If our bodies exist in space and time, subject to the laws of physics, our minds must be somehow hidden within them like strange immaterial 'Ghosts in the Machine'. Introspection may give us direct access to our own mental world, but we can never know much about other people's. Such views have been regarded as common sense since Descartes, argues Gilbert Ryle, but they are based on a disastrous 'category-mistake'. This epoch-making book cuts through confused thinking and forces us to re-examine many cherished ideas about knowledge, emotion, imagination, consciousness and the intellect. The result is a classic example of philosophy in action.