Ever since John Locke, Western personal identity theorists have been preoccupied with looking at life backwards, through the lens of memory. Locke, for instance, used his prince and cobbler example to make the point that because someone might remember the experiences had by someone who inhabited a different body, people could switch bodies - a consideration thought by many to refute bodily continuity theories. As recently as the mid-1960s, bodily continuity theorists have tried to turn the tables by arguing that only genuine memories can sustain personal identity and only memories brought about by their normal physical causes can be genuine (Martin and Deutscher, 1966).

Beginning in the late 1960s, however, and increasingly since then, forward-looking perspectives have come to the fore, ushered in, as we have seen, by the consideration of fission examples. What makes fission examples so theoretically interesting is that they have seemed - and still do seem - to many to support the idea that people could lose their identities yet obtain what either should or does matter primarily to them in their so-called self-interested concern to survive. So, unlike the traditional (pre-1970s) debate, which, insofar as it influenced contemporary theory, focused almost exclusively on specifying the conditions under which identity is preserved, with memory as the primary focus of concern, more recently there have been the additional problems of trying to discover what should or does matter primarily in survival (with some still convinced it is identity), and then specifying the conditions under which that (whatever it is) obtains.