A monophthong is a pure vowel, one in which the tongue position and lip shape remain relatively stable throughout the sound. This contrasts with diphthongs, where the tongue glides from one position to another, and triphthongs, which involve three positions.
Received Pronunciation (RP) has 12 monophthong phonemes:
| Phoneme | Keyword | Description |
|---|---|---|
| /ɪ/ | kit | Near-close, near-front, unrounded |
| /e/ | dress | Open-mid, front, unrounded |
| /æ/ | trap | Near-open, front, unrounded |
| /ʌ/ | strut | Open-mid, central, unrounded |
| /ɒ/ | lot | Open, back, rounded |
| /ʊ/ | foot | Near-close, near-back, rounded |
| /ə/ | about, comma | Mid, central, unrounded (see Schwa) |
| Phoneme | Keyword | Description |
|---|---|---|
| /iː/ | fleece | Close, front, unrounded |
| /ɑː/ | bath, palm | Open, back, unrounded |
| /ɔː/ | thought, north | Open-mid, back, rounded |
| /uː/ | goose | Close, back, rounded |
| /ɜː/ | nurse | Open-mid, central, unrounded |
The length mark /ː/ indicates that long vowels are typically longer in duration than short vowels, though the distinction is one of quality as much as quantity: long and short vowels differ in tongue position and tenseness, not just duration.
Vowels are plotted on a quadrilateral (trapezium) representing the vowel space, determined by two dimensions:
Front Central Back
Close iː ɪ ʊ uː
ə
Open-mid e ɜː ʌ ɔː
Near-open æ
Open ɑː ɒLip rounding correlates with backness in English: back vowels /ɒ ɔː ʊ uː/ are rounded; front and central vowels are unrounded.
The traditional "long vs short" labels are somewhat misleading:
| L1 | Typical inventory | Key English difficulties |
|---|---|---|
| Vietnamese | 11-14 monophthongs (varies by dialect) | Similar size, but different qualities; /æ/ and /ʌ/ are problematic |
| Spanish | 5 vowels /a e i o u/ | Most English distinctions collapsed: /ɪ/-/iː/, /ʊ/-/uː/, /æ/-/ʌ/ |
| Japanese | 5 vowels /a i u e o/ | Same issues as Spanish |
| Arabic | 3 short + 3 long /a i u aː iː uː/ | Severely reduced system; many English contrasts absent |
Some monophthong contrasts carry heavy communicative weight:
In unstressed syllables, most monophthongs reduce to schwa /ə/ (see Vowel Reduction). Learners from syllable-timed languages often maintain full vowel quality in unstressed positions, affecting rhythm.