Gilbert Ryle was a mid-twentieth-century British philosopher who made major contributions to philosophical psychology, most notably in his influential work The Concept of Mind. Often associated with behaviorism, Ryle rejected Cartesian dualism and the conception of the mind as a non-physical substance. As a leading figure in ordinary language philosophy, he argued that many philosophical problems arise from misunderstandings of how mental terms function in everyday language. Central to his critique of dualism was the idea of category mistakes, whereby mental concepts are systematically misclassified, giving rise to misguided theories of mind. Against dualism, Ryle proposed that mental states are better understood as dispositions to behave, think, and feel in certain ways. In addition, he developed the influential distinction between knowing how and knowing that, challenged the notion of inner acts of volition, and questioned the idea that individuals have privileged access to their own mental states.