Like all general concepts of fundamental scope, that of monism also
is liable to different definitions and divergent modifications,—the
natural result of individual differences of subjective conception. In the
determinate sense in which monism is at present employed by the majority
of philosophers and physical inquirers, the sense which I believe I
was the first to establish in 1866 in my “General Morphology” (Vol. I,
p. 105), it denotes a unitary or _natural_ conception of the world, in
opposition to a _supernatural_ or mystical one, that is, in opposition
to _dualism_. For us, accordingly, there exists (in the sense of Goethe)
_no_ opposition whatsoever between nature and mind, between World and
God. Mental existences, “spirits,” outside nature, or in opposition to
nature, do not exist. What are commonly termed the “mental sciences,”—for
example, philology, history, and philosophy,—are in reality simply a part
of _physical philosophy_, of _Natur-philosophie_. The latter discipline
embraces, in our opinion, the entire body of human knowledge; it is
based upon _empiricism_, on the experiences, the observations, and the
experiments of physical inquiry; but it does not become _philosophy_
until it has brought together and united its empiric products, abstracted
general laws from its isolated experiential facts, and _synthetised_ the
isolated results which _analysis_ has empirically ascertained.