postulate to the dignity of an 'axiom'--_i.e._, a principle which it is
incredible anyone should think worth disputing--whereas repeated failure
in application degrades it to the position of a prejudice--_i.e._, an _a
priori_ opinion which is always belied by its consequences.

A 'postulate' thus differs essentially from the '_a priori_ truth' by
its dependence upon the will, by its being the product of a free choice.
We have always to select the assumptions upon which we mean to act in
our commerce with reality. We select the rules upon which we go, and we
select the 'facts' by which we claim to support our rules, stripping
them of all the 'irrelevant' details involved by their position in the
flux of happenings. Thus we emphasize that side of things which fits in
with our expectations, until the facts are 'faked' sufficiently to
figure as 'cases' of our 'law.' Postulation and the verifying of
postulates is thus a process of reciprocal discrimination and selection.
The postulate once formulated, we seek in the flux for confirmations of
it, and thus construct a system of 'facts' which are relative to it;
that is how the postulate reacts upon experience. If, on the other hand,
this process of selection is unfruitful, and the confirmations of our
rule turn out infinitesimal, we alter the rule; and thus the 'facts' in
the case reject the postulate.

This continuous process of selection and rejection of 'principles' and
'facts' has, as we have said, a thoroughly _biological_ tinge. The
fitness of a postulate to survive is being continually tested. It
springs in the first place from a human hope that events may be
systematized in a certain way, and it endures so long as it enables men
to deal with them in that way. If it fails, the formation of fresh
ideals and fresh hypotheses is demanded; but that which causes one
postulate to prevail over another is always the satisfaction which, if