Substance dualism is the view that there are fundamentally two kinds of substances of entities: soul and body. Descartes' version of substance dualism defines them as follows:
Soul = Soul is non-spatio-temporal, and it is directly related to thought.
Body = Body is spatio-temporal, and it is characteristically extended in spatio-temporal realms.
In order for substance duality to exist you must mistakenly believe, imagined that mind, Spirit, Soul exists as a Material, Physical, Reality.