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A monophthong (Greek monóphthongos[1] from mónos "single" and phthóngos "sound") is a pure vowel sound, one whose articulation at both beginning and end is relatively fixed, and which does not glide up or down towards a new position of articulation. The monophthongs can be contrasted with diphthongs, where the vowel quality changes within the same syllable, and hiatus, where two vowels are next to each other in different syllables.

Sound changes[edit]

The conversion of monophthongs to diphthongs (diphthongization) or of diphthongs to monophthongs (monophthongization) is a major element of language change and is likely the cause of further changes.


Some English sounds that may be perceived by native speakers as single vowels are in fact diphthongs; the vowel sound in pay — pronounced /ˈpeɪ/ — is an example of this. Some dialects of English make monophthongs out of former diphthongs. For instance, Southern American English tends to alter the diphthong /aɪ/ as in eye to an [aː] somewhere between /ɑ/ and /æ/. On the other hand, former monophthongs have in some cases become diphthongs in Southern American English. For instance, the /ɪ/ in words like pin may change to [ɪə]. Many sets of words have switched between monophthongs and diphthongs in the historical development of English: for some significant examples, see Great Vowel Shift, and Phonological history of English vowels.


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 /e/ and /o/ are conceptually ai and au and are written that way in the Devanagari and related alphabets. The sounds /ai/ and /au/ 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.


Classical Arabic has two diphthongs, /ai/ and /au/. In the majority of modern Arabic dialects, these diphthongs are realised as the long vowels /e/ and /o/, respectively. One notable exception is the Lebanese dialect, which preserves the original pronunciations.

See also[edit]


  1. ^ μονόφθογγος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project