Consciousness is a characteristic of the mind generally regarded to comprise qualities such as subjectivity, self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and one's environment. It is a subject of much research in philosophy of mind, psychology, neuroscience, and cognitive science.
Some philosophers divide consciousness into phenomenal consciousness, which is subjective experience itself, and access consciousness, which refers to the global availability of information to processing systems in the brain. Phenomenal consciousness is a state with qualia. Phenomenal consciousness is being something and access consciousness is being conscious of something.
An understanding of necessary preconditions for consciousness in the human brain may allow us to address important ethical questions. For instance, how is the presence of consciousness to be assessed in severely ill or disabled individuals? To what extent are non-human animals conscious? At what point in fetal development does consciousness begin? Can machines achieve conscious states? Are today's autonome and intelligent machines already conscious? These issues are of great interest to those concerned with the ethical treatment of other beings, be they animals, fetuses, or, in the future, machines.
In common parlance, consciousness denotes being awake and responsive to one's environment; this contrasts with being asleep or being in a coma.