It is easier to imagine than to act, so no human being is free of this tendency. But what does the normal man do? He diverts these thoughts into channels where fancy has a legitimate place--he writes romances; he imagines himself using an instrument to talk with his friend miles away and invents the telephone; he imagines a better society than the one which galls him, and writes a "Utopia"; above all he theorizes and speculates. According to his age or ability these speculations give us alchemy or chemistry, astrology or astronomy, magic or religion, spiritism or psychology, the were-wolf or psycho-analysis, phrenology or psychiatry, and so on. Now three generalizations can be made about these primitive or elaborated philosophizings: first, they all represent a constructive tendency; second, the degree to which this constructive tendency is exhibited is historically a measure of the cultural development of any age, an index of the development of the sense of reality of the time, that is, the particular speculation is not only accepted as reasonable but has its practical application for the period; and third, the more primitive forms of these speculations are represented in the delusions of insane, particularly dementia praecox, patients. Following a suggestion of Dr. Hoch we have termed these ideas "constructive delusions." As they correspond to what was historically a compromise between reality and phantasy, they should represent a corresponding mildness or severity in the psychosis where they appear. Our observations--far from being extensive--have so far demonstrated this that we feel justified in offering the hypothesis that when such delusions are present one can base a mild prognosis on their presence with a rather specific relationship between the crudity of construction and the degree of deterioration. It must be borne in mind, however, that we make no claim as to the invariable presence of such delusions when marked deterioration does not take place. We hope only to show that when present this particular form of content may constitute a valuable prognostic guide, as it represents the degree to which the patient has gone in recapitulating the history of his civilization.