tain data uncritically, and declines to challenge the ele-
ments between which its own 'laws' obtain, and from
which its own deductions are carried on. Psychology, the
science of finite individual minds, assumes as its data (1)
thoughts and feelings, and (2) a physical world in time and
space with which they coexist and which (3) they know. Of
course these data themselves are discussable; but the dis-
cussion of them (as of other elements) is called meta-
physics and falls outside the province of this book. This
book, assuming that thoughts and feelings exist and are
vehicles of knowledge, thereupon contends that psychology
when she has ascertained the empirical correlation of the
various sorts of thought or feeling with definite conditions
of the brain, can go no farther--can go no farther, that is,
as a natural science. If she goes farther she becomes
metaphysical. All attempts to explain our phenomenally
given thoughts as products of deeper-lying entities
(whether the latter be named 'Soul,' 'Transcendental
Ego,' 'Ideas,' or 'Elementary Units of Consciousness') are
metaphysical. This book consequently rejects both the
associationist and the spiritualist theories; and in this
strictly positivistic point of view consists the only feature
of it for which I feel tempted to claim originality. Of
course this point of view is anything but ultimate. Men
must keep thinking; and the data assumed by psychology,
just like those assumed by physics and the other natural
sciences, must some time be overhauled. The effort to
overhaul them clearly and thoroughly is metaphysics;
but metaphysics can only perform her task well when dis-
tinctly conscious of its great extent. Metaphysics fragmen-
tary, irresponsible, and half-awake, and unconscious that
she is metaphysical, spoils two good things when she in-
jects herself into a natural science. And it seems to me
that the theories both of a spiritual agent and of associated
'ideas' are, as they figure in the psychology-books, just such
metaphysics as this. Even if their results be true, it
would be as well to keep them, as thus presented, out of
psychology as it is to keep the results of idealism out of
physics.

I have therefore treated our passing thoughts as inte-

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