Monophthong
In the English language, there are in practice relatively few monophthongs. The position, beginnings, and endings of vowel articulation are perhaps the chief distinguishing feature among the various dialects of English; the deep gulf between British English and American English is a result of the different realization of vowel sounds. The conversion of monophthongs to diphthongs, or of diphthongs to monophthongs, is a major cause of language change. Some sounds that are (arguably) perceived as monophthongs in both these varieties of English are in fact diphthongs, such as the vowel sound in pay — IPA{
Historically, some languages treat vowel sounds that were formerly diphthongs as monophthongs. Such is the case in Sanskrit, in whose grammar the sounds now realised as and are conceptually ai and au, and are written that way in the Devanagari and related alphabets. The sounds and exist in Sanskrit, but are written as if they were āi and āu, with long initial vowels. Similar processes of the creation of new monophthongs from old diphthongs are preserved in the traditional spellings of languages as diverse as French and modern Greek.
See also