From The Art and Popular Culture Encyclopedia
Vulgar Latin (in Latin, sermo vulgaris, "common speech") is a blanket term covering the vernacular dialects and sociolects of the Latin language until those dialects, diverging still further, evolved into the early Romance languages — a distinction usually made around the ninth century. It includes late Latin and the terms are often used synonymously. However, Vulgar Latin is also used to refer to vernacular speech from other time periods including the Classical period.
This spoken Latin came to differ from Classical Latin in its pronunciation, vocabulary, and grammar.
What was Vulgar Latin?
The name "vulgar" simply means "common"; it is derived from the Latin word vulgaris, meaning "common", or "of the people".
Vulgar Latin led to vernacular literature
The Italian poet Dante Alighieri, in his De vulgari eloquentia, was possibly the first European writer to argue cogently for the promotion of literature in the vernacular. Important early vernacular works include Dante's Divine Comedy, Giovanni Boccaccio's Decameron (both written in Italian) and Geoffrey Chaucer's Canterbury Tales (written in English). Indeed Dante's work actually created in part the Italian language.
Medieval vernacular literature
One of the features of the renaissance which marked the end of the medieval period is the rise in the use of the vernacular or the language of the common people for literature (as opposed to Latin). The compositions in these local languages were often about the legends and history of the areas in which they were written which gave the people some form of national identity. Epic poems, sagas, chansons de geste and acritic songs (songs of heroic deeds) were often about the great men, real or imagined, and their achievements like Arthur, Charlemagne and El Cid.
The earliest recorded European vernacular literature is that written in the Irish language. Given that Ireland had escaped absorption into the Roman empire, this had time to develop into a highly sophisticated literature with well-documented formal rules and highly organised Bardic schools. The result was a large body of prose and verse recording the ancient myths and sagas of the Gaelic-speaking people of the island, as well as poems on religious, political and geographical themes and a body of nature poetry.
The formality which Latin had gained through its long written history was often not present in the vernaculars which began producing poetry, and so new techniques and structures emerged, often derived from oral literature. This is particularly noticeable in the Germanic languages, which, unlike the Romance languages, are not direct descendants from Latin. Alliterative verse, where many of the stressed words in each line start with the same sound, was often used in the local poetry of that time. Other features of vernacular poetry of this time include kennings, internal rhyme, and slant rhyme. Indeed Latin poetry traditionally used meter rather than rhyme and only began to adopt rhyme after being influenced by these new poems.