It is a purpose of philosophic analysis to clarify the meaning of concepts used in scientific discourse. An attempt to do so has been made here, with special reference to the value-terms used in psychiatry. Such terms as "mental health," "mental illness," "normal," "abnormal," "neurosis," "psychosis," "perversion," "psychopathic" or "sociopathic" personality have been subject to scrutiny. It has been shown that such terms cannot be defined scientifically. Therefore, it is suggested either that they not be used or that a precise statement of the basis of their use in any given case be made. Such attention to our use of language will bring rewards both in the clarity of our discourse and in the elimination of issues hitherto considered unsolved problems of science.