Updated on January 9, 2024
What’s the deal with a diphthong?
In English, we learn that the vowels are A, E, I, O, U (and sometimes Y!). That seems like the end of the story, but there is more.
When vowels connect or become diphthongs, they have special pronunciation rules. Diphthongs get our mouths moving to make new vowel sounds. It’s not just English; lots of languages have diphthongs too.
Today, we will learn all about diphthongs and how to read them properly.
A diphthong is a combination of two vowel sounds where the pronunciation moves from one vowel to the other. That’s why diphthongs are also known as gliding vowels. The root words in ancient Greek mean “two sounds.”
Diphthongs are complex vowels in contrast to monophthongs – single or simple vowel sounds that don’t make your tongue move.
You may be thinking, “Wait, there are only five vowels in English.” That’s true for spelling, but when it comes to pronunciation in American English, there are 20 unique vowel sounds: 12 vowel monophthongs and five (or eight) vowel diphthongs. More on that below.
So how do you identify diphthongs? Not based on spelling. There are words in English that are spelled with two vowels together that are not diphthongs. Words like:
Sure they have two vowels together, but they’re not diphthongs. The examples above are actually monophthongs.
The key to the diphthong definition is whether your tongue moves to produce the sound.
The word “no” on the other hand, is a diphthong /oʊ/ (“oh”) spelled with only one vowel.
Diphthongs are all about pronunciation. As you probably know, English has different pronunciations around the world. For example, American and British English don’t pronounce vowels the same. Our examples focus on General American English Pronunciation (GAEP).
| Diphthong (phonetic writing) | Pronunciation | Examples |
|---|---|---|
| /eɪ/ | Sounds like “aim” | able, break, way, sane |
| /ɔɪ/ | Sounds like “boy” | point, foil, oil, joy |
| /oʊ/ | Sounds like “no” | so, doe, show, blown, over |
| /aɪ/ | Sounds like “why” | I, like, wine, dine, sign |
| /aʊ/ | Sounds like “how” | out, frown, hound, now |
Before we mentioned there are five or eight diphthongs in American English. The number depends on what linguist or English teacher you talk to.
In our list, we included five diphthongs. The other three are called “r-colored” or “r-controlled” vowels in American English. These vowels make your tongue move like a diphthong, but it’s because they are always next to an “r” sound.
Many languages have diphthongs. You’ll recognize similar diphthong sounds in these non-English examples.
| Language | Diphthong | Pronunciation in English | Examples in the Language |
|---|---|---|---|
| Spanish | ai | Sounds like “my” | Bailar, traigo |
| Spanish | ei | Sounds like “hey” | Seis, ley, reina |
| French | oi or oy | Sounds like “wa” | Moi, joie, joyeux |
| French | ou | Sounds like “too” | Tout, vous |
| German | ei | Sounds like “eye” | Ei, eins, Eingang |
| German | au | Sounds like “now” | Blau, schau, grau |
Learning pronunciation of German, French and Spanish takes a lot of work for learners, but this knowledge of diphthongs makes it easier.
Diphthongs are a combination of complex vowel sounds that require your tongue to move.
Don’t be fooled: you can’t always spot a diphthong based on spelling. Some double vowels are monophthongs, while some single vowels are diphthongs. Notice how your tongue moves and you will perfect the right pronunciation.
