Relation of Illusion to Mental Pathology. The imaginative process described above answers to the normal working of the reproductive function in its broadest aspect. Yet this faculty is subject to various forms of derangement, which greatly widen its sphere of influence in the mental life, and at the same time afford us unexpected means of gaining insight into its real nature. The study of illusions belongs properly to the Pathology of mind.
In this connection, however, we have only to deal with those irregular states of mind to which the regular processes sometimes give rise: that is, with individual unexpected states, rather than with the general and permanent irregularities which constitute mental disease. Our view includes the beginning of mental tendencies away from the line of average results; tendencies which, like all other mental products, become fixed, through habit, in forms of chronic delusion. It is in the reproductive faculty that mental aberration generally takes its rise. We can readily see how a failure in attentive selection of images gives constructions which are untrue, how mistaken vistas of memory may lead to fallacious processes of thought and mistaken forms of action. The imagination stands midway between perception and thought, and errors in its results cause far-reaching illusion.
General Character of Illusion. By illusion, therefore, in its broadest sense, we understand metal deception, or____________________