Ghost in the Machine

The "Ghost in the Machine" is a metaphor in philosophy. The philosopher Gilbert Ryle called mind the "Ghost in the Machine", and the idea that it was separate from the brain was the mistaken "official doctrine".
Ryle was referring to René Descartes' mind-body dualism. In dualist systems like Descartes', mental activity carries on in parallel to physical action, but the means of interaction are unknown or speculative. Ryle thought this was absurd, and as a kind of error which he called a "category mistake". It is like saying something like "cars move by motive spirit".