 The diagnostic and statistical classificatory manuals and international disease classifications (DSMs and ICDs) share broad features in providing a categorical scheme of separate mental disorders: each disorder is idiopathic in arising at least in part from morbid factors within the person, and each is identified on the basis not of causal explanation but “descriptively”, using polythetic (disjunctive) criteria to be employed with clinical observation of individual patients (including their self-report). Aside from serving the institutions providing services, their uniformity is aimed to enhance inter-diagnostician reliability; and research based on these reliable classifications, it has been hoped, should eventually allow validation of the categories (APA 1980). (Failure of this hope to achieve its promised yield in research findings partly motivated the revised research domain criteria (RDoC), described later in this section.) 