Simply put, Ryle regards the traditional philosophical concept of the mind as something of a myth. He regards it as a holdover from the days of Descartes, whose mind/body dualism had exercised such profound influence on the development of Western philosophy. Ryle famously characterizes Descartes's mind-body dualism as "the ghost in the machine". In other words, he thinks it palpably false that the mind can be conceived of as somehow separate from the body, as Descartes argued.
For Ryle, mental processes can never be separated, even conceptually, from bodily processes. The two are part of the selfsame reality. In contrast to Descartes, Ryle does not believe that the body is some kind of mechanism with a distinct entity inside it called a mind that calls the shots and causes the body to move. On the contrary, he argues that the workings of the mind can better be understood as the actions of the body.
Ryle's emphasis, therefore, is on the body and its movements, not some strange, mysterious phantom floating around inside our brains which, according to his reading of Descartes, is supposed to be controlling all our bodily movements. For him, there is no contradiction in saying that an action—say, a movement of the arm, for example—is caused by physical laws while at the same time being governed by principles of reasoning.