Abstract
Dummett's formulation presupposes a realistic attitude towards modality. And as also remarked, realism in this sense has not gone unchallenged. This chapter discusses a different form the realism it opposes may assume which entails, but goes appreciably beyond, the comparatively modest variety just sketched, and which has been the focus of much recent discussion: realism about possible worlds. It begins by drawing some distinctions among different notions of necessity and possibility. Probably the single most important distinction to be drawn is between absolute and relative kinds or senses. In an early defense of realism, David Lewis gives some prominence to an argument which represents the central thesis of his realism. Lewis is chary of saying outright whether worlds themselves are concrete entities, pending clarification of the abstract/concrete distinction. Lewis's own discussion of the charge that his position is epistemologically bankrupt largely in presupposing that it will be based upon a causal constraint on knowledge.