Descartes' mind—body dualism is frequently thought to lie at the origins of our concerns about the relationship of the mental to the physical. His approach to the issue is very different from that of most current philosophers and he is frequently a target for their criticism, as contemporary philosophers tend not to be dualists but are generally more inclined towards some form or other of materialism. There is, however, another significant difference between Descartes and current discussions: unlike contemporary philosophers, Descartes focused on arguing for substance dualism. The question he addressed at length was the question whether thinking and material qualities could belong to the same substance. He thought it pretty obvious that thinking is not identical with motion or other material qualities¹ and he never addressed other ways in which thinking or consciousness might fail to be a metaphysically fundamental category distinct from material qualities. Contemporary philosophers, however, focus on the relationship between mental and physical states; the classical notion of substance has disappeared from the scene.