  Those familiar with the contemporary literature on personal identity, with its emphasis on the necessary and sufficient conditions under which a person remains identical over time, may wonder: if Reid holds that memory is not the criterion of identity, and if Reid’s substance dualism rules out bodily identity as a criterion of personal identity, in what does personal identity consist? Reid’s answer is that identity cannot be accounted for in any terms other than itself. This is neither quietism nor epistemic humility on Reid’s part. Rather, Reid argues that the nature of personal identity—its simplicity and indivisibility—rules out any reductive account that appeals to notions other than identity in explaining how a person persists over time.