We take the view expressed in Labov (1973) that "the competence of the native speaker reaches far beyond the dialect he uses himself'. Adult speakers of a certain language variety are capable of understanding and, to a lesser extent, imitating the utterances of speakers of varieties (flects) other than their own. We also subscribe to a variationist approach to language study. Any definitive grammar, or part thereof, must take cognizance of variation as a salient feature of language, but to date scarcely any grammar of any language has systematically done so. There are many grammars of contemporary English, for instance, but even the most detailed and comprehensive of them cannot claim to account for the variability attested in English, even if definition of the language is so limited as to subsume only varieties used in the UK and USA.