If the question is asked, What then do we know about matter and motion?
there is but one reply possible. All that we know about motion is
that it is a name for certain changes in the relations of our visual,
tactile, and muscular sensations; and all that we know about matter
is that it is the hypothetical substance of physical phenomena, the
assumption of the existence of which is as pure a piece of metaphysical
speculation as is that of the existence of the substance of mind.
Our sensations, our pleasures, our pains, and the relations of these,
make up the sum total of the elements of positive, unquestionable
knowledge. We call a large section of these sensations and
then-relations matter and motion; the rest we term mind and thinking;
and experience shows that there is a certain constant order of
succession between some of the former and some of the latter.
This is all that just metaphysical criticism leaves of the idols set
up by the spurious metaphysics of vulgar common sense. It is consistent
either with pure Materialism, or with pure Idealism, but it is neither.
For the Idealist, not content with declaring the truth that our
knowledge is limited to facts of consciousness, affirms the wholly
unprovable proposition that nothing exists beyond these and the
substance of mind. And, on the other hand, the Materialist, holding
by the truth that, for anything that appears to the contrary, material
phenomena are the causes of mental phenomena, asserts his unprovable
dogma, that material phenomena and the substance of matter are the sole
primary existences. Strike out the propositions about which neither
controversialist does or can know anything, and there is nothing left
for them to quarrel about. Make a desert of the Unknowable, and the
divine Astraea of philosophic peace will commence her blessed reign.