Compositionality, Understanding, and Proofs forthcoming in Mind

The principle of semantic compositionality, as Jerry Fodor and Ernie Lep-ore have emphasised, imposes constraints on theories of meaning that are hard to meet by psychological or epistemic accounts. Here I argue that this general tendency is exemplified in Michael Dummett’s account of meaning. On that account, the so-called manifestability requirement has the effect that the speaker who understands a sentence s must be able to tell whether or not s satisfies central semantic conditions. This requirement is not met by truth conditional accounts of meaning. On Dummett’s view, it is met by a proof conditional account: understanding amounts to knowledge of what counts as a proof of a sentence. A speaker is supposed always to be capable of de-ciding whether or not a given object is a proof of a given sentence she un-derstands. This requirement comes into conflict with compositionality. If meaning is compositionally determined, then all you need for understand-ing a sentence is what you get from combining your understanding of th