consciousness consciousness consciousness, at its simplest, is sentience and awareness of internal and external existence. however, its nature has led to millennia of analyses, explanations and debates by philosophers, theologians, linguists, and scientists. opinions differ about what exactly needs to be studied or even considered consciousness. in some explanations, it is synonymous with the mind, and at other times, an aspect of mind. in the past, it was one's "inner life", the world of introspection, of private thought, imagination and volition. today, it often includes any kind of cognition, experience, feeling or perception. it may be awareness, awareness of awareness, or self-awareness either continuously changing or not. the disparate range of research, notions and speculations raises a curiosity about whether the right questions are being asked. representation of consciousness from the seventeenth century by robert fludd, an english paracelsian physician examples of the range of descriptions, definitions or explanations are: simple wakefulness, one's sense of selfhood or soul explored by "looking within"; being a metaphorical "stream" of contents, or being a mental state, mental event or mental process of the brain. inter-disciplinary perspectives western philosophers since the time of descartes and locke have struggled to comprehend the nature of consciousness and how it fits into a larger picture of the world. these questions remain central to both continental and analytic philosophy, in phenomenology and the philosophy of mind, respectively. consciousness has also become a significant topic of interdisciplinary research in cognitive science, involving fields such as psychology, linguistics, anthropology, neuropsychology and neuroscience. the primary focus is on understanding what it means biologically and psychologically for information to be present in consciousness—that is, on determining the neural and psychological correlates of consciousness. in medicine, consciousness is assessed by observing a patient's arousal and responsiveness, and can be seen as a continuum of states ranging from full alertness and comprehension, through disorientation, delirium, loss of meaningful communication, and finally loss of movement in response to painful stimuli. issues of practical concern include how the presence of consciousness can be assessed in severely ill, comatose, or anesthetized people, and how to treat conditions in which consciousness is impaired or disrupted. the degree of consciousness is measured by standardized behavior observation scales such as the glasgow coma scale. etymology john locke, british enlightenment philosopher from the 17th century in the late 20th century, philosophers like hamlyn, rorty, and wilkes have disagreed with kahn, hardie and modrak as to whether aristotle even had a concept of consciousness. aristotle does not use any single word or terminology to name the phenomenon; it is used only much later, especially by john locke. caston contends that for aristotle, perceptual awareness was somewhat the same as what modern philosophers call consciousness. the origin of the modern concept of consciousness is often attributed to locke's essay concerning human understanding, published in 1690. locke defined consciousness as "the perception of what passes in a man's own mind". his essay influenced the 18th-century view of consciousness, and his definition appeared in samuel johnson's celebrated dictionary (1755). "consciousness" (french: conscience) is also defined in the 1753 volume of diderot and d'alembert's encyclopédie, as "the opinion or internal feeling that we ourselves have from what we do". the earliest english language uses of "conscious" and "consciousness" date back, however, to the 1500s. the english word "conscious" originally derived from the latin conscius (con- "together" and scio "to know"), but the latin word did not have the same meaning as the english word—it meant "knowing with", in other words, "having joint or common knowledge with another". there were, however, many occurrences in latin writings of the phrase conscius sibi, which translates literally as "knowing with oneself", or in other words "sharing knowledge with oneself about something". this phrase had the figurative meaning of "knowing that one knows", as the modern english word "conscious" does. in its earliest uses in the 1500s, the english word "conscious" retained the meaning of the latin conscius. for example, thomas hobbes in leviathan wrote: "where two, or more men, know of one and the same fact, they are said to be conscious of it one to another." the latin phrase conscius sibi, whose meaning was more closely related to the current concept of consciousness, was rendered in english as "conscious to oneself" or "conscious unto oneself". for example, archbishop ussher wrote in 1613 of "being so conscious unto myself of my great weakness". locke's definition from 1690 illustrates that a gradual shift in meaning had taken place. a related word was conscientia, which primarily means moral conscience. in the literal sense, "conscientia" means knowledge-with, that is, shared knowledge. the word first appears in latin juridical texts by writers such as cicero. here, conscientia is the knowledge that a witness has of the deed of someone else. rené descartes (1596–1650) is generally taken to be the first philosopher to use conscientia in a way that does not fit this traditional meaning. descartes used conscientia the way modern speakers would use "conscience". in search after truth (regulæ ad directionem ingenii ut et inquisitio veritatis per lumen naturale, amsterdam 1701) he says "conscience or internal testimony" (conscientiâ, vel interno testimonio). the problem of definition about forty meanings attributed to the term consciousness can be identified and categorized based on functions and experiences. the prospects for reaching any single, agreed-upon, theory-independent definition of consciousness appear remote. the dictionary definitions of the word consciousness extend through several centuries and reflect a range of seemingly related meanings, with some differences that have been controversial, such as the distinction between 'inward awareness' and 'perception' of the physical world, or the distinction between 'conscious' and 'unconscious', or the notion of a "mental entity" or "mental activity" that is not physical. the common usage definitions of consciousness in webster's third new international dictionary (1966 edition, volume 1, page 482) are as follows: awareness or perception of an inward psychological or spiritual fact; intuitively perceived knowledge of something in one's inner self inward awareness of an external object, state, or fact concerned awareness; interest, concern—often used with an attributive noun the state or activity that is characterized by sensation, emotion, volition, or thought; mind in the broadest possible sense; something in nature that is distinguished from the physical the totality in psychology of sensations, perceptions, ideas, attitudes, and feelings of which an individual or a group is aware at any given time or within a particular time span—compare stream of consciousness waking life (as that to which one returns after sleep, trance, fever) wherein all one's mental powers have returned . . . the part of mental life or psychic content in psychoanalysis that is immediately available to the ego—compare preconscious, unconscious the cambridge dictionary defines consciousness as "the state of understanding and realizing something." the oxford living dictionary defines consciousness as "the state of being aware of and responsive to one's surroundings.", "a person's awareness or perception of something." and "the fact of awareness by the mind of itself and the world." philosophers have attempted to clarify technical distinctions by using a jargon of their own. the routledge encyclopedia of philosophy in 1998 defines consciousness as follows: consciousness—philosophers have used the term 'consciousness' for four main topics: knowledge in general, intentionality, introspection (and the knowledge it specifically generates) and phenomenal experience... something within one's mind is 'introspectively conscious' just in case one introspects it (or is poised to do so). introspection is often thought to deliver one's primary knowledge of one's mental life. an experience or other mental entity is 'phenomenally conscious' just in case there is 'something it is like' for one to have it. the clearest examples are: perceptual experience, such as tastings and seeings; bodily-sensational experiences, such as those of pains, tickles and itches; imaginative experiences, such as those of one's own actions or perceptions; and streams of thought, as in the experience of thinking 'in words' or 'in images'. introspection and phenomenality seem independent, or dissociable, although this is controversial. many philosophers and scientists have been unhappy about the difficulty of producing a definition that does not involve circularity or fuzziness. in the macmillan dictionary of psychology (1989 edition), stuart sutherland expressed a skeptical attitude more than a definition: consciousness—the having of perceptions, thoughts, and feelings; awareness. the term is impossible to define except in terms that are unintelligible without a grasp of what consciousness means. many fall into the trap of equating consciousness with self-consciousness—to be conscious it is only necessary to be aware of the external world. consciousness is a fascinating but elusive phenomenon: it is impossible to specify what it is, what it does, or why it has evolved. nothing worth reading has been written on it. a partisan definition such as sutherland's can hugely affect researchers' assumptions and the direction of their work: if awareness of the environment . . . is the criterion of consciousness, then even the protozoans are conscious. if awareness of awareness is required, then it is doubtful whether the great apes and human infants are conscious. many philosophers have argued that consciousness is a unitary concept that is understood by the majority of people despite the difficulty philosophers have had defining it. others, though, have argued that the level of disagreement about the meaning of the word indicates that it either means different things to different people (for instance, the objective versus subjective aspects of consciousness), that it encompasses a variety of distinct meanings with no simple element in common, or that we should eliminate this concept from our understanding of the mind, a position known as consciousness semanticism. philosophy of mind most writers on the philosophy of consciousness have been concerned with defending a particular point of view, and have organized their material accordingly. for surveys, the most common approach is to follow a historical path by associating stances with the philosophers who are most strongly associated with them, for example, descartes, locke, kant, etc. an alternative is to organize philosophical stances according to basic issues. coherence of the concept philosophers differ from non-philosophers in their intuitions about what consciousness is. while most people have a strong intuition for the existence of what they refer to as consciousness, skeptics argue that this intuition is false, either because the concept of consciousness is intrinsically incoherent, or because our intuitions about it are based in illusions. gilbert ryle, for example, argued that traditional understanding of consciousness depends on a cartesian dualist outlook that improperly distinguishes between mind and body, or between mind and world. he proposed that we speak not of minds, bodies, and the world, but of individuals, or persons, acting in the world. thus, by speaking of "consciousness" we end up misleading ourselves by thinking that there is any sort of thing as consciousness separated from behavioral and linguistic understandings. types ned block argued that discussions on consciousness often failed to properly distinguish phenomenal (p-consciousness) from access (a-consciousness), though these terms had been used before block. p-consciousness, according to block, is raw experience: it is moving, colored forms, sounds, sensations, emotions and feelings with our bodies and responses at the center. these experiences, considered independently of any impact on behavior, are called qualia. a-consciousness, on the other hand, is the phenomenon whereby information in our minds is accessible for verbal report, reasoning, and the control of behavior. so, when we perceive, information about what we perceive is access conscious; when we introspect, information about our thoughts is access conscious; when we remember, information about the past is access conscious, and so on. although some philosophers, such as daniel dennett, have disputed the validity of this distinction, others have broadly accepted it. david chalmers has argued that a-consciousness can in principle be understood in mechanistic terms, but that understanding p-consciousness is much more challenging: he calls this the hard problem of consciousness. some philosophers believe that block's two types of consciousness are not the end of the story. william lycan, for example, argued in his book consciousness and experience that at least eight clearly distinct types of consciousness can be identified (organism consciousness; control consciousness; consciousness of; state/event consciousness; reportability; introspective consciousness; subjective consciousness; self-consciousness)—and that even this list omits several more obscure forms. there is also debate over whether or not a-consciousness and p-consciousness always coexist or if they can exist separately. although