Distinction highlighted by Chomsky, between the knowledge that we have of the language we speak, and the actual use we make of that knowledge. Competence might be modelled as the system of grammatical and semantical rules that identify a language, and in some sense guide the speaker who knows the language, whereas performance is the widely variable and idiosyncratic use an individual may then make of that system. The distinction is similar to that drawn by Saussure between langue and parole. The notion of competence is sometimes extended to cover implicit knowledge of other conventional but rule-governed matters, such as the forms of fiction or poetry.