This paper re-evaluates Derek Parfit’s attack on the commonly held view that personal identity is necessarily determinate and that it is what matters. In the first part we first argue against the Humean view of personal identity; secondly, we classify the remaining alternatives into three kinds: the body theory and the brain theory, the quasi-Humean theory, and the soul theory, and thirdly we deploy Parfit’s arguments and related considerations to the point that none of the materialistic alternatives is consistent with the commonly held view. This leaves us with the alternative: either we accept the radical and highly implausible materialistic view Parfit calls ‘Reductionism’, or we accept the view that we are nonphysical indivisible entities—Cartesian egos, or souls. The second part of the paper discusses Parfit’s objections against the Cartesian view: that there is no reason to believe in the existence of such nonphysical entities; that if such entities exist, there is no evidence that they are enduring (to span a human life); that even if they exist and are enduring, they are irrelevant for the psychological profile and temporal continuity of a person; that experiments with ‘brain-splitted’ patients provide strong evidence against the Cartesian view. We argue that these objections are in part mistaken, and that the remaining (sound) part is not strong enough to make the Cartesian view less plausible than Reductionism.