In this chapter we have to ask ourselves whether, in any sense at all,
there is such a thing as matter. Is there a table which has a certain
intrinsic nature, and continues to exist when I am not looking, or is
the table merely a product of my imagination, a dream-table in a very
prolonged dream? This question is of the greatest importance. For if
we cannot be sure of the independent existence of objects, we cannot
be sure of the independent existence of other people's bodies, and
therefore still less of other people's minds, since we have no grounds
for believing in their minds except such as are derived from observing
their bodies. Thus if we cannot be sure of the independent existence of
objects, we shall be left alone in a desert--it may be that the whole
outer world is nothing but a dream, and that we alone exist. This is an
uncomfortable possibility; but although it cannot be strictly proved to
be false, there is not the slightest reason to suppose that it is true.
In this chapter we have to see why this is the case.
Before we embark upon doubtful matters, let us try to find some more
or less fixed point from which to start. Although we are doubting the
physical existence of the table, we are not doubting the existence
of the sense-data which made us think there was a table; we are not
doubting that, while we look, a certain colour and shape appear to us,
and while we press, a certain sensation of hardness is experienced by
us. All this, which is psychological, we are not calling in question.
In fact, whatever else may be doubtful, some at least of our immediate
experiences seem absolutely certain.
Descartes (1596-1650), the founder of modern philosophy, invented a
method which may still be used with profit--the method of systematic
doubt. He determined that he would believe nothing which he did not see
quite clearly and distinctly to be true. Whatever he could bring himself
to doubt, he would doubt, until he saw reason for not doubting it.
By applying this method he gradually became convinced that the only
existence of which he could be _quite_ certain was his own. He imagined
a deceitful demon, who presented unreal things to his senses in a
perpetual phantasmagoria; it might be very improbable that such a demon
existed, but still it was possible, and therefore doubt concerning
things perceived by the senses was possible.
But doubt concerning his own existence was not possible, for if he did
not exist, no demon could deceive him. If he doubted, he must exist; if
he had any experiences whatever, he must exist. Thus his own existence
was an absolute certainty to him. 'I think, therefore I am,' he said
(_Cogito, ergo sum_); and on the basis of this certainty he set to work
to build up again the world of knowledge which his doubt had laid in
ruins. By inventing the method of doubt, and by showing that subjective
things are the most certain, Descartes performed a great service to
philosophy, and one which makes him still useful to all students of the
subject.
But some care is needed in using Descartes' argument. 'I think,
therefore I am' says rather more than is strictly certain. It might seem
as though we were quite sure of being the same person to-day as we were
yesterday, and this is no doubt true in some sense. But the real Self is
as hard to arrive at as the real table, and does not seem to have that
absolute, convincing certainty that belongs to particular experiences.
When I look at my table and see a certain brown colour, what is quite
certain at once is not '_I_ am seeing a brown colour', but rather,
'a brown colour is being seen'. This of course involves something (or
somebody) which (or who) sees the brown colour; but it does not of
itself involve that more or less permanent person whom we call 'I'. So
far as immediate certainty goes, it might be that the something which
sees the brown colour is quite momentary, and not the same as the
something which has some different experience the next moment.
Thus it is our particular thoughts and feelings that have primitive
certainty. And this applies to dreams and hallucinations as well as to
normal perceptions: when we dream or see a ghost, we certainly do have
the sensations we think we have, but for various reasons it is held that
no physical object corresponds to these sensations. Thus the certainty
of our knowledge of our own experiences does not have to be limited in
any way to allow for exceptional cases. Here, therefore, we have, for
what it is worth, a solid basis from which to begin our pursuit of
knowledge.
The problem we have to consider is this: Granted that we are certain of
our own sense-data, have we any reason for regarding them as signs of
the existence of something else, which we can call the physical object?
When we have enumerated all the sense-data which we should naturally
regard as connected with the table, have we said all there is to say
about the table, or is there still something else--something not a
sense-datum, something which persists when we go out of the room? Common
sense unhesitatingly answers that there is. What can be bought and sold
and pushed about and have a cloth laid on it, and so on, cannot be
a _mere_ collection of sense-data. If the cloth completely hides the
table, we shall derive no sense-data from the table, and therefore, if
the table were merely sense-data, it would have ceased to exist, and
the cloth would be suspended in empty air, resting, by a miracle, in
the place where the table formerly was. This seems plainly absurd; but
whoever wishes to become a philosopher must learn not to be frightened
by absurdities.
One great reason why it is felt that we must secure a physical object
in addition to the sense-data, is that we want the same object for
different people. When ten people are sitting round a dinner-table,
it seems preposterous to maintain that they are not seeing the same
tablecloth, the same knives and forks and spoons and glasses. But the
sense-data are private to each separate person; what is immediately
present to the sight of one is not immediately present to the sight of
another: they all see things from slightly different points of view, and
therefore see them slightly differently. Thus, if there are to be public
neutral objects, which can be in some sense known to many different
people, there must be something over and above the private and
particular sense-data which appear to various people. What reason, then,
have we for believing that there are such public neutral objects?
The first answer that naturally occurs to one is that, although
different people may see the table slightly differently, still they all
see more or less similar things when they look at the table, and
the variations in what they see follow the laws of perspective and
reflection of light, so that it is easy to arrive at a permanent object
underlying all the different people's sense-data. I bought my table from
the former occupant of my room; I could not buy _his_ sense-data,
which died when he went away, but I could and did buy the confident
expectation of more or less similar sense-data. Thus it is the fact that
different people have similar sense-data, and that one person in a given
place at different times has similar sense-data, which makes us suppose
that over and above the sense-data there is a permanent public object
which underlies or causes the sense-data of various people at various
times.
Now in so far as the above considerations depend upon supposing that
there are other people besides ourselves, they beg the very question at
issue. Other people are represented to me by certain sense-data, such as
the sight of them or the sound of their voices, and if I had no
reason to believe that there were physical objects independent of my
sense-data, I should have no reason to believe that other people exist
except as part of my dream. Thus, when we are trying to show that there
must be objects independent of our own sense-data, we cannot appeal to
the testimony of other people, since this testimony itself consists of
sense-data, and does not reveal other people's experiences unless our
own sense-data are signs of things existing independently of us. We must
therefore, if possible, find, in our own purely private experiences,
characteristics which show, or tend to show, that there are in the world
things other than ourselves and our private experiences.
In one sense it must be admitted that we can never prove the existence
of things other than ourselves and our experiences. No logical absurdity
results from the hypothesis that the world consists of myself and my
thoughts and feelings and sensations, and that everything else is mere
fancy. In dreams a very complicated world may seem to be present, and
yet on waking we find it was a delusion; that is to say, we find that
the sense-data in the dream do not appear to have corresponded with such
physical objects as we should naturally infer from our sense-data. (It
is true that, when the physical world is assumed, it is possible to
find physical causes for the sense-data in dreams: a door banging, for
instance, may cause us to dream of a naval engagement. But although, in
this case, there is a physical cause for the sense-data, there is not a
physical object corresponding to the sense-data in the way in which an
actual naval battle would correspond.) There is no logical impossibility
in the supposition that the whole of life is a dream, in which we
ourselves create all the objects that come before us. But although this
is not logically impossible, there is no reason whatever to suppose that
it is true; and it is, in fact, a less simple hypothesis, viewed as a
means of accounting for the facts of our own life, than the common-sense
hypothesis that there really are objects independent of us, whose action
on us causes our sensations.
The way in which simplicity comes in from supposing that there really
are physical objects is easily seen. If the cat appears at one moment in
one part of the room, and at another in another part, it is natural
to suppose that it has moved from the one to the other, passing over
a series of intermediate positions. But if it is merely a set of
sense-data, it cannot have ever been in any place where I did not see
it; thus we shall have to suppose that it did not exist at all while I
was not looking, but suddenly sprang into being in a new place. If
the cat exists whether I see it or not, we can understand from our own
experience how it gets hungry between one meal and the next; but if
it does not exist when I am not seeing it, it seems odd that appetite
should grow during non-existence as fast as during existence. And if the
cat consists only of sense-data, it cannot be hungry, since no hunger
but my own can be a sense-datum to me. Thus the behaviour of the
sense-data which represent the cat to me, though it seems quite natural
when regarded as an expression of hunger, becomes utterly inexplicable
when regarded as mere movements and changes of patches of colour, which
are as incapable of hunger as a triangle is of playing football.
But the difficulty in the case of the cat is nothing compared to the
difficulty in the case of human beings. When human beings speak--that
is, when we hear certain noises which we associate with ideas, and
simultaneously see certain motions of lips and expressions of face--it
is very difficult to suppose that what we hear is not the expression
of a thought, as we know it would be if we emitted the same sounds. Of
course similar things happen in dreams, where we are mistaken as to the
existence of other people. But dreams are more or less suggested by what
we call waking life, and are capable of being more or less accounted for
on scientific principles if we assume that there really is a physical
world. Thus every principle of simplicity urges us to adopt the natural
view, that there really are objects other than ourselves and our
sense-data which have an existence not dependent upon our perceiving
them.
Of course it is not by argument that we originally come by our belief in
an independent external world. We find this belief ready in ourselves as
soon as we begin to reflect: it is what may be called an _instinctive_
belief. We should never have been led to question this belief but for
the fact that, at any rate in the case of sight, it seems as if the
sense-datum itself were instinctively believed to be the independent
object, whereas argument shows that the object cannot be identical
with the sense-datum. This discovery, however--which is not at all
paradoxical in the case of taste and smell and sound, and only slightly
so in the case of touch--leaves undiminished our instinctive belief that
there _are_ objects _corresponding_ to our sense-data. Since this belief
does not lead to any difficulties, but on the contrary tends to simplify
and systematize our account of our experiences, there seems no good
reason for rejecting it. We may therefore admit--though with a slight
doubt derived from dreams--that the external world does really exist,
and is not wholly dependent for its existence upon our continuing to
perceive it.
The argument which has led us to this conclusion is doubtless less
strong than we could wish, but it is typical of many philosophical
arguments, and it is therefore worth while to consider briefly its
general character and validity. All knowledge, we find, must be built
up upon our instinctive beliefs, and if these are rejected, nothing
is left. But among our instinctive beliefs some are much stronger than
others, while many have, by habit and association, become entangled with
other beliefs, not really instinctive, but falsely supposed to be part
of what is believed instinctively.
Philosophy should show us the hierarchy of our instinctive beliefs,
beginning with those we hold most strongly, and presenting each as much
isolated and as free from irrelevant additions as possible. It should
take care to show that, in the form in which they are finally set forth,
our instinctive beliefs do not clash, but form a harmonious system.
There can never be any reason for rejecting one instinctive belief
except that it clashes with others; thus, if they are found to
harmonize, the whole system becomes worthy of acceptance.
It is of course _possible_ that all or any of our beliefs may be
mistaken, and therefore all ought to be held with at least some slight
element of doubt. But we cannot have _reason_ to reject a belief except
on the ground of some other belief. Hence, by organizing our instinctive
beliefs and their consequences, by considering which among them is most
possible, if necessary, to modify or abandon, we can arrive, on the
basis of accepting as our sole data what we instinctively believe, at an
orderly systematic organization of our knowledge, in which, though the
_possibility_ of error remains, its likelihood is diminished by the
interrelation of the parts and by the critical scrutiny which has
preceded acquiescence.
This function, at least, philosophy can perform. Most philosophers,
rightly or wrongly, believe that philosophy can do much more than
this--that it can give us knowledge, not otherwise attainable,
concerning the universe as a whole, and concerning the nature of
ultimate reality. Whether this be the case or not, the more modest
function we have spoken of can certainly be performed by philosophy, and
certainly suffices, for those who have once begun to doubt the adequacy
of common sense, to justify the arduous and difficult labours that
philosophical problems involve.