Interactionism is a dualist position in the philosophy of mind which argues that (1) mind and body are separate, but that (2) there is causal interaction between the two.

Cartesian dualism, the position of René Descartes is the most famous example of interactionism.

Descartes was an interactionist, and a substance dualist who believed that the mind and body had a causal link. However, a problem arises when interactionalism and substance dualism are coupled — namely, how can an immaterial entity with no extension in the physical world cause changes in a physical body, and how can a physical body cause changes, moods or feelings in a non-physical mind?

Descartes at one point suggested that the pineal gland in the brain may be the link between the soul and the body, but later abandoned the idea admitting that he did not have an answer to the problem. Other followers of Descartes' tradition later suggested that the causal link between mind and body was occasion for divine intervention — that the apparent cause and effect were not direct, but that the hand of God was the actual cause of action in the physical world.

See: mind-body problem, René Descartes, occasionalism