mary constituent of
reality: it was a fact on its own account.[6] Common sense seemed to
testify to this, not only when confronted with the "I think, therefore I
am" of Descartes, but whenever a thought produced an action. Since mind
and body interacted,[7] each must be as real as the other and, as it were,
on the same plane of being. Locke, like a good Protestant, felt the right
of the conscious inner man to assert himself: and when he looked into his
own mind, he found nothing to define this mind except the ideas which
occupied it. The existence which he was so sure of in himself was
therefore the existence of his ideas.

Here, by an insensible shift in the meaning of the word "idea", a
momentous revolution had taken place in psychology. Ideas had originally
meant objective terms distinguished in thought-images, qualities,
concepts, propositions. But now ideas began to mean living thoughts,
moments or states of consciousness. They became atoms of mind,
constituents of experience, very much as material atoms were conceived to
be constituents of natural objects. Sensations became the only objects of
sensation, and ideas the only objects of ideas; so that the material world
was rendered superfluous, and the only scientific problem was now to
construct a universe in terms of analytic psychology. Locke himself did
not go so far, and continued to assign physical causes and physical
objects to some, at least, of his mental units; and indeed sensations and
ideas could not very well have other than physical causes, the existence
of which this new psychology was soon to deny: so that about the origin of
its data it was afterwards compelled to preserve a discreet silence. But
as to their combinations and reappearances, it was able to invoke the
principle of association: a thread on which many shrewd observations may
be strung, but which also, when pressed, appears to be nothing but a
verbal mask for organic habits in matter.

The fact is that there are two sorts of unobjectionable psychology,
neither of which describes a mechanism of disembodied mental states, such
as the followers of Locke developed into modern idealism, to the
confusion of common sense.[8] One unobjectionable sort of psychology is
biological, and studies life from the outside. The other sort, relying on
memory and dramatic imagination, reproduces life from the inside, and is
literary. If the literary psychologist is a man of genius, by the
clearness and range