Thus the theory of spiritualism, although not directly refutable by any
process of logic, is certainly enfeebled by its collision with the
instincts of physical science. In necessarily holding the facts of
consciousness and volition super-natural, extra-natural, or non-natural,
the theory is opposed to the principle of continuity.

Spiritualism being thus unsatisfactory, and materialism impossible, is
there yet any third hypothesis in which we may hope to find intellectual
rest? In my opinion there is. If we unite in a higher synthesis the
elements both of spiritualism and of materialism, we obtain a product
which satisfies every fact of feeling on the one hand, and of
observation on the other. The manner in which this synthesis may be
effected is perfectly simple. We have only to suppose that the
antithesis between mind and motion--subject and object--is itself
phenomenal or apparent: not absolute or real. We have only to suppose
that the seeming duality is relative to our modes of apprehension; and,
therefore, that any change taking place in the mind, and any
corresponding change taking place in the brain, are really not two
changes, but one change. When a violin is played upon we hear a musical
sound, and at the same time we see a vibration of the strings.
Relatively to our consciousness, therefore, we have here two sets of
changes, which appear to be very different in kind; yet we know that in
an absolute sense they are one and the same: we know that the diversity
in consciousness is created only by the difference in our modes of
perceiving the same event--whether we see or whether we hear the
vibration of the strings. Similarly, we may suppose that a vibration of
nerve-strings and a process of thought are really one and the same
event, which is dual or diverse only in relation to our modes of
perceiving it.

The great advantage of this theory is that it supposes only one stream
of causation, in which both mind and motion are simultaneously
concerned. The theory, therefore, escapes all the difficulties and
contradictions with which both spiritualism and materialism are beset.
Thus, motion is supposed to be producing nothing but motion;
mind-changes nothing but mind-changes: both producing both
simultaneously, neither could be what it is without the other, because
without the other neither could be the cause which in fact it is.
Impossible, therefore, is the supposition of the materialist that
consciousness is adve