  The key for Locke is that what grounds both prudential concern and moral responsibility is the personal identity relation, a relation uniquely unifying temporally distinct person-stages via consciousness. And it was because Locke prized apart personal identity from biological identity, and any other sort of substance-based identity, that later philosophers like Joseph Butler and Thomas Reid objected to it. So, for example, Butler accuses Locke of a “wonderful mistake,” which is that he failed to recognize that the relation of consciousness presupposes identity, and thus cannot constitute it (Butler 1736, 100). In other words, I can remember only my own experiences, but it is not my memory of an experience that makes it mine; rather, I remember it only because it's already mine. So while memory can reveal my identity with some past experiencer, it does not make that experiencer me. What I am remembering, insists Butler, are the experiences of a substance, namely, the same substance that constitutes me now.