In
phonetics, a
diphthong, pronounced
/'d?f.???/ or
/'d?p.???/, (also
gliding vowel) (from
Greek d?f??????,
diphthongos, literally "two sounds" or "two tones") is a
contour vowel—that is, a unitary vowel that changes
quality during its pronunciation, or "glides", with a smooth movement of the tongue from one articulation to another, as in the
English words
eye,
boy, and
cow. This contrasts with "pure" vowels, or
monophthongs, where the tongue is held still, as in the English word
papa.
[1]Diphthongs often form when separate vowels are run together in rapid speech. However, there are also unitary diphthongs, as in the English examples above, which are heard by listeners as single-vowel sounds (phonemes).[2]
In the International Phonetic Alphabet, pure vowels are transcribed with one letter, as in English sun [s?n]. Diphthongs are transcribed with two letters, as in English sign [sa??n] or sane [se??n]. The two vowel symbols are chosen to represent the beginning and ending positions of the tongue, though this can be only approximate. The diacritic <&_160;&_160;?> is placed under the less prominent component to show that it is part of a diphthong rather than a separate vowel, though it is sometimes omitted in languages such as English, where there is not likely to be any confusion. (In precise transcription, [ai] represents two vowels in hiatus, found for example in Hawaiian and in the English word naïve, and does not represent the diphthong, for instance, in the Finnish word laiva, "ship").
In closing diphthongs, the second element is more close than the first (e.g. [ai]); in opening diphthongs, the second element is more open (e.g. [ia]). Closing diphthongs tend to be falling ([ai?]), and opening diphthongs are generally rising ([i?a]), 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 /ie?/ and /uo?/ are true falling diphthongs, since they begin louder and with higher pitch and fall in prominence during the diphthong.
