Noam Chomsky claims that we know the grammatical principles of our languages in pretty much the same sense that we know ordinary things about the world (e.g. facts), a view about linguistic knowledge that I term ''cognitivism''. In much recent philosophy of linguistics (including that sympathetic to Chomsky's general approach to language), cognitivism has been rejected in favour of an account of grammatical competence as some or other form of mental mechanism, describable at various levels of abstraction (''non-cognitivism''). I argue for cognitivism and against non-cognitivism. First, I show that the distinction between competence and performance in current linguistics is as clearly made as ever it was, in spite of recent interest in linguistic processing modules. Second, I use these facts about the practice of theoretical linguistics to refute various proposals for a non-cognitivist construal of grammatical competence, and to support cognitivism by reflecting on the inapplicability of a multi-level account of linguistic competence. Cognitivism is then defended against several objections centring around the problems of rational integration and conceptualization of grammatical knowledge. Finally, the conception of competence argued for in relation to linguistics is placed in the larger context of cognitive science research and its implications for philosophy of mind.