In the course of the eighteenth century Locke’s work on personal identity was followed up in divergent ways: some pursued his thoughts in the same direction, emphasizing especially the ‘science-fiction’ accounts he gave of the possibility of brain-fission, and generating further problems not only about the diachronic continuity of the person but eventually, as in the case of William Hazlitt (whose work in this area was almost entirely neglected at the time), as to whether it is rational to worry about our future selves, immortal or not.1 Other post-Lockeans, like Stillingfleet, Butler and Reid saw grave moral and spiritual danger in Locke’s claims, above all in that he seemed to suggest that persons are to be viewed not in terms of continuing substances but in terms of relations between material parts of the human being.