This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.
Explanations of consciousness fall into four broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural.
Identity theory of mindEdit
The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that "mind states" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical "middle step" is superfluous.
Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness.
Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia.
According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness.
Functionalism's explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a "machine" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve:
Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the "physical stuff" -- that being computer hardware or biological structure -- could achieve consciousness.
This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor.
Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf
This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid's Natural Dualism the non-physical place is a point-soul that looks out at the world.
Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will 'emerge' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known.
Higher order thoughtEdit
This section is a stub and needs expansion
Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called 'folk psychology') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level.
Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate.
Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and 'vital force' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness).
Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam's Razor is the rationale behind eliminativism and reductionism.
The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements.
New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained.
Owen Flanagan noted in his 1991 book "Science of the Mind" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them "the new mysterians" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The "old mysterians" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, "How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp." [6, p. 229, quote]
Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding.
The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don't have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism.
For example, in the mind-body problem, emergent materialism claims that humans aren't smart enough to determine "the relationship between mind and matter."  Strong agnosticism is a religious application of this position.
Colin McGinn is the leading proponent of the New Mysterian position.
Critics argue this philosophy isn't useful and encourages capitulation. One critic noted:
the extreme "Mysterian" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. 
 McGinn, Colin - The Problem of Consciousness
 McGinn, Colin - Problems in Philosophy: the limits of enquiry
 McGinn, Colin - The Mysterious Flame
 Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two
 Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge
 Horgan, John - The Undiscovered Mind (1999), Phoenix, ISBN 0753810980