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The Problems of Philosophy
Bertrand Russell

PREFACE

In the following pages I have confined myself in the main to those
problems of philosophy in regard to which I thought it possible to say
something positive and constructive, since merely negative criticism
seemed out of place. For this reason, theory of knowledge occupies a
larger space than metaphysics in the present volume, and some topics
much discussed by philosophers are treated very briefly, if at all.

I have derived valuable assistance from unpublished writings of
G. E. Moore and J. M. Keynes: from the former, as regards the
relations of sense-data to physical objects, and from the latter as
regards probability and induction. I have also profited greatly by
the criticisms and suggestions of Professor Gilbert Murray.

1912

CHAPTER I
APPEARANCE AND REALITY

Is there any knowledge in the world which is so certain that no
reasonable man could doubt it? This question, which at first sight
might not seem difficult, is really one of the most difficult that can
be asked. When we have realized the obstacles in the way of a
straightforward and confident answer, we shall be well launched on the
study of philosophy--for philosophy is merely the attempt to answer
such ultimate questions, not carelessly and dogmatically, as we do in
ordinary life and even in the sciences, but critically, after
exploring all that makes such questions puzzling, and after realizing
all the vagueness and confusion that underlie our ordinary ideas.

In daily life, we assume as certain many things which, on a closer
scrutiny, are found to be so full of apparent contradictions that only
a great amount of thought enables us to know what it is that we really
may believe. In the search for certainty, it is natural to begin with
our present experiences, and in some sense, no doubt, knowledge is to
be derived from them. But any statement as to what it is that our
immediate experiences make us know is very likely to be wrong. It
seems to me that I am now sitting in a chair, at a table of a certain
shape, on which I see sheets of paper with writing or print. By
turning my head I see out of the window buildings and clouds and the
sun. I believe that the sun is about ninety-three million miles from
the earth; that it is a hot globe many times bigger than the earth;
that, owing to the earth's rotation, it rises every morning, and will
continue to do so for an indefinite time in the future. I believe
that, if any other normal person comes into my room, he will see the
same chairs and tables and books and papers as I see, and that the
table which I see is the same as the table which I feel pressing
against my arm. All this seems to be so evident as to be hardly worth
stating, except in answer to a man who doubts whether I know anything.
Yet all this may be reasonably doubted, and all of it requires much
careful discussion before we can be sure that we have stated it in a
form that is wholly true.

To make our difficulties plain, let us concentrate attention on the
table. To the eye it is oblong, brown and shiny, to the touch it is
smooth and cool and hard; when I tap it, it gives out a wooden sound.
Any one else who sees and feels and hears the table will agree with
this description, so that it might seem as if no difficulty would
arise; but as soon as we try to be more precise our troubles begin.
Although I believe that the table is 'really' of the same colour all
over, the parts that reflect the light look much brighter than the
other parts, and some parts look white because of reflected light. I
know that, if I move, the parts that reflect the light will be
different, so that the apparent distribution of colours on the table
will change. It follows that if several people are looking at the
table at the same moment, no two of them will see exactly the same
distribution of colours, because no two can see it from exactly the
same point of view, and any change in the point of view makes some
change in the way the light is reflected.

For most practical purposes these differences are unimportant, but to
the painter they are all-important: the painter has to unlearn the
habit of thinking that things seem to have the colour which common
sense says they 'really' have, and to learn the habit of seeing things
as they appear. Here we have already the beginning of one of the
distinctions that cause most trouble in philosophy--the distinction
between 'appearance' and 'reality', between what things seem to be and
what they are. The painter wants to know what things seem to be, the
practical man and the philosopher want to know what they are; but the
philosopher's wish to know this is stronger than the practical man's,
and is more troubled by knowledge as to the difficulties of answering
the question.

To return to the table. It is evident from what we have found, that
there is no colour which pre-eminently appears to be _the_ colour of
the table, or even of any one particular part of the table--it appears
to be of different colours from different points of view, and there is
no reason for regarding some of these as more really its colour than
others. And we know that even from a given point of view the colour
will seem different by artificial light, or to a colour-blind man, or
to a man wearing blue spectacles, while in the dark there will be no
colour at all, though to touch and hearing the table will be
unchanged. This colour is not something which is inherent in the
table, but something depending upon the table and the spectator and
the way the light falls on the table. When, in ordinary life, we
speak of _the_ colour of the table, we only mean the sort of colour
which it will seem to have to a normal spectator from an ordinary
point of view under usual conditions of light. But the other colours
which appear under other conditions have just as good a right to be
considered real; and therefore, to avoid favouritism, we are compelled
to deny that, in itself, the table has any one particular colour.

The same thing applies to the texture. With the naked eye one can see
the grain, but otherwise the table looks smooth and even. If we
looked at it through a microscope, we should see roughnesses and hills
and valleys, and all sorts of differences that are imperceptible to
the naked eye. Which of these is the 'real' table? We are naturally
tempted to say that what we see through the microscope is more real,
but that in turn would be changed by a still more powerful microscope.
If, then, we cannot trust what we see with the naked eye, why should
we trust what we see through a microscope? Thus, again, the
confidence in our senses with which we began deserts us.

The shape of the table is no better. We are all in the habit of
judging as to the 'real' shapes of things, and we do this so
unreflectingly that we come to think we actually see the real shapes.
But, in fact, as we all have to learn if we try to draw, a given thing
looks different in shape from every different point of view. If our
table is 'really' rectangular, it will look, from almost all points of
view, as if it had two acute angles and two obtuse angles. If
opposite sides are parallel, they will look as if they converged to a
point away from the spectator; if they are of equal length, they will
look as if the nearer side were longer. All these things are not
commonly noticed in looking at a table, because experience has taught
us to construct the 'real' shape from the apparent shape, and the
'real' shape is what interests us as practical men. But the 'real'
shape is not what we see; it is something inferred from what we see.
And what we see is constantly changing in shape as we move about the
room; so that here again the senses seem not to give us the truth
about the table itself, but only about the appearance of the table.

Similar difficulties arise when we consider the sense of touch. It is
true that the table always gives us a sensation of hardness, and we
feel that it resists pressure. But the sensation we obtain depends
upon how hard we press the table and also upon what part of the body
we press with; thus the various sensations due to various pressures or
various parts of the body cannot be supposed to reveal _directly_ any
definite property of the table, but at most to be _signs_ of some
property which perhaps _causes_ all the sensations, but is not
actually apparent in any of them. And the same applies still more
obviously to the sounds which can be elicited by rapping the table.

Thus it becomes evident that the real table, if there is one, is not
the same as what we immediately experience by sight or touch or
hearing. The real table, if there is one, is not _immediately_ known
to us at all, but must be an inference from what is immediately known.
Hence, two very difficult questions at once arise; namely, (1) Is
there a real table at all? (2) If so, what sort of object can it be?

It will help us in considering these questions to have a few simple
terms of which the meaning is definite and clear. Let us give the
name of 'sense-data' to the things that are immediately known in
sensation: such things as colours, sounds, smells, hardnesses,
roughnesses, and so on. We shall give the name 'sensation' to the
experience of being immediately aware of these things. Thus, whenever
we see a colour, we have a sensation _of_ the colour, but the colour
itself is a sense-datum, not a sensation. The colour is that _of_
which we are immediately aware, and the awareness itself is the
sensation. It is plain that if we are to know anything about the
table, it must be by means of the sense-data--brown colour, oblong
shape, smoothness, etc.--which we associate with the table; but, for
the reasons which have been given, we cannot say that the table is the
sense-data, or even that the sense-data are directly properties of the
table. Thus a problem arises as to the relation of the sense-data to
the real table, supposing there is such a thing.

The real table, if it exists, we will call a 'physical object'. Thus
we have to consider the relation of sense-data to physical objects.
The collection of all physical objects is called 'matter'. Thus our
two questions may be re-stated as follows: (1) Is there any such thing
as matter? (2) If so, what is its nature?

The philosopher who first brought prominently forward the reasons for
regarding the immediate objects of our senses as not existing
independently of us was Bishop Berkeley (1685-1753). His _Three
Dialogues between Hylas and Philonous, in Opposition to Sceptics and
Atheists_, undertake to prove that there is no such thing as matter at
all, and that the world consists of nothing but minds and their ideas.
Hylas has hitherto believed in matter, but he is no match for
Philonous, who mercilessly drives him into contradictions and
paradoxes, and makes his own denial of matter seem, in the end, as if
it were almost common sense. The arguments employed are of very
different value: some are important and sound, others are confused or
quibbling. But Berkeley retains the merit of having shown that the
existence of matter is capable of being denied without absurdity, and
that if there are any things that exist independently of us they
cannot be the immediate objects of our sensations.

There are two different questions involved when we ask whether matter
exists, and it is important to keep them clear. We commonly mean by
'matter' something which is opposed to 'mind', something which we
think of as occupying space and as radically incapable of any sort of
thought or consciousness. It is chiefly in this sense that Berkeley
denies matter; that is to say, he does not deny that the sense-data
which we commonly take as signs of the existence of the table are
really signs of the existence of _something_ independent of us, but he
does deny that this something is non-mental, that it is neither mind
nor ideas entertained by some mind. He admits that there must be
something which continues to exist when we go out of the room or shut
our eyes, and that what we call seeing the table does really give us
reason for believing in something which persists even when we are not
seeing it. But he thinks that this something cannot be radically
different in nature from what we see, and cannot be independent of
seeing altogether, though it must be independent of _our_ seeing. He
is thus led to regard the 'real' table as an idea in the mind of God.
Such an idea has the required permanence and independence of
ourselves, without being--as matter would otherwise be--something
quite unknowable, in the sense that we can only infer it, and can
never be directly and immediately aware of it.

Other philosophers since Berkeley have also held that, although the
table does not depend for its existence upon being seen by me, it does
depend upon being seen (or otherwise apprehended in sensation) by
_some_ mind--not necessarily the mind of God, but more often the whole
collective mind of the universe. This they hold, as Berkeley does,
chiefly because they think there can be nothing real--or at any rate
nothing known to be real except minds and their thoughts and feelings.
We might state the argument by which they support their view in some
such way as this: 'Whatever can be thought of is an idea in the mind
of the person thinking of it; therefore nothing can be thought of
except ideas in minds; therefore anything else is inconceivable, and
what is inconceivable cannot exist.'

Such an argument, in my opinion, is fallacious; and of course those
who advance it do not put it so shortly or so crudely. But whether
valid or not, the argument has been very widely advanced in one form
or another; and very many philosophers, perhaps a majority, have held
that there is nothing real except minds and their ideas. Such
philosophers are called 'idealists'. When they come to explaining
matter, they either say, like Berkeley, that matter is really nothing
but a collection of ideas, or they say, like Leibniz (1646-1716), that
what appears as matter is really a collection of more or less
rudimentary minds.

But these philosophers, though they deny matter as opposed to mind,
nevertheless, in another sense, admit matter. It will be remembered
that we asked two questions; namely, (1) Is there a real table at all?
(2) If so, what sort of object can it be? Now both Berkeley and
Leibniz admit that there is a real table, but Berkeley says it is
certain ideas in the mind of God, and Leibniz says it is a colony of
souls. Thus both of them answer our first question in the
affirmative, and only diverge from the views of ordinary mortals in
their answer to our second question. In fact, almost all philosophers
seem to be agreed that there is a real table: they almost all agree
that, however much our sense-data--colour, shape, smoothness,
etc.--may depend upon us, yet their occurrence is a sign of something
existing independently of us, something differing, perhaps, completely
from our sense-data, and yet to be regarded as causing those
sense-data whenever we are in a suitable relation to the real table.

Now obviously this point in which the philosophers are agreed--the
view that there _is_ a real table, whatever its nature may be--is
vitally important, and it will be worth while to consider what reasons
there are for accepting this view before we go on to the further
question as to the nature of the real table. Our next chapter,
therefore, will be concerned with the reasons for supposing that there
is a real table at all.

Before we go farther it will be well to consider for a moment what it
is that we have discovered so far. It has appeared that, if we take
any common object of the sort that is supposed to be known by the
senses, what the senses _immediately_ tell us is not the truth about
the object as it is apart from us, but only the truth about certain
sense-data which, so far as we can see, depend upon the relations
between us and the object. Thus what we directly see and feel is
merely 'appearance', which we believe to be a sign of some 'reality'
behind. But if the reality is not what appears, have we any means of
knowing whether there is any reality at all? And if so, have we any
means of finding out what it is like?

Such questions are bewildering, and it is difficult to know that even
the strangest hypotheses may not be true. Thus our familiar table,
which has roused but the slightest thoughts in us hitherto, has become
a problem full of surprising possibilities. The one thing we know
about it is that it is not what it seems. Beyond this modest result,
so far, we have the most complete liberty of conjecture. Leibniz
tells us it is a community of souls: Berkeley tells us it is an idea
in the mind of God; sober science, scarcely less wonderful, tells us
it is a vast collection of electric charges in violent motion.

Among these surprising possibilities, doubt suggests that perhaps
there is no table at all. Philosophy, if it cannot _answer_ so many
questions as we could wish, has at least the power of _asking_
questions which increase the interest of the world, and show the
strangeness and wonder lying just below the surface even in the
commonest things of daily life.

CHAPTER II
THE EXISTENCE OF MATTER

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.

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