 This and other problems with cross-world identity suggest that some other weaker relation, of similarity or what David Lewis calls counterparthood, should be employed in a possible world analysis of modal discourse. Since similarity is not transitive this allows us to say that the bicycle might have had some different parts without having to say that it might have been wholly different. On the other hand, such a substitution does not seem unproblematic, for a claim about what I might have done hardly seems, at first sight, to be correctly interpretable as a claim about what someone else (however similar to me) does in another possible world (Kripke 1972 [1980], note 13).