Consciousness is a spectrum. There are several states between a fully conscious state and a fully unconscious state. In medicine, the degree of loss of consciousness is measured by using Glasgow Coma Scale (GCS); a score between 3 and 15 is given to each person at any time, to show how conscious he or she is. Higher scores show more conscious states.
The opposite of consciousness is subconsciousness/unconsciousness. This means people do things that are instinctive and do not think about them like breathing and making one's heart beat.
It is unclear what mechanism determines consciousness. Consequently, it is difficult to know if another entity is indeed conscious. For example, if a robot seems to react to its environment, how does one assign a consciousness (see artificial life).
- Dorland, W.A. Newman. Dorland's Illustrated Medical Dictionary (29th edition ed.). WB Saunders. ISBN 0-8089-2186-X