 The modal-dimensionalist version of possibilist realism is capable of offering the ready answer, “The planet at w and the planet at w′ are both (world stages of) Vulcan”, but faces an only slightly different challenge of its own. It seems intuitive to say that there is a possible world at which Vulcan exists between Sun and Mercury and some remote heavenly body distinct from Vulcan but qualitatively identical with it in relevant respects (such as mass, shape, size, chemical composition, etc.) also exists. Let w1 be such a world and call Vulcan’s double at w1 ‘Nacluv’. Thus at w1, Vulcan and Nacluv exist, Vulcan is between Sun and Mercury, and Nacluv is somewhere far away. It is possible for Vulcan and Nacluv to switch positions. So there is a possible world, w2, which is exactly like w1 except that at w2 Nacluv is between Sun and Mercury and Vulcan is far away. Since Vulcan and Nacluv are two distinct objects, w1 and w2 are two distinct worlds. But this difference seems empty. Given that w1 and w2 are exact qualitative duplicates of each other, on what ground can we say that the object between Sun and Mercury at w1 and far away at w2 is Vulcan and the object far away at w1 and between Sun and Mercury at w2 is Nacluv, rather than the other way around? It is unhelpful to say that Vulcan and Nacluv are distinguished by the fact that Vulcan possesses Vulcan’s haecceity and Nacluv does not. An object’s haecceity is the property of being that very object (Kaplan 1975, Adams 1979, Lewis 1986: 220–48). Since what is at issue is the question of which object is Vulcan, it does not help to be told that Vulcan is the object possessing the property of being that very object, unless the property of being that very object is clarified independently. To say that it is the property of being that very object which is Vulcan is clearly uninformative. It is not obvious that there is any way to clarify it independently.