The biological perspective has dominated the psychiatric literature since the late 1960s. Today many articles and textbooks are written as though it has been established that major mental disorders are caused by brain disorders. The evidence on which these statements are founded however, is often equivocal. Biological theorists are reductionisms. They assume that brain-behavior explanations proceed in one direction, from brain to behavior. Psychosocial factors are considered to be secondary influences, if they are considered at all, in explanations of mental disorders. These theorists tend to overlook two fundamental aspects of reductionistic explanatory models: (1) mental and social phenomena cannot be adequately understood at the level of physical processes, and (2) brain-behavior influences can proceed in either direction. This paper will review the reasons why much evidence of biological causality of mental disorders should be considered to be tentative rather than conclusive. It is argued that adequate explanatory models of mental disorders require adoption of a General Systems Theory model that will allow for the integration of knowledge from multiple levels of analysis, including biological, psychosocial, and cultural influences.

Key wards: reductionism, biological psychiatry, general systems theory.