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Consciousness | Britannica.com

Consciousness, a psychological condition defined by the English philosopher John Locke as “the perception of what passes in a man’s own mind.” The ability to notice and react to one’s environment is not an on-off phenomenon but a continuum. From full alertness a person can descend through drowsiness to stupor, a condition in which awareness is greatly reduced and the best motor response to stimulation is… In the early 19th century the concept was variously considered. Some philosophers regarded it as a kind of substance, or “mental stuff,” quite different from the material substance of the physical world. Others thought of it as an attribute characterized by sensation and voluntary movement, which separated animals and men from lower forms of life and also described the difference between the normal waking state of animals and men and their condition when asleep, in a coma, or under anesthesia (the latter condition was described as unconsciousness). Other descriptions included an analysis of consciousness as a form of relationship or act of the mind toward objects in nature, and a view that consciousness was a continuous field or stream of essentially mental “sense data,” roughly similar to the “ideas” of earlier empirical philosophers. The method employed by most early writers in observing consciousness was introspection—looking within one’s own mind to discover the laws of its operation. The limitations of the method became apparent when it was found that because of differing preconceptions, trained observers in the laboratory often could not agree on fundamental observations. The failure of introspection to reveal consistent laws led to the rejection of all mental states as proper subjects of scientific study. In behaviourist psychology, derived primarily from work of the American psychologist John B. Watson in the early 1900s, the concept of consciousness was irrelevant to the objective investigation of human behaviour and was doctrinally ignored in research. Neobehaviourists, however, adopted a more liberal posture toward mentalistic states such as consciousness.

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https://www.britannica.com/topic/consciousness