The functional psychoses, medical diseases with no known biological causes (for example, schizophrenia and anxiety disorders), continue to be classed as illnesses of unknown origin, and the validity of diagnostic concepts therefore also depends on extrinsic criteria such as course and outcome, results of biological and genetic investigation, and response to treatment. Operational diagnostic criteria, or the process of defining a psychosis by studying its manifestations, are the main subject of this book, which presents a comprehensive review of the present state of diagnostic formulations for...