In his recent book, Reasons and Persons, Derek Parfit propounds a version of the psychological criterion of personal identity.1 According to the variant he adopts, the numerical identity through time of persons consists in non-branching psychological continuity no matter how it is caused. One traditional objection to a view of this sort is that it is circular, since psychological continuity presupposes personal identity. Although Parfit frequently denies the importance of personal identity, he considers his own psychological account of identity important (...) enough to attempt to defend it against the charge of circularity. The aim of this paper is to argue that Parfit's attempted defence is unsuccessful because it ultimately rests on an analysis of the unity of consciousness that is itself either circular or otherwise inadequate. (shrink)