Diphthongs in English: A Mouth Movement Guide

Diphthongs in English are vowel sounds that move.

Your mouth starts in one vowel position, then glides to another position inside the same syllable. This is different from a simple vowel, where your mouth stays mostly still.

To pronounce English diphthongs clearly, you need focus on four parts of English pronunciation mouth placement at the same time:

1. Mouth opening

2. Lip shape

3. Tongue position

4. Smooth airflow

The sound should glide. It should not stop between the two vowel parts.

What Is a Diphthong?

A diphthong is one vowel sound with movement.

To pronounce a diphthong, your tongue, lips, and jaw shift while your voice continues. The airflow stays open because diphthongs are vowel sounds.

That means you should not block the air, stop your voice, or make two separate syllables.

For example, “my” is not “mah-ee” as two syllables. It is one smooth sound: my /maɪ/.

/eɪ/ as in “day”

To make /eɪ/, start with your jaw slightly open and your tongue in a mid-front position, near the sound “eh.” As you continue the vowel, raise the front of your tongue toward the hard palate and close your jaw slightly. Keep your lips relaxed or lightly spread, with no rounding. Your airflow should stay smooth and voiced from start to finish. 

The sound should move from “eh” toward “ih,” but it should stay one connected vowel: day /deɪ/.

/aɪ/ as in “my”

To make /aɪ/, start with your mouth open and your tongue low in the mouth, near the sound “ah.” Then glide upward and forward by raising the front of your tongue toward “ih” while your jaw closes slightly. Keep your lips neutral or lightly spread. Do not round them. Your voice and airflow should continue without a break. 

The sound should feel like “ah” moving toward “ih,” but not as two syllables: my /maɪ/.

/ɔɪ/ as in “boy”

To make /ɔɪ/, start with a rounded back vowel. Your jaw should be moderately open, your tongue should sit toward the back of the mouth, and your lips should be rounded. As the sound moves, bring the tongue forward and upward toward “ih” while the jaw closes slightly. At the same time, relax the lips from rounded to more neutral or lightly spread. Keep the airflow open and the voice continuous. 

The sound should glide from “aw” toward “ih”: boy /bɔɪ/.

/aʊ/ as in “now”

To make /aʊ/, start with your mouth open and your tongue low, near the sound “ah.” Then move the tongue upward and slightly backward as your jaw closes a little. At the end of the sound, round your lips toward “oo,” but do not add a strong separate /w/ sound. Keep the airflow smooth and voiced through the full movement. 

The sound should glide from “ah” toward “oo” as one vowel: now /naʊ/.

/oʊ/ as in “go”

To make /oʊ/, start with a mid-back vowel. Your jaw should be slightly open, your tongue should sit in the back-middle area of the mouth, and your lips should already be rounded. As the sound continues, raise the back of the tongue slightly and round the lips a little more. The jaw closes gently, and the voice stays steady. 

The sound should move from “oh” toward “oo” without a break: go /goʊ/.

/ɪə/ as in “near”

To make /ɪə/, start with the front of your tongue high in the mouth, near “ih” or “ee,” and keep your jaw almost closed. Then relax the jaw slightly and move the tongue toward the center of the mouth for a soft “uh” sound. Keep the lips relaxed and neutral, with no rounding. Your airflow should stay gentle and voiced. 

Note: In many British English accents, this creates a clear glide: near /nɪə/. In many American English accents, the final rhotic R changes the sound, so near sounds more like /nɪr/.

/eə/ as in “hair”

To make /eə/, start with your jaw slightly open and the front of your tongue in a mid position, near eh. Then relax the tongue toward the center of the mouth as the sound moves toward uh. The lips can begin slightly spread, then return to neutral. Keep the airflow open and smooth.

Note: In many British English accents, this creates the diphthong hair /heə/. In many American English accents, the R changes the vowel, so hair sounds more like /her/ or /hɛr/.

/ʊə/ as in “pure”

To make /ʊə/, start with the back of your tongue high and your lips rounded, near oo. Your jaw should stay fairly closed at the start. Then relax the jaw slightly, move the tongue toward the center of the mouth, and let the lips relax from rounded to neutral. Keep your voice steady and the airflow open through the whole glide. 

Note: In many British English accents, this creates pure /pjʊə/. In many American English accents, the R changes the ending, so pure often sounds like /pjʊr/ or /pjɚ/.

The Most Important Rule: Keep the Glide Smooth!

A diphthong should feel like one movement.

Do not say:

• my = mah-ee

• day = deh-ee

• now = nah-oo

Instead, connect the movement:

• my = /maɪ/

• day = /deɪ/

• now = /naʊ/

Your voice should continue from start to finish. Your mouth changes shape, but the sound stays connected.

Common Diphthong Mistakes

Keeping the Mouth Too Still

Some learners pronounce diphthongs like simple vowels. For example, “day” may sound like “deh” because the mouth does not move enough. To fix this, make sure the tongue and jaw glide from the first vowel position toward the second.

Moving Too Much

Some learners split the diphthong into two full syllables. For example, “my” may become “mah-ee.” To fix this, keep the second part shorter and lighter. The sound should move, but it should stay one syllable.

Forgetting Lip Movement

Lip shape matters in several English diphthongs. In /aʊ/, the lips move from neutral to rounded. In /oʊ/, the lips start rounded and round more. In /ɔɪ/, the lips start rounded and then relax. If the lips do not move correctly, the vowel can sound unclear.

Moving the Tongue in the Wrong Direction

Each diphthong has a movement path. /eɪ/ and /aɪ/ move upward and forward. /ɔɪ/ moves from back-rounded to front. /aʊ/ moves from open-low to back-rounded. /oʊ/ moves higher and more rounded. /ɪə/, /eə/, and /ʊə/ move toward the relaxed center. If the tongue moves in the wrong direction, the sound may change.

Short Practice Routine

Use this routine for English accent training with one diphthong at a time.

Step 1: Start Slowly

Choose one diphthong, such as /aɪ/. Begin with the first mouth position: open jaw, low tongue, and neutral lips.

Step 2: Glide to the Second Position

Move smoothly toward the second position. For /aɪ/, raise the front of the tongue and close the jaw slightly.

Step 3: Keep One Syllable

Connect the movement into one sound: ah → ih → eye. Do not pause between the two parts!

Step 4: Add One Word

Say one word with the diphthong, such as my. Keep the movement clear but short.

Step 5: Add One Sentence

Use the word in a short sentence: This is my bag. Keep the diphthong natural. Do not over-pronounce it.

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Step 6: Record Yourself

Listen carefully and get feedback on three things:

1. Did the vowel move?

2. Did the sound stay one syllable?

3. Did the mouth shape match the target diphthong?

How Syranto Helps You Practice Diphthongs

Diphthongs can be hard to correct alone because you may not hear the missing movement in your own speech.

For diphthongs, Syranto can help you find vowel sounds that sound unclear, practice mouth movement step by step, compare your pronunciation to a model, repeat difficult sounds in words and sentences, and track your accent progress over time

You’ll stop guessing and start adjusting your speech with clearer feedback!

Anccentize helps you practice English pronunciation with targeted exercises and immediate feedback.