This thesis has as its central aim to explain, discuss, and defend a particular theory of possible worlds - modal realism. This aim is approached in a number of stages. In Part One I start by introducing the notion of possible worlds, placing it in an historical context (from Leibniz to the present day), and looking briefly at its usefulness for philosophy. Secondly, I review the main rival approaches to possible-worlds metaphysics, including modal and non-modal actualism, deflationism, and realism. Thirdly, I look briefly at an alternative to possible worlds put forward by writers such as Humberstone and Edgington - possible situations.
In the first two chapters in Part Two I deal with the questions of trans-world identity and of impossibilia. These questions have implications for virtually all possible-worlds theorists. I then go on to examine the most important arguments against modal realism, attempting to defend against them or, where this is not possible, to suggest amendments of Lewis s current version of his theory.
I conclude by finding modal realism to be the best available possible-worlds theory, able to withstand most of the main attacks upon it, and to evade the remainder by means of relatively minor alterations. Nevertheless, I cannot deny or overcome the genuine worries that lie behind what Lewis has called 'the Incredulous Stare', and I end by suggesting that those who feel this incredulity should perhaps react by searching for an alternative, not merely to modal realism, but to the very use of the notion of possible worlds.
( to the first page, or to the page about me.)