Introduction

Personal identity as a modern philosophical problem concerns attempts to specify necessary and sufficient conditions for re-identifying persons over time; that is, it involves specifying the conditions under which a person at time t + 1 may be said to be the same person as at some earlier time t. Standard histories of philosophy trace the modern formulation and initial solution of this problem to Locke's ideas regarding the connected nature of consciousness, a connectedness cashed out in terms of memory. What makes a person now the same person as at some earlier time is current consciousness of, the ability consciously to remember, that earlier time, or as Locke himself puts it: “as far as this consciousness can be extended backwards to any past Action or Thought, so far reaches the Identity of that Person; it is the same self now it was then” (Locke 1975: 335). For Locke, then, personal identity depends exclusively upon certain psychological relations obtaining, which is simultaneously to insist that personal identity does not depend on any physical relations obtaining. The continuation of a person owes everything to the continuation of the mind (or soul) and nothing to the continuation of the body.

If anything links otherwise disparate theorizers about personal identity over more than three centuries it may be their penchant for often fanciful, at times downright bizarre, thought experiments. Even Locke contributes a few in support of his psychological criterion, of which probably the best known involves a body-switch between a prince and a cobbler, purporting to illustrate the difference between persons and men: “For should the Soul of a Prince, carrying with it the consciousness of the Prince’s past life, enter and inform the body of a Cobler as soon as deserted by his own Soul, everyone sees he would be the same Person with the Prince, accountable only for the Prince’s Actions: But who would say it was the same Man?” (Locke 1975: 340).