  Locke's account of personal identity appealed to what seems a crucial condition of moral agency, namely, self-reflective consciousness. On  his view, a person – a moral agent – Y at  t2 is identical to a person X at  t1 just in case Y's consciousness  “can be extended backwards” to X  (Ibid., 39), and this is typically taken to mean that  Y remembers X's thoughts and experiences.  This is what we might call a relational account of identity, for it maintains that persons at different times are identical to one another in virtue of some relation(s) between them, where such relations  might be psychological or physical. Locke thus rejected what we might call a substance-based view of identity, which maintains  that persons at different times are identical to one another in virtue of  their consisting in one and the same substance.