There is a common impression that everything that we believe ought to be
capable of proof, or at least of being shown to be highly probable. It
is felt by many that a belief for which no reason can be given is an
unreasonable belief. In the main, this view is just. Almost all our
common beliefs are either inferred, or capable of being inferred, from
other beliefs which may be regarded as giving the reason for them. As a
rule, the reason has been forgotten, or has even never been consciously
present to our minds. Few of us ever ask ourselves, for example, what
reason there is to suppose the food we are just going to eat will not
turn out to be poison. Yet we feel, when challenged, that a perfectly
good reason could be found, even if we are not ready with it at the
moment. And in this belief we are usually justified.
But let us imagine some insistent Socrates, who, whatever reason we
give him, continues to demand a reason for the reason. We must sooner
or later, and probably before very long, be driven to a point where we
cannot find any further reason, and where it becomes almost certain that
no further reason is even theoretically discoverable. Starting with the
common beliefs of daily life, we can be driven back from point to point,
until we come to some general principle, or some instance of a general
principle, which seems luminously evident, and is not itself capable
of being deduced from anything more evident. In most questions of
daily life, such as whether our food is likely to be nourishing and not
poisonous, we shall be driven back to the inductive principle, which we
discussed in Chapter VI. But beyond that, there seems to be no further
regress. The principle itself is constantly used in our reasoning,
sometimes consciously, sometimes unconsciously; but there is no
reasoning which, starting from some simpler self-evident principle,
leads us to the principle of induction as its conclusion. And the same
holds for other logical principles. Their truth is evident to us, and we
employ them in constructing demonstrations; but they themselves, or at
least some of them, are incapable of demonstration.
Self-evidence, however, is not confined to those among general
principles which are incapable of proof. When a certain number of
logical principles have been admitted, the rest can be deduced from
them; but the propositions deduced are often just as self-evident as
those that were assumed without proof. All arithmetic, moreover, can
be deduced from the general principles of logic, yet the simple
propositions of arithmetic, such as 'two and two are four', are just as
self-evident as the principles of logic.
It would seem, also, though this is more disputable, that there are some
self-evident ethical principles, such as 'we ought to pursue what is
good'.
It should be observed that, in all cases of general principles,
particular instances, dealing with familiar things, are more evident
than the general principle. For example, the law of contradiction states
that nothing can both have a certain property and not have it. This is
evident as soon as it is understood, but it is not so evident as that a
particular rose which we see cannot be both red and not red. (It is of
course possible that parts of the rose may be red and parts not red, or
that the rose may be of a shade of pink which we hardly know whether to
call red or not; but in the former case it is plain that the rose as a
whole is not red, while in the latter case the answer is theoretically
definite as soon as we have decided on a precise definition of 'red'.)
It is usually through particular instances that we come to be able to
see the general principle. Only those who are practised in dealing with
abstractions can readily grasp a general principle without the help of
instances.
In addition to general principles, the other kind of self-evident truths
are those immediately derived from sensation. We will call such truths
'truths of perception', and the judgements expressing them we will
call 'judgements of perception'. But here a certain amount of care
is required in getting at the precise nature of the truths that are
self-evident. The actual sense-data are neither true nor false. A
particular patch of colour which I see, for example, simply exists: it
is not the sort of thing that is true or false. It is true that there is
such a patch, true that it has a certain shape and degree of brightness,
true that it is surrounded by certain other colours. But the patch
itself, like everything else in the world of sense, is of a radically
different kind from the things that are true or false, and therefore
cannot properly be said to be _true_. Thus whatever self-evident truths
may be obtained from our senses must be different from the sense-data
from which they are obtained.
It would seem that there are two kinds of self-evident truths of
perception, though perhaps in the last analysis the two kinds may
coalesce. First, there is the kind which simply asserts the _existence_
of the sense-datum, without in any way analysing it. We see a patch
of red, and we judge 'there is such-and-such a patch of red', or more
strictly 'there is that'; this is one kind of intuitive judgement of
perception. The other kind arises when the object of sense is complex,
and we subject it to some degree of analysis. If, for instance, we see a
_round_ patch of red, we may judge 'that patch of red is round'. This is
again a judgement of perception, but it differs from our previous kind.
In our present kind we have a single sense-datum which has both colour
and shape: the colour is red and the shape is round. Our judgement
analyses the datum into colour and shape, and then recombines them by
stating that the red colour is round in shape. Another example of this
kind of judgement is 'this is to the right of that', where 'this'
and 'that' are seen simultaneously. In this kind of judgement the
sense-datum contains constituents which have some relation to each
other, and the judgement asserts that these constituents have this
relation.
Another class of intuitive judgements, analogous to those of sense and
yet quite distinct from them, are judgements of _memory_. There is some
danger of confusion as to the nature of memory, owing to the fact that
memory of an object is apt to be accompanied by an image of the object,
and yet the image cannot be what constitutes memory. This is easily seen
by merely noticing that the image is in the present, whereas what is
remembered is known to be in the past. Moreover, we are certainly able
to some extent to compare our image with the object remembered, so
that we often know, within somewhat wide limits, how far our image is
accurate; but this would be impossible, unless the object, as opposed to
the image, were in some way before the mind. Thus the essence of memory
is not constituted by the image, but by having immediately before the
mind an object which is recognized as past. But for the fact of memory
in this sense, we should not know that there ever was a past at all,
nor should we be able to understand the word 'past', any more than a man
born blind can understand the word 'light'. Thus there must be intuitive
judgements of memory, and it is upon them, ultimately, that all our
knowledge of the past depends.
The case of memory, however, raises a difficulty, for it is notoriously
fallacious, and thus throws doubt on the trustworthiness of intuitive
judgements in general. This difficulty is no light one. But let us
first narrow its scope as far as possible. Broadly speaking, memory is
trustworthy in proportion to the vividness of the experience and to its
nearness in time. If the house next door was struck by lightning half a
minute ago, my memory of what I saw and heard will be so reliable that
it would be preposterous to doubt whether there had been a flash at
all. And the same applies to less vivid experiences, so long as they are
recent. I am absolutely certain that half a minute ago I was sitting in
the same chair in which I am sitting now. Going backward over the day,
I find things of which I am quite certain, other things of which I am
almost certain, other things of which I can become certain by thought
and by calling up attendant circumstances, and some things of which I
am by no means certain. I am quite certain that I ate my breakfast this
morning, but if I were as indifferent to my breakfast as a philosopher
should be, I should be doubtful. As to the conversation at breakfast,
I can recall some of it easily, some with an effort, some only with a
large element of doubt, and some not at all. Thus there is a continual
gradation in the degree of self-evidence of what I remember, and a
corresponding gradation in the trustworthiness of my memory.
Thus the first answer to the difficulty of fallacious memory is to say
that memory has degrees of self-evidence, and that these correspond
to the degrees of its trustworthiness, reaching a limit of perfect
self-evidence and perfect trustworthiness in our memory of events which
are recent and vivid.
It would seem, however, that there are cases of very firm belief in a
memory which is wholly false. It is probable that, in these cases, what
is really remembered, in the sense of being immediately before the mind,
is something other than what is falsely believed in, though something
generally associated with it. George IV is said to have at last believed
that he was at the battle of Waterloo, because he had so often said that
he was. In this case, what was immediately remembered was his repeated
assertion; the belief in what he was asserting (if it existed) would
be produced by association with the remembered assertion, and would
therefore not be a genuine case of memory. It would seem that cases of
fallacious memory can probably all be dealt with in this way, i.e. they
can be shown to be not cases of memory in the strict sense at all.
One important point about self-evidence is made clear by the case of
memory, and that is, that self-evidence has degrees: it is not a quality
which is simply present or absent, but a quality which may be more or
less present, in gradations ranging from absolute certainty down to an
almost imperceptible faintness. Truths of perception and some of the
principles of logic have the very highest degree of self-evidence;
truths of immediate memory have an almost equally high degree. The
inductive principle has less self-evidence than some of the other
principles of logic, such as 'what follows from a true premiss must be
true'. Memories have a diminishing self-evidence as they become remoter
and fainter; the truths of logic and mathematics have (broadly speaking)
less self-evidence as they become more complicated. Judgements of
intrinsic ethical or aesthetic value are apt to have some self-evidence,
but not much.
Degrees of self-evidence are important in the theory of knowledge,
since, if propositions may (as seems likely) have some degree of
self-evidence without being true, it will not be necessary to abandon
all connexion between self-evidence and truth, but merely to say that,
where there is a conflict, the more self-evident proposition is to be
retained and the less self-evident rejected.
It seems, however, highly probable that two different notions are
combined in 'self-evidence' as above explained; that one of them,
which corresponds to the highest degree of self-evidence, is really an
infallible guarantee of truth, while the other, which corresponds to
all the other degrees, does not give an infallible guarantee, but only a
greater or less presumption. This, however, is only a suggestion, which
we cannot as yet develop further. After we have dealt with the nature
of truth, we shall return to the subject of self-evidence, in connexion
with the distinction between knowledge and error.