This paper has three objectives. The first is to show how David Lewis' influential account of how a population is related to its language requires that speakers be 'conceptually autonomous' in a way that is incompatible with content ascriptions following from the assumption that its speakers share a language. The second objective is to sketch an alternate account of the psychological and sociological facts that relate a population to its language. The third is to suggest a modification of Lewis' account of convention that will allow one to preserve the claim that there are conventions of language.