I
Quite a number of delusions find a common point of origin in the natural tendency to view our mental life—the aggregate of our thoughts and doings—as coextensive with the experiences of which our consciousness gives information and which our will directs. The significance of the unconscious and the involuntary is apt to be underestimated or disregarded. We are more ready to acknowledge that in certain unusual and semi-morbid conditions persons will exhibit these peculiar expressions of the subterranean strata of our mental structure—that some have the habit of walking or talking in their sleep, that others occasionally fall into an automatic, trance-like condition, that hypnotism and hysteria and obscure lapses of consciousness and alterations of personality bring to the surface curious specimens of the mysteries of this underworld,—but we are slow to appreciate that the subconscious and the involuntary find a common and a natural place amidst the soundly reasoned and aptly directed activities of our own intelligence. While it is reasonable and proper to have faith in the testimony of consciousness, it is desirable that this confidence should be accompanied by an understanding of the conditions under which such testimony is presumably valid, and when presumably defective or misleading. Sense-deceptions, faulty observation, distraction, exaggeration, illusion, fallacy, and error are not idle abstract fancies of the psychologist, but stern realities; and their existence emphasizes the need in the determination of truth and the maintenance of a sound rationality, of a calm, unprejudiced judgment, of an experienced and balanced intelligence, of a discerning sense for nice distinctions, of an appreciation of the circumstances under which it is peculiarly human to err. A demonstration of the readiness with which perfectly normal individuals may be induced to yield visible evidence of unconscious and involuntary processes, thus possesses a special interest; for when the naturalness of a few definite types of involuntary movements is made clear, the application of the experience to more complex and more indefinite circumstances will easily and logically follow. While the circumstances under which involuntary indications of mental activity are ordinarily given, are too various to enable one to say ab uno disce omnes, yet the principle demonstrated in one case is capable of a considerable generalization, which will go far to prevent misconception of apparently mysterious and exceptional phenomena.