The description, classification, and judgment of severity of the functional mental disorders is made, in the absence of any physiological and biochemical criteria, on a phenomenological level. Clinicians approach this task in terms of specific classes of mental disorders which are derived for the most part from the Kraepelinian taxonomy. While there has been much emphasis in current American psychiatry on dynamic conceptions of the etiology of mental illness, no new comprehensive classificatory system has been established as a substitute for the older system. Although there is strong agreement concerning the prototypes of various mental disorders, in actual practice these are manifested in terms of syndromes which often do not conform to the ideal descriptions furnished in the literature and taught in the schools. Furthermore, theoretical conceptions of etiology held by different schools of psychiatry influence judgments of diagnosis and severity. Studies of the