In linguistics, vowel length is the perceived duration of a vowel sound. Often the chroneme, or the "longness", acts like a consonant, and may etymologically be one such as in Australian English. While not distinctive in most dialects of English, vowel length is an important phonemic factor in many other languages, for instance in Arabic, Czech, Hindi, Sanskrit, Fijian, Finnish, Japanese, Hawaiian, Hungarian, Classical Latin, Classical Nahuatl, Lombard, German, Dutch, Latvian, Old English, Samoan, Lao, Thai, and Vietnamese. It plays a phonetic role in the majority of English dialects, and is said to be phonemic in a few dialects, such as Australian English and New Zealand English. It also plays a lesser phonetic role in Cantonese, which is exceptional among the spoken variants of Chinese.
Most languages do not distinguish vowel length, and for those that do, usually the only distinction is between short vowels and long vowels. There are very few languages that distinguish three vowel lengths, for instance Mixe. Some languages, such as Finnish, Estonian and Japanese, also have words where long vowels are immediately followed by more vowels, e.g. Japanese hōō "phoenix" or Estonian jäääär "ice edge".
Stress is often reinforced by allophonic vowel length, especially when it is lexical. For example, French long vowels always occur on stressed syllables. Finnish, a language with two phonemic lengths, indicates the stress by adding allophonic length. This 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, e.g. i-so.
Among the languages that have distinctive vowel length, there are some where it may only occur in stressed syllables, e.g. in the Alemannic German dialect. In languages such as Czech, Finnish or Classical Latin, vowel length is distinctive in unstressed syllables as well.
In some languages, vowel length is sometimes better analyzed as a sequence of two identical vowels. In Baltic-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, e.g. jää " ← Proto-Finno-Ugric *jäŋe. In noninitial 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 this and some modern dialects.
In Japanese, most long vowels are the results of the phonetic change of diphthongs; au and ou became ō, iu became yū, eu became yō, and now ei is becoming ē. The change occurred after the loss of intervocalic phoneme /h/. For example, modern kyōto (Kyoto) exhibits the following changes: kyauto → kyoːto. Another example is shōnen (boy): seunen → syoːnen (shoːnen). There is no lengthening.
Long vowels may or may not be separate phonemes. In Latin and Hungarian, long vowels are separate phonemes from short vowels, thus doubling the number of vowel phonemes.
Japanese long vowels are analyzed as either two same vowels or a vowel + the pseudo-phoneme /H/, and the number of vowels is five.
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)". One of the very few languages to have three lengths, independent of vowel quality or syllable structure, is Mixe. An example from Mixe is "guava", "spider", "knot". Similar claims have been made for Yavapai and Wichita.
Four-way distinctions have been claimed, but these are actually long-short distinctions on adjacent syllables. For example, in kiKamba, there is , , , "hit", "dry", "bite", "we have chosen for everyone and are still choosing".
Vowel length, when applied to English, has several different related meanings.
Traditionally, the vowels (as in bait beet bite boat beauty) are said to be the "long" counterparts of the vowels (as in bat bet bit bot but) which are said to be "short". This terminology reflects their pronunciation before the Great Vowel Shift, rather than their present-day pronunciations. A linguistically more accurate description is that the former are diphthongs (except for ), while the latter are monophthongs ("pure" vowels).
In certain dialects of the modern English language, for instance General American and, to some extent, British Received Pronunciation, there is allophonic vowel length: vowel phonemes are realized as longer vowel allophones before voiced consonant phonemes in the coda of a syllable. For example, the vowel phoneme in ‘bat’ is realized as a short allophone in , because the phoneme is unvoiced, while the same vowel phoneme in ‘bad’ is realized as a long allophone (which could be transcribed as ), because is voiced. (Incidentally, the final consonant allophones in these syllables also have different relative lengths; the of bat is longer than the of bad.)
Symbolic representation of the two allophonic rules:
|→||| _ /+con +vcd/|
|→||| _ /+con -vcd/|
In addition, the vowels of Received Pronunciation are commonly divided into short and long, as obvious from their transcription. The short vowels are (as in kit), (as in foot), (as in dress), (as in strut), (as in trap), (as in lot), and (as in the first syllable of ago and in the second of sofa). The long vowels are (as in fleece), (as in goose), (as in nurse), as in north and thought, and (as in father and start). While a different degree of length is indeed present, there are also differences in the quality (lax vs tense) of these vowels, and the currently prevalent view tends to emphasise the latter rather than the former.
In Australian English, there is contrastive vowel length between long and short [ɪ], [e], [æ] and [ä]. The following are minimal pairs of length for many speakers:
|span past tense of spin||vs||as in wing span|
|can meaning able to||vs||as in tin can|
The long vowel may often be traced to assimilation. In Australian English, the second element of a diphthong has assimilated to the preceding vowel, giving the pronunciation of bared as , creating a contrast with bed . Another etymology is the vocalization of a fricative such as the voiced velar fricative or voiced palatal fricative, e.g. Finnish illative case, or even an approximant, as the English 'r'.
Estonian, of Balto-Finnic languages, exhibits a rare phenomenon, where allophonic length variation becomes phonemic following the deletion of the suffixes causing the allophony. Estonian already distinguishes two vowel lengths, but a third one has been introduced by this phenomenon. For example, the Balto-Finnic imperative marker *-k caused the preceding vowels to be articulated shorter, and following the deletion of the marker, the allophonic length became phonemic, as shown in the example below. Similarly, the Australian English phoneme was created by the incomplete application of a rule extending before certain voiced consonants, a phenomenon known as the bad-lad split.
In the International Phonetic Alphabet the sign (two triangles facing each other in an hourglass shape) is used for both vowel and consonant length. This may be doubled for an extra-long sound, or the top half () used to indicate a sound is "half long". A breve is used to mark a short vowel or consonant.
Estonian has a three-way phonemic contrast:
saada "to get"
Although not phonemic, the distinction can also be illustrated in certain dialects of English:
Consistent use: byta 'to change' vs bytta 'tub' and koma 'coma' vs komma 'to come'
Inconsistent use: fält 'a field' and kam 'a comb' (but the verb 'to comb' is kamma)
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 from 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.