A PRESENTATION WITHOUT AN EXAMPLE? 191 This is another paradox of inclusion, like Russell's paradox. What I think may make this one especially interesting is that it could tum out to be resistant to certain popular treatments of such paradoxes. This paradox arises involving natural predicates in a natural expression of a natural if somewhat exaggerated thesis.1 University College London, Gower Street, London WCI E 6BT 1 I am happy to thank Jerry Valberg, Jo Wolfl; Malcolm Budd and G. A. Cohen for their advice and encouragement. IF AL5ELY BELIEVE THAT P By MARK CRl'.\t'.\fl~S 'You have known me for years', explained Gonzales, 'But there is something you have not discovered. You know me under two guises, just as Lois Lane knows Superman. You do not realize that I am the person you know under another guise. On that way of thinking about me, you have quite different opinions of me. In fact, you think me an idiot.' 'Knowing your cleverness', I replied, 'I must with some embarrassment accept what you say. Since I do not know what guise you mean, I do not know which belief to revise. Until I find out, it seems, I falsely believe that you are an idiot!' Cornell University, Ithaca, NY 14853, USA A NOTE ON LEWIS'S ONTOLOGY By JosEPH MELIA A CCORDING TO LEWIS, possible worlds are the same kind of object as the actual world. For Lewis, possible worlds are concrete, spatio-temporally extended entities, containing causally efficacious objects (see Lewis [l], pp. 84-91 and Lewis [2] for details). One obvious criticism of this theory of possible worlds is that it is ontologically unparsimonious: the plurality of distinct possible worlds Lewis needs to represent every possible way the world could have been is a large plurality indeed.