Dualism is a position in philosophy of mind that states that, in some fundamental or important way, the mind exists as something separate from the brain, or body. Most forms of mind-body dualism claim that the mind is not a physical thing.

Plato was an early dualist. The Phaedo asserts that the soul exists separately from the body, in the realm of the forms, and temporarily inhabits the body during the course of mortal life, only to be released and rejoin the forms upon death.

René Descartes remains one of the most important dualists from a historical context. In addition to his modern framing of the mind-body problem, Descartes presents a classic argument for dualism. His Meditations on First Philosophy begins with a process of extreme doubt, in which Descartes becomes skeptical of all of his beliefs, such as his sense perception of the world. He concludes, however, that he cannot doubt his own existence — for to doubt is to think, and to think requires that he be a thinking thing. From this he formulates his famous argument: Je pense donc je suis, or Cogito, ergo sum, which both amount to “I think, therefore I am”.

As Descartes continues his meditations, he builds up a number of ways in which the mind is different than the body. Descartes concludes that the mind is a sort of substance separate from the physical body. Descartes' dualism, known as Cartesian Dualism also states that mind and body causally interact, making his view a form of interactionism.

There are various forms and variations within dualism. Some of these are:

Interactionism

Occasionalism

Parallelism

Property Dualism

Substance Dualism

See: mind-body problem