conditions of body and mind to be something very
occasional and relatively unimportant. Our perceptions may be regarded
as the reaction of the mind on the impressions borne in from the
external world, or as a process of adjustment of internal mental
relations to external physical relations. If this process is, in the
main, a right one, we need not greatly trouble, because it is not
invariably so. We should accept the occasional failure of the
intellectual mechanism as an inseparable accompaniment of its general
efficiency.

To this it must be added that many of the illusions described above can
hardly be called cases of non-adaptation at all, since they have no
relation to the practical needs of life, and consequently are, in a
general way, unattended to. In other cases, again, namely, where the
precise nature of a present sensation, being practically an unimportant
matter, is usually unattended to, as in the instantaneous recognition of
objects by the eye under changes of illumination, etc., the illusion is
rather a part of the process of adaptation, since it is much more
important to recognize the permanent object signified by the sensation
than the precise nature of the present sensational "sign" itself.

Finally, it should never be forgotten that in normal states of mind
there is always the possibility of rectifying an illusion. What
distinguishes abnormal from normal mental life is the persistent
occupation of the mind by certain ideas, so that there is no room for
the salutary corrective effect of reflection on the actual impression
of the moment, by which we are wont to "orientate," or take our bearings
as to the position of things about us. In sleep, and in certain
artificially produced states, much the same thing presents itself.
Images become realities just because they are not instantly recognized
as such by a reference to the actual surroundings of the moment. But in
normal waking life this power of correction remains with us. We may not
exercise it, it is true, and thus the illusion will tend to become more
or less persistent and recurring; for the same law applies to true and
to false perception: repetition makes the process easier. But if we only
choose to exert ourselves, we can always keep our illusions in a nascent
or imperfectly developed stage. This applies not only to those
half-illusions into which we voluntarily fall, but also to the more
irresistible passive illusions, and those arising from an