 The
Problems of Philosophy
Bertrand Russell
CHAPTER XIV
THE LIMITS OF PHILOSOPHICAL KNOWLEDGE
IN all that we have said hitherto concerning philosophy,
we have scarcely touched on many matters that occupy a great
space in the writings of most philosophers. Most philosophers
-- or, at any rate, very many -- profess to be able to prove,
by a priori metaphysical reasoning, such things
as the fundamental dogmas of religion, the essential rationality
of the universe, the illusoriness of matter, the unreality
of all evil, and so on. There can be no doubt that the hope
of finding reason to believe such theses as these has been
the chief inspiration of many life-long students of philosophy.
This hope, I believe, is vain. It would seem that knowledge
concerning the universe as a whole is not to be obtained
by metaphysics, and that the proposed proofs that, in virtue
of the laws of logic such and such things must
exist and such and such others cannot, are not capable of
surviving a critical scrutiny. In this chapter we shall
briefly consider the kind of way in which such reasoning
is attempted, with a view to discovering whether we can
hope that it may be valid.
The great representative, in modern times, of the kind
of view which we wish to examine, was Hegel (1770-1831).
Hegel's philosophy is very difficult, and commentators differ
as to the true interpretation of it. According to the interpretation
I shall adopt, which is that of many, if not most, of the
commentators and has the merit of giving an interesting
and important type of philosophy, his main thesis is that
everything short of the Whole is obviously fragmentary,
and obviously incapable of existing without the complement
supplied by the rest of the world. Just as a comparative
anatomist, from a single bone, sees what kind of animal
the whole must have been, so the metaphysician, according
to Hegel, sees, from any one piece of reality, what the
whole of reality must be -- at least in its large outlines.
Every apparently separate piece of reality has, as it were,
hooks which grapple it to the next piece; the next piece,
in turn, has fresh hooks, and so on, until the whole universe
is reconstructed. This essential incompleteness appears,
according to Hegel, equally in the world of thought and
in the world of things. In the world of thought, if we take
any idea which is abstract or incomplete, we find, on examination,
that if we forget its incompleteness, we become involved
in contradictions; these contradictions turn the idea in
question into its opposite, or antithesis; and in order
to escape, we have to find a new, less incomplete idea,
which is the synthesis of our original idea and its antithesis.
This new idea, though less incomplete than the idea we started
with, will be found, nevertheless, to be still not wholly
complete, but to pass into its antithesis, with which it
must be combined in a new synthesis. In this way Hegel advances
until he reaches the 'Absolute Idea', which, according to
him, has no incompleteness, no opposite, and no need of
further development. The Absolute Idea, therefore, is adequate
to describe Absolute Reality; but all lower ideas only describe
ality as it appears to a partial view, not as it is to one
who simultaneously surveys the Whole. Thus Hegel reaches
the conclusion that Absolute Reality forms one single harmonious
system, not in space or time, not in any degree evil, wholly
rational, and wholly spiritual. Any appearance to the contrary,
in the world we know, can be proved logically -- so he believes
-- to be entirely due to our fragmentary piecemeal view
of the universe. If we saw the universe whole, as we may
suppose God sees it, space and time and matter and evil
and all striving and struggling would disappear, and we
should see instead an eternal perfect unchanging spiritual
unity.
In this conception, there is undeniably something sublime,
something to which we could wish to yield assent. Nevertheless,
when the arguments in support of it are carefully examined,
they appear to involve much confusion and many unwarrantable
assumptions. The fundamental tenet upon which the system
is built up is that what is incomplete must be not self-subsistent,
but must need the support of other things before it can
exist. It is held that whatever has relations to things
outside itself must contain some reference to those outside
things in its own nature, and could not, therefore,
be what it is if those outside things did not exist. A man's
nature, for example, is constituted by his memories and
the rest of his knowledge, by his loves and hatreds, and
so on; thus, but for the objects which he knows or loves
or hates, he could not be what he is. He is essentially
and obviously a fragment: taken as the sum-total of reality
he would be self-contradictory.
This whole point of view, however, turns upon the notion
of the 'nature' of a thing, which seems to mean 'all the
truths about the thing'. It is of course the case that a
truth which connects one thing with another thing could
not subsist if the other thing did not subsist. But a truth
about a thing is not part of the thing itself, although
it must, according to the above usage, be part of the 'nature'
of the thing. If we mean by a thing's 'nature' all the truths
about the thing, then plainly we cannot know a thing's 'nature'
unless we know all the thing's relations to all the other
things in the universe. But if the word 'nature' is used
in this sense, we shall have to hold that the thing may
be known when its 'nature' is not known, or at any rate
is not known completely. There is a confusion, when this
use of the word 'nature' is employed, between knowledge
of things and knowledge of truths. We may have knowledge
of a thing by acquaintance even if we know very few propositions
about it -- theoretically we need not know any propositions
about it. Thus, acquaintance with a thing does not involve
knowledge of its 'nature' in the above sense. And although
acquaintance with a thing is involved in our knowing any
one proposition about a thing, knowledge of its 'nature',
in the above sense, is not involved. Hence, (1) acquaintance
with a thing does not logically involve a knowledge of its
relations, and (2) a knowledge of some of its relations
does not involve a knowledge of all of its relations nor
a knowledge of its 'nature' in the above sense. I may be
acquainted, for example, with my toothache, and this knowledge
may be as complete as knowledge by acquaintance ever can
be, without knowing all that the dentist (who is not acquainted
with it) can tell me about its cause, and without therefore
knowing its 'nature' in the above sense. Thus the fact that
a thing has relations does not prove that its relations
are logically necessary. That is to say, from the mere fact
that it is the thing it is we cannot deduce that it must
have the various relations which in fact it has. This only
seems to follow because we know it already.
It follows that we cannot prove that the universe as a
whole forms a single harmonious system such as Hegel believes
that it forms. And if we cannot prove this, we also cannot
prove the unreality of space and time and matter and evil,
for this is deduced by Hegel from the fragmentary and relational
character of these things. Thus we are left to the piecemeal
investigation of the world, and are unable to know the characters
of those parts of the universe that are remote from our
experience. This result, disappointing as it is to those
whose hopes have been raised by the systems of philosophers,
is in harmony with the inductive and scientific temper of
our age, and is borne out by the whole examination of human
knowledge which has occupied our previous chapters.
Most of the great ambitious attempts of metaphysicians
have proceeded by the attempt to prove that such and such
apparent features of the actual world were self-contradictory,
and therefore could not be real. The whole tendency of modern
thought, however, is more and more in the direction of showing
that the supposed contradictions were illusory, and that
very little can be proved a priori from considerations
of what must be. A good illustration of this is
afforded by space and time. Space and time appear to be
infinite in extent, and infinitely divisible. If we travel
along a straight line in either direction, it is difficult
to believe that we shall finally reach a last point, beyond
which there is nothing, not even empty space. Similarly,
if in imagination we travel backwards or forwards in time,
it is difficult to believe that we shall reach a first or
last time, with not even empty time beyond it. Thus space
and time appear to be infinite in extent.
Again, if we take any two points on a line, it seems evident
that there must be other points between them, however small
the distance between them may be: every distance can be
halved, and the halves can be halved again, and so on ad
infinitum. In time, similarly, however little time
may elapse between two moments, it seems evident that there
will be other moments between them. Thus space and time
appear to be infinitely divisible. But as against these
apparent facts -- infinite extent and infinite divisibility
-- philosophers have advanced arguments tending to show
that there could be no infinite collections of things, and
that therefore the number of points in space, or of instants
in time, must be finite. Thus a contradiction emerged between
the apparent nature of space and time and the supposed impossibility
of infinite collections.
Kant, who first emphasized this contradiction, deduced
the impossibility of space and time, which he declared to
be merely subjective; and since his time very many philosophers
have believed that space and time are mere appearance, not
characteristic of the world as it really is. Now, however,
owing to the labours of the mathematicians, notably Georg
Cantor, it has appeared that the impossibility of infinite
collections was a mistake. They are not in fact self-contradictory,
but only contradictory of certain rather obstinate mental
prejudices. Hence the reasons for regarding space and time
as unreal have become inoperative, and one of the great
sources of metaphysical constructions is dried up.
The mathematicians, however, have not been content with
showing that space as it is commonly supposed to be is possible;
they have shown also that many other forms of space are
equally possible, so far as logic can show. Some of Euclid's
axioms, which appear to common sense to be necessary, and
were formerly supposed to be necessary by philosophers,
are now known to derive their appearance of necessity from
our mere familiarity with actual space, and not from any
a priori logical foundation. By imagining worlds
in which these axioms are false, the mathematicians have
used logic to loosen the prejudices of common sense, and
to show the possibility of spaces differing -- some more,
some less -- from that in which we live. And some of these
spaces differ so little from Euclidean space, where distances
such as we can measure are concerned, that it is impossible
to discover by observation whether our actual space is strictly
Euclidean or of one of these other kinds. Thus the position
is completely reversed. Formerly it appeared that experience
left only one kind of space to logic, and logic showed this
one kind to be impossible. Now logic presents many kinds
of space as possible apart from experience, and experience
only partially decides between them. Thus, while our knowledge
of what is has become less than it was formerly supposed
to be, our knowledge of what may be is enormously increased.
Instead of being shut in within narrow walls, of which every
nook and cranny could be explored, we find ourselves in
an open world of free possibilities, where much remains
unknown because there is so much to know.
What has happened in the case of space and time has happened,
to some extent, in other directions as well. The attempt
to prescribe to the universe by means of a priori
principles has broken down; logic instead of being, as formerly,
the bar to possibilities, has become the great liberator
of the imagination, presenting innumerable alternatives
which are closed to unreflective common sense, and leaving
to experience the task of deciding, where decision is possible,
between the many worlds which logic offers for our choice.
Thus knowledge as to what exists becomes limited to what
we can learn from experience -- not to what we can actually
experience, for, as we have seen, there is much knowledge
by description concerning things of which we have no direct
experience. But in all cases of knowledge by description,
we need some connexion of universals, enabling us, from
such and such a datum, to infer an object of a certain sort
as implied by our datum. Thus in regard to physical objects,
for example, the principle that sense-data are signs of
physical objects is itself a connexion of universals; and
it is only in virtue of this principle that experience enables
us to acquire knowledge concerning physical objects. The
same applies to the law of causality, or, to descend to
what is less general, to such principles as the law of gravitation.
Principles such as the law of gravitation are proved, or
rather are rendered highly probable, by a combination of
experience with some wholly a priori principle,
such as the principle of induction. Thus our intuitive knowledge,
which is the source of all our other knowledge of truths,
is of two sorts: pure empirical knowledge, which tells us
of the existence and some of the properties of particular
things with which we are acquainted, and pure a priori
knowledge, which gives us connexions between universals,
and enables us to draw inferences from the particular facts
given in empirical knowledge. Our derivative knowledge always
depends upon some pure a priori knowledge and usually
also depends upon some pure empirical knowledge.
Philosophical knowledge, if what has been said above is
true, does not differ essentially from scientific knowledge;
there is no special source of wisdom which is open to philosophy
but not to science, and the results obtained by philosophy
are not radically different from those obtained from science.
The essential characteristic of philosophy which makes it
a study distinct from science, is criticism. It
examines critically the principles employed in science and
in daily life; it searches out any inconsistencies there
may be in these principles, and it only accepts them when,
as the result of a critical inquiry, no reason for rejecting
them has appeared. If, as many philosophers have believed,
the principles underlying the sciences were capable, when
disengaged from irrelevant detail, of giving us knowledge
concerning the universe as a whole, such knowledge would
have the same claim on our belief as scientific knowledge
has; but our inquiry has not revealed any such knowledge,
and therefore, as regards the special doctrines of the bolder
metaphysicians, has had a mainly negative result. But as
regards what would be commonly accepted as knowledge, our
result is in the main positive: we have seldom found reason
to reject such knowledge as the result of our criticism,
and we have seen no reason to suppose man incapable of the
kind of knowledge which he is generally believed to possess.
When, however, we speak of philosophy as a criticism
of knowledge, it is necessary to impose a certain limitation.
If we adopt the attitude of the complete sceptic, placing
ourselves wholly outside all knowledge, and asking, from
this outside position, to be compelled to return within
the circle of knowledge, we are demanding what is impossible,
and our scepticism can never be refuted. For all refutation
must begin with some piece of knowledge which the disputants
share; from blank doubt, no argument can begin. Hence the
criticism of knowledge which philosophy employs must not
be of this destructive kind, if any result is to be achieved.
Against this absolute scepticism, no logical argument
can be advanced. But it is not difficult to see that scepticism
of this kind is unreasonable. Descartes' 'methodical doubt',
with which modern philosophy began, is not of this kind,
but is rather the kind of criticism which we are asserting
to be the essence of philosophy. His 'methodical doubt'
consisted in doubting whatever seemed doubtful; in pausing,
with each apparent piece of knowledge, to ask himself whether,
on reflection, he could feel certain that he really knew
it. This is the kind of criticism which constitutes philosophy.
Some knowledge, such as knowledge of the existence of our
sense-data, appears quite indubitable, however calmly and
thoroughly we reflect upon it. In regard to such knowledge,
philosophical criticism does not require that we should
abstain from belief. But there are beliefs -- such, for
example, as the belief that physical objects exactly resemble
our sense-data -- which are entertained until we begin to
reflect, but are found to melt away when subjected to a
close inquiry. Such beliefs philosophy will bid us reject,
unless some new line of argument is found to support them.
But to reject the beliefs which do not appear open to any
objections, however closely we examine them, is not reasonable,
and is not what philosophy advocates.
The criticism aimed at, in a word, is not that which, without
reason, determines to reject, but that which considers each
piece of apparent knowledge on its merits, and retains whatever
still appears to be knowledge when this consideration is
completed. That some risk of error remains must be admitted,
since human beings are fallible. Philosophy may claim justly
that it diminishes the risk of error, and that in some cases
it renders the risk so small as to be practically negligible.
To do more than this is not possible in a world where mistakes
must occur; and more than this no prudent advocate of philosophy
would claim to have performed.
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