15-01-2013, 11:26 AM
In philosophy
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The philosophy of mind has given rise to many stances regarding consciousness. Any attempt to impose an organization on them is bound to be somewhat arbitrary. Stuart Sutherland exemplified the difficulty in the entry he wrote for the 1989 version of the Macmillan
Dictionary of Psychology:
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.[8]
Most writers on the philosophy of consciousness have been concerned to defend 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. The main alternative, followed in the present article, is to organize philosophical stances according to the answers they give to a set of basic questions about the nature and status of consciousness.
Is consciousness a valid concept?
Philosophers and non-philosophers differ in their intuitions about what consciousness is.[9] While most people have a strong intuition for the existence of what they refer to as consciousness,[citation needed] 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.[10] More generally, many philosophers and scientists have been unhappy about the difficulty of producing a definition that does not involve circularity or fuzziness.[8]
Is it a single thing?
Many philosophers have argued that consciousness is a unitary concept that is understood intuitively by the majority of people in spite of the difficulty in defining it.[11] 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, or else is an umbrella term encompassing a variety of distinct meanings with no simple element in common.[12]
Ned Block proposed a distinction between two types of consciousness that he called phenomenal (P-consciousness) and access (A-consciousness).[13] P-consciousness, according to Block, is simply 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,[14] 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.[15]
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.[16]
How does it relate to the physical world?
Illustration of dualism by René Descartes. Inputs are passed by the sensory organs to the pineal gland and from there to the immaterial spirit.
The first influential philosopher to discuss this question specifically was Descartes, and the answer he gave is known as Cartesian dualism. Descartes proposed that consciousness resides within an immaterial domain he called res cogitans (the realm of thought), in contrast to the domain of material things which he called res extensa (the realm of extension).[17] He suggested that the interaction between these two domains occurs inside the brain, perhaps in a small midline structure called the pineal gland.[18]
Although it is widely accepted that Descartes explained the problem cogently, few later philosophers have been happy with his solution, and his ideas about the pineal gland have especially been ridiculed.[19] Alternative solutions, however, have been very diverse. They can be divided broadly into two categories: dualist solutions that maintain Descartes's rigid distinction between the realm of consciousness and the realm of matter but give different answers for how the two realms relate to each other; and monist solutions that maintain that there is really only one realm of being, of which consciousness and matter are both aspects. Each of these categories itself contains numerous variants. The two main types of dualism are substance dualism (which holds that the mind is formed of a distinct type of substance not governed by the laws of physics) and property dualism (which holds that the laws of physics are universally valid but cannot be used to explain the mind). The three main types of monism are physicalism (which holds that the mind consists of matter organized in a particular way), idealism (which holds that only thought truly exists and matter is merely an illusion), and neutral monism (which holds that both mind and matter are aspects of a distinct essence that is itself identical to neither of them). There are also, however, a large number of idiosyncratic theories that cannot cleanly be assigned to any of these camps.[20]
How can we know whether non-human animals are conscious?
The topic of animal consciousness is beset by a number of difficulties. It poses the problem of other minds in an especially severe form, because animals, lacking the ability to express human language, cannot tell us about their experiences.[36] Also, it is difficult to reason objectively about the question, because a denial that an animal is conscious is often taken to imply that it does not feel, its life has no value, and that harming it is not morally wrong. Descartes, for example, has sometimes been blamed for mistreatment of animals due to the fact that he believed only humans have a non-physical mind.[37] Most people have a strong intuition that some animals, such as dogs, are conscious, while others, such as insects, are not; but the sources of this intuition are not obvious.[36]
Philosophers who consider subjective experience the essence of consciousness also generally believe, as a correlate, that the existence and nature of animal consciousness can never rigorously be known. Thomas Nagel spelled out this point of view in an influential essay titled What Is it Like to Be a Bat?. He said that an organism is conscious "if and only if there is something that it is like to be that organism — something it is like for the organism"; and he argued that no matter how much we know about an animal's brain and behavior, we can never really put ourselves into the mind of the animal and experience its world in the way it does itself.[38] Other thinkers, such as Douglas Hofstadter, dismiss this argument as incoherent.[39] Several psychologists and ethologists have argued for the existence of animal consciousness by describing a range of behaviors that appear to show animals holding beliefs about things they cannot directly perceive — Donald Griffin's 2001 book Animal Minds reviews a substantial portion of the evidence.[40]
Could a machine ever be conscious?
The idea of an artifact made conscious is an ancient theme of mythology, appearing for example in the Greek myth of Pygmalion, who carved a statue that was magically brought to life, and in medieval Jewish stories of the Golem, a magically animated homunculus built of clay.[41] However, the possibility of actually constructing a conscious machine was probably first discussed by Ada Lovelace, in a set of notes written in 1842 about the Analytical Engine invented by Charles Babbage, a precursor (never built) to modern electronic computers. Lovelace was essentially dismissive of the idea that a machine such as the Analytical Engine could think in a humanlike way. She wrote:
It is desirable to guard against the possibility of exaggerated ideas that might arise as to the powers of the Analytical Engine. ... The Analytical Engine has no pretensions whatever to originate anything. It can do whatever we know how to order it to perform. It can follow analysis; but it has no power of anticipating any analytical relations or truths. Its province is to assist us in making available what we are already acquainted with.[42]