The grammarians of antiquity, unlike some of their modern counterparts, seem to have had little interest in investigating ‘what every speaker knows’, at least as a largescale project, consciously articulated and embarked on. The object of such a project would be to determine what constitutes such knowledge—or mastery, or cognition, or whatever name it is given—in actual speakers. An alternative goal would be an account of something knowledge of which would count as knowledge of the language in question, even if this is not what actual speakers know. No ancient author seems to have set himself either task; indeed, the whole question of what it is to know a language seems to have been raised only very occasionally in classical antiquity. (Protagoras’ allusion to a ‘teacher of Greek’ in Plato's dialogue (327e2–328a1) is probably the best known of these rare discussions.) Kaimio is surely justified in making the still more sweeping observation that ‘The concept of language knowledge was rather vague amongst ancient peoples’ (1979: 316).