David Lewis

Lewis is the principal twentieth-century philosophical advocate of modal realism — the doctrine that all possible worlds are concrete and real. This is the philosophical-metaphysical analogue of physical-cosmological multiverse theories.

"I believe, and so do you, that things could have been different in countless ways. But what does this mean? I suggest it means that there are many ways things could have been besides the way they actually are." (On the Plurality of Worlds)

Lewis is, with Kripke, the principal twentieth-century systematic analytic metaphysician; the contemporary methodology of analytic metaphysics is largely shaped by his work.

"Humean supervenience is the doctrine that all there is to the world is a vast mosaic of local matters of particular fact." (Papers in Metaphysics and Epistemology, Introduction)

Lewis's programme of Humean supervenience and his reduction of modal and dispositional claims to non-modal natural facts is a thoroughly naturalistic metaphysics.

"There is no need to postulate any necessary connections in nature beyond the supervenient pattern of local qualities." (Humean Supervenience programme)

Lewis's realism about possible worlds, properties (as classes), and mathematical structures places him in a broadly Platonist register about abstract objects, even where he reinterprets them set-theoretically.

"Possible worlds are not abstract entities; they are concrete particulars, like our own world." (Plurality of Worlds, distinguishing his from abstractionist accounts)

Lewis defended a B-theoretic eternalism about time and a four-dimensionalist account of persistence; the past and the future exist on a par with the present.

"Persistence through time is the having of different temporal parts at different times." (Papers in Metaphysics)