Theory of phonetics

Stability of articulation. There are two possible varieties:

1. 
   the tongue position is stable;
   
2. 
   it changes, that is the tongue moves from one position to another.
   

In the first case the articulated vowel is relatively pure, in the second case a vowel consists of two clearly perceptible elements. There exists in addition a third variety, an intermediate case

3. 
   when the change in the tongue position is fairly weak.
   

So, according to this principle the English vowels are subdivided into:

• 
  monophthongs;
  
• 
  diphthongs;
  
• 
  diphthongoids ([i:], [u:]).
  

A. C. Gimson distinguishes 20 vocalic phonemes which are made of vowels and vowel glides:
1) short phonemes (7) - [I], [e], [x], [P], [V], [A], [q]
2) long phonemes (13) - [R], [L], [W], [J], [H], [eI], [EV],
[aI], [aV], [Pu], [Iq], [Fq], [Vq].
3) relatively pure (5) - [R], [L], [W], [J], [H]
4) the rest are referred to long phonemes with different glides:
- [eI], [aI], [PI] – with a glide to [I];
- [EV], [aV] - with a glide to [V];
- [Iq], [Fq], [Vq] - with a glide to [q].
In modern English the tendency for diphthongization is becoming gradually
stronger. Diphthongs are complex entities just like affricates. Soviet scholars (V. A. Vassilyev, L. R. Zinder) grant the English diphthongs monophonemic status on the basis of articulatory, morphological and syllabic indivisibility as well as the criteria of duration and commutability. As to articulatory indivisibility of the diphthongs it could be proved by the fact that neither morpheme nor syllable boundary that separate the nucleus and the glide can pass within it. For example, saying ['seI-IN], crying ['kraI-IN], enjoying [In-'GOI-IN], lower ['lEV-q], going ['gEV-IN], nearer ['nIq-rq], staring ['stFq-rIN], poorer ['pVq-rq]. The present study of the duration of diphthongs shows that the length of diphthongs is the same as that that characterizes the English long monophthongs in the same phonetic context. For example, [baIt] – [bi:t], [bEVt] – [bLt]. Any diphthong could be commutated with practically any vowel.
In Russian there are no diphthongs or diphthongoids as phonemic entities. Such combinations of sounds as [йа, йо, йу], [ой, ай], [ау, уа] (яр, йог, юный, бой, май, мяукать, пуанты), and others are biphonemic clusters, consisting of either of a vowel and the Russian consonant [й] or two vowels. Both elements are equally energetic and distinct. The English diphthongs consist of two elements, the first of which, the nucleus, being strong and distinct and the second, the glide, being very weak and indistinct.