Vowel

In phonetics, a vowel is a sound in spoken language, such as English ah! [ɑː] or oh! [oʊ], pronounced with an open vocal tract so that there is no build-up of air pressure at any point above the glottis. This contrasts with consonants, such as English sh! [ʃː], where there is a constriction or closure at some point along the vocal tract. A vowel is also understood to be syllabic: an equivalent open but non-syllabic sound is called a semivowel.

In all languages, vowels form the nucleus or peak of syllables, whereas consonants form the onset and (in languages which have them) coda. However, some languages also allow other sounds to form the nucleus of a syllable, such as the syllabic l in the English word table [ˈteɪ.bl̩] (the stroke under the l indicates that it is syllabic; the dot separates syllables), or the r in Serbian vrt [vr̩t] "garden".

We might note the conflict between the phonetic definition of 'vowel' (a sound produced with no constriction in the vocal tract) and the phonological definition (a sound that forms the peak of a syllable).^[1] The approximants [j] and [w] illustrate this conflict: both are produced without much of a constriction in the vocal tract (so phonetically they seem to be vowel-like), but they occur on the edge of syllables, such as at the beginning of the English words 'yes' and 'wet' (which suggests that phonologically they are consonants). The American linguist Kenneth Pike suggested the terms 'vocoid' for a phonetic vowel and 'vowel' for a phonological vowel,^[2] so using this terminology, [j] and [w] are classified as vocoids but not vowels.

The word vowel comes from the Latin word vocalis, meaning "speaking", because in most languages words and thus speech are not possible without vowels. Vowel is commonly used to mean both vowel sounds and the written symbols that represent them.

Articulation

In spoken language, the articulatory features that distinguish different vowel sounds are said to determine the vowel's quality. Daniel Jones developed the cardinal vowel system to describe vowels in terms of the common features height (vertical dimension), backness (horizontal dimension) and roundedness (lip position). These three parameters are indicated in the schematic IPA vowel diagram on the right. There are however still more possible features of vowel quality, such as the velum position (nasality), type of vocal fold vibration (phonation), and tongue root position.

Height

X-rays of Daniel Jones' [i, u, a, ɑ]

Vowel height is named for the vertical position of the tongue relative to either the roof of the mouth or the aperture of the jaw. In high vowels, such as [i] and [u], the tongue is positioned high in the mouth, whereas in low vowels, such as [a], the tongue is positioned low in the mouth. The IPA prefers the terms close vowel and open vowel, respectively, which describes the jaw as being relatively open or closed. However, vowel height is an acoustic rather than articulatory quality, and is defined today not in terms of tongue height, or jaw openness, but according to the relative frequency of the first formant (F1). The higher the F1 value, the lower (more open) the vowel; height is thus inversely correlated to F1.^[3]

True mid vowels do not contrast with both close-mid and open-mid in any language, and the letters [e ø ɤ o] are typically used for either close-mid or mid vowels.

Although English contrasts all six contrasting heights in its vowels, these are interdependent with differences in backness, and many are parts of diphthongs. It appears that some varieties of German have five contrasting vowel heights independently of length or other parameters. The Bavarian dialect of Amstetten has thirteen long vowels, reported to distinguish four heights (close, close-mid, mid, and near-open) each among the front unrounded, front rounded, and back rounded vowels, plus an open central vowel: /i e ɛ̝ æ̝/, /y ø œ̝ ɶ̝/, /u o ɔ̝ ɒ̝/, /a/. Otherwise, the usual limit on the number of contrasting vowel heights is four.

The parameter of vowel height appears to be the primary feature of vowels cross-linguistically in that all languages use height contrastively. No other parameter, such as front-back or rounded-unrounded (see below), is used in all languages. Some languages have vertical vowel systems in which, at least at a phonemic level, only height is used to distinguish vowels.

Backness

Vowel backness is named for the position of the tongue during the articulation of a vowel relative to the back of the mouth. In front vowels, such as [i], the tongue is positioned forward in the mouth, whereas in back vowels, such as [u], the tongue is positioned towards the back of the mouth. However, vowels are defined as back or front not according to actual articulation, but according to the relative frequency of the second formant (F2). The higher the F2 value, the fronter the vowel; backness is thus inversely correlated to F2.

Tongue positions of cardinal front vowels with highest point indicated. The position of the highest point is used to determine vowel height and backness

Although English has vowels at all five degrees of backness, there is no known language that distinguishes all five without additional differences in height or rounding.

Roundedness

Roundedness refers to whether the lips are rounded or not. In most languages, roundedness is a reinforcing feature of mid to high back vowels, and is not distinctive. Usually the higher a back vowel is, the more intense the rounding. However, some languages treat roundedness and backness separately, such as French and German (with front rounded vowels), most Uralic languages (Estonian has a rounding contrast for /o/ and front vowels), Turkic languages (with an unrounded /u/), Vietnamese (with back unrounded vowels), and Korean (with a contrast in both front and back vowels).

Nonetheless, even in languages such as German and Vietnamese, there is usually some phonetic correlation between rounding and backness: front rounded vowels tend to be less front than front unrounded vowels, and back unrounded vowels tend to be less back than back rounded vowels. That is, the placement of unrounded vowels to the left of rounded vowels on the IPA vowel chart is reflective of their typical position.

Different kinds of labialization are also possible. In mid to high rounded back vowels the lips are generally protruded ("pursed") outward, a phenomenon known as exolabial rounding because the insides of the lips are visible, whereas in mid to high rounded front vowels the lips are generally "compressed", with the margins of the lips pulled in and drawn towards each other, a phenomenon known as endolabial rounding. However, not all languages follow this pattern. The Japanese /u/, for example, is an endolabial (compressed) back vowel, and sounds quite different than an English exolabial /u/. Swedish and Norwegian are the only two known languages where this feature is contrastive, having both endo- and exo-labial close front rounded vowels and close central rounded vowels, respectively. In many phonetic treatments, both are considered types of rounding, but some phoneticians do not believe that these are subsets of a single phenomenon of rounding, and prefer instead the three independent terms rounded (exolabial), compressed (endolabial), and spread (unrounded).

Nasalization

Nasalization refers to whether some of the air escapes through the nose. In nasal vowels, the velum is lowered, and some air travels through the nasal cavity as well as the mouth. An oral vowel is a vowel in which all air escapes through the mouth. French, Polish and Portuguese contrast nasal and oral vowels.

Phonation

Voicing describes whether the vocal cords are vibrating during the articulation of a vowel. Most languages only have voiced vowels, but several Native American languages, such as Cheyenne and Totonac, contrast voiced and devoiced vowels. Vowels are devoiced in whispered speech. In Japanese and Quebec French, vowels that are between voiceless consonants are often devoiced.

Modal voice, creaky voice, and breathy voice (murmured vowels) are phonation types that are used contrastively in some languages. Often, these co-occur with tone or stress distinctions; in the Mon language, vowels pronounced in the high tone are also produced with creaky voice. In cases like this, it can be unclear whether it is the tone, the voicing type, or the pairing of the two that is being used for phonemic contrast. This combination of phonetic cues (i.e. phonation, tone, stress) is known as register or register complex.

Tongue root retraction

Advanced tongue root (ATR) is a feature common across much of Africa. The contrast between advanced and retracted tongue root resembles the tense/lax contrast acoustically, but they are articulated differently. ATR vowels involve noticeable tension in the vocal tract.

Secondary narrowings in the vocal tract

A stronger degree of pharyngealisation occurs in the Northeast Caucasian languages and the Khoisan languages. These might be called epiglottalized, since the primary constriction is at the tip of the epiglottis.

The greatest degree of pharyngealisation is found in the strident vowels of the Khoisan languages, where the larynx is raised, and the pharynx constricted, so that either the epiglottis or the arytenoid cartilages vibrate instead of the vocal cords.

Note that the terms pharyngealized, epiglottalized, strident, and sphincteric are sometimes used interchangeably.

Rhotic vowels

Tenseness/checked vowels vs. free vowels

Tenseness is used to describe the opposition of tense vowels as in leap, suit vs. lax vowels as in lip, soot. This opposition has traditionally been thought to be a result of greater muscular tension, though phonetic experiments have repeatedly failed to show this.

Unlike the other features of vowel quality, tenseness is only applicable to the few languages that have this opposition (mainly Germanic languages, e.g. English), whereas the vowels of the other languages (e.g. Spanish) cannot be described with respect to tenseness in any meaningful way. In discourse about the English language, "tense and lax" are often used interchangeably with "long and short", respectively, because the features are concomitant in the common varieties of English. This cannot be applied to all English dialects or other languages.

In most Germanic languages, lax vowels can only occur in closed syllables. Therefore, they are also known as checked vowels, whereas the tense vowels are called free vowels since they can occur in any kind of syllable.

Acoustics

The acoustics of vowels are fairly well understood. The different vowel qualities are realized in acoustic analyses of vowels by the relative values of the formants, acoustic resonances of the vocal tract which show up as dark bands on a spectrogram. The vocal tract acts as a resonant cavity, and the position of the jaw, lips, and tongue affect the parameters of the resonant cavity, resulting in different formant values. The acoustics of vowels can be visualized using spectrograms, which display the acoustic energy at each frequency, and how this changes with time.

The first formant, abbreviated "F1", corresponds to vowel openness (vowel height). Open vowels have high F1 frequencies while close vowels have low F1 frequencies, as can be seen at right: The [i] and [u] have similar low first formants, whereas [ɑ] has a higher formant.

The second formant, F2, corresponds to vowel frontness. Back vowels have low F2 frequencies while front vowels have high F2 frequencies. This is very clear at right, where the front vowel [i] has a much higher F2 frequency than the other two vowels. However, in open vowels the high F1 frequency forces a rise in the F2 frequency as well, so an alternative measure of frontness is the difference between the first and second formants. For this reason, some people prefer to plot as F1 vs. F2 – F1. (This dimension is usually called 'backness' rather than 'frontness', but the term 'backness' can be counterintuitive when discussing formants.)

In the third edition of his textbook, Peter Ladefoged recommended use of plots of F1 against F2 – F1 to represent vowel quality.^[4] However, in the fourth edition, he changed to adopt a simple plot of F1 against F2,^[5] and this simple plot of F1 against F2 was maintained for the fifth (and final) edition of the book.^[6] Katrina Hayward compares the two types of plots and concludes that plotting of F1 against F2 – F1 "is not very satisfactory because of its effect on the placing of the central vowels",^[7] so she also recommends use of a simple plot of F1 against F2. In fact, this kind of plot of F1 against F2 has been used by analysts to show the quality of the vowels in a wide range of languages, including RP British English,^[8]^[9] the Queen's English,^[10] American English,^[11] Singapore English,^[12] Brunei English,^[13] North Frisian,^[14] Turkish Kabardian,^[15] and various indigenous Australian languages.^[16]

Rounding is generally realized by a complex relationship between F2 and F3 that tends to reinforce vowel backness. One effect of this is that back vowels are most commonly rounded while front vowels are most commonly unrounded; another is that rounded vowels tend to plot to the right of unrounded vowels in vowel charts. That is, there is a reason for plotting vowel pairs the way they are.

Prosody and intonation

The features of vowel prosody are often described independently from vowel quality. In non-linear phonetics, they are located on parallel layers. The features of vowel prosody are usually considered not to apply to the vowel itself, but to the syllable, as some languages do not contrast vowel length separately from syllable length.

Intonation encompasses the changes in pitch, intensity, and speed of an utterance over time. In tonal languages, in most cases the tone of a syllable is carried by the vowel, meaning that the relative pitch or the pitch contour that marks the tone is superimposed on the vowel. If a syllable has a high tone, for example, the pitch of the vowel will be high. If the syllable has a falling tone, then the pitch of the vowel will fall from high to low over the course of uttering the vowel.

Length or quantity refers to the abstracted duration of the vowel. In some analyses this feature is described as a feature of the vowel quality, not of the prosody. Japanese, Finnish, Hungarian, Arabic and Latin have a two-way phonemic contrast between short and long vowels. The Mixe language has a three-way contrast among short, half-long, and long vowels, and this has been reported for a few other languages, though not always as a phonemic distinction. Long vowels are written in the IPA with a triangular colon, which has two equilateral triangles pointing at each other in place of dots ([iː]). The IPA symbol for half-long vowels is the top half of this ([iˑ]). Longer vowels are sometimes claimed, but these are always divided between two syllables.

It should be noted that the length of the vowel is a grammatical abstraction, and there may be more phonologically distinctive lengths. For example, in Finnish, there are five different physical lengths, because stress is marked with length on both grammatically long and short vowels. However, Finnish stress is not lexical and is always on the first two moras, thus this variation serves to separate words from each other.

In non-tonal languages, like English, intonation encompasses lexical stress. A stressed syllable will typically be pronounced with a higher pitch, intensity, and length than unstressed syllables. For example in the word intensity, the vowel represented by the letter 'e' is stressed, so it is longer and pronounced with a higher pitch and intensity than the other vowels.

Monophthongs, diphthongs, triphthongs

A vowel sound whose quality doesn't change over the duration of the vowel is called a monophthong. Monophthongs are sometimes called "pure" or "stable" vowels. A vowel sound that glides from one quality to another is called a diphthong, and a vowel sound that glides successively through three qualities is a triphthong.

All languages have monophthongs and many languages have diphthongs, but triphthongs or vowel sounds with even more target qualities are relatively rare cross-linguistically. English has all three types: the vowel sound in hit is a monophthong [ɪ], the vowel sound in boy is in most dialects a diphthong [ɔɪ], and the vowel sounds of, flower (BrE [aʊə] AmE [aʊɚ]) form a triphthong (disyllabic in the latter cases), although the particular qualities vary by dialect.

In phonology, diphthongs and triphthongs are distinguished from sequences of monophthongs by whether the vowel sound may be analyzed into different phonemes or not. For example, the vowel sounds in a two-syllable pronunciation of the word flower (BrE [flaʊə] AmE [flaʊɚ]) phonetically form a disyllabic triphthong, but are phonologically a sequence of a diphthong (represented by the letters <ow>) and a monophthong (represented by the letters <er>). Some linguists use the terms diphthong and triphthong only in this phonemic sense.

Written vowels

The name "vowel" is often used for the symbols that represent vowel sounds in a language's writing system, particularly if the language uses an alphabet. In writing systems based on the Latin alphabet, the letters A, E, I, O, U, W and Y are all used to represent vowels, although not all of these letters represent vowels in all languages (some of them, especially W and Y, are also used to represent approximants); in addition, extensions of the Latin alphabet have independent vowel letters such as Ä, Ö, Ü, Å, æ, and Ø.

The phonetic values vary by language, and some languages use I and Y for the consonant [j], e.g. initial I in Romanian and initial Y in English. In the original Latin alphabet, there was no written distinction between V and U, and the letter represented the approximant [w] and the vowels [u] and [ʊ]. In Modern Welsh, the letter W represents these same sounds. Similarly, in Creek, the letter V stands for [ə]. There is not necessarily a direct one-to-one correspondence between the vowel sounds of a language and the vowel letters. Many languages that use a form of the Latin alphabet have more vowel sounds than can be represented by the standard set of five vowel letters. In English spelling, the five letters A E I O and U can represent a variety of vowel sounds, while the letter Y frequently represents vowels (as in e.g. "gym" or "happy"); to an extremely limited extent, W can also represent a vowel (e.g. the borrowed word "cwm").

Other languages cope with the limitation in the number of Latin vowel letters in similar ways. Many languages, like English, make extensive use of combinations of vowel letters to represent various sounds. Other languages use vowel letters with modifications, e.g. Ä in Finnish, or add diacritical marks, like umlauts, to vowels to represent the variety of possible vowel sounds. Some languages have also constructed additional vowel letters by modifying the standard Latin vowels in other ways, such as æ or ø that are found in some of the Scandinavian languages. The International Phonetic Alphabet has a set of 28 symbols to represent the range of basic vowel qualities, and a further set of diacritics to denote variations from the basic vowel.

Use of vowels in languages

The importance of vowels in distinguishing one word from another varies from language to language. The alphabets used to write the Semitic languages, such as the Hebrew alphabet and the Arabic alphabet, do not ordinarily mark all the vowels, since they are frequently unnecessary in identifying a word. These alphabets are technically called abjads. Although it is possible to construct simple English sentences that can be understood without written vowels (cn y rd ths?), extended passages of English lacking written vowels are difficult if not impossible to completely understand (consider dd, which could be any of add, aided, dad, dada, dead, deed, did, died, dodo, dud, dude, eddie, iodide, or odd).

In most languages, vowels serve mainly to distinguish separate lexemes, rather than different inflectional forms of the same lexeme. For example, while English man becomes men in the plural, moon is not a different form of the same word. Vowels are especially important to the structures of words in languages that have very few consonants (like Polynesian languages such as Maori and Hawaiian), and in languages whose inventories of vowels are larger than their inventories of consonants.