1.2.3. Vowels

In the production of vowel sounds, the articulators do not come very close together, and the pasage of the air stream is relatively unobstructed. Vowels cannot easily be described in terms of 'a place of articulation'. Instead, they are classified in terms of an abstract vowel space which is represented by the four-sided figure known as the 'Vowel Quadrilateral' (trapezium) or Vowel Chart. This space bears a relation, though not an exact one, to the position of the tongue in vowel production (Figure 6).

For the vowel labelled /i:/ in heed the body of the tongue is displaced forwards and upwards in the mouth, towards the hard palate. By taking it to the extreme position (after which the air becomes turbulent, resulting in a fricative) we can get the first reference point for vowel description. Since the tongue is near the roof of the mouth this vowel is described as close, and since the highest point of the tongue is at the front of the area where vowel articulations are possible, it is described as front.

Conversely, for the vowel labelled /a:/ as in father, the tongue body is displaced downwards and backwards, narrowing the pharynx. The most extreme version of this sound is taken as a second reference point. The space between the tongue and the roof of the mouth is as large as possible, so this vowel is described as open, and the tongue is near the back of the mouth, so it is described as back.

The positions of the tongue for /u:/, a close back vowel in doom, and for /ae/ in RP cat, a front open vowel, will also provide fixed references. By joining the circles representing the highest points of the tongue in the four references we can get the boundary of the space within which vowels can be produced. The vowel space can be stylized as the quadrilateral in which two fully front vowels /e/ and /e/ are defined by auditory impressions between /i:/ and /ae/, and two fully back vowels, /э:/ and /n/, are defined as the two steps between /u:/ and /a:/ (Figure 7).

As a result we will have four degrees of closeness-openness for English: high (close), mid-high, mid-low (mid-open), low (open) and three divisions along the front-back dimension: front, central, back. The amount of four vertical and three horizontal divisions is maximal for any language of the world. In Russian, for instance, there is only one low open vowel [a], so the vowel chart will look like a triangle (Figure 8):

The position of the lips varies considerably in different English vowels. They are generally closer together in the mid and high back vowels, as /u, u:, o:, t>, эи, аи/ in book, food, cord, cot, coat, cow. Vowels may be described as being rounded (with lip rounding) or unrounded (the lips are in the neu­tral position). In English lip rounding is not contrastive because no two vowels are contrasted in being rounded or unrounded without a change in quality which always comes first, but it is an indispensable feature of the vowels listed above.

The features we have looked at are the most important ones, but there are many other ways in which vowels differ from each other. Relatively slight movements of the tongue produce quite distinct auditory differences in vowel quality. If the quality of a vowel stays unchanged during its articulation, the term pure vowel, or monophthong, is used, as in red, car, sit, sat. If there is an evident change in quality, it is a gliding vowel. If two auditory elements are involved, the vowel is referred to as a diphthong, e.g. light, say, go; if three elements, as a triphthong, e.g. fire, hour (which tend to be monophthongs today).

Note: In American English historically long vowels and diphthongs are defined as one group of tense vowels, and the glides of diphthongs are not indicated in the symbols: /e/, for example, is a symbol of diphthong /ei/, /o/ is a symbol of the British diphthong /эо/, actually pronounced by Americans as [oo]. The reason for it is that long vowels and diphthongs have a lot in common: they are peripheral in the vowel space, and there­fore long and tense; long monophthongs are also diphthongized, at least /i:/ and /u:/ certainly are. Incidentally, these vowels are represented in American books as /i/ and /u/, with length unmarked. The facts show that classification depends on the framework of the school and the author.

Yet another way of classifying vowels is in terms of the amount of muscular tension required to produce them: vowels articulated in extreme positions are more tense than those articulated nearer the centre of the mouth, which are lax: cf. seat vs. sit, flute vs. foot.

There are also differences in vowel length, and some languages con­trast long and short vowels. British English, RP accent, for example, is claimed to have 20 vowels, usually divided into the following groups:

• short vowels: i, e, зе, л, d, и, з

• long vowels: i:, а:, з:, о:, и:

• diphthongs: ei, ai, or, au, эи, is, еэ, из

In English long vowels and diphthongs happen to be more peripheral sounds which require more tension and time for their articulation, and they also have specific vowel quality to identify them. Therefore, for the English language classification of vowels into long and short also means grouping them into tense and lax, while the identity of each particular vowel may rest on vowel quality alone. In other words, all long vowels and diphthongs are long and tense; short vowels are lax. There are no two vowels in English which are different in length or tenseness alone as there is always a distinctive vowel quality to identify each vowel. This accounts for the fact that vowel classifications in English are normally based on vowel quality alone.

The long/short, tense/lax categories of vowels are also distinguished from the point of view of energy discharge: short vowels are checked due to the accompanying glottal activity, involving a rapid energy discharge in a short time interval, while long vowels are unchecked (sometimes called free because of the fading nature of energy discharge), which applies to all non-glottalized sounds, signalled acoustically by a lower energy discharge over a large time interval.

To complete the list of possible vowel distinctions in different languages we can say that some languages have nasalized vowels in addition to normal (oral) ones; in these some of the air-flow is allowed to escape through the nose. French is a well-known example — the vowels in fin, bon, dans, brun are nasalized. Among other European languages, Portuguese and Polish also have nasalized vowels. In English nasalized vowels are pro­nounced under certain circumstances, before a nasal consonant, for example, in men but this quality change is allophonic, i.e. it does not change the meaning of a word (see Part II. Phonology).

In summary, vowels can be classified in terms of the following factors among which the first three are most important for English vowel quality:

• height of the body of the tongue (high, mid-high, mid-low, low)

• front-back position of the tongue (front, central, back)

• degree of lip rounding (rounded, unrounded)

• stability of articulation (monophthong, diphthong)

• duration (length) of the vowel segment (short, long)

• tenseness of the vocal organs (lax, tense)

• position of the soft palate (oral, nasal)

• energy discharge (checked, unchecked).

It should be noted here that, useful as it is for practical phonetics of teaching English, the description of vowels in terms of articulation is not quite accurate. Actually the two high vowels, /i:/ and /u:/ for example, are not equally high, /i:/ being much higher. Then there is the shape of the tongue and of the pharynx which affect the quality of vowels. We have to turn to acoustics to measure vowel sound properties more objectively.