Illusions | Page 3

feeble
minds that are still subject to these self-deceptions.
According to this view, illusion is something essentially abnormal and
allied to insanity. And it would seem to follow that its nature and origin
can be best studied by those whose speciality it is to observe the
phenomena of abnormal life. Scientific procedure has in the main
conformed to this distinction of common sense. The phenomena of
illusion have ordinarily been investigated by alienists, that is to say,
physicians who are brought face to face with their most striking forms
in the mentally deranged.
While there are very good reasons for this treatment of illusion as a
branch of mental pathology, it is by no means certain that it can be a
complete and exhaustive one. Notwithstanding the flattering
supposition of common sense, that illusion is essentially an incident in
abnormal life, the careful observer knows well enough that the case is
far otherwise.
There is, indeed, a view of our race diametrically opposed to the
flattering opinion referred to above, namely, the humiliating judgment
that all men habitually err, or that illusion is to be regarded as the
natural condition of mortals. This idea has found expression, not only
in the cynical exclamation of the misanthropist that most men are fools,
but also in the cry of despair that sometimes breaks from the weary
searcher after absolute truth, and from the poet when impressed with
the unreality of his early ideals.
Without adopting this very disparaging opinion of the intellectual
condition of mankind, we must recognize the fact that most men are

sometimes liable to illusion. Hardly anybody is always consistently
sober and rational in his perceptions and beliefs. A momentary fatigue
of the nerves, a little mental excitement, a relaxation of the effort of
attention by which we continually take our bearings with respect to the
real world about us, will produce just the same kind of confusion of
reality and phantasm, which we observe in the insane. To give but an
example: the play of fancy which leads to a detection of animal and
other forms in clouds, is known to be an occupation of the insane, and
is rightly made use of by Shakespeare as a mark of incipient mental
aberration in Hamlet; and yet this very same occupation is quite natural
to children, and to imaginative adults when they choose to throw the
reins on the neck of their phantasy. Our luminous circle of rational
perception is surrounded by a misty penumbra of illusion. Common
sense itself may be said to admit this, since the greatest stickler for the
enlightenment of our age will be found in practice to accuse most of his
acquaintance at some time or another of falling into illusion.
If illusion thus has its roots in ordinary mental life, the study of it
would seem to belong to the physiology as much as to the pathology of
mind. We may even go further, and say that in the analysis and
explanation of illusion the psychologist may be expected to do more
than the physician. If, on the one hand, the latter has the great privilege
of observing the phenomena in their highest intensity, on the other hand,
the former has the advantage of being familiar with the normal
intellectual process which all illusion simulates or caricatures. To this it
must be added that the physician is naturally disposed to look at
illusion mainly, if not exclusively, on its practical side, that is, as a
concomitant and symptom of cerebral disease, which it is needful to be
able to recognize. The psychologist has a different interest in the
subject, being specially concerned to understand the mental antecedents
of illusion and its relation to accurate perception and belief. It is pretty
evident, indeed, that the phenomena of illusion form a region common
to the psychologist and the mental pathologist, and that the complete
elucidation of the subject will need the co-operation of the two classes
of investigator.
In the present volume an attempt will be made to work out the

psychological side of the subject; that is to say, illusions will be viewed
in their relation to the process of just and accurate perception. In the
carrying out of this plan our principal attention will be given to the
manifestations of the illusory impulse in normal life. At the same time,
though no special acquaintance with the pathology of the subject will
be laid claim to, frequent references will be made to the illusions of the
insane. Indeed, it will be found that the two groups of phenomena--the
illusions of the normal and of the abnormal condition--are so similar,
and pass into one another by such insensible gradations, that it is
impossible to discuss the one apart from the other. The view of illusion
which will