This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Linguistics. Please check back later for the full article.
Middle English is the name given to the English of the period from approximately 1100 to approximately 1450. This period is marked by substantial developments in all areas of English grammar. It is also the period of English when different dialects are the most fully attested in the texts. At the beginning of the Middle English period, the sociolinguistic status of English was low due to the Norman Invasion, and although religious texts of Old English composition continued to be copied and updated, few original compositions are extant. By the end of the period, English had regained its status as the language of government, law, and literature generally.
Although some notable changes to the phonemic inventory of consonants date from the Middle English period, the most dramatic phonological developments of the period involve vowels. The reduction of the vowels of unstressed syllables, one of the changes that marks the beginning of the Middle English period, is a phonological change with substantial morphological effects, as it substantially reduced the number of distinctive inflectional forms. Constituent order replaced case marking as the primary means of signaling grammatical relations. By the end of the Middle English period, subject-verb-object order had become established as the norm.
The lexicon of English was transformed in this period by an enormous influx of French words. The role of derivational morphology declined as its functions were to some extent replaced by the adoption of French words. Most Scandinavian loans in English first appear in the texts of this period. The Scandinavian loans are typically everyday words, while the words adopted from French are more often in areas of government, law, and higher culture, reflecting the nature of the contact between English speakers and the speakers of these languages.
The density of the Scandinavian population in the northern part of England is generally held to be responsible for the earlier appearance of changes in the north than in the south. The replacement of the third person plural personal pronoun hie by the Scandinavian they is an example of a development which is apparent only in the north early in Middle English but became general in English by the end of this period.
An important phonological development of later Middle English is the beginning of the Great Vowel Shift, which affected long vowels and involved successive changes and was implemented differently in different dialects, the north-south divide being the most evident.
Early Middle English is a language that cannot be understood by Modern English readers without special study, while the language of the late Middle English period, especially that coming from the London area, can be understood with the heavy use of explanatory notes.