Place-names and a few runic inscriptions indicate that dialectal varieties of English existed before the 8th cent. Such variation presumably owed much to the differing sources of the Anglo-Saxon settlers, but equally must have been encouraged by the emergence of political and economic groupings within Britain itself. The fuller records of the 8th and 9th cents. show the existence of four major dialects (Northumbrian, Mercian, West Saxon, and Kentish) though our knowledge of them is largely limited to the practices of certain scriptoria. By the later 10th cent. a form based on West Saxon had acquired the status of a standard written language, used alike by scribes at such centres as Winchester, Canterbury, and York, whose own spoken forms differed widely from each other. The adoption of this standard reflected the political and ecclesiastical power of Wessex and the early literary exploitation of the West Saxon dialect by Alfred.
After the Norman Conquest the grip of this standard written language was broken by the new social order and for the next four centuries all English dialects seem to have had similar status. Increasingly, however, in the 14th cent. writers show themselves sensitive to the fact that language variety was an obstacle to widespread understanding and transmission of their work; Chaucer's envoi to Troilus and Criseyde provides one well-known expression of such concerns. But already within Chaucer's period a new written standard was emerging which was based upon the language of London, itself now dominated by the dialectal preferences of the southern and eastern midlands where lay much of the country's wealth. The introduction of printing at the end of the 15th cent. helped further to standardize and spread the use of this form. It was one variety of the language of London also which, from the 15th cent. onwards, acquired the status of a standard spoken language. In this case it was essentially the language of the court but, until the 19th cent., its acquisition depended largely on familiarity with certain circles in the capital; thereafter, through the influence of the public schools, reformed universities, and finally the British Broadcasting Corporation, it was widely diffused on a basis which was purely social and non-localized. See also English language.
Richard N. Bailey
"dialects." The Oxford Companion to British History. . Encyclopedia.com. (February 16, 2019). https://www.encyclopedia.com/history/encyclopedias-almanacs-transcripts-and-maps/dialects
"dialects." The Oxford Companion to British History. . Retrieved February 16, 2019 from Encyclopedia.com: https://www.encyclopedia.com/history/encyclopedias-almanacs-transcripts-and-maps/dialects