Mind, as used in psychology and philosophy, the part of a person that thinks, and that experiences such feelings as enjoyment, annoyance, anxiety, love, and hate. Mind is usually distinguished from that part of an animal organism that makes purely physical responses to physical stimulation. In humans, nearly all responses are under control of the mind, at least in part. There is evidence that even such automatic functions as heartbeat can be modified.

Modern psychologists define mind as an activity, or group of activities, of the brain in cooperation with other parts of the nervous and glandular systems. Some psychologists limit this definition to mental activities of which a person is conscious. Others also recognize the unconscious mind—mental activity of which the person is unaware.


Some philosophers believe that, although the mind cannot exist without brain function, it is not to be identified with this function. They hold that mind is a phase, or aspect, of the whole, living organism. These philosophers do not concern themselves with the bodily processes that produce mind, but leave this study to psychologists and physiologists.

Early concepts of the mind linked it with the soul. Most of the ancient Greek philosphers thought of psyche (mind, or soul) as separate from soma (body). In Hebrew theology, as expressed in the Old Testament, mind and body were considered to be interrelated parts of a unified whole. The philosophical theory of mind and body as distinct entities is called Dualism; that of mind-body unity is called Monism.

Medieval philosophy, including Christian theology, was strongly influenced by dualism. This influence continued, and was further developed in the 17th century by a French philosopher, Ren Descartes, and by John Locke, an English philosopher.

Some Monists are Idealists; they believe that minds are the only realities. George Berkeley (1685–1753), an Irish philosopher, was a leading exponent of this theory. Other Monists are known as Materialists because they believe that mind is a bodily process. Thomas Hobbes (1588–1679), an English philosopher, expounded the theory that mind is only matter in motion.

Behaviorism, a school of psychology led by John B. Watson (1878–1958), tried to explain mental activity in physiological terms—as response to stimuli affecting the nervous system. Psychoanalysis, developed in the late 19th century by Sigmund Freud of Austria, is a subjective method of investigating and treating mental maladjustments. It is based on Freud's theory of the unconscious mind.

Dualism, together with the identification of mind with soul, had great influence upon scientific research, especially in the medical field. The body was treated by physicians, the mind by priests or ministers. The modern materialistic theory of mind as distinct from the religious concept of a soul, has made possible the scientific study of mental activity, and the medical treatment of mental illness. Psychosomatic medicine, which treats the patient as a unified being, is a scientific development of older monistic (but not necessarily materialistic) theories of mind and body.