I. According to the stability of articulation all English vowels are divided into 3 groups:
1. Pure vowels or monophthongs (12)
2. Diphthongs (8)
3. Diphthongoids (2)
Monophthongs are vowels the articulation of which is almost unchanging. The quality of such vowels is relatively pure. The English monophthongs are [i, e, æ, ɑ:, ɒ, ɔ:, ʌ, ɜ:, ə, ʊ].
In the pronunciation of diphthongs the organs of speech glide from one vowel position to another within one syllable. The starting point, the nucleus, is strong and distinct. The glide which shows the direction of the quality change is weak. The English diphthongs are [ei, ai, ɔi, aʊ, iə, ɛə, ʊə].
In the pronunciation of diphthongoids the articulation is slightly changing but the difference between the starting point and the end is not distinct as it is in the case of diphthongs. English diphthongoids are [i:, u:]. In Russian the initial [o] may serve as an example of a Russian diphthongoid in the word “очень”.
II. The changes in the position of the tongue determine largely the shape of the mouth and pharyngeal cavities. The tongue may move forward and backward, up and down, thus changing the quality of vowel sounds. According to the tongue position English vowels may be:
1. Frontvowels: [i:, e, æ] – the tongue is in the front part of the mouth and the front part of it is raised to the hard palate.
2. Front-retracted vowels: [i] – the tongue is in the front part of the mouth and is slightly retracted and the part of the tongue is nearer to front is raised.
3. Centralvowel: [ʌ, ɜ:, ə,]
4. Back vowels: [ɑ:, ɒ, ɔ:, u:]
5. Back-advanced vowels: [ʊ]
Moving up and down in the mouth various parts of the tongue may be raised to different height towards the roof of the mouth (close, mid, open vowels). To make classification more precise it is necessary to distinguish broad and narrow variants of close, mid and open vowels. There are:
|| Narrow variant
|| Broad variant
| Close vowels
|| [i:, u:]
|| [i, ʊ ]
| Mid vowels
|| [e, ɜ:, ɜ ]
|| [ʌ, ə, ɛ]
| Open vowels
|| [ɔ:, ɔ]
|| [æ, ɑ:, ɒ, a]
III. According to the lip position there are:
1. Unrounded vowels [i:, i, e, æ, ɑ:, ʌ, ɜ:, ə ] – the lips are neutral or spread.
2. Rounded vowels [ɒ, ɔ:, ʊ, u:] - lips are protruded.
IV. The quality of all monophthongs in the stressed position is strongly affected by the following consonant of the same syllable. According to the character of vowel end the vowels may be:
1. Checked (better, cart) – a stressed vowel is followed by a strong voiceless consonant and a vowel is cut off by it.
2. Free (before, money,begger, bead) – a vowel is followed by a weak consonant or by no consonant and the end of it is weak. Such vowels are in closed syllables ending in a voiced consonant or in an open syllable.
V. According to the length the vowels may be:
1. Long [i; ɑ:, ɔ:, u:, ɜ:]
2. Short [i, e, ɒ , ʊ, ʌ, ə]