The distinction between vowels and consonants is very old. Vowel is a sound of noise, which is formed without obstruction, when the air goes through pharynx and mouth.
There are general principals of vowel articulation in the English language:
1) Vowels are based on voice.
2) The muscular tension is spread over all the organs of speech.
3) the air stream passes through supra-laringal cavities freely.
4) the breath force is rather weak.
The whole speech apparatus takes part in producing them.
Each phoneme has its own specific features, which distinguish it from the other phoneme of the same language.
The vowel system in English consists of 20 vowels.
According to the stability of articulation, they are divided into three groups:
1. short monophthongs [æ, I, e, ɔ, ə, ʌ, u]
2. long monophthongs [a:, i:, ɔ:, ə:, u:]
3. diphthongs [ai, ei, ɔi, au, əu, iə, uə, ɛə]
Monophthong – a single vowel articulated without change in quality.
Diphthong – a vowel phoneme which consists of two elements: nucleus and glide.
Triphthong – a vowel sound which consists of two elements: diphthong and neutral sound.
According to the position of the tongue in the horizontal plane, there are front, back, mixed vowels.
According to the position of the tongue in the vertical plane they may be open and closed.
According to the quantity they are long or short.
According to the position of the lips, they may be rounded and unrounded.
Not all the vowels are free in their distribution. Neutral sound has a place only in unstressed position. The other vowels may be in stressed and unstressed position.
Short vowels are only in closed syllables, while long monophthongs and diphthongs are used in both types of syllables.
The English vowels have various functions:
1) they distinguish the form of the verbs ( rise- rose)
2) they distinguish parts of speech ( nation – national)