rmly
believe, if it is true, is called _knowledge_, provided it is either
intuitive or inferred (logically or psychologically) from intuitive
knowledge from which it follows logically. What we firmly believe, if it
is not true, is called _error_. What we firmly believe, if it is neither
knowledge nor error, and also what we believe hesitatingly, because it
is, or is derived from, something which has not the highest degree of
self-evidence, may be called _probable opinion_. Thus the greater
part of what would commonly pass as knowledge is more or less probable
opinion.

In regard to probable opinion, we can derive great assistance from
_coherence_, which we rejected as the _definition_ of truth, but may
often use as a _criterion_. A body of individually probable opinions,
if they are mutually coherent, become more probable than any one of them
would be individually. It is in this way that many scientific hypotheses
acquire their probability. They fit into a coherent system of probable
opinions, and thus become more probable than they would be in isolation.
The same thing applies to general philosophical hypotheses. Often in a
single case such hypotheses may seem highly doubtful, while yet, when
we consider the order and coherence which they introduce into a mass of
probable opinion, they become pretty nearly certain. This applies, in
particular, to such matters as the distinction between dreams and
waking life. If our dreams, night after night, were as coherent one with
another as our days, we should hardly know whether to believe the dreams
or the waking life. As it is, the test of coherence condemns the
dreams and confirms the waking life. But this test, though it increases
probability where it is successful, never gives absolute certainty,
unless there is certainty already at some point in the coherent system.
Thus the mere organization of probable opinion will never, by itself,
transform it into indubitable knowledge.

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