 where P* is the possible-worlds paraphrase of P. According to the fiction employed by Rosen 1990 (i.e. the theory which David Lewis offers as fact), there are many co-existing concrete possible worlds — each one its own cosmos. Furthermore, this claim is true at any of these possible worlds. So, according to the modal fiction, at all worlds it is true that there are many other possible worlds. However, it follows from the biconditional that since, according to the modal fiction, at all worlds, there are many possible worlds, it follows that necessarily, there are many possible worlds. Since necessarily P implies P, it follows that there are (literally!) many possible worlds. But the whole point of modal fictionalism was to deny (or at least avoid asserting) that there were many possible worlds. So modal fictionalism, at least of the variety described, is self-refuting.