Ghost in the machine

The "ghost in the machine" is British philosopher Gilbert Ryle's derogatory description of René 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.