Mind–body dualism
Ontological dualism makes dual commitments about the nature of existence as it relates to mind and matter, and can be divided into three different types:Substance dualism is a type of dualism most famously defended by René Descartes, which states that there are two kinds of foundation: mental and body. This philosophy states that the mental can exist outside of the body, and the body cannot think. Substance dualism is important historically for having given rise to much thought regarding the famous mind–body problem. Substance dualism is a philosophical position compatible with most theologies which claim that immortal souls occupy an independent realm of existence distinct from that of the physical world.
Non-physical entity
Dualism is the division of two contrasted or opposed aspects.The dualist school supposes the existence of non-physical entities, the most widely discussed one being the mind. But beyond that it runs into stumbling blocks. Pierre Gassendi put one such problem directly to René Descartes in 1641, in response to Descartes's "Meditations":
Descartes' response to Gassendi, and to Princess Elizabeth who asked him similar questions in 1643, is generally considered nowadays to be lacking, because it did not address what is known in the philosophy of mind as the interaction problem. This is a problem for non-physical entities as posited by dualism: by what mechanism, exactly, do they interact with physical entities, and how can they do so? Interaction with physical systems requires physical properties which a non-physical entity does not possess.