What is a vernacular grammar?

To many people nowadays the word ‘vernacular’ means ‘colloquial’ or ‘informal’, smacking of street usage, graffiti, perhaps obscenity – certainly not the sort of thing you'd expect to find in a grammar. ‘Vernacular’ contrasts with ‘formal’, one's linguistic Sunday best; in contemporary English, the distinction is more a matter of register than anything else. In medieval Europe the situation was more complex. The Italian poet Dante described the vernacular in 1304 as the language which we pick up from those around us without any rules. In the Italy of Dante's day, some dialect of Italian would have been the local vernacular; across the Alps, in Germany, some form of Middle High or Low German would have fulfilled that role, while in France Old French and Occitan, and in England Middle English and Anglo-Norman French were the most widespread vernaculars. Although little by little all these languages were coming to be used in writing, they were still far from offering serious competition to Latin. Latin maintained its status as the language of serious written scholarship and of international communication to the end of the Middle Ages and well beyond. Latin, Greek and Hebrew were regarded as qualitatively very different from any vernacular; as Dante puts it, ‘We also have a secondary form of speech called grammar by the Romans … Few people succeed in mastering it, for we learn its rules and doctrine only by devoting much time and effort to it.’