David Balcarras

This article investigates David Lewis's influential account of the implicit definition of theoretical terms, especially his curious, often overlooked use of non-classical logic. It is explained why Lewis opted for the positive free logic of descriptions FD2, which implausibly renders all identities between empty terms true. And it is argued that Lewis's account is best implemented in the weaker free logic of descriptions MFD, with classical second-order logic as an alternative. The philosophical core of Lewis's account is also clarified and motivated, including the controversial view that true term-introducing theories are uniquely realized.

In this article, I argue that if tacit knowledge of grammar is analyzable in functional‐computational terms, then it cannot ground linguistic meaning, structure, or sound. If to know or cognize a grammar is to be in a certain computational state playing a certain functional role, there can be no unique grammar cognized. Satisfying the functional conditions for cognizing a grammar G entails satisfying those for cognizing many grammars disagreeing with G about expressions' semantic, phonetic, and syntactic values. This threatens the Chomskyan view that expressions have such values for speakers because they cognize grammars assigning them those values. For if this is true, semantics, syntax, and phonology must be indeterminate, thanks to the indeterminacy of grammar‐cognizing (qua functional‐computational state). So, the fact that a speaker cognizes a grammar cannot explain the determinate character of their language.