THE CARTESIAN PICTURE

An important component of our everyday conception of the mind began as a lively philosophical thesis and evolved into common sense. The philosophical thesis was spelled out by Descartes, and, without suggesting that Descartes was its sole author, I shall, for convenience, refer to it as the Cartesian conception. According to this conception, minds are entities, sentient organs on a par with hearts and livers. Whereas the heart circulates blood, and the liver regulates metabolism, the mind feels and thinks. Minds receive stimuli from bodily receptors via impulses born by nerves that connect receptors to the brain. According to official Cartesian doctrine, the mind and the brain are separate entities, and events occurring in the mind are distinct from events occurring in the brain. Descartes believed that the brain operated on exclusively mechanical principles, whereas the mind was governed by principles of reason. There was, he thought, no prospect of deriving the latter from the former; hence minds must be separate, nonphysical substances, and brains turn out to be physical modes. Even God could not build a sentient robot, a physical device with the capacity to feel or think. Feelings and thoughts require a nonphysical, mental basis.