The Middle English creole hypothesis is the concept that the English language is a creole, i.e. a language that developed from a pidgin. The vast differences between Old and Middle English have led some historical linguists to claim that the language underwent creolisation at around the 11th-century, during the Norman Conquest. The theory was first proposed in 1977 by C. Bailey and K. Maroldt and has since found both supporters and detractors in the academic world. Different versions of the hypothesis refer to creolisation through contact between Old English and Norman French, between Old English and Old Norse, or even interaction between Common Brittonic and English, though evidence supporting any influence of the Celtic languages on English is scant.
The argument in favour of calling Middle English a creole comes from the extreme reduction in inflected forms from Old English to Middle English. The system of declension of nouns was radically simplified and analogized. The verb system also lost many old patterns of conjugation. Many strong verbs were reanalysed as weak verbs. The subjunctive mood became much less distinct. Syntax was also simplified somewhat, with word order patterns becoming more rigid. These grammatical simplifications resemble those observed in pidgins, creoles and other contact languages, which arise when speakers of different languages need to communicate. Such contact languages usually lack the inflections of either parent language, or drastically simplify them. However, many say that English is probably not a creole because it retains a high number (283) of irregular verbs, just like other Germanic languages, a linguistic trait that is usually first to disappear among creoles and pidgins. It is certain that Old English underwent grammatical changes, e.g. the collapse of all cases into genitive and common. However, the reduction of unstressed vowels to schwa, due to a fixed stress location, contributed to this process, a pattern that is common to many Germanic languages.
During the Old English period, large numbers of Vikings settled in England. The immigrants were mainly Danish in Yorkshire and the East Midlands, and Norwegian in Cumbria and Lancashire. English borrowed many words from their language, Old Norse, including "give," "take," "egg," "skill," "muck," "get," "bait," and "scowl." It is likely that contact with Old Norse sped up the process by which English went from a highly inflected language with a free word order to a more analytic one. Unlike the later Normans, the Danish and Norwegian invaders left a substantial legacy on English toponymy, in place names including features such as "-by" (Derby, Grimsby), "-thorpe" (Scunthorpe), "-thwaite" (Satterthwaite), and "-toft" (Lowestoft).
English has numerous French and Norman loanwords, which came into use gradually over the course of the Middle English period. English began to retake its position from French as England's official national language by 1362 when, under Edward III, Parliament was addressed in English for the first time since the Norman Conquest of 1066. Later Middle English works such as Geoffrey Chaucer's Canterbury Tales include large amounts of French-derived vocabulary.
It has been speculated that French influence affected English pronunciation as well. Whereas Old English had the unvoiced fricative sounds [f], [s], [θ] (as in thin), and [ʃ] (shin), French influence helped to distinguish their voiced counterparts [v], [z], [ð] (the), and [ʒ] (mirage), and also contributed the diphthong [ɔj] (boy). The combination of a largely French-speaking aristocracy and a largely English-speaking peasantry gave rise to many pairs of words with a Latinate word in the higher register and a Germanic word in the lower register (e.g., French poultry vs Germanic chicken).