Post-War philosophy of mind has been dominated by a near unanimous agreement that dualism is incorrect. The disagreement has been over identifying the fundamental fault in the dualist theory, and hence over what alternative way of thinking is correct. We can, then, plot the development of theories during this period in terms of one anti-dualist theory being replaced by another because reflection revealed (or seemed to reveal) that the first response itself involved an unconvincing or unacceptable commitment. Thus, for example, Ryle (to give a very crude characterisation of his view) thought that the Cartesian Dualist's fundamental error was that of miscategorising our psychological vocabulary, of regarding its terms as standing for entity-like, episodic, things, whereas according to him, the correct approach was to regard them as ascribing disposition-like states. This was eventually rejected because it seemed itself to miscategorise experiential (or conscious) occurrences, which precisely are real occurrences with causal properties.¹ The need to accommodate this conviction within an anti-dualist framework resulted in the early versions of the psycho-physical identity theory.