ceptions and realisable
conceptions. For we may mean that one of the two propositions presents
terms which cannot possibly be rendered into thought at all in the relation
which the proposition alleges to subsist between them; or we may mean that
one of the two propositions presents terms in a relation which is more
congruous with the habitual tenor of our thoughts than does the other
proposition. Thus, as an example of the former usage, we may say, It is
more conceivable that two and two should make four than that two and two
should make five; and, as an example of the latter usage, we may say, It is
more conceivable that a man should be able to walk than that he should be
able to fly. Now, for the sake of distinction, I shall call the first of
these usages the test of _absolute_ inconceivability, and the second the
test of _relative_ inconceivability. Doubtless, when the word
"inconceivability" is used in the sense of relative inconceivability, it is
incorrectly used, unless it is qualified in some way; because, if used
without qualification, there is danger of its being confused with
inconceivability in its absolute sense. Nevertheless, if used with some
qualifying epithet, it becomes quite unexceptionable. For the process of
conception being in all cases the process of establishing relations in
thought, we may properly say, It is relatively more conceivable that a man
should walk than that a man should fly, since it is _more easy_ to
establish, the necessary relations in thought in the case of the former
than in the case of the latter proposition. The only difference, then,
between what I have called absolute inconceivability and what I have called
relative inconceivability consists in this--that while the latter admits of
_degrees_, the former does not.[33]

With this distinction clearly understood, I may now proceed to observe that
in everyday life we constantly apply the test of relative inconceivability
as a test of truth. And in the vast majority of cases this test of relative
inconceivability is, for all practical purposes, as valid a test of truth
as is the test of absolute conceivability. For as every man is more or less
in harmony with his environment, his habits of thought with regard to his
environment are for the most part stereotyped correctly; so that the most
ready and the most trustworthy gauge of probability that he has is an
immediate appeal to consciousness as to whether he _feels_ the probability.