Professor Ryle sets out to expose the myth of Descartes doctrine of the separateness of mental and physical existences, an attitude still fundamental to much philosophical and psychological thinking today and based on an aversion to the mechanistic assumption that 'human nature differs only in degree of complexity from clockwork'. The influence of the idea of a 'ghost in the machine' is traced, explained, and combated in traditional theories of will, feeling, imagination, perception, and thought. The nature of knowledge is carefully analyzed and a theory of min emerges from which does justice to our ordinary common-sense views about the workings of our own, and other people's, minds.