Concern about the existence of abnormality or the reality of the distinction between sanity and insanity is in large part philosophical puzzlement. It can be alleviated by an . analysis of the meaning and significance of scientific concepts and facts. The question whether insanity and its causes reside in people or in their environments relates to psychologists' preferences among psycho-10"ical theories differing in terminology and in . assumptions about the useful-ne~s of phenomenological and behavioral concepts. Psychodiagnostic concepts, like all dispositional concepts in psychology, concern behavior in a given context. Statements of relations between behaviors and their correlates have the same logical status as psychodiagnoses and are subject to the same validation;tl tests. The reliability of psychodiagnostic classification is limited by our knowledge of the laws of behavior and the training of clinicians; even so, it is not demonstrably poorer than many useful diagnostic groupings. in general medicine. One cannot establish the unreliability or uselessness of any diagnostic method by showing that pathological symptoms can be faked, and one augbt not judge the effectiveness •of psychiatric treatment solely by the impressions of those who know they are normal and suspect many other patients also are normal.The summary of Rosenhan's (1973a) article in Science, "On Being Sane in Insane Places," begins as follows:It is clear that we cannot distinguish the sane from the insane in psychiatric hospitals. The hospital itself imposes a special environment in which the meanings of behavior can easily be misunderstood. The consequence to patients hospitalized in such an environment-the powerlessness, depersonalization, segregation, mortification, and self-labeling seem undoubtedly countertherapeutic. (p. 257) Requests for reprints should be sent to r. E.