 An alternative reply to Williamson is that the objection is question-begging. It is clearly false that counterfactuals allow substitution of identical terms (of any type). ‘Had Aristotle never taught, Aristotle would still have been Aristotle’ is true, and Aristotle is the teacher of Alexander, yet ‘had Aristotle never taught, Aristotle would still have been the teacher of Alexander’ is clearly false. The substitution principle must be restricted to rigid designators: terms that denote the same entity in all metaphysically possible worlds. But one may then reply: what’s so special about the class of metaphysically possible worlds, when it comes to evaluating counterfactuals? It seems question-begging (against an account in terms of both possible and impossible worlds) to insist the metaphysically possible worlds play a special role here. (Note that if we consider terms that are rigid with respect to the nomically possible worlds, or to all worlds, then no problem arises for the account.) 