Theory of phonetics

Vowel length or quantity. Any vowel has a physical duration – time which is required for its production (articulation). When in connected speech they influence one another. Duration is one of the characteristics of a vowel which is modified by and depends on the following factors:

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  its own length;
  
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  the accent (stress) in which it occurs;
  
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  phonetic context;
  
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  the sound position in a syllable;
  
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  the position in a rhythmic structure;
  
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  the position in a tone group;
  
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  the position in a phrase;
  
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  the position in an utterance;
  
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  the tempo of the whole utterance;
  
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  the type of pronunciation;
  
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  the style of pronunciation.
  

The approach of D. Jones*, an outstanding British phonetician, extends the principle, underlining phonological relevance (meaningfulness) of vowel quantity. (Jones D. Phoneme: its nature and Use. – Cambridge, 1967) That means that words in such pairs as [kIn] – [ki:n], [bIt] – [bi:t], ['fLwE:d] (foreword) - ['fLwqd] (forward) are distinguished from one another by the opposition of different length, which D. Jones calls chronemes. This difference is considered to be decisive and the difference in quality (the position of the active organ of speech) is subordinate to the difference in quantity. The following oppositions can be:
[V] – [H] full – fool;
[E:] – [q] is fairly specific because the [q] phoneme never occurs in a stressed syllable and forms the core of unstressed vocalism in English. The phoneme [E:]
seldom occurs in an unstressed syllable.
[R] – [A] is arbitrary as in cart – cut.
[L] – [P] this quantitative correlation exists, i.e. forks – fox.
It is generally known that a voiced consonant following a vowel increases its length, so in the word beat [i:] is only half about as long as the [i:] of the word bee and may approximately have the same duration as the [I] vowel of bid. But still the words bid and bead are perceived as different words because the vowels are different in quality, [I] being front retracted, a pure monophthong, and [i:] being front close (narrow) and a diphthongized vowel.