An analysis of the problems involved in psychiatric diagnosis, its validity, reliability, purpose, and achievement in light of the authors' own opinions and empirical evidence. They conclude that a classificatory system in psychiatry serves the same essential purpose as taxonomy in science in general, and that a simple, coherent, and meaningful system of classification based on behavioral correlates of psychiatric symdromes is possible. (77 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)