THE differential classification of schizophrenic disorders originated with Kraepelin's (1896) designation of paranoia, catatonia, and hebephrenia as three forms of a single disturbance, dementia praecox, rather than as separate pathologic entities. As reviewed in Chapter 1, Bleuler ( 1911) accepted Kraepelin's approach to differential classification but delineated four primary forms of schizophrenia: the paranoid form, characterized by delusions of grandeur, persecution, and reference; the catatonic form, identified by episodiC stupor, immobility, and/or agitated hyperkinesis; the hebephrenic form, marked by shallow, inappropriate affect and deterioration of personal habits; and the simple form, a category introduced by Bleuler to describe those schizophrenic persons who present a socially withdrawn, affectively blunted picture undistinguished by prominent paranoid, catatonic, or hebephrenic features. Bleuler reported that among hospitalized schizophrenics catatonic and hebephrenic forms of the disturbance were equally frequent and more common than paranoId forms, and he hypothesized that simple schizophrenia, which was seldom seen in the hospital, was probably the most prevalent form of the disturbance among nonhospitalized schizophrenics.