Diphthongs versus monophthongs in English

We present evidence for the analysis of the vowels in English and as biphonemic diphthongs /ɛi/ and /əu/, based on neutralization patterns, regular alternations, and foot structure. /ɛi/ and /əu/ are hence structurally on a par with the so called “true diphthongs” /ɑi/, /ɐu/, /ɔi/, but also share prosodic organization with the monophthongs /i/ and /u/. The phonological evidence is supported by dynamic measurements based on the American English TIMIT database. Calculations of F2-slopes proved to be especially suited to distinguish the relevant groups in accordance with their phonologically motivated prosodic organizations.