The relation of consciousness to the material world is puzzle, which has its origin in dualism, a philosophy of mind which posits their fundamental separation. Dualism, in turn, has its roots in folk wisdom. The belief that humans are more than bodies and that there is something in human nature that survives bodily death has its origins in prehistory; it becomes explicit in the mythology of Ancient Egypt and Assyria and was formulated into a philosophical position in the Platonic thought of Ancient Greece. But the contemporary view that the interaction of consciousness with matter poses a problem which may be beyond scientific understanding can be traced to a clearer formulation of dualism proposed by Descartes. According to Descartes (1644) the Universe is composed of two fundamentally different substances, res cogitans, a substance which thinks, and res extensa, a substance which extends in space. Res extensa is the stuff of which the material world is made, including living bodies and brains; res cogitans is the stuff of consciousness. Descartes maintained that, in humans, res cogitans and res extensa interact via the pineal gland, located in the center of the brain. However, even in the seventeenth century, the causal interaction of substances as different as these was thought by some to pose an insuperable problem. Leibniz (1686), for example, argued that only physical events could cause physical events and only mental events could cause mental events. Fortunately, he thought, God has arranged physical events and mental events into a pre-established harmony so that given sequences of mental and physical events unfailingly accompany each other ("parallelism"). Consequently, there is an apparent causal interaction of mind with body rather than an actual one. This view resurfaces in the contemporary assumption that for every conscious experience there is a distinct neural "correlate." However, attribution of such correspondences to ...
