"The \"ghost in the machine\" is British philosopher Gilbert Ryle's description of Ren\u00E9 Descartes' mind-body dualism. The phrase was introduced in Ryle's book The Concept of Mind (1949) to highlight the perceived absurdity of dualist systems like Descartes' where mental activity carries on in parallel to physical action, but where their means of interaction are unknown or, at best, speculative."@en .