Is anyone aware of research that indicates that the centering diphthongs in English are actually sets of monophthongs?
If so I would be interested in reading some sources and be greatly appreciative for any advice where to look.
Linguistics Stack Exchange is a question and answer site for professional linguists and others with an interest in linguistic research and theory. It only takes a minute to sign up.Sign up to join this community
Centering diphthongs are not a "myth" per se: they really exist/existed in some English accents. These accents are not universal, obviously: they are/were only used by certain groups of speakers in certain historical periods. It's true that many modern British English speakers use monophthongs, not centering diphthongs, in words like care, beer, pure. You can find a description of this in Geoff Lindsey's blog post The British English vowel system, which tries to describe the phonetic differences between what he calls "Standard Southern British" and Received Pronunciation as transcribed by Gimson. In that post, he transcribes the vowel of square as /ɛː/, the vowel of near as /ɪː/ or disyllabic /ɪjə/ = FLEECE followed by COMMA, and the vowel of pure as /ɵː/, /oː/, or disyllabic /ʉwə/ = GOOSE followed by COMMA.
You may be aware of this already, but the use of e.g. /eə/ to transcribe the SQUARE phoneme does not necessarily mean that the transcriber intends to indicate a phonetically diphthongal pronunciation. For example, John Wells used /eə/ in his transcriptions for the Longman Pronunciation Dictionary but he has a blog post explaining that this is meant to cover monophthongal pronunciations as well.