222 HERBERT SPENCER

granted that all existence distinguished as subjective,
is resolvable into units of consciousness similar in
nature to those which we know as nervous shocks 5
each of which is the correlative of a rhythmical motion
of a material unit, or group of units. Can we then
think of the subjective and objective activities as the
same ? Can the oscillation of a molecule be repre-
sented in consciousness side by side with a nervous
shock, and the two be recognised as one ? No effort
enables us to assimilate them. That a unit of feeling
has nothing in common with a unit of motion, becomes
more than ever manifest when we bring the two
into juxtaposition " (Principles of Psychology, i. p. 158).
He concluded that " there is not the remotest possi-
bility of interpreting Mind in terms of Matter."
Since our "ideas of Matter and Motion, merely
symbolic of unknowable realities, are complex states
of consciousness built out of units of feeling," "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."

The obvious difficulty, of which Spencer was well
aware, is " how mental evolution is to be affiliated on
Evolution at large, regarded as a process of physical
transformation ?

" Specifically stated, the problem is to interpret
mental evolution in terms of the redistribution of
Matter and Motion. Though under its subjective
aspect Mind is known only as an aggregate of states of
consciousness, which cannot be conceived as forms of
Matter and Motion, and do not therefore necessarily
conform to the same laws of redistribution; yet
under its objective aspect, Mind is known as anher betions of