earance of several objects. If it happens to be in a brain,
it may be called a confused perception of these objects. All actual
perception is confused to a greater or less extent.

We can now interpret in terms of our theory the distinction between
those mental occurrences which are said to have an external stimulus,
and those which are said to be "centrally excited," i.e. to have no
stimulus external to the brain. When a mental occurrence can be regarded
as an appearance of an object external to the brain, however irregular,
or even as a confused appearance of several such objects, then we may
regard it as having for its stimulus the object or objects in question,
or their appearances at the sense-organ concerned. When, on the other
hand, a mental occurrence has not sufficient connection with objects
external to the brain to be regarded as an appearance of such objects,
then its physical causation (if any) will have to be sought in the
brain. In the former case it can be called a perception; in the latter
it cannot be so called. But the distinction is one of degree, not of
kind. Until this is realized, no satisfactory theory of perception,
sensation, or imagination is possible.

LECTURE VIII. SENSATIONS AND IMAGES

The dualism of mind and matter, if we have been right so far, cannot be
allowed as metaphysically valid. Nevertheless, we seem to find a certain
dualism, perhaps not ultimate, within the world as we observe it. The
dualism is not primarily as to the stuff of the world, but as to causal
laws. On this subject we may again quote William James. He points out
that when, as we say, we merely "imagine" things, there are no such
effects as would ensue if the things were what we call "real." He takes
the case of imagining a fire.

"I make for myself an experience of blazing fire; I place it near my
body; but it does not warm me in the least. I lay a stick upon it and
the stick either burns or remains green, as I please. I call up water,
and pour it on the fire, and absolutely no difference ensues. I account
for all such facts by calling this whole train of experiences unreal, a
mental train. Mental fire is what won't burn real sticks; mental water
is what won't necessarily (though of course it may) put out even a
mental fire.... With 'real' objects, on the contrary, consequences
always accrue; and thus the real experiences get sifted from the mental
ones, the things from our thoughts of them, fanciful or tru