therefore, if the supposition of causality is taken to be an
essential feature of Materialism, Materialism would be in no wise affected
by substituting for the words Matter and Motion the symbols _x_ and _y_.

The second of the three stages consisted in showing that Mr. Spencer's
argument as to the possible identity of Force and Feeling is not in itself
sufficient to overthrow the doctrine that what we know as Matter and Motion
may be the cause of what we know as Mind. For the mere fact of its being
more _conceivable_ that units of Force should resemble units of Feeling
than conversely, is no warrant for concluding that in reality any
corresponding probability obtains. The test of conceivability, although the
most ultimate test that is available, is here rendered vague and valueless
by the _a priori_ consideration that _whatever_ the cause of Mind may be
(if it has a cause), we must find it more easy to conceive of this cause as
resembling Mind than to conceive of it as resembling any other entity of
which we are only conscious indirectly.

Lastly, in the third place, we saw that even if Mr. Spencer's argument were
fully subscribed to, and Mind in its substantial essence were conceded to
be causeless, the central position of Materialism would still remain
unaffected. For Mr. Spencer does not suppose that his "units of Force" are
themselves endowed with consciousness, any more than Professor Clifford
supposes his "moving molecules of inorganic matter" to be thus endowed. So
that the only change which these possibilities, even if conceded to be
actualities, produce in the speculative standing of Materialism, is to show
that the raw material of consciousness, instead of requiring to be _caused_
by other substances--Matter and Force, _x_ and _y_,--occurs ready made as
those substances. But the essential feature of Materialism remains
untouched--namely, that what we know as Mind is dependent (whether by way
of causality or not is immaterial) on highly complex forms of _what we
know_ as Matter, in association with highly peculiar distributions of _what
we know_ as Force.

* * * * *

IV.

THE FINAL MYSTERY OF THINGS.

Some physicists are inclined to dispute the fundamental proposition in
which the whole of Mr. Spencer's system of philosophy may be said to
rest--the proposition, namely, that the fact of the "persistence of force"
constitutes the ultimate basis of science. For my own part, I