one important respect it is less
unphilosophical than the opposite theory of materialism. For
spiritualism supposes the causation to proceed from that which is the
source of our idea of causality--the mind: not from that into which this
idea has been read--the brain. Therefore, if causation were to be
accepted as a possibility either way, it would be less unreasonable to
suppose mental changes the causes of material changes than _vice versa_;
for we should then at least be starting from the basis of immediate
knowledge, instead of from the reflection of that knowledge in what we
call the external world. Seeing that the external world is known to us
only as motion, it is logically impossible for the mind to infer its own
causation from the external world; for this would be to infer that it is
an effect of motion, which would be the same as saying that it is an
effect of its own knowledge; and this would be absurd. But, on the other
hand, it is not thus logically impossible for the mind to infer that it
may be the cause of some of its own knowledge, or, in other words, that
it may have in some measure the power of producing what it knows as
motion. And when the mind does infer this, no logic on earth is able to
touch the inference; the position of pure idealism is beyond the reach
of argument. Nevertheless, it is opposed to the whole momentum of
science. For if mind is supposed, on no matter how small a scale, to be
a cause of motion, the fundamental axiom of science is impugned. This
fundamental axiom is that energy can neither be created nor
destroyed--that just as motion can produce nothing but motion, so,
conversely, motion can be produced by nothing but motion. Regarded,
therefore, from the stand-point of physical science, the theory of
spiritualism is in precisely the same case as the theory of materialism:
that is to say, if the supposed causation takes place, it can only be
supposed to do so by way of miracle.

And this is a conclusion which the more clear-sighted of the idealists
have expressly recognized. That subtle and most entertaining thinker,
for example, the late Professor Green of Oxford, has said that the
self-conscious volition of man 'does not consist in a series of natural
events, ... is not natural in the ordinary sense of that term; not
natural at any rate in any sense in which naturalness would imply its
determination by antecedent events, or by conditions of which it is not
itself the source.'