Abstract: According to Lewis's original account, the laws of nature in a given possible world are the principles of the best scientific theory of that world, where ‘best’ denotes an optimal combination of strength and simplicity. This serves to provide content to a notion of physical necessity, but needed to be qualified with a restriction of such possible descriptions to languages whose predicates have a special status (in the simplest case, that of standing for ‘natural’ classes of entities in that world). Lewis provides an anti-nominalist metaphysics, while staying as close as possible to the nominalist preferences that had characterized e.g. Quine's philosophical work. This Chapter argues that his account is at best deceptively successful, and solves the problem of inference at the cost of an inability to address the problem of identification.

Keywords: anti-nominalism, David Lewis, metaphysics, necessity, nominalism, possible world, scientific theory, simplicity,