This is the continuance of physical structures in a body over time. Individual atoms may be replaced, but the replacement atoms must be of the same elements as the atoms lost, so that the structures retain their functional characteristics over time. More specifically, it is the ability to retrieve egocentric episodes as a temporal chain of life events. If the definition is to be substantial, it should exclude purely reflexive physiologies and behaviors. Reflexes do not separate, or abstract, conscious experience from primitive sensation.
Bare reflexes are almost certainly inadequate for subjective awareness.
Inanimates Each criterion of personal identity heads its respective column. For the limited purpose of estimating the reach of personal identity, they will do. The classes of entities are arranged bottom-up, in rough order of increasing complexity. This arrangement is something of a taxonomic tradition, so we keep it here. This ordering also makes for an easier exposition.