Stability of articulation:

1. monophthongs,

2. diphthongs,

3. diphthongoids.

Monophthongs don’t change their articulation during the pronunciation (with the exception of [i:] – [u:]). They are divided into short and long.

3. Vowel length gives us two groups of vowel sounds:

   1. long;

   2. short

which are distinct in a number of features, such as:

4. Tenseness – characterizes the state of the organs of speech at the moment of production a vowel. Long vowels, including diphthongs, are tense, short vowels are lax,

5. Energy discharge – the quality depends on the character of the articulatory transition from a vowel to a consonant. Long vowels are unchecked (free), and short vowels are checked, i.e. produced with accompanying glottal activity, involving a rapid energy discharge in a short time interval,

6. Position of the lips may distinguish:

   1. rounded;

   2. unrounded vowels

The higher the tongue raises the more rounded the lips are.

7. Position of the soft palate: all English vowels are oral; other languages, like French, for example, may have nasal vowels; English vowels may be nasalized before a nasal consonant but the nasal quality change is not phonemic as it is not contrastive, it is allophonic.

All the 20 vowel phonemes can be distinguished by quality alone, and that makes this feature phonemic.

Thus the 20 RP English vowels are grouped in the following way: twelve monophthongs (seven short vowels and five long ones) and eight diphthongs:

υә