 As indicated, Kripke denies that his argument (for the necessity of origin) applies to the case of change over time: “The question whether the table could have changed into ice is irrelevant here” (1972, 1980). So the question whether \(O\) could change into \(S\) is supposedly “irrelevant.” But Kripke does not give a reason for this claim, and if cases of trans-temporal identity and trans-world identity differ markedly in relevant respects — respects relevant to Kripke’s argument for the necessity of origin, it is not obvious what they are. (But see Forbes 1985, and Lewis 1986, for discussion.) The argument above was simply that \(O\) and \(S\) cannot be the same ship since there is a possible world in which they differ. If this argument is incorrect it is no doubt because there are conclusive reasons showing that \(S\) and \(S'\) differ. Even so, such reasons are clearly not “irrelevant.” One may suspect that, if applied to the trans-temporal case, Kripke’s reasoning will yield an argument for mereological essentialism. Indeed, a trans-world counterpart of such an argument has been tried (Chandler 1976, though Chandler views his argument somewhat differently). In its effect, this argument does not differ essentially from the “paradox” sketched in the previous paragraph (which may well be viewed as an argument for mereological essentialism). Subsequent commentators, e.g., Salmon, (1979) and Chandler (1975, 1976), do not seem to take Kripke’s admonition of irrelevance seriously.