 One such argument, adapted from Chisholm 1967, goes as follows. Taking Adam and Noah in the actual world as our examples (and pretending, for the sake of the example, that the biblical characters are real people), then, on the plausible assumption that not all of their properties are essential to them, it seems that there is a possible world in which Adam is a little more like the actual Noah than he actually was, and Noah a little more like the actual Adam than he actually was. But if there is such a world, then it seems that there should be a further world in which Adam is yet more like the actual Noah, and Noah yet more like the actual Adam. Proceeding in this way, it looks as if we may arrive ultimately at a possible world that is exactly like the actual world, except that Adam and Noah have ‘switched roles’ (plus any further differences that follow logically from this, such as the fact that in the ‘role-switching’ world Eve is the consort of a man who plays the Adam role, but is in fact Noah). But if this can happen with Adam and Noah, then it seems that it could happen with any two actual individuals. For example, it looks as if there will be a possible world that is a duplicate of the actual world except for the fact that in this world you play the role that Queen Victoria plays in the actual world, and she plays the role that you play in the actual world (cf. Chisholm 1967, p. 83 in 1979). But this may seem intolerable. Is it really the case that Queen Victoria could have had all your actual properties (except for identity with you) while you had all of hers (except for identity with her)?