This chapter explores how to establish a chronology of the development of Latin into the Romance languages using the methodology of historical sociolinguistics, whilst at the same time attempting to model this change in a historically informed way. Certain features of synchronic sociolinguistics can be identified which have a direct bearing on diachronic studies. Indeed, at the beginning of the fifth century, Latin presents a communicative continuum which is not very different from what one would find in other sociolinguistic contexts, ancient and modern. St. Augustine was a Roman from Africa who displayed great learning and prodigious linguistic gifts, but he was unafraid to exploit language, including clashes of register and asperities of style. The chapter also discusses the development of the relationship between writing and speech from late spoken Latin to proto-French, linking the various stages to the stages proposed for the development of speech and communication.