Parfit's Fission Dilemma: Why Relation R Doesn't Matter

Abstract

In his work on personal identity, Derek Parfit makes two revolutionary claims: firstly, that personal identity is not what matters in survival; and secondly, that what does matter is relation R. In this article I demonstrate his position here to be inconsistent, with the former claim being defensible only in case the latter is false. Parfit intends his famous fission argument to establish the unimportance of identity – a conclusion disputed by, among others, Mark Johnston. My approach is to critically assess their debate, focusing on Johnston's reductio of Parfit's position. I contend that although Parfit's own response fails, there are other ways to save the fission argument. The unimportance of identity then comes at a cost, however, because the reductio can only be avoided by accepting either that nothing matters in survival, or else that facts about particles and forces do. Either way, relation R cannot be what matters.