Descartes and Malebranche on Mind and Mind-Body Union

I n a famous pair of letters sent in 1643 to Princess Elisabeth of Bohemia, Descartes responded to queries concerning interaction of human mind and its body when he noted that this sort of mind is united in a special way to such a body. Notoriously, recent commentators agree neither on whether mind-body interaction constitutes a problem for Descartes, nor on whether his remarks to Elisabeth concerning mind-body union even address this problem. Critics of Descartes have claimed that his own principles preclude interaction of substances as distinct in nature as mind and body, and thus that he faces what has been dubbed the problem of heterogeneity.' Among critics, Dasie Radner has suggested that Descartes's claim to Elisabeth that human mind and body are united so as to form a single substance was a desperate attempt to overcome such a problem.2 More sympathetic com-