Dualism

Dualism, as a position on "the mind-body problem," reacts to the apparent problem that the physical self and the mind (or soul) appear to be two separate things by saying that they actually are. The problem is one of consciousness, which does not feel physical. On the other hand, no one has ever seen a mind, unless they have viewed a brain scan of somebody that is not dead (and assuming this is considered a mind, which dualism denies).

The term 'dualist' also refers to any worldview which supposes the world is composed of two fundamental and independent forces: good and evil (such as in Zoroastrianism and Gnosticism), female and male (such as in Wicca), yin and yang (such as in Taoism), etc. However, the remainder of this article concerns just the philosophy of mind definition.

The dualist view of the mind-matter relationship holds that mind and matter are two separate and independently existing substances, and either can exist without the other. The other two chief views are materialism—matter is the fundamental existent, the existence of mind is dependent upon that of matter, matter can exist without mind but mind cannot exist without matter; and idealism—mind is the fundamental existent, the existence of matter is dependent upon that of mind, mind can exist without matter but matter cannot exist without mind.

History
Dualism has its written origins with Plato and Aristotle; however, it is central to most religious thought. The concept of the soul as something immaterial and separate from the body is a sine qua non of Christian belief. In philosophy, Descartes is probably the father of "modern" dualism.

Types of dualism
There are three main branches of dualism: Substance dualism, property dualism, and hylomorphic dualism.

Substance dualism
Substance dualism is often what most people refer to when they say "dualism." It holds that "matter" and "mind" are two different kinds of substances. The major issue for substance dualism is to explain how, if mind and matter are separate substances, neither reducible to the other, do they appear to interact with each other? If one is reducible to the other (as in materialism or idealism), then clearly the two can interact, since their interaction can ultimately be reduced to the interaction of the more fundamental one with itself.

Dualists have proposed the following theories of how matter and the soul may interact:
 * Interactionism: this affirms that matter and soul really do interact; the problem is to explain how. Descartes thought the interaction happened in the pineal gland of the brain, but neuroscience has not found any evidence of the pineal gland having such a special role in the mind. A modern alternative is that the soul influences quantum indeterminacy, which in turn influences neuronal events. But again, there is no evidence for this from quantum physics or neuroscience.
 * Pre-established Harmony and Occasionalism: mind and soul never actually interact, they only appear to.
 * God established them both at the beginning of the world, to evolve separately, each in accordance with its own laws — like how two perfect clocks set to keep the same time, will agree on the same time, without ever interacting with each other to maintain this agreement. This was the view of Leibniz.
 * Every time matter needs to act on mind (e.g. sense experience), God miraculously intervenes in the world to alter mind to have that sense experience. Every time mind needs to act on matter (e.g. waving one's arm), God miraculously intervenes in the world to alter matter to perform the action desired by mind. So mind and matter never directly interact, but their interaction is mediated by the constant miraculous action of God. This was the view of many medieval Islamic theologians, most notably Ghazali.

Ghost in the machine
The ghost in the machine is a sarcastic description coined by British philosopher Gilbert Ryle, referring to René Descartes's ideas about mind-body dualism. He introduced the phrase in his 1949 book The Concept of Mind, in order to demonstrate the silliness of Descartes' dualist system which hypothesized that mental activity is carried on separately and without any obvious connection to physical activity. The phrase was used by Arthur Koestler for one of his book titles.

Property dualism
The advent of modern biology and neuroscience has dealt a serious blow to substance dualism. The findings of neuroscience, including brain centers dealing with specific memories, thoughts, and emotions show that human intelligence is part of the body. "Soul" (which is distinct from the "mind") is a spiritual concept, and scientists will not consider it unless they can find a way to quantify it. In the wake of the collapse of substance dualism, property dualism arose as an anti-reductionist position in the philosophy of mind. Property dualism holds that only the physical mind exists, but that it has two different properties (as opposed to substances): the physical and the mental. Who is or is not a property dualist also seems to be as big a matter of debate as to whether or not the position is true. David Chalmers openly defends property dualism. John Searle has been characterized as a dualist, but calls his position "biological naturalism" and denies holding a dualist position. Daniel Dennett contends that a number of philosophers of mind and researchers in the behavioral sciences implicitly accept property dualism with his term "Cartesian theater."

Hylomorphic (or hylemorphic) dualism
This is the Aristotelian-Thomist position. It claims that living things are a compound of matter (hyle) and substantial form (morphe), and that the latter is the soul. One argument against this view is that it only makes sense if one accepts an Aristotelian ontology, when it is unclear why one should prefer an Aristotelian ontology to competing ones. Furthermore, there are arguments that Aristotle treats the relationship between matter and form in an inconsistent way when you compare his analysis of living human bodies to his analysis of inanimate objects such as bronze statues.

In a nutshell
QualiaSoup provides a brief and educational 2-part view on the problems associated with the idea that mind and body are separate substances.