Vowel

A vowel is a speech sound pronounced without any stricture in the vocal tract. Vowels are one of the two principal classes of speech sounds, the other being the consonant. Vowels vary in quality, loudness, and length. They are usually voiced and are closely involved in prosodic variation such as tone, intonation and stress. The nucleus, or "center", of a syllable typically consists of a vowel sound (though this is not always the case). The word vowel comes from the Latin word vocalis, meaning "vocal" (i.e. relating to the voice). In English, the word vowel is commonly used to refer both to vowel sounds and to the written symbols that represent them: ⟨a⟩, ⟨e⟩, ⟨i⟩, ⟨o⟩, ⟨u⟩, and sometimes ⟨y⟩, and ⟨w⟩.

Definition There are two complementary definitions of vowel, one phonetic and the other phonological.

In the phonetic definition, a vowel is a sound, such as the English "ah" or "oh" , produced with an open vocal tract; it is median (the air escapes along the middle of the tongue), oral (at least some of the airflow must escape through the mouth), frictionless and continuant. There is no significant build-up of air pressure at any point above the glottis. This contrasts with consonants, such as the English "sh" [ʃ], which have a constriction or closure at some point along the vocal tract. In the phonological definition, a vowel is defined as syllabic, the sound that forms the peak of a syllable. A phonetically equivalent but non-syllabic sound is a semivowel. In oral languages, phonetic vowels normally form the peak (nucleus) of many or all syllables, whereas consonants form the onset and (in languages that have them) coda. Some languages allow other sounds to form the nucleus of a syllable, such as the syllabic (i.e., vocalic) l in the English word table [ˈtʰeɪ.bl̩] (when not considered to have a weak vowel sound: [ˈtʰeɪ.bəl]) or the syllabic r in the Serbo-Croatian word vrt [ʋr̩̂t] "garden". The phonetic definition of "vowel" (i.e. a sound produced with no constriction in the vocal tract) does not always match the phonological definition (i.e. a sound that forms the peak of a syllable). The approximants [j] and [w] illustrate this: both are without much of a constriction in the vocal tract (so phonetically they seem to be vowel-like), but they occur at the onset of syllables (e.g. in "yet" and "wet") which suggests that phonologically they are consonants. A similar debate arises over whether a word like bird in a rhotic dialect has an r-colored vowel /ɝ/ or a syllabic consonant /ɹ̩/. The American linguist Kenneth Pike (1943) suggested the terms "vocoid" for a phonetic vowel and "vowel" for a phonological vowel; under this terminology, semivowels [j] and [w] are classified as vocoids but not vowels. However, Maddieson and Emmory (1985) demonstrated from a range of languages that semivowels are produced with a narrower constriction of the vocal tract than vowels, and so may be considered consonants on that basis.

Articulation

The traditional view of vowel production, reflected for example in the terminology and presentation of the International Phonetic Alphabet, is one of articulatory features that determine a vowel's quality as distinguishing it from other vowels. Daniel Jones developed the cardinal vowel system to describe vowels in terms of the features of tongue height (vertical dimension), tongue backness (horizontal dimension) and roundedness (lip articulation). These three parameters are indicated in the schematic quadrilateral IPA vowel diagram on the right. There are additional features of vowel quality, such as the velum position (nasality), type of vocal fold vibration (phonation), and tongue root position. This conception of vowel articulation has been known to be inaccurate since 1928. Peter Ladefoged said that "early phoneticians... thought they were describing the highest point of the tongue, but they were not. They were actually describing formant frequencies." (See § Acoustics below.) In the IPA Handbook, the vowels [i u a ɑ] are regarded as fixed articulatory reference points, with precise tongue positioning, while the remaining vowels are defined "so that the differences between each vowel and the next in the series are auditorily equal". As such, the Handbook concedes:

The use of auditory spacing in the definition of these vowels means vowel description is not based purely on articulation, and is one reason why the vowel quadrilateral must be regarded as an abstraction and not a direct mapping of tongue position. Nonetheless, the concept that vowel qualities are determined primarily by tongue position and lip rounding continues to be used in pedagogy, as it provides an intuitive explanation of how vowels are distinguished.

Height Theoretically, according to the traditional models, vowel height refers to the vertical position of either the tongue or the jaw (depending on the model), relative to either the roof of the mouth or the aperture of the jaw. There are two terms commonly applied to refer to two degrees of vowel height: in close vowels, also known as high vowels, such as [i] and [u], the tongue is positioned close to the palate (i.e. high in the mouth), whereas in open vowels, also known as low vowels, such as [a], the jaw is open and the tongue is positioned low in the mouth. In John Esling's usage, where fronted vowels are distinguished in height by the position of the jaw rather than the tongue, only the terms 'open' and 'close' are used, as 'high' and 'low' refer to the position of the tongue. The International Phonetic Alphabet defines letters for six degrees of vowel height for full vowels (plus the reduced mid vowel [ə]), but it is extremely unusual for a language to distinguish this many degrees without other attributes. The IPA letters distinguish (sorted according to height, with the top-most one being the highest and the bottom-most being the lowest):

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