English Diphthongs: Master the oi/oy and ou/ow Sounds (Complete Guide)

Diphthongs are some of the most distinctive sounds in English, yet they often challenge Spanish speakers. These "sliding" vowel sounds move smoothly from one vowel position to another within a single syllable, creating the flowing quality that makes English sound natural.

This guide focuses on two essential diphthongs that appear frequently in everyday English: oi/oy and ou/ow.

What Are Diphthongs?

A diphthong is a vowel sound that glides from one vowel position to another. Unlike simple vowels that stay in one position, diphthongs create a smooth sliding motion in your mouth.

Think of it as two vowel sounds blended together so quickly they become one sound.

The oi/oy Diphthong /ɔɪ/

This diphthong starts with the /ɔ/ sound (as in "dog") and glides to the /ɪ/ sound (as in "sit").

How to Make the /ɔɪ/ Sound

1. Start position: Drop your jaw, round your lips slightly, raise the back of your tongue
2. Glide motion: Raise your jaw while spreading your lips and moving your tongue forward
3. End position: Tongue high and forward, lips spread

Spelling Patterns

Use 'oi' in the middle of words:

Use 'oy' at the end of words:

The ou/ow Diphthong /aʊ/

This diphthong starts with the /a/ sound (as in "father") and glides to the /ʊ/ sound (as in "book").

How to Make the /aʊ/ Sound

1. Start position: Drop your jaw low, tongue low and back, lips neutral
2. Glide motion: Raise your jaw while rounding your lips and raising the back of your tongue
3. End position: Lips rounded, back of tongue raised

Spelling Patterns

Use 'ou' in the middle of words:

Use 'ow' at the end of words or before n/l:

Common Mistakes for Spanish Speakers

Mistake 1: Making Two Separate Sounds

Wrong: Pronouncing "coin" as "co-in" (two syllables) Right: Smooth glide from /ɔ/ to /ɪ/ in one syllable

Mistake 2: Using Spanish Vowel Sounds

Wrong: Using Spanish /o/ and /i/ sounds Right: Use English /ɔ/ gliding to /ɪ/

Mistake 3: Not Completing the Glide

Wrong: Stopping at the first vowel sound Right: Complete the full sliding motion

Quick Practice Sentences

Try these sentences to practice both diphthongs:

1. The boy found a coin in the house.
2. I enjoy the sound of rain outside.
3. Make a choice about how to destroy the toy.
4. The cow made a noise around the town.

Minimal Pairs Practice

Practice distinguishing these diphthongs from similar sounds:

oi/oy vs. other sounds:

• coin /kɔɪn/ vs. cone /koʊn/
• boy /bɔɪ/ vs. bow /boʊ/ (ribbon)

ou/ow vs. other sounds:

• house /haʊs/ vs. hose /hoʊz/
• cow /kaʊ/ vs. coo /ku/

Memory Tips

For oi/oy: Think "oh-ee" but say it quickly as one sound For ou/ow: Think "ah-oo" but blend it smoothly

Remember: The spelling often tells you which diphthong to use, but the mouth movement is the same regardless of spelling.

Next Steps

Master these diphthongs by:

1. Practicing the mouth movements slowly, then speeding up
2. Recording yourself saying the example words
3. Listening to native speakers and mimicking their pronunciation
4. Using these words in conversation daily

These two diphthongs appear in hundreds of common English words. Once you master the sliding motion, your English will sound much more natural and fluent.

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