Philosophy of mind
Dualism is a set of views about the relationship between mind and matter (or body). It begins with the claim that mental phenomena are, in some respects, non-physical. One of the earliest known formulations of mind–body dualism was expressed in the eastern Sankhya and Yoga schools of Hindu philosophy (c. 650 BCE), which divided the world into purusha (mind/spirit) and prakriti (material substance). Specifically, the Yoga Sutra of Patanjali presents an analytical approach to the nature of the mind.
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.