According to the tongue position.
According to the lip position.
According to the length of the vowel.
According to the degree of tenseness.
(I). In vowel production the tongue may move in a) a horizontal direction (forward and backward) and b) in a vertical direction (to various heights in the mouth).
a) According to the position of the bulk of the tongue (or the horizontal movement of the tongue) vowels are divided into five groups: a) front, b) front-retracted, c) central, d) back and e) back-advanced.
When the bulk of the tongue moves forward, the front part of the tongue is raised highest towards the hard palate. Vowels produced with this position of the tongue are called front and are subdivided into:
fully front: /i:, e, æ/, the nuclei of the diphthongs /eı, εə, aı/;
front-retracted: /ı/ and the nuclei of the diphthongs /aʊ, aı/.
Central vowels are those in which the central part of the tongue is raised towards the juncture between the hard and the soft palate. In the production of central vowels (/Λ, ə:, ə/ and the nucleus of the diphthong /ǝʊ/) the tongue is almost flat.
When the bulk of the tongue moves backwards, it is usually the back part of the tongue that is raised highest towards the soft palate. Vowels produced with the tongue in this position are called back. They are subdivided into:
fully back: /ɒ, ɔ:, u:/, the nucleus of the diphthong /ɔı/.
back - advanced: /ʊ, ɑ:, Λ/.
NOTE:
Some phoneticians (G.P. Torsuyev, A.L. Trakhterov, H. Sweet) considered that /ə:/ and /ə/ are mixed not central vowels. Shcherba does not mention central vowels at all, he considers /ə:, ə/ mixed.
b) According to the vertical movement of the tongue vowels are subdivided into three groups:
a) close (or high): /i:, ı, u:, ʊ/;
b) mid-open (or half-open, or mid): /e, ə:, ə, ɔ:/ and the nuclei of /εə/, /ǝʊ/; c) open (or low): /æ, α:, ɒ, Λ/ and the nuclei of /aı/, /aʊ/.
Each of these three main tongue-positions has two variations: narrow and broad.
narrow
variation: /i:, u:/
high
broad variation: /ı, ʊ/
narrow variation: /e, ə:/ and the nucleus of /əʊ/
mid
broad variation: /ɔ:, ə/ and the nucleus of /εə/
narrow variation: /Λ, ɔ:/ and the nucleus of /ɔı/
low
broad variation: /æ, ɑ:, ɒ/ and the nuclei of /aı/ and /aʊ/.
(II). According to the position of the lips vowels are classified into: a) rounded /ɒ, ɔ:, ʊ, u:/ and the nuclei of /ǝʊ/, /ɔı/ and b) unrounded /i:, ı, e, æ, α:, Λ, ə:, ə/ and the nuclei of all the diphthongs except those of /ǝʊ/, /ɔı/.
NOTE:
Rounded – produced when the lips are more or less rounded and slightly protruded.
Unrounded – produced when the lips are spread or neutral.
The Russian rounded vowels are pronounced with more lip protrusion than the English rounded vowels.
(III). According to their length English vowels are subdivided into a) (historically) long /i:/, /ɑ:/, /ɔ:/, /u:/, /ə:/ and b) (historically) short /ı/, /e/, /æ/, /ɒ/, /ʊ/, Λ/, /ə/.
NOTE:
There is no differentiation of Russian vowel phonemes according to length.
Vowel length may depend on a number of linguistic factors:
1) position of the vowel in a word,
2) word stress,
3) the number of syllables in a word,
4) the character of the syllabic structure,
5) sonority.
1) Positional dependence of length can be illustrated by the following example:
be - bead - beat
tie - tied - tight
we - weed - wheat
In the terminal position a vowel is the longest, it shortens before a voiced consonant, it is the shortest before a voiceless consonant.
2) A vowel is longer in a stressed syllable than in an unstressed one:
forecast n /’fɔ:kɑ:st/ прогноз
forecast v /fɔ:’kɑ:st/ предсказывать погоду
In the verb /ɔ:/ is shorter than in the noun, though it may be pronounced with /ɔ:/ equally long.
3) If we compare a one-syllable word and a word consisting of more than one syllable, we may observe that similar vowels are shorter in a polysyllabic word. Thus in the word verse /ə:/ is longer than in university.
4) In words with open type of syllable the vowel length is greater than in words with closed type of syllable.
5) Vowels of low sonority are longer than vowels of greater sonority, because the speaker unconsciously makes more effort to produce greater auditory effect while pronouncing vowels of lower sonority, thus making them longer (e.g. /ı/ is longer than /ɒ/; /i:/ is longer than /ɑ:/, etc.).
Besides vowel length depends on the tempo of speech: the higher the rate of speech the shorter the vowels.
D. Jones treats quantity independently of the vowel sounds themselves. Thus he treats /i:, ı/ as positional allophones of one phoneme.
Length is a non-phonemic feature in English but it may serve to differentiate the meaning of a word. This can be proved by minimal pairs, e.g.
beat /bi:t/ бить - bit /bıt/ кусочек
deed /di:d/ дело (деяние) - did /dıd/ (с)делал
G.P. Torsuyev considered /æ/ to be a long vowel, but he admits that in certain position /æ/ can be a short phoneme. English phoneticians state that it is a short one, though in some words it may be long.
(IV). According to the degree of tenseness long vowels are defined as tense (produced when the organs of speech (the muscles of the tongue, the walls of the mouth resonator and of the pharynx) are tense) and short as lax (produced with lesser tenseness of the speech organs). The term “tense” was introduced by H. Sweet, who stated that the tongue is tense when vowels of narrow variety are articulated.
In other words, when the muscles of the lips, tongue, cheeks and the back walls of the pharynx are tense, the vowels produced can be characterized as “tense”. When these organs are relatively relaxed, lax vowels are produced.
NOTE:
Russian vowel phonemes are not differentiated according to their tenseness, but one and the same vowel is more tense in a stressed syllable than in an unstressed one.
D. Jones considers only the long /i:/ and /u:/ to be tense. G.P. Torsuyev defines all long English vowels as tense as well as /æ/, all short vowels he considers to be lax.
This problem can be solved accurately only with the help of electromyography.
In addition to the above principles, the English vowels are also classified according to the character of their end. From this point of view they may be a) checked and b) unchecked/free.
Checked vowels are those which are pronounced without any lessening the force of utterance towards their end. They have, therefore, a strong end. They end abruptly and are interrupted by the following consonant. Therefore they can only occur in a closed syllable, i.e. a syllable ending in a consonant sound. The English short vowels under stress are checked. So are the English long vowels and diphthongs when followed by voiceless consonants, e.g. /bet/, /nɒt/, /pʊl/, /hæt/, /spi:k/, /taıp/.
Unchecked vowels are those which are pronounced with lessening the force of utterance towards their end. Therefore, they have a weak end.
The English long vowels and diphthongs when stressed both in open and in closed syllables followed by voiced consonants are unchecked. The same is true of all the English unstressed vowels no matter whether long or short, e.g. /fri:/, /kɑ:d/, /taım/, /´ætıtju:d/, /´wındǝʊ/, /´sıtı/, /´fɑ:ðə/. In Russian all vowels are unchecked.
NOTE:
This principle is not singled out by British and American phoneticians.
The English vowel /ə/ does not occur in a stressed context. It must be regarded outside the free/checked classes.
The classification of vowels suggested by Soviet authors is more exact from the articulatory point of view than that suggested by foreign authors.