 The
Problems of Philosophy
Bertrand Russell
CHAPTER III
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 uppose 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. A 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.
|
