David Lewis is probably best known among philosophers for making grand metaphysics and systematic theory building fashionable again.
Lewis made numerous and significant contributions to the philosophical world. One of his first major works was a revision of his doctoral thesis, which was published as Convention: A Philosophical Study. This work opened up new territory in the philosophy of language.
Lewis is probably best known for his work in the metaphysics of modality (possibility and necessity). His work in this area began with the classic 1973 Counterfactuals and reached its culmination in the highly controversial On The Plurality Of Worlds (1986). At its heart, this book addressed the key question of the metaphysical grounding of possibility (that which could be, but need not be) and necessity (that which must be). Unlike previous philosophers, Lewis was not content to explicate possibility and necessity in terms of mere concepts. He argued for the existence of possible worlds, as real as our own world (the actual world), which serve to ground claims about possibility and necessity. For example, if it is true that JFK might not have been assassinated, then there is some possible world in which he made it safely out of Dallas and went on to finish his term. Of course, the JFK in that world is not the same JFK who died in our world – they are counterparts of each other. Unlike in some science fiction tales, we cannot journey to other possible worlds – they are isolated from each other in all ways but one: according to Lewis, we have doxastic accessibility to these worlds (put roughly, we can know about them).
Not surprisingly, this extravagant metaphysics led to many incredulous stares which were followed by a raft of objections and interpretations. This acceptance of possible worlds as real entities, known as ‘modal realism’ or more aptly ‘possible worlds realism’, was found to have great philosophic power and was soon applied to semantics, linguistics, economics, game theory, and many other areas.
Regardless of what one thinks of possible worlds, most philosophers credit Lewis with helping to make metaphysics, especially systematic metaphysics, respectable again. Through his many works, he is taken to have produced a unified thesis, which has been dubbed ‘Humean supervenience’. On this view the world is a vast mosaic of tiny facts and, at any moment in time, what it is and what can be said about it supervenes (depends) on the patterns of these facts. The typical analogy is that the facts are like the dots in a newsprint picture or a pointillist painting. On this view, no specific event at a specific point determines events at other points. Rather it is the totality of occurrences that sets everything else. Lewis noted that the problem of chance could short-circuit the thesis, but was unable to complete his solution to the problem.
Lewis’ works were skillfully written and often included humorous content (his famous article on mad pain and Martian pain included a Martian who reacted to injury by inflating bladders in his feet) as well as references to science fiction (he lists Larry Niven among the works cited in On the Plurality of Worlds).
Personally, Lewis was best known for his modesty, generosity and a general inability to engage in small talk. Though he bore a more than passing resemblance to Kris Kringle, he was graced with the nickname ‘Machine in the Ghost’.
Lewis formed ties with Australian philosophers Jack Smart and David Armstrong (best known for his theory of immanent universals) and became quite a fan of Australian football. Though reports on his singing voice vary, he is said to have been a very enthusiastic singer of Australian folk ballads.
Lewis’ favourite hobby was his model train set. His basement, which he expanded, featured a rather impressive railway layout (developed, some say, with the same systemic methodology he used in philosophy).
On the Plurality of Worlds, David Lewis (Blackwell)
Counterfactuals, David Lewis (Blackwell)
Reality and Humean Supervenience: Essays on the Philosophy of David Lewis, eds. Gerhard Preyer and Frank Siebelt (Rowman & Littlefield)