Diphthong

A diphthong, also known as a gliding vowel or a vowel glide, is a combination of two adjacent vowel sounds within the same syllable. Technically, a diphthong is a vowel with two different targets: that is, the tongue moves during the pronunciation of the vowel. In most varieties of English, the phrase "no highway cowboys" 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. For instance, in English, the word ah is spoken as a monophthong, while the word ow is spoken as a diphthong in most varieties. Where two adjacent vowel sounds occur in different syllables the result is described as hiatus, not as a diphthong.
Diphthongs often form when separate vowels are run together in rapid speech during a conversation. However, there are also unitary diphthongs, as in the English examples above, which are heard by listeners as single-vowel sounds.
The word comes,.

Transcription

In the International Phonetic Alphabet, monophthongs are transcribed with one symbol, as in English sun, in which represents a monophthong. Diphthongs are transcribed with two symbols, as in English high or cow, in which and represent diphthongs.
Diphthongs may be transcribed with two vowel symbols or with a vowel symbol and a semivowel symbol. In the words above, the less prominent member of the diphthong can be represented with the symbols for the palatal approximant and the labiovelar approximant, with the symbols for the close vowels and, or the symbols for the near-close vowels and :

vowel and semivowel		broad transcription
two vowel symbols		broad transcription
two vowel symbols		narrow transcription

Some transcriptions are broader or narrower than others. Transcribing the English diphthongs in high and cow as or is a less precise or broader transcription, since these diphthongs usually end in a vowel sound that is more open than the semivowels or the close vowels. Transcribing the diphthongs as is a more precise or narrower transcription, since the English diphthongs usually end in the near-close vowels.
The non-syllabic diacritic, the inverted breve below, is placed under the less prominent part of a diphthong to show that it is part of a diphthong rather than a vowel in a separate syllable:. When there is no contrastive vowel sequence in the language, the diacritic may be omitted. Other common indications that the two sounds are not separate vowels are a superscript,, or a tie bar, or. The tie bar can be useful when it is not clear which symbol represents the syllable nucleus, or when they have equal weight. Superscripts are especially used when an on- or off-glide is particularly fleeting.
The period is the opposite of the non-syllabic diacritic: it represents a syllable break. If two vowels next to each other belong to two different syllables, meaning that they do not form a diphthong, they can be transcribed with two vowel symbols with a period in between. Thus, lower can be transcribed, with a period separating the first syllable,, from the second syllable,.
The non-syllabic diacritic is used only when necessary. It is typically omitted when there is no ambiguity, as in. No words in English have the vowel sequences, so the non-syllabic diacritic is unnecessary.

Types

Falling and rising

Falling diphthongs start with a vowel quality of higher prominence and end in a semivowel with less prominence, like in eye, while rising diphthongs begin with a less prominent semivowel and end with a more prominent full vowel, similar to the in yard. The less prominent component in the diphthong may also be transcribed as an approximant, thus in eye and in yard. However, when the diphthong is analysed as a single phoneme, both elements are often transcribed with vowel symbols. Semivowels and approximants are not equivalent in all treatments, and in the English and Italian languages, among others, many phoneticians do not consider rising combinations to be diphthongs, but rather sequences of approximant and vowel. There are many languages that contrast one or more rising diphthongs with similar sequences of a glide and a vowel in their phonetic inventory.

Closing, opening, and centering

In closing diphthongs, the second element is more close than the first ; in opening diphthongs, the second element is more open. Closing diphthongs tend to be falling, and opening diphthongs are generally rising, as open vowels are more sonorous and therefore tend to be more prominent. However, exceptions to this rule are not rare in the world's languages. In Finnish, for instance, the opening diphthongs and are true falling diphthongs, since they begin louder and with higher pitch and fall in prominence during the diphthong.
A third, rare type of diphthong that is neither opening nor closing is height-harmonic diphthongs, with both elements at the same vowel height. These may have occurred in Old English:

beorht "bright"
ċeald "cold"

A centering diphthong is one that begins with a more peripheral vowel and ends with a more central one, such as,, and in Received Pronunciation or and in Irish. Many centering diphthongs are also opening diphthongs.
Diphthongs may contrast in how far they open or close. For example, Samoan contrasts low-to-mid with low-to-high diphthongs:

ai 'probably'
ae 'but'
'auro 'gold'
ao 'a cloud'
Narrow and wide

Narrow diphthongs are the ones that end with a vowel which on a vowel chart is quite close to the one that begins the diphthong, for example Northern Dutch, and. 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. Examples of wide diphthongs are RP/GA English and.

Length

Languages differ in the length of diphthongs, measured in terms of morae. In languages with phonemically short and long vowels, diphthongs typically behave like long vowels, and are pronounced with a similar length. In languages with only one phonemic length for pure vowels, however, diphthongs may behave like pure vowels. For example, in Icelandic, both monophthongs and diphthongs are pronounced long before single consonants and short before most consonant clusters.
Some languages contrast short and long diphthongs. In some languages, such as Old English, these behave like short and long vowels, occupying one and two morae, respectively. Languages that contrast three quantities in diphthongs are extremely rare, but not unheard of; Northern Sami is known to contrast long, short and "finally stressed" diphthongs, the last of which are distinguished by a longer second element.

Phonology

In some languages, diphthongs are single phonemes, while in others they are analyzed as sequences of two vowels, or of a vowel and a semivowel.

Sound changes

Certain sound changes relate to diphthongs and monophthongs. Vowel breaking or diphthongization is a vowel shift in which a monophthong becomes a diphthong. Monophthongization or smoothing is a vowel shift in which a diphthong becomes a monophthong.

Difference from semivowels and vowel sequences

While there are a number of similarities, diphthongs are not the same phonologically as a combination of a vowel and an approximant or glide. Most importantly, diphthongs are fully contained in the syllable nucleus while a semivowel or glide is restricted to the syllable boundaries. This often manifests itself phonetically by a greater degree of constriction, but the phonetic distinction is not always clear. 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 and so when it occurs in a language, it does not contrast with. However, it is possible for languages to contrast and.
Diphthongs are also distinct from sequences of simple vowels. The Bunaq language of Timor, for example, distinguishes 'exit' from 'be amused', 'dance' from 'stare at', and 'choice' from 'good'.
Some languages or dialects also articulate the component sounds of a diphthong differently than when those sounds are produced in hiatus. For example, due to English diphthong raising, many North American English speakers pronounce with closer vowels than, and, among a subset of those, the diphthong may be similarly raised as compared to.

Examples

Indo-European languages

English

In words coming from Middle English, most cases of the Modern English diphthongs originate from the Middle English long monophthongs through the Great Vowel Shift, although some cases of originate from the Middle English diphthongs.

Dutch

The dialect of Hamont has five centring diphthongs and contrasts long and short forms of,,, and.

Afrikaans

The Afrikaans language has its origin in Dutch but differs in many significant ways, including the use of diphthongs in the place of several non-diphthong Dutch double vowels, or double-vowels being pronounced differently.
Examples include:

ee as in leer
eu as in deur
ui as in buite
Falling diphthongs. Their first element may be short or somewhat lengthened.
Rising diphthongs. These variants do not seem to appear word-finally. The sequence is commonly realised as or, more often,, with realised as breathy
The scholar Daan Wissing argues that is not a phonetically correct transcription and that is more accurate. In his analysis, he found that makes for 65% of the realisations, the other 35% being monophthongal,, and.
Most often, has an unrounded offset. For some speakers, the onset is also unrounded. That can cause to merge with, which is considered non-standard.
occur mainly in loanwords.
Older sources describe as a narrow back diphthong. However, newer sources describe its onset as more front. For example,, states that the onset of is central.
* In some words which, in English, are pronounced with, the Afrikaans equivalent tends to be pronounced with, rather than. That happens because Afrikaans is more similar to the usual South African realization of English.

Phoneme	IPA	Orthography	Gloss
		seun	'son'
		hy	'he'
		weet	'to know'
		huis	'house'
			'burlap'
		brood	'bread'
		koud	'cold'
		baie	'many'

The long diphthongs are phonemically sequences of a free vowel and a non-syllabic equivalent of or :. Both and tend to be pronounced as, but they are spelled differently: the former as, the latter as.
In diminutives ending in formed to monosyllabic nouns, the vowels are realised as closing diphthongs. In the same environment, the sequences are realized as, i.e. as closing diphthongs followed by palatal nasal.

The suffixes and and the diminutive suffix are realised as , rather than.
In practice, the diphthong is realised the same as the phonemic diphthong.
, when it has arisen from diphthongisation of, differs from the phonemic diphthong by having a slightly different onset, although the exact nature of that difference is unclear. This means that puntjie 'point' sounds somewhat different from puintjie 'rubble'.