The thought-experiment presented by Bernard Williams in 'The self and the future' continues to draw the attention of writers in the debate about personal identity. While few of them agree on what implications it has for the debate, almost all agree that those implications are significant ones. Some have even claimed that it has consequences not only for personal identity, but also concerning the viability of thought-experiment as a method. This paper surveys what these consequences might be at both levels (...) - as a substantive contribution to the debate on identity, and as to what it shows about the usefulness of thought-experiments. It argues ultimately that thought-experiments like Williams's do provide a useful philosophical tool as long as we temper our expectations of them, and that it offers some support to a view of personal identity but one which is at odds with Williams's own view. (shrink)