Soon after the publication of Gareth Evans’s classic one-page Analysis paper on vagueness in 1978, Lewis was struck by how many misunderstood what Evans was up to. He wrote several letters about this issue. His letter to Allen Hazen, 15 November 1978, led to Lewis’s contribution: ‘Vague identity: Evans misunderstood’, Analysis vol. 48 (1988). Briefly, Lewis thinks that Evans’s argument is an argument ultimately for a semanticist conception of vagueness. After his article was published, others chimed in.

In this letter, Lewis responds to David Over’s attempt to argue that Evans was putting forth a flawed argument. It seems that Over was also interested in showing in what ways non-classical logic can help the friend of vague objects.

Lewis explains that Evans’s indefinitely and definitely operator can be interdefined with operators in modal logic. He also explains that the indefinitely and definitely operator are to be interpreted as ‘it is indefinitely whether’ and ‘it is definitely whether’ respectively. Then Lewis outlines how Evans’s argument can be fixed by adding ‘definitely A’ to ‘A’ as opposed to ‘definitely A’ replacing ‘A’.

Lewis’s final point goes beyond his exegesis of Evans. It is actually a metaphilosophical point about the place of logic in philosophical debate. The upshot is that anyone can escape refutation. As a result, many debates end in stalemate. No one can convert their opponents. This is a recurring theme in Lewis’s letters that is implicit in his published writings. It makes philosophical debate more about identifying and agreeing on the costs and benefits of each theory and less about converting others. Stalemate or impasse is not bad in one sense. It just means our dialogue on what the costs and benefits of the relevant competing theories has ended.

View Fullscreen