The problem of diachronic personal identity is this: what explains why a person P1 at time T1 is numerically identical with a person P2 at a later time T2, even if they are not at those times qualitatively identical? One traditional explanation is the soul theory, according to which persons persist in virtue of their nonphysical souls. I argue here that this view faces a new and arguably insuperable dilemma: either souls, like physical bodies, change over time, in which case (...) the soul theory faces an analogue problem of diachronic soul identity, or souls, unlike physical bodies, do not change over time, in which case the soul theory cannot explain why souls relate to particular bodies over time and so at best only partially explains personal identity. I conclude that the soul theory fares no better than physicalist-friendly accounts of personal identity such as bodily- or psychological-continuity-based views. (shrink)