Diphthong

In most varieties of English, the phrase "no highway cowboy" (/noʊ ˈhaɪweɪ ˈkaʊbɔɪ/ noh HY-way KOW-boy) has five distinct diphthongs, one in every syllable.

Diphthongs contrast with monophthongs, where the tongue or other speech organs do not move and the syllable contains only a single vowel sound.

Where two adjacent vowel sounds occur in different syllables (e.g. in the English word re-elect) the result is described as hiatus, not as a diphthong.

However, there are also unitary diphthongs, as in the English examples above, which are heard by listeners as single-vowel sounds (phonemes).

[6] The tie bar can be useful when it is not clear which symbol represents the syllable nucleus, or when they have equal weight.

The less prominent component in the diphthong may also be transcribed as an approximant, thus [aj] in eye and [ja] in yard.

There are many languages (such as Romanian) that contrast one or more rising diphthongs with similar sequences of a glide and a vowel in their phonetic inventory[10] (see semivowel for examples).

[12] These may have occurred in Old English: A centering diphthong is one that begins with a more peripheral vowel and ends with a more central one, such as [ɪə̯], [ɛə̯], and [ʊə̯] in Received Pronunciation or [iə̯] and [uə̯] in Irish.

Wide diphthongs are the opposite – they require a greater tongue movement, and their offsets are farther away from their starting points on the vowel chart.

[19] The English word yes, for example, consists of a palatal glide followed by a monophthong rather than a rising diphthong.

In addition, the segmental elements must be different in diphthongs [ii̯] and so when it occurs in a language, it does not contrast with [iː].

The Bunaq language of Timor, for example, distinguishes /sa͡i/ [saj] 'exit' from /sai/ [saʲi] 'be amused', /te͡i/ [tej] 'dance' from /tei/ [teʲi] 'stare at', and /po͡i/ [poj] 'choice' from /loi/ [loʷi] 'good'.

The dialect of Hamont (in Limburg) has five centring diphthongs and contrasts long and short forms of [ɛɪ̯], [œʏ̯], [ɔʊ̯], and [ɑʊ̯].

[32] In diminutives ending in /ki/ formed to monosyllabic nouns, the vowels /u, ɪə, ʊə, ɛ, ə, œ, ɔ, a, ɑː/ are realised as closing diphthongs [ui, ei, oi, ɛi, əi, œi, ɔi, ai, ɑːi].

In the same environment, the sequences /ɛn, ən, œn, ɔn, an/ are realized as [ɛiɲ, əiɲ, œiɲ, ɔiɲ, aiɲ], i.e. as closing diphthongs followed by palatal nasal.

[39] In standard Eastern Catalan, rising diphthongs (that is, those starting with [j] or [w]) are possible only in the following contexts:[40] There are also certain instances of compensatory diphthongization in the Majorcan dialect so that /ˈtroncs/ ('logs') (in addition to deleting the palatal plosive) develops a compensating palatal glide and surfaces as [ˈtrojns] (and contrasts with the unpluralized [ˈtronʲc]).

A [w] onglide after /k/ or /ɡ/ and before all vowels as in quando [ˈkwɐ̃du] ('when') or guarda [ˈɡwaɾðɐ ~ ˈɡwaʁdɐ] ('guard') may also form rising diphthongs and triphthongs.

Additionally, in casual speech, adjacent heterosyllabic vowels may combine into diphthongs and triphthongs or even sequences of them.

[47] In addition, phonetic diphthongs are formed in most Brazilian Portuguese dialects by the vocalization of /l/ in the syllable coda with words like sol [sɔw] ('sun') and sul [suw] ('south') as well as by yodization of vowels preceding /s/ or its allophone at syllable coda [ʃ ~ ɕ] in terms like arroz [aˈʁojs ~ ɐˈʁo(j)ɕ] ('rice'),[47] and /z/ (or [ʒ ~ ʑ]) in terms such as paz mundial [ˈpajz mũdʒiˈaw ~ ˈpa(j)ʑ mũdʑiˈaw] ('world peace') and dez anos [ˌdɛjˈz‿ɐ̃nu(j)s ~ ˌdɛjˈz‿ɐ̃nuɕ] ('ten years').

In general, unstressed /i e o u/ in hiatus can turn into glides in more rapid speech (e.g. biennale [bi̯enˈnaːle] 'biennial'; coalizione [ko̯alitˈtsi̯oːne] 'coalition') with the process occurring more readily in syllables further from stress.

[53] There are no perfect minimal pairs to contrast /o̯a/ and /wa/,[10] and because /o̯a/ does not appear in the final syllable of a prosodic word, there are no monosyllabic words with /o̯a/; exceptions might include voal ('veil') and trotuar ('sidewalk'), though Ioana Chițoran argues[54] that these are best treated as containing glide-vowel sequences rather than diphthongs.

In addition to these, the semivowels /j/ and /w/ can be combined (either before, after, or both) with most vowels, while this arguably[55] forms additional diphthongs and triphthongs, only /e̯a/ and /o̯a/ can follow an obstruent-liquid cluster such as in broască ('frog') and dreagă ('to mend'),[56] implying that /j/ and /w/ are restricted to the syllable boundary and therefore, strictly speaking, do not form diphthongs.

For example, in the first line of the national anthem of Croatia, Lijepa naša domovina, ije is pronounced as a diphthong, but in the first line of the national anthem of Montenegro, Oj, svijetla majska zoro, ije is pronounced as two syllables.

Some Serbo-Croatian dialects also have uo, as in kuonj, ruod, uon[58] whereas, in Standard Croatian and Serbian, these words are konj, rod, on.

There are additional diphthongs less commonly used, such as [eu] in Euroopa (Europe), [øɑ] in söandama (to dare), and [æu] in näuguma (to mew).

Vowel combinations across syllables may in practice be pronounced as diphthongs, when an intervening consonant has elided, as in näön [næøn] instead of [næ.øn] for the genitive of näkö ('sight').