In linguistics, vowel length is the perceived length of a vowel sound: the corresponding physical measurement is duration. In some languages vowel length is an important phonemic factor, meaning vowel length can change the meaning of the word, for example in: Arabic, Finnish, Fijian, Kannada, Japanese, Latin, Old English, Scottish Gaelic, and Vietnamese. While vowel length alone does not change word meaning in most dialects of English, it is said to do so in a few dialects, such as Australian English, Lunenburg English, New Zealand English, and South African English. It also plays a lesser phonetic role in Cantonese, unlike in other varieties of Chinese.
Many languages do not distinguish vowel length phonemically, meaning that vowel length does not change meaning, and the length of a vowel is affected by other factors such as the values[clarification needed] of the sounds around it. Languages that do distinguish vowel length phonemically usually only distinguish between short vowels and long vowels. Very few languages distinguish three phonemic vowel lengths, such as Estonian, Luiseño, and Mixe. However, some languages with two vowel lengths also have words in which long vowels appear adjacent to other short or long vowels of the same type: Japanese h "phoenix" or Ancient Greek [a.á:.a.tos] "inviolable". Some languages that do not ordinarily have phonemic vowel length but permit vowel hiatus may similarly exhibit sequences of identical vowel phonemes that yield phonetically long vowels, such as Georgian ? [?a.a.ad.vil.eb] "you will facilitate it".
Stress is often reinforced by allophonic vowel length, especially when it is lexical. For example, French long vowels are always in stressed syllables. Finnish, a language with two phonemic lengths (i.e. vowel length changes meaning), indicates the stress by adding allophonic length, which gives four distinctive lengths and five physical lengths: short and long stressed vowels, short and long unstressed vowels, and a half-long vowel, which is a short vowel found in a syllable immediately preceded by a stressed short vowel: i-so.
Among the languages with distinctive vowel length, there are some in which it may occur only in stressed syllables, such as in Alemannic German, Scottish Gaelic and Egyptian Arabic. In languages such as Czech, Finnish, some Irish dialects and Classical Latin, vowel length is distinctive also in unstressed syllables.
In some languages, vowel length is sometimes better analyzed as a sequence of two identical vowels. In Finnic languages, such as Finnish, the simplest example follows from consonant gradation: haka -> haan. In some cases, it is caused by a following chroneme, which is etymologically a consonant: jää "ice" Proto-Uralic *jä?e. In non-initial syllables, it is ambiguous if long vowels are vowel clusters; poems written in the Kalevala meter often syllabicate between the vowels, and an (etymologically original) intervocalic -h- is seen in that and some modern dialects (taivaan vs. taivahan "of the sky"). Morphological treatment of diphthongs is essentially similar to long vowels. Some old Finnish long vowels have developed into diphthongs, but successive layers of borrowing have introduced the same long vowels again so the diphthong and the long vowel now again contrast (nuotti "musical note" vs. nootti "diplomatic note").
In Japanese, most long vowels are the results of the phonetic change of diphthongs; au and ou became ?, iu became y?, eu became y?, and now ei is becoming ?. The change also occurred after the loss of intervocalic phoneme /h/. For example, modern Ky?to (Kyoto) has undergone a shift: /kjauto/ -> /kjo:to/. Another example is sh?nen (boy): /seune?/ -> /sjo:ne?/ [?o:ne?].
As noted above, only a relatively few of the world's languages make a phonemic distinction between long and short vowels, this means that saying the word with a long vowel changes the meaning over saying the same word with a short vowel: Arabic, Italian, Sanskrit, Japanese, Biblical Hebrew, Scottish Gaelic, Finnish, Hungarian, etc.
|sentì vs. sentii||sentì||/sen'ti/||short||Lat. s?nsit||"he heard"|
|sentii||/sen'ti:/||long||Lat. s?ns?||"I heard"|
|corte vs. coorte||corte||/'kor.te/||short||Both from Lat. cohors
|re vs. ree||re||/'re/||short||Lat. r?x||"king"|
|ree||/'re:/||long||Lat. reae||"guilty" (f. pl.)|
Long vowels may or may not be analyzed as separate phonemes. In Latin and Hungarian, long vowels are analyzed as separate phonemes from short vowels, which doubles the number of vowel phonemes.
Vowel length contrasts with more than two phonemic levels are rare, and several hypothesized cases of three-level vowel length can be analysed without postulating this typologically unusual configuration.Estonian has three distinctive lengths, but the third is suprasegmental, as it has developed from the allophonic variation caused by now-deleted grammatical markers. For example, half-long 'aa' in saada comes from the agglutination *saata+ka "send+(imperative)", and the overlong 'aa' in saada comes from *saa+ta "get+(infinitive)". As for languages that have three lengths, independent of vowel quality or syllable structure, these include Dinka, Mixe, Yavapai and Wichita. An example from Mixe is [po?] "guava", [po] "spider", [po:?] "knot". In Dinka the longest vowels are three moras long, and so are best analyzed as overlong /o::/ etc.
Four-way distinctions have been claimed, but these are actually long-short distinctions on adjacent syllables. For example, in kiKamba, there is [ko.ko.na], [kóó.ma?], [ko.óma?], [nétónubáné.éet] "hit", "dry", "bite", "we have chosen for everyone and are still choosing".
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One way in which accents of English differ from each other is in their vowel length. In many accents of English a difference in length by itself does not change the meaning of a word. In descriptions of Received Pronunciation and more widely in some descriptions of English phonology it has been conventional to group all non-diphthongal vowels into the categories "long" and "short"; these are convenient terms for grouping the many vowels of English, but in almost all cases there are differences of vowel quality involved as well. Vowels vary greatly in length according to phonological context. The terms tense and lax are alternative terms that do not directly refer to length.
The usual pairings for RP are i: + ?, ?: + æ, ?: + ?, ?: + ?, u + ?
|/'fe?i:/ ferry||/'fe:?i:/ fairy|
|/'k?t/ cut||/'k?:t/ cart|
In most varieties of English, for instance Received Pronunciation and General American, there is allophonic variation in vowel length depending on the value of the consonant that follows it: vowels are shorter before voiceless consonants and are longer when they come before voiced consonants. Thus, the vowel in bad /bæd/ is longer than the vowel in bat /bæt/. Also compare neat with need . The vowel sound in "beat" is generally pronounced for about 190 milliseconds, but the same vowel in "bead" lasts 350 milliseconds in normal speech, the voiced final consonant influencing vowel length.
The vowel sounds (phonetic values) of what are called "long vowels" and "short vowels" (less confusing would be "vowel letters") in the teaching of reading (and therefore in everyday English) are represented in this table:
|a||/æ/||/e?/||mat / mate|
|e||/?/||/i:/||pet / Pete|
|i||/?/||/a?/||twin / twine|
|o||/?/||/o?/||not / note|
|u||/?/||/ju:/||cub / cube|
In English, the term "vowel" is often used to refer to vowel letters even though these often represent combinations of vowel sounds (diphthongs), approximants, and even silence, not just single vowel sounds (monophthongs). Most of the present article is concerned with the length of vowel sounds (not vowel letters) in English. Even classroom materials for teaching reading also use the terms "long" and "short" in referring to vowel letters, while confusingly calling them "vowels". For example, in English spelling, vowel letters in words of the form consonant + vowel letter + consonant (CVC) are called "short" and "long" depending on whether or not they are followed by the letter e (CVC vs. CVCe) although those vowel letters called "long" actually represent combinations of two different vowels (diphthongs). Thus a vowel letter is called "long" if it is pronounced the same as the letter's name and "short" if it is not. This is commonly used for educational purposes when teaching children.
In some types of phonetic transcription (e.g. pronunciation respelling), "long" vowel letters may be marked with a macron; for example, may be used to represent the IPA sound /e?/. This is sometimes used in dictionaries, most notably in Merriam-Webster (see Pronunciation respelling for English for more).
Similarly, the short vowel letters are rarely represented in teaching reading of English in the classroom by the symbols ?, ?, ?, ?, and ?. The long vowels are more often represented by a horizontal line above the vowel, ?, ?, ?, ?. 
Vowel length may often be traced to assimilation. In Australian English, the second element [?] of a diphthong [e?] has assimilated to the preceding vowel, giving the pronunciation of bared as [be:d], creating a contrast with the short vowel in bed [bed].
Another common source is the vocalization of a consonant such as the voiced velar fricative [?] or voiced palatal fricative, e.g. Finnish illative case, or even an approximant, as the English 'r'. An historically-important example is the laryngeal theory, which states that long vowels in the Indo-European languages were formed from short vowels, followed by any one of the several "laryngeal" sounds of Proto-Indo-European (conventionally written h1, h2 and h3). When a laryngeal sound followed a vowel, it was later lost in most Indo-European languages, and the preceding vowel became long. However, Proto-Indo-European had long vowels of other origins as well, usually as the result of older sound changes, such as Szemerényi's law and Stang's law.
Vowel length may also have arisen as an allophonic quality of a single vowel phoneme, which may have then become split in two phonemes. For example, the Australian English phoneme /æ:/ was created by the incomplete application of a rule extending /æ/ before certain voiced consonants, a phenomenon known as the bad-lad split. An alternative pathway to the phonemicization of allophonic vowel length is the shift of a vowel of a formerly-different quality to become the short counterpart of a vowel pair. That too is exemplified by Australian English, whose contrast between /a/ (as in duck) and /a:/ (as in dark) was brought about by a lowering of the earlier /?/.
Estonian, a Finnic language, has a rare phenomenon in which allophonic length variation has become phonemic after the deletion of the suffixes causing the allophony. Estonian had already inherited two vowel lengths from Proto-Finnic, but a third one was then introduced. For example, the Finnic imperative marker *-k caused the preceding vowels to be articulated shorter. After the deletion of the marker, the allophonic length became phonemic, as shown in the example above.
In the International Phonetic Alphabet the sign : (not a colon, but two triangles facing each other in an hourglass shape; Unicode
U+02D0) is used for both vowel and consonant length. This may be doubled for an extra-long sound, or the top half (?) may be used to indicate that a sound is "half long". A breve is used to mark an extra-short vowel or consonant.
Estonian has a three-way phonemic contrast:
Although not phonemic, a half-long distinction can also be illustrated in certain accents of English:
Some languages make no distinction in writing. This is particularly the case with ancient languages such as Latin and Old English. Modern edited texts often use macrons with long vowels, however. Australian English does not distinguish the vowels /æ/ from /æ:/ in spelling, with words like 'span' or 'can' having different pronunciations depending on meaning.
In non-Latin writing systems, a variety of mechanisms have also evolved.