The author reviews some current concepts concerning the definitions and uses of the concepts of health and illness. Starting from the definitions in Psychiatry, "normality" is considered from the statistic, the normative and the clinical standpoints, and as a part of a continuum stretching from health to illness. Several approaches are analyzed, among which Wittaker's, who sets forth the following indicators of normality: a) self-knowledge; b) self-esteem; c) self-security; d) capacity for giving and receiving affection; e) satisfaction of corporal needs; f) productivity and capacity for happiness; g) lack of tensions and of hipersensitivity. 2. The concept of illness as an operative concept is also analyzed, leading to the following statements: a) it is inexistent in non-biological sciences; b) it appears in social sciences only through extrapolation; c) in medicine it means the breacking of homeosthasis; d) in psychology and dynamic psychiatry it means the abnormal stressing of normal mechanisms, common to all persons. 3. The concept of health as equilibrium is also analyzed, with the following precisions: a) equilibrium is defined within a system as affecting the whole of it, and implying transformation and self-regulation; b) homeosthasis is a case of equilibrium for steady complex systems; c) adaptation is the maintenance of equilibrium when there are exchanges with the evironment. 4. Finally, those concepts are applied to mental illness and its limits, and the following criteria are set forth: a) amount of anguish; b) depression related to its motives, intensity, persistence and frequency; c) regression to previous development stages; d) use of defense mechanisms in an inadequate or stereotyped way.
