Parameters for Describing the Diphthongs of the English Sound System
Parameters for Describing the Diphthongs of the English Sound System
When we speak English, we do not always use simple vowel sounds. Sometimes the voice starts from one vowel position and moves smoothly towards another vowel position within the same syllable. This moving vowel sound is called a diphthong.
A simple example is the vowel sound in my /maɪ/. The sound does not stay in one place. It begins with /a/ and glides towards /ɪ/. That movement is what makes it a diphthong.
In simple terms, a diphthong is a vowel sound that glides from one vowel quality to another in one syllable (Roach, 2009; Ladefoged & Johnson, 2014).
What Makes a Diphthong Different from a Pure Vowel?
A pure vowel, also called a monophthong, has one steady sound. For example, the vowel in see /siː/ is fairly steady. The tongue and lips do not move much while the vowel is being pronounced.
A diphthong, however, changes as it is spoken. The mouth begins in one position and moves towards another. For example:
| Word | IPA | Vowel movement |
|---|---|---|
| day | /deɪ/ | /e/ glides towards /ɪ/ |
| my | /maɪ/ | /a/ glides towards /ɪ/ |
| boy | /bɔɪ/ | /ɔ/ glides towards /ɪ/ |
| go | /ɡəʊ/ | /ə/ glides towards /ʊ/ |
| now | /naʊ/ | /a/ glides towards /ʊ/ |
So, the key idea is movement. A diphthong is not two separate syllables. It is one vowel sound with a glide inside it.
The Main Parameters for Describing English Diphthongs
English diphthongs can be described by looking at a few simple features. These features help us explain how the sound is made and how it differs from other vowel sounds.
1. The Starting Point of the Sound
The first thing to describe is where the diphthong begins. This is the first vowel quality heard in the sound.
For example, in /aɪ/, as in my /maɪ/, the sound starts with /a/. In /eɪ/, as in day /deɪ/, the sound starts with /e/.
| Diphthong | Example | Starting point |
|---|---|---|
| /eɪ/ | day /deɪ/ | starts around /e/ |
| /aɪ/ | my /maɪ/ | starts around /a/ |
| /ɔɪ/ | boy /bɔɪ/ | starts around /ɔ/ |
| /əʊ/ | go /ɡəʊ/ | starts around /ə/ |
| /aʊ/ | now /naʊ/ | starts around /a/ |
The starting point matters because it helps us separate one diphthong from another. For instance, /eɪ/ in day and /aɪ/ in my both move towards /ɪ/, but they begin from different places.
2. The Ending Point of the Sound
The second thing to describe is where the sound moves to. This is called the glide or the ending point.
In English, many diphthongs move towards /ɪ/ or /ʊ/. Some move towards /ə/ in British-style descriptions of English pronunciation (Roach, 2009).
| Diphthong | Example | Ending point |
|---|---|---|
| /eɪ/ | face /feɪs/ | moves towards /ɪ/ |
| /aɪ/ | price /praɪs/ | moves towards /ɪ/ |
| /ɔɪ/ | choice /tʃɔɪs/ | moves towards /ɪ/ |
| /əʊ/ | goat /ɡəʊt/ | moves towards /ʊ/ |
| /aʊ/ | mouth /maʊθ/ | moves towards /ʊ/ |
| /ɪə/ | near /nɪə/ | moves towards /ə/ |
| /eə/ | square /skweə/ | moves towards /ə/ |
| /ʊə/ | cure /kjʊə/ | moves towards /ə/ |
This is why diphthongs are often described as gliding vowels. The tongue does not stay still. It moves from one vowel position towards another.
3. The Direction of Tongue Movement
Another important parameter is the direction of movement in the mouth. The tongue may move upwards, backwards, forwards, or towards the centre of the mouth.
Some diphthongs are called closing diphthongs because the mouth becomes more closed as the sound is produced. For example:
| Closing diphthong | Example |
|---|---|
| /eɪ/ | day /deɪ/ |
| /aɪ/ | my /maɪ/ |
| /ɔɪ/ | boy /bɔɪ/ |
| /əʊ/ | go /ɡəʊ/ |
| /aʊ/ | now /naʊ/ |
They are called closing diphthongs because the tongue moves towards a closer vowel position, such as /ɪ/ or /ʊ/.
Some diphthongs are called centring diphthongs because they move towards the central vowel /ə/. Examples include:
| Centring diphthong | Example |
|---|---|
| /ɪə/ | near /nɪə/ |
| /eə/ | hair /heə/ |
| /ʊə/ | poor /pʊə/ |
These are common in many British-style descriptions of English, though pronunciation differs from accent to accent.
4. Tongue Height
Tongue height means how high or low the tongue is in the mouth when the sound begins and ends.
For example, /aɪ/ begins with a low/open vowel quality /a/ and moves towards a higher/closer vowel quality /ɪ/. The word time /taɪm/ shows this clearly.
The diphthong /eɪ/, as in face /feɪs/, begins from a mid vowel position and moves towards the higher vowel /ɪ/.
So, when describing a diphthong, we can ask:
Does the tongue begin low, mid or high?
Does it move higher as the sound continues?
This helps us explain the physical movement behind the sound.
5. Tongue Position: Front, Central or Back
Another parameter is whether the tongue is in the front, centre or back part of the mouth.
For example:
| Diphthong | Example | Simple description |
|---|---|---|
| /eɪ/ | day /deɪ/ | front area moving towards /ɪ/ |
| /aɪ/ | my /maɪ/ | open area moving towards /ɪ/ |
| /ɔɪ/ | boy /bɔɪ/ | back rounded area moving towards /ɪ/ |
| /əʊ/ | go /ɡəʊ/ | central area moving towards /ʊ/ |
| /aʊ/ | now /naʊ/ | open area moving towards /ʊ/ |
This means that a diphthong is not described only by its spelling. It is described by the actual movement of the tongue and mouth.
6. Lip Shape
Lip shape also matters. Some diphthongs involve rounded lips, while others do not.
For example, /ɔɪ/ as in boy /bɔɪ/ begins with a rounded vowel quality. The lips are rounded at the beginning, then relax as the sound moves towards /ɪ/.
The diphthong /əʊ/, as in British English go /ɡəʊ/, moves towards /ʊ/, which usually involves lip rounding. The same is true of /aʊ/, as in now /naʊ/.
| Diphthong | Example | Lip movement |
|---|---|---|
| /ɔɪ/ | boy /bɔɪ/ | begins with rounded lips |
| /əʊ/ | go /ɡəʊ/ | moves towards rounded lips |
| /aʊ/ | now /naʊ/ | moves towards rounded lips |
| /eɪ/ | day /deɪ/ | generally unrounded |
| /aɪ/ | my /maɪ/ | generally unrounded |
Lip shape is especially useful when comparing sounds such as /aɪ/ and /aʊ/. They may start in a similar open position, but they move in different directions.
7. Length and Stress
Diphthongs in English are usually longer than short pure vowels. For example, the vowel sound in sit /sɪt/ is short, while the vowel sound in side /saɪd/ is longer.
Stress can also affect how clearly a diphthong is pronounced. In stressed syllables, the glide is usually clearer. In weak or fast speech, the glide may become less noticeable.
Compare:
| Word | IPA | Comment |
|---|---|---|
| my | /maɪ/ | clear diphthong |
| maybe | /ˈmeɪbi/ | /eɪ/ is clear in the stressed syllable |
| today | /təˈdeɪ/ | /eɪ/ is clearer in the stressed final syllable |
This is why pronunciation may sound slightly different in careful speech and fast everyday speech.
8. Accent Variation
English diphthongs vary across accents. British English, American English, Nigerian English, Australian English and other varieties of English may pronounce some diphthongs differently.
For example, the vowel in go is often written as /əʊ/ in many British English descriptions, but as /oʊ/ in many American English descriptions. So:
| Word | British-style transcription | American-style transcription |
|---|---|---|
| go | /ɡəʊ/ | /ɡoʊ/ |
| boat | /bəʊt/ | /boʊt/ |
| home | /həʊm/ | /hoʊm/ |
Also, centring diphthongs such as /ɪə/, /eə/ and /ʊə/ may be pronounced differently in rhotic accents, especially where /r/ is pronounced after vowels, as in many forms of American English (Wells, 1982; Roach, 2009).
This does not mean one accent is “wrong”. It simply means that English has widely accepted varieties.
Common English Diphthongs
A common British-style list of English diphthongs includes the following:
| Diphthong | Example word | IPA transcription |
|---|---|---|
| /eɪ/ | face | /feɪs/ |
| /aɪ/ | price | /praɪs/ |
| /ɔɪ/ | choice | /tʃɔɪs/ |
| /əʊ/ | goat | /ɡəʊt/ |
| /aʊ/ | mouth | /maʊθ/ |
| /ɪə/ | near | /nɪə/ |
| /eə/ | square | /skweə/ |
| /ʊə/ | cure | /kjʊə/ |
Some modern speakers may pronounce a few of these differently. For example, poor may be pronounced /pʊə/ by some speakers, but /pɔː/ by others. This is why accent must always be considered when discussing diphthongs.
How to Describe a Diphthong Fully
To describe a diphthong well, we can answer these questions:
Where does the sound begin?
Where does it glide to?
Is the tongue moving upwards, backwards, forwards or towards the centre?
Are the lips rounded or unrounded?
Is the diphthong closing or centring?
Does the pronunciation change across accents?
For example, /aɪ/ as in my /maɪ/ can be described like this:
The diphthong /aɪ/ starts with an open vowel quality /a/ and glides towards /ɪ/. The tongue moves upwards and forwards. It is a closing diphthong. The lips are generally unrounded. It occurs in words such as my /maɪ/, time /taɪm/ and price /praɪs/.
Another example is /aʊ/ as in now /naʊ/:
The diphthong /aʊ/ starts with an open vowel quality /a/ and glides towards /ʊ/. The tongue moves upwards and backwards, and the lips become more rounded towards the end of the sound. It is a closing diphthong. It occurs in words such as now /naʊ/, mouth /maʊθ/ and house /haʊs/.
Why Diphthongs Matter
Diphthongs are important because they can change the meaning of words. For example:
| Word 1 | Word 2 | Difference |
|---|---|---|
| late /leɪt/ | let /let/ | /eɪ/ vs /e/ |
| fine /faɪn/ | fan /fæn/ | /aɪ/ vs /æ/ |
| coat /kəʊt/ | cot /kɒt/ | /əʊ/ vs /ɒ/ |
| loud /laʊd/ | lad /læd/ | /aʊ/ vs /æ/ |
For learners of English, diphthongs are especially important because English spelling does not always show the sound clearly. The same diphthong may be spelt in different ways.
For example, /eɪ/ appears in:
| Spelling | Word | IPA |
|---|---|---|
| a | late | /leɪt/ |
| ai | rain | /reɪn/ |
| ay | day | /deɪ/ |
| ea | break | /breɪk/ |
| ei | eight | /eɪt/ |
This shows why IPA is useful. It helps us focus on the sound, not just the spelling.
Conclusion
Diphthongs are an important part of the English sound system. They are vowel sounds that move from one position to another within the same syllable. To describe them properly, we look at their starting point, ending point, tongue movement, lip shape, length, stress and accent variation.
In simple terms, a diphthong is a gliding vowel. The sound begins in one place and moves smoothly towards another. Examples include /eɪ/ in day, /aɪ/ in my, /ɔɪ/ in boy, /əʊ/ in go, and /aʊ/ in now.
Once we understand this movement, English pronunciation becomes easier to explain, teach and learn.
References
International Phonetic Association. (1999). Handbook of the International Phonetic Association: A guide to the use of the International Phonetic Alphabet. Cambridge University Press.
Ladefoged, P., & Johnson, K. (2014). A course in phonetics (7th ed.). Cengage Learning.
Roach, P. (2009). English phonetics and phonology: A practical course (4th ed.). Cambridge University Press.
Wells, J. C. (1982). Accents of English. Cambridge University Press.
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