical space in which physical objects are,
the relative positions of physical objects in physical space must more
or less correspond to the relative positions of sense-data in our
private spaces. There is no difficulty in supposing this to be the
case. If we see on a road one house nearer to us than another, our
other senses will bear out the view that it is nearer; for example, it
will be reached sooner if we walk along the road. Other people will
agree that the house which looks nearer to us is nearer; the ordnance
map will take the same view; and thus everything points to a spatial
relation between the houses corresponding to the relation between the
sense-data which we see when we look at the houses. Thus we may
assume that there is a physical space in which physical objects have
spatial relations corresponding to those which the corresponding
sense-data have in our private spaces. It is this physical space
which is dealt with in geometry and assumed in physics and astronomy.
Assuming that there is physical space, and that it does thus
correspond to private spaces, what can we know about it? We can know
_only_ what is required in order to secure the correspondence. That
is to say, we can know nothing of what it is like in itself, but we
can know the sort of arrangement of physical objects which results
from their spatial relations. We can know, for example, that the
earth and moon and sun are in one straight line during an eclipse,
though we cannot know what a physical straight line is in itself, as
we know the look of a straight line in our visual space. Thus we come
to know much more about the _relations_ of distances in physical space
than about the distances themselves; we may know that one distance is
greater than another, or that it is along the same straight line as
the other, but we cannot have that immediate acquaintance with
physical distances that we have with distances in our private spaces,
or with colours or sounds or other sense-data. We can know all those
things about physical space which a man born blind might know through
other people about the space of sight; but the kind of things which a
man born blind could never know about the space of sight we also
cannot know about physical space. We can know the properties of the
relations required to preserve the correspondence with sense-data, but
we cannot know the nature of the terms between which the relations
hold.
With regard to time, our _feeling_ of duration or of the lapse of time
is notoriously an unsafe guide as to the time that has elapsed by the
clock. Times when we are bored or suffering pain pass slowly, times
when we are agreeably occupied pass quickly, and times when we are
sleeping pass almost as if they did not exist. Thus, in so far as
time is constituted by duration, there is the same necessity for
distinguishing a public and a private time as there was in the case of
space. But in so far as time consists in an _order_ of before and
after, there is no need to make such a distinction; the time-order
which events seem to have is, so far as we can see, the same as the
time-order which they do have. At any rate no reason can be given for
supposing that the two orders are not the same. The same is usually
true of space: if a regiment of men are marching along a road, the
shape of the regiment will look different from different points of
view, but the men will appear arranged in the same order from all
points of view. Hence we regard the order as true also in physical
space, whereas the shape is only supposed to correspond to the
physical space so far as is required for the preservation of the
order.
In saying that the time-order which events seem to have is the same as
the time-order which they really have, it is necessary to guard
against a possible misunderstanding. It must not be supposed that the
various states of different physical objects have the same time-order
as the sense-data which constitute the perceptions of those objects.
Considered as physical objects, the thunder and lightning are
simultaneous; that is to say, the lightning is simultaneous with the
disturbance of the air in the place where the disturbance begins,
namely, where the lightning is. But the sense-datum which we call
hearing the thunder does not take place until the disturbance of the
air has travelled as far as to where we are. Similarly, it takes
about eight minutes for the sun's light to reach us; thus, when we see
the sun we are seeing the sun of eight minutes ago. So far as our
sense-data afford evidence as to the physical sun they afford evidence
as to the physical sun of eight minutes ago; if the physical sun had
ceased to exist within the last eight minutes, that would make no
difference to the sense-data which we call 'seeing the sun'. This
affords a fresh illustration of the necessity of distinguishing
between sense-data and physical objects.
What we have found as regards space is much the same as what we find
in relation to the correspondence of the sense-data with their
physical counterparts. If one object looks blue and another red, we
may reasonably presume that there is some corresponding difference
between the physical objects; if two objects both look blue, we may
presume a corresponding similarity. But we cannot hope to be
acquainted directly with the quality in the physical object which
makes it look blue or red. Science tells us that this quality is a
certain sort of wave-motion, and this sounds familiar, because we
think of wave-motions in the space we see. But the wave-motions must
really be in physical space, with which we have no direct
acquaintance; thus the real wave-motions have not that familiarity
which we might have supposed them to have. And what holds for colours
is closely similar to what holds for other sense-data. Thus we find
that, although the _relations_ of physical objects have all sorts of
knowable properties, derived from their correspondence with the
relations of sense-data, the physical objects themselves remain
unknown in their intrinsic nature, so far at least as can be
discovered by means of the senses. The question remains whether there
is any other method of discovering the intrinsic nature of physical
objects.
The most natural, though not ultimately the most defensible,
hypothesis to adopt in the first instance, at any rate as regards
visual sense-data, would be that, though physical objects cannot, for
the reasons we have been considering, be _exactly_ like sense-data,
yet they may be more or less like. According to this view, physical
objects will, for example, really have colours, and we might, by good
luck, see an object as of the colour it really is. The colour which
an object seems to have at any given moment will in general be very
similar, though not quite the same, from many different points of
view; we might thus suppose the 'real' colour to be a sort of medium
colour, intermediate between the various shades which appear from the
different points of view.
Such a theory is perhaps not capable of being definitely refuted, but
it can be shown to be groundless. To begin with, it is plain that the
colour we see depends only upon the nature of the light-waves that
strike the eye, and is therefore modified by the medium intervening
between us and the object, as well as by the manner in which light is
reflected from the object in the direction of the eye. The
intervening air alters colours unless it is perfectly clear, and any
strong reflection will alter them completely. Thus the colour we see
is a result of the ray as it reaches the eye, and not simply a
property of the object from which the ray comes. Hence, also,
provided certain waves reach the eye, we shall see a certain colour,
whether the object from which the waves start has any colour or not.
Thus it is quite gratuitous to suppose that physical objects have
colours, and therefore there is no justification for making such a
supposition. Exactly similar arguments will apply to other
sense-data.
It remains to ask whether there are any general philosophical
arguments enabling us to say that, if matter is real, it must be of
such and such a nature. As explained above, very many philosophers,
perhaps most, have held that whatever is real must be in some sense
mental, or at any rate that whatever we can know anything about must
be in some sense mental. Such philosophers are called 'idealists'.
Idealists tell us that what appears as matter is really something
mental; namely, either (as Leibniz held) more or less rudimentary
minds, or (as Berkeley contended) ideas in the minds which, as we
should commonly say, 'perceive' the matter. Thus idealists deny the
existence of matter as something intrinsically different from mind,
though they do not deny that our sense-data are signs of something
which exists independently of our private sensations. In the
following chapter we shall consider briefly the reasons--in my opinion
fallacious--which idealists advance in favour of their theory.
