 Paull and Sider appeal to a plausible principle to show that the existence of Petrie’s w1 and w2 entail the existence of a pair of worlds that constitutes a counterexample to the global supervenience of A-properties on B-properties (1992, 838). The basic idea is that for any object in any possible world, there is another world containing an “isolated duplicate” of it. Intuitively, the duplicate exists all alone in its world; more precisely, an object y is isolated in a world “if and only if that world contains only (i) y, (ii) y’s parts, and (iii) objects whose existence is entail by any of the objects mentioned in (i) and (ii)” (1992, 838–9). Crucially, isolated duplicates share the intrinsic properties of the things with which they are duplicates. (Two caveats. First, this is not intended to be a definition of ‘intrinsic’. For some attempts to do so, see e.g., Lewis 1983a, Langton and Lewis 1998, and a variety of articles in Philosophy and Phenomenological Research 63). Second, notice that the principle does not say that each thing can itself exist in isolation; it simply says that each thing has a duplicate that does. It consequently does not entail that nothing has any essential extrinsic properties.)