 An assessment of the counterpart theoretic analysis is vital not just to understanding modal discourse, however, but also to getting to the correct account of identity over time. For, as we saw, the argument against perdurance theory outlined at the end of the last section depends on the correct interpretation of modal discourse. In fact, it is invalid on a counterpart theoretic analysis which allows different counterpart relations (different similarity relations) to be invoked according to the sense of the singular term which is the subject of the de re modal predication (Lewis 1986, Ch. 4), since the counterpart relation relevant to the assessment of a de re modal predication with a singular term whose sense determines that it refers to a person will be different from that relevant to the assessment of a de re modal predication with a singular term whose sense determines that it refers to a sum of person-stages. “I might have existed for only five years” means on the Lewisian account “There is a person in some possible world similar to me in those respects important to personhood who exists for only five years”; “The maximal summation of person stages of which this current stage is a stage might have existed for only five years” means “There is a summation of person stages similar to this one in those respects important to the status of an entity as a summation of stages which exists for only five years”. Since the two similarity relations in question are distinct the first modal statement may be true and the second false even if I am identical with the sum of stages in question.