The English Vowel and Diphthong System: A Comprehensive Guide
The English Vowel System
The English vowel system of Received Pronunciation (RP) is generally considered to consist of twelve pure vowels and eight diphthongs.
What is a Vowel?
In phonetics, a vowel is a speech sound characterized by the continuous vibration of the vocal cords (voicing) and the absence of any narrowing or obstruction of the airflow. The quality of a vowel phoneme distinguishes it from others and is primarily determined by the position of the tongue body and the shape of the lips.
The Vowel Quadrilateral
Phoneticians use a vowel quadrilateral to represent the position of the tongue within the oral cavity. This chart symbolizes the two fundamental dimensions of vowel quality:
- The part of the tongue that is raised (front, central, or back)
- The height to which it is raised (high, mid-high, mid-low, or low)
Classifying Vowels
Based on these dimensions, vowels are categorized as follows:
- Front Vowels: /iː ɪ e æ/
- Central Vowels: /ɜː ə ʌ/
- Back Vowels: /ɑː ɒ ɔː ʊ uː/
Lip Rounding and Quantity
Vowel sounds are also characterized by the position or shape of the lips:
- Rounded: /ɒ ɔː ʊ uː/
- Unrounded: /iː ɪ e æ ɑː ʌ ɜː ə/
Another important characteristic is quantity, often indicated by the length mark [:].
- Long Vowels: /iː ɑː ɔː uː ɜː/
- Short Vowels: /ɪ e æ ɒ ʊ ə ʌ/
However, vowel length can be influenced by the surrounding phonetic environment. For instance, prefortis clipping occurs when long vowels are followed by voiceless consonants like /p, t, k, tʃ, f, θ, s, ʃ/, causing them to become shorter or half-long. In such cases, vowel quality becomes more significant than quantity.
Checked and Free Vowels
Vowels can be checked or free based on their phonological distribution:
- Checked Vowels: /ɪ e æ ɒ ʊ ə ʌ/ cannot occur in final stressed open syllables.
- Free Vowels: Long vowels and diphthongs have no such restriction.
Stressed and Unstressed Syllables
English distinguishes between stressed and unstressed syllables. Stressed syllables can contain any vowel phoneme (except schwa) and any of the eight diphthongs, forming the strong vowel system. Unstressed syllables typically contain vowels from the weak system: /ə ɪ ʊ/.
Weak vowels are also commonly found in monosyllabic function words like articles, prepositions, possessive adjectives, conjunctions, auxiliary verbs, and pronouns.
The English Diphthongs
While pure vowels (monophthongs) have a steady quality, diphthongs are vowel glides where the tongue moves from one position to another, resulting in a change in vowel quality.
Characteristics of Diphthongs
The eight diphthongs of RP English (/aɪ eɪ ɔɪ aʊ ɪə eə ʊə/) share characteristics with long vowels, including length and susceptibility to shortening effects of voiceless consonants.
Classifying Diphthongs
Diphthongs are classified based on several features:
- Falling/Diminuendo: All RP diphthongs are stressed on the first element.
- Wide/Narrow: Based on the degree of tongue movement (e.g., /taɪ/ is wide, /teɪk/ is narrow).
- Front/Back: Based on the quality of the starting point.
- Closing/Centring: Based on the quality of the end point (e.g., /aɪ eɪ ɔɪ aʊ əʊ/ are closing, /ɪə eə ʊə/ are centring).
The schwa element in centring diphthongs often derives historically from [r], which was lost in non-rhotic accents like RP except before a vowel. Therefore, the letter ‘r’ in many spellings can be seen as an orthographic representation of schwa.