d by some degree
of impulse to movement, though, for some reason or another, in natural
and healthy sleep these impulses are restricted to the stage of faint
nascent stirrings of motor activity which hardly betray themselves
externally. This difference, involving a great difference in the
possible practical consequences of the two conditions of natural and
hypnotic sleep, clearly serves to bring the latter condition nearer to
that of insanity than the former condition is brought. A strong
susceptibility to the hypnotic influence, such as Dr. Heidenhain
describes, might, indeed, easily prove a very serious want of
"adaptation of internal to external relations," whereas a tendency to
dreaming would hardly prove a maladaptation at all.

CHAPTER VIII.

ILLUSIONS OF INTROSPECTION.

We have now, perhaps, sufficiently reviewed sense-illusions, both of
waking life and of sleep. And having roughly classified them according
to their structure and origin, we are ready to go forwards and inquire
whether the theory thus reached can be applied to other forms of
illusory error. And here we are compelled to inquire at the outset if
anything analogous to sense-illusion is to be found in that other great
region of presentative cognition usually marked off from external
perception as internal perception, self-reflection, or introspection.

_Illusions of Introspection defined._

This inquiry naturally sets out with the question: What is meant by
introspection? This cannot be better defined, perhaps, than by saying
that it is the mind's immediate reflective cognition of its own states
as such.

In one sense, of course, everything we know may be called a mental
state, actual or imagined. Thus, a sense-impression is known, exactly
like any other feeling of the mind, as a mental phenomenon or mental
modification. Yet we do not usually speak of introspectively
recognizing a sensation. Our sense-impressions are marked off from all
other feelings by having an objective character, that is to say, an
immediate relation to the external world, so that in attending to one of
them our minds pass away from themselves in what Professor Bain calls
the attitude of objective regard. Introspection is confined to feelings
which want this intimate connection with the external region, and
includes sensation only so far as it is viewed apart from external
objects and on its mental side as a feeling, a process which is next to
impossible where t