Philosophers struggle to explain why human beings with deep cognitive impairments have a higher moral status than certain non-human animals. Modal personism promises to solve this problem. It claims that humans who lack the capacities of “personhood” and the potential to develop them nonetheless could have been persons. I argue that modal personism has poor prospects because it's hard to see how we could offer a plausible account of modal personhood. I search for an adequate understanding of modal personhood by (...) considering existing accounts and sketching new ones. But each account fails, either because it objectionably excludes some deeply cognitively impaired humans from the class of modal persons or because it makes modal personhood doubtfully relevant to moral status. And the modal personist cannot solve this problem by appealing to the misfortune suffered by modal persons. (shrink)