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The
Limits of Philosophical Knowledge
by Bertrand Russell
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. ... 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 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 reality
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 labors 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
connection 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 connection 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
connections 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 skepticism 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
skepticism, no logical argument can be advanced.
But it is not difficult to see that skepticism 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.
Excerpted from The Problems
of Philosophy, by Bertrand Russell
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The
Problems of
Philosophy,
by
Bertrand Russell
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