1.the state of being conscious; awareness of one’sown existence, sensations, thoughts,surroundings, etc. 2.the thoughts and feelings, collectively, of anindividual or of an aggregate of people: the moral consciousness of a nation. 3.full activity of the mind and senses, as in waking life: to regain consciousness after fainting. 4.awareness of something for what it is; internal knowledge: consciousness of wrongdoing. 5.concern, interest, or acute awareness: class consciousness. 6.the mental activity of which a person is aware ascontrasted with unconscious mental processes. 7.Philosophy. the mind or the mental faculties ascharacterized by thought, feelings, and volition. Explaining the nature of consciousness is one of the most important and perplexing areas of philosophy, but the concept is notoriously ambiguous. The abstract noun “consciousness” is not frequently used by itself in the contemporary literature, but is originally derived from the Latin con (with) and scire (to know). Perhaps the most commonly used contemporary notion of a conscious mental state is captured by Thomas Nagel’s famous “what it is like” sense (Nagel 1974). When I am in a conscious mental state, there is something it is like for me to be in that state from the subjective or first-person point of view. But how are we to understand this? For instance, how is the conscious mental state related to the body? Can consciousness be explained in terms of brain activity? What makes a mental state be a conscious mental state? The problem of consciousness is arguably the most central issue in current philosophy of mind and is also importantly related to major traditional topics in metaphysics, such as the possibility of immortality and the belief in free will. This article focuses on Western theories and conceptions of consciousness, especially as found in contemporary analytic philosophy of mind. The two broad, traditional and competing theories of mind are dualism and materialism (or physicalism). While there are many versions of each, the former generally holds that the conscious mind or a conscious mental state is non-physical in some sense, whereas the latter holds that, to put it crudely, the mind is the brain, or is caused by neural activity. It is against this general backdrop that many answers to the above questions are formulated and developed. There are also many familiar objections to both materialism and dualism. For example, it is often said that materialism cannot truly explain just how or why some brain states are conscious, and that there is an important “explanatory gap” between mind and matter. On the other hand, dualism faces the problem of explaining how a non-physical substance or mental state can causally interact with the physical body. Some philosophers attempt to explain consciousness directly in neurophysiological or physical terms, while others offer cognitive theories of consciousness whereby conscious mental states are reduced to some kind of representational relation between mental states and the world. There are a number of such representational theories of consciousness currently on the market, including higher-order theories which hold that what makes a mental state conscious is that the subject is aware of it in some sense. The relationship between consciousness and science is also central in much current theorizing on this topic: How does the brain “bind together” various sensory inputs to produce a unified subjective experience? What are the neural correlates of consciousness? What can be learned from abnormal psychology which might help us to understand normal consciousness? To what extent are animal minds different from human minds? Could an appropriately programmed machine be conscious?