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 forms
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[201]--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_ (Sec. 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
pessimism.

II. While the starting-point of Spencer was biological or
cosmological, psychical evolution being conceived as in analogy with
physical, a group of eminent thinkers--in Germany Wundt, in