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.
Philosophy of religion
World Religions put forth various theories which affirm life after death and different kinds of postmortem existence. This is often tied to belief in an immortal individual soul or self (Sanskrit: atman) separate from the body which survives death, as defended by Plato, Descartes, Monotheistic religions like Christianity and many Indian philosophers. This view is also a position on the mind body problem, mainly, dualism. This view then must show not only that dualism is true and that souls exist, but also that souls survive death. As Kant famously argued, the mere existence of a soul does not prove its immortality, for one could conceive that a soul, even if it is totally simple, could still fade away or lose its intensity. H.H. Price is one modern philosopher who has speculated at length about what it would be like to be a disembodied soul after death.