Consciousness is defined as the state or quality of awareness, or, of being aware of an external object or something within oneself. It has been defined variously in terms of sentience, awareness the ability to experience or to feel, wakefulness, having a sense of selfhood or soul and the executive control system of the mind .In contemporary philosophy its definition is often hinted at via the logical possibility of its absence, the philosophical zombie, which is defined as a being whose behaviour and function are identical to one's own yet there is "no-one in there" experiencing it.