With Maurizio Dardano he has written a reference grammar of the Italian language.[2] With Luca Serianni he has edited the Storia della lingua italiana in three volumes (1993-1994), with contributions by fifty scholars.[3]
His research activity embraces various fields, ranging from the analysis of grammatical structures of contemporary Italian to the history of literary and popular language, mainly with reference to the relationship between linguistic change and social life.
He also carried out studies on the following topics:
- plurilingualism of 16th century (I cantici di Fidenzio, 1981);
- language of politics (Dizionario politico popolare, 1981);
- Roman dialect and regional varieties of Italian (Roma e il Lazio, 1992; Storia linguistica di Roma, 2008; Città italiane, storie di lingue e culture, 2015);
- language of theatre (L'italiano a teatro, 2000; La lingua del teatro, 2015, first part);
- Italian language of the Renaissance (Rinascimento dal basso, 2006);
- Italian linguistic identity (Lingua e identità, 2006 new edition 2009);
- Italian "irregular" language from Dante until today (Malalingua, 2007);
- linguistic impact of national factionalism (Storia linguistica dell'Italia disunita, 2010);
- diffusion of the common Italian language (Pocoinchiostro. Storia dell'italiano comune, 2017).