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David Lewis (1941-2001)

by Chris Bloor

David Kellogg Lewis died on October 14th as a result of complications arising from diabetes. He was 60. Although he was primarily as a logician, his work encompassed a wide range of philosophical issues, including language, ethics, mathematics, and the philosophy of mind.

Lewis was born in Ohio and educated at Swarthmore College, in Pennsylvania. Like Daniel Dennett, he was an American scientist who was converted to philosophy by encountering Gilbert Ryle at Oxford. Lewis spent a term there and came away fascinated by the problem of explaining our conception of the mind and its relation to brain functions. After obtaining his doctorate from Harvard in 1967, Lewis taught at UCLA in California. His thesis was published as Convention: A Philosophical Study. In 1970 he joined Princeton and became a full professor in 1973.

Counterfactuals, published in the same year, concerns the truth in contrary-to-fact conditionals. (An example might be: “if Al Gore had won the last American election, the situation would be handled very differently.”) Lewis dealt with these statements by considering the ‘possible worlds’ in which the first half of the conditional was true. This led him to develop a theory of alternative realities called ‘modal realism’, which he later explored in his 1986 book On The Plurality of Worlds. The theory says that the world in which we exist is but one of many, and that “we who inhabit this world are only a few out of all the inhabitants of all the worlds.” What Lewis meant by ‘possible’, and how far we are to imagine the existence of alternate worlds, continues to be debated. Lewis himself was less interested in the scientific issues involved than he was in the leverage it gave him to attack philosophical problems. These included personal identity and which circumstances or events can be classed as possible, contingent, or impossible.

With respect to questions about the mind, Lewis was a functionalist. His particular variety is directed at the specific circumstances surrounding an experience designated by a term such as ‘pain’. Such words, he argued, do not hold a specific meaning which is directly attributable in all similar physical circumstances. He wrote, “It is a contingent matter what state the concept and the word apply to. It depends on what causes what. The same goes for the rest of our concepts and ordinary names of mental states.” In his influential article ‘Mad Pain and Martian Pain’ he suggested examples to show that whether we call something pain depends on our understanding of the specific situation in which it is experienced; the examples include a mad mathematician who uses pain to focus and clarify his thoughts on logic; while ‘Martian pain’ is experienced by organisms so different from our own that we are forced to admit it is not physical.

Lewis also wrote on set theory in mathematics, induction, causation, time travel, the prisoners’ dilemma, universals, and nuclear deterrence.

In the Philosophical Papers he noted that his thinking had led him towards what he called ‘Humean supervenience’, which he described as “the doctrine that all there is to the world is a vast mosaic of matters of particular fact.” We tend to assume that individual events cause other specific events, but Lewis suggests that the world which exists and is comprehended depends on the pattern revealed by the totality of these facts.

Before his death he had turned to the subject of how personal identity is affected by our existing in multiple possible worlds, and the extent to which this might be called immortality.

© Chris Bloor 2001

Chris Bloor is Director of Development of the Oxford Philosophy Trust, which promotes philosophy in areas outside academia. He runs a pub philosophy group, ‘The Bloomsbury Set’.

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