African-American vernacular English, the distinct language used by many black Americans, is thriving and shifting further from white American speech.
There is still debate over whether it was originally similar to white American English or creole. But Guy Bailey, of the University of Texas at San Antonio, said that grammar patterns in speech are innovations of this century to reduce grammatical ambiguity.
Professor Bailey has analysed speech patterns from early recordings of African-Americans. He found that in speech from before 1921, 21 per cent of verbs used were ambiguous. Their form could not be classified. But for people born between 1921 and 1945 this reduced to 18 per cent and for those born after 1970 just 14 per cent.