Personal Identity and Reductionism

1. Suppose (as many philosophers anyway believe) that the Cartesian conception of persons is false: persons are not immaterial (i.e., non-spatial) substances. Suppose, further, that we accept the plausible view that the identity of a person over time admits of analysis in terms of relations of physical and/or psychological continuity (the Continuity Theory).' One instance of the Continuity Theory is the Psychological Criterion according to which person A at time t1 is identical to person B at time t2 iff A and B stand to each other in the relation of (non-branching) psychological continuity. (Competing versions of the Psychological Criterion differ over whether the cause of the psychological continuity, if it is to be identity-preserving, must be normal-i.e., the continued existence of the brain and central nervous system-as opposed, e.g., to the operation of a Star Trek Teletransporter.) Another instance of the Continuity Theory is the Physical Criterion according to which the identity of a person over time is analysable exclusively in terms of relations of physical continuity (in particular, spatiotemporal continuity of the body and/or brain) which hold between persons at different times. Yet other-Mixed--Criteria assign varying degrees of importance to both physical and psychological continuity.2