This chapter describes the development of the rules for inferring schizophrenia is given in support of, apparently, all the alleged validating criteria; no specific reference is given for the claim to a differential response to somatic therapy. The presence or absence of family resemblance in an already-observed pattern might help clarify the nature of its antecedents; they cannot themselves reliably indicate that a proposed cluster does form a pattern. The role of ‘prior duration’ was further examined in another series of analyses. Subjects were assessed by interview at 2-year follow-up using four assessment instruments – the Present State Examination (PSE) to assess ‘symptoms’, a Psychiatric History Schedule, a Social Description Schedule and a Diagnostic Assessment Schedule. The authors of DSM-III claim that its concept of schizophrenia is valid, finally, in terms of a deterioration in social and occupational functioning.