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Thinkers

David Lewis

Analytic · North America · 1941 to 2001

American philosopher who argued that every possible world is real, as real as our own.

What it is

David Lewis (1941 to 2001) was an American philosopher, born in Oberlin, Ohio. He taught at the University of California, Los Angeles from 1966 and at Princeton from 1970 until his death. He wrote on language, logic, mind and metaphysics, and is best known for the claim that every possible world is real.

He studied at Swarthmore College, spent a year at Oxford where Iris Murdoch tutored him, and did his doctorate at Harvard under W. V. O. Quine.

The main ideas

  • Convention. In his first book he argued that social conventions, such as driving on one side of the road, are solutions to co-ordination problems, a kind of problem in which the people involved are not in conflict but need to act in a matching way.
  • Counterfactuals. A statement of the form "if this had been so, that would have followed" is true when it holds in the possible worlds most like ours in which the first part is true. Everything turns on how similar worlds are to ours.
  • Modal realism. Possible worlds are real and concrete, not stories or convenient fictions. Something is possible if it is true at one of them, and our world is one among many equally real.
  • Counterparts. He developed counterpart theory, a way of thinking about what could have been true of an individual, which he used to deal with several puzzles about modal properties.
  • Humean supervenience. He held that reality is a spread of small local facts through space and time, and tried to fit laws, chances and causes into that picture.

What it looks like in practice

Imagine someone who misses a train by a minute and wonders whether, had they left earlier, they would have caught it. Lewis would say the answer depends on which worlds are closest to this one: those where only the departure time changes. This is an illustration of his method, not a passage from his writing.

Books and moments

  • Convention (1969) came out of his doctoral work at Harvard.
  • Counterfactuals (1973) gave his account of what such statements mean.
  • On the Plurality of Worlds (1986) is the book in which he defended modal realism.

Questions and criticism

  • Knowing other worlds. The other worlds are cut off from ours, so it is unclear how anyone could know what goes on in them.
  • Too many things. It is argued that counting every world as real adds an enormous number of things to what exists.
  • Paradox. It has been argued that the view leads to paradox or undermines everyday practice, and Lewis replied to such objections.

Close neighbours

The pages on W. V. O. Quine, his teacher, and on Saul Kripke are the natural next reads.

Written by epchē in our own words, and checked against independent sources on 29 October 2026. The sources are listed below.

Who they connect to

Influenced by

  • W. V. O. Quine · He studied under Quine and began from his clear, exact way of arguing.

Other Analytic thinkers

Sources we used

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