idea.]

Association by similarity is a fusion of impressions merging what is
common in them, interchanging what is peculiar, and cancelling in the
end what is incompatible; so that any excitement reaching that centre
revives one generic reaction which yields the idea. These concrete
generalities are actual feelings, the first terms in mental discourse,
the first distinguishable particulars in knowledge, and the first
bearers of names. Intellectual dominion of the conscious stream begins
with the act of recognising these pervasive entities, which having
character and ideal permanence can furnish common points of reference
for different moments of discourse. Save for ideas no perception could
have significance, or acquire that indicative force which we call
knowledge. For it would refer to nothing to which another perception
might also have referred; and so long as perceptions have no common
reference, so long as successive moments do not enrich by their
contributions the same object of thought, evidently experience, in the
pregnant sense of the word, is impossible. No fund of valid ideas, no
wisdom, could in that case be acquired by living.

[Sidenote: Ideas are ideal.]

Ideas, although their material is of course sensuous, are not sensations
nor perceptions nor objects of any possible immediate experience: they
are creatures of intelligence, goals of thought, ideal terms which
cogitation and action circle about. As the centre of mass is a body,
while it may by chance coincide with one or another of its atoms, is no
atom itself and no material constituent of the bulk that obeys its
motion, so an idea, the centre of mass of a certain mental system, is no
material fragment of that system, but an ideal term of reference and
signification by allegiance to which the details of consciousness first
become parts of a system and of a thought. An idea is an ideal. It
represents a functional relation in the diffuse existences to which it
gives a name and a rational value. An idea is an expression of life,
and shares with life that transitive and elusive nature which defies
definition by mere enumeration of its materials. The peculiarity of life
is that it lives; and thought also, when living, passes out of itself
and directs itself on the ideal, on the eventual. It is an activity.
Activity does not consist in velocity of change but in constancy of
purpose; in the conspiracy of many moments and many processes toward one
ideal har