David Lewis: on the Plurality of Worlds

entities, and abstract entities are actual by nature; or perhaps they are “analytic actualists,” holding that ersatz possibilia are actual because it is analytic that everything is actual. Either way, the ersatzist seems to have an advantage over the modal realist in agreeing with common sense that whatever exists is actual. More importantly, the ersatzist has an advantage over the modal realist in agreeing with common sense about the extent of concrete reality: there are no more concrete donkeys, for example, than we ordinarily think there are. True, the ersatzist believes in countless infinities of abstract representations of donkeys; but common sense does not have a firm opinion as to the extent of abstract reality, and so the positing of abstract possibilia does not offend common sense beliefs. At any rate, so says the ersatzist. Now, if the ersatzist can supply a sufficient plenitude of ersatz worlds and individuals, then she can take over the analyses proffered by the modal realist. For example, she can say that it is possible that a donkey talk just in case some ersatz world represents that a donkey talks. And where the modal realist constructs entities out of concrete possibilia to play various theoretical roles – for example, to serve as meanings or properties – the ersatz modal realist can mimic that construction using ersatz worlds and individuals. It seems, then, that the ersatzist can have the benefits of Lewis’s possibilia without bearing the costs. But, Lewis argues, appearances here are deceiving. Lewis believes there are severe costs to ersatz modal realism, but different versions have different costs. So he divides the various versions into three sorts depending upon how the ersatz worlds represent (or misrepresent) the one concrete world. According to linguistic ersatzism, ersatz worlds are like stories or theories, they are constructed from the words or sentences of some language (called the “worldmaking language”), and they