 With these modifications incorporated the memory criterion has come to be known as the psychological continuity criterion of personal identity. The psychological continuity criterion is an improvement on the original memory criterion. Nevertheless one of the problems confronting the original memory criterion, its putative conflict with the transitivity of identity, can be brought against its successor in a different form. We saw that making certain identifications in a fission case such as the ship of Theseus [see Section 4: Diachronic Identity Puzzles] threatens the transitivity of identity. One much discussed type of fission case, hemispheric division, is taken by many to show that the psychological continuity criterion is, after all, incompatible with the transitivity of identity (Nagel 1975).