evolution, based on a great variety
of examples, has made this concept clearer and more definite than
before. It contains the three elements; integration, differentiation and
equilibration. It is true that a concept which is to be valid for all
domains of experience must have an abstract character, and between the
several domains there is, strictly speaking, only a relation of analogy.
So there is only analogy between psychical and physical evolution. But
this is no serious objection, because general concepts do not express
more than analogies between the phenomena which they represent. Spencer
takes his leading terms from the material world in defining evolution
(in the simplest form) as integration of matter and dissipation of
movement; but as he--not always quite consistently (Cf. my letter
to him, 1876, now printed in Duncan's "Life and Letters of Herbert
Spencer", page 178, London, 1908.)--assumed a correspondence of mind and
matter, he could very well give these terms an indirect importance for
psychical evolution. Spencer has always, in my opinion with full right,
repudiated the ascription of materialism. He is no more a materialist
than Spinoza. In his "Principles of Psychology" (paragraph 63) he
expressed himself very clearly: "Though it seems easier to translate
so-called matter into so-called spirit, than to translate so-called
spirit into so-called matter--which latter is indeed wholly
impossible--yet no translation can carry us beyond our symbols." These
words lead us naturally to a group of thinkers whose starting-point
was psychical evolution. But we have still one aspect of Spencer's
philosophy to mention.

Spencer founded his "laws of evolution" on an inductive basis, but
he was convinced that they could be deduced from the law of the
conservation of energy. Such a deduction is, perhaps, possible for the
more elementary forms of evolution, integration and differentiation; but
it is not possible for the highest form, the equilibration, which is a
harmony of integration and differentiation. Spencer can no more deduce
the necessity for the eventual appearance of "moving equilibria" of
harmonious totalities than Hegel could guarantee the "higher unities"
in which all contradictions should be reconciled. In Spencer's hands the
theory of evolution acquired a more decidedly optimistic character
than in Darwin's; but I shall deal later with the relation of Darwin's
hypothesis to the opposition of optimism and p