According to David Lewis, it is a ‘platitude – something only a philosopher would dream of denying’ – that language is governed by conventions (1983, 166). Noam Chomsky, Donald Davidson, and their followers beg to differ. In recent years, they have fervently attacked the idea that rules, conventions, or a common language have a useful role to play in an account of language.

Although the question has been discussed mostly by reference to Chomsky and Davidson, it has wider implications. For it epitomizes several fundamental controversies in contemporary philosophy of language and beyond.

The first is the conflict between naturalists and normativists. Naturalists believe that there is no genuine knowledge outside natural science (epistemological naturalism), and that the phenomena studied by natural science (roughly, matter, energy, spatiotemporal objects and events) exhaust what there is. Against this position, philosophers since Kant have objected that logic, knowledge and language depend on norms that cannot be captured by the factual descriptions and causal explanations of the natural sciences.

The second is the conflict between individualistic and communitarian perspectives on language. According to individualists, the fundamental linguistic phenomenon is the idiolect, the language of an individual. According to communitarians, the fundamental phenomenon is that of a shared public language. They treat language as a social practice or a kind of institution which is more than the sum of individual speakers or idiolects.

Finally, this debate has repercussions beyond philosophy, notably for our understanding of culture and society. Individualism is hospitable to the idea of an extremely multifaceted and fragmented society. We not only hold diverse beliefs and values, we need not even share a common language. Communitarians, by contrast, insist that we must share at least a linguistic medium in which to express our conflicting viewpoints. And because they treat language as an intersubjective practice, they can acknowledge and deplore phenomena such as ‘language death’, the increasingly common disappearance of natural languages such as Cornish. According to individualists, on the other hand, so-called language death is merely a quantitative shift in patterns of verbal behaviour, no more significant than, for example, the death of an individual speaker (see Glock 2004a).