THE STUDY OF ILLUSION.
C
ommon sense, knowing nothing of fine distinctions, is wont to draw a
sharp line between the region of illusion and that of sane intelligence. To
be the victim of an illusion is, in the popular judgment, to be excluded from
the category of rational men. The term at once calls up images of stunted
figures with ill-developed brains, half-witted creatures, hardly distinguish-
able from the admittedly insane. And this way of thinking of illusion and
its subjects is strengthened by one of the characteristic sentiments of our age.
The nineteenth century intelligence plumes itself on having got at the bot-
tom of mediaeval visions and church miracles, and it is wont to commiserate
the 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 ab-
normal life. Scientific procedure has in the main conformed to this distinc-
tion of common sense. The phenomena of illusion have ordinarily been
3 JAMES SULLY
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 ex-
haustive 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 exclama-
tion of the misanthropist that most men are fools, but also in the cry of de-
spair 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 condi-
tion 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 men-
tal 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 detec-
tion 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 nat-
ural to children, and to imaginative adults when they choose to throw the
