Online Papers - Brian Weatherson

David Lewis
David Lewis (1941–2001) was one of the most important philosophers
of the 20th Century. He made significant contributions to philosophy
of language, philosophy of mathematics, philosophy of science, decision
theory, epistemology, meta-ethics and aesthetics. In most of these fields
he is essential reading; in many of them he is among the most important
figures of recent decades. And this list leaves out his two most significant
contributions.
In philosophy of mind, Lewis developed and defended at length a new
version of materialism (see the entry on physicalism). He started by
showing how the motivations driving the identity theory of mind and
functionalism could be reconciled in his theory of mind. He called
this an identity theory, though his theory motivated the position now
known as analytic functionalism. And he developed detailed accounts
of mental content (building on Davidson’s interpretationism) and phenomenal
knowledge (building on Nemirow’s ability hypothesis) that are
consistent with his materialism. The synthesis Lewis ended up with is
one of the central positions in contemporary debates in philosophy of
mind.
But his largest contributions were in metaphysics. One branch of his
metaphysics was his Hume-inspired reductionism about the nomological.
He developed a position he called “Humean supervenience”, the theory
that said that there was nothing to reality except the spatio-temporal
distribution of local natural properties. And he did this by showing in
detail how laws, chances, counterfactual dependence, causation, dispositions
and colours could be located within this Humean mosaic. The
other branch of his metaphysics was his modal realism. Lewis held that
the best theory of modality posited concrete possible worlds. A proposition
is possible iff it is true at one of these worlds. Lewis defended this
view in his most significant book, On the Plurality of Worlds. Alongside
this, Lewis developed a new account of how to think about modal properties
of individuals, namely counterpart theory, and showed how this
theory resolved several long-standing puzzles about modal properties.
† Penultimate draft only. Please cite published version if possible. Final version published in Stanford
Encyclopaedia of Philosophy. I’ve learned a lot over the years from talking about Lewis’s philosophy with
Wolfgang Schwarz. I trust his book (2009) is excellent on all these topics, but unfortunately it’s only out in
German so far, which I don’t read. But a lot of important points are collected on his blog, which is listed
under other internet resources. The best book in English on Lewis is Daniel Nolan’s David Lewis (2005).
Without that book, section 7.5 of this entry wouldn’t exist, section 6.3 would be unintelligible, and every
section would be worse. Much of the biographical information in the introduction is taken from Hájek
(2010). Many people helpfully spotted typos and infelicities of expression in earlier versions of this entry.
Thanks especially to Zachary Miller for many suggested improvements and revisions. The bibliography is
based in large part on a bibliography provided to me by Stephanie Lewis.