Review of possible worlds [Book Review]

This book is a survey, fortified by original material, of metaphysical theories of modality set in terms of possible worlds. Those theories include what Divers calls “genuine realism”, or “GR” — this is David Lewis’s “genuine modal realism” — and what Divers calls “actualist realism”, or “AR” — this seems to be the same as what Lewis called “ersatz modal realism”, which has also become widely know as “ersatzism”. Two important kinds of theory are not included: those that treat modality by means not involving possible worlds at all (for example, modalism, various kind of non-cognitivism, and Quinean eliminativism about modality); and those that, while treating modality by talking about possible worlds, go on to deny that there are any possible worlds in one way or another (for example, Rosen’s fictionalism, and Divers’ own agnosticism about possible worlds). These get a short discussion towards the end of the introductory part of the book (sections 2.4–2.6), and Divers is planning to write a companion volume covering them.