  One line of thought appeals to the transference theory of causality. Here the idea is that identity—the persistence of  something from cause to effect—provides the needed link. If  something in a soul could become present in a body, this could  bridge the immaterial and material. Descartes himself appears  to accept such a theory, declaring in the Third Meditation that there could be nothing in an effect not present in its total efficient  cause (Descartes 1642/1996, p. 28). But now the problem reasserts itself:  if, as the substance dualist insists, bodies and minds are radically different,  they have no properties in common. According to Descartes, a body’s properties are modes of extension, ways of being extended,  while a soul’s properties are modes of something quite different,  thought or consciousness. If causation involved transference, a  Cartesian soul could not interact with a body  (but see Hart 1988; Hoffman and Rosenkrantz 1991).