 This is narrower than the persistence question. We may want to know whether each of us was ever an embryo or a foetus, or whether someone could survive in an irreversible vegetative state (where the resulting being is biologically alive but has no mental properties). These are clearly questions about what it takes for us to persist. But being a person is most often defined as having special mental properties. Locke, for instance, said that a person is “a thinking intelligent being, that has reason and reflection, and can consider itself as itself, the same thinking thing, in different times and places” (1975: 335). This implies that something is a person at a given time only if it has those mental properties then. It follows that early-term foetuses and human beings in a vegetative state, having no mental properties at all, are not people at those times. In that case we cannot infer anything about whether you were once an embryo or could come to be a vegetable from a principle about what it takes for a past or future person to be you.