What’s a Diphthong? (And How to Say Them)

Say these words out loud: cow, boy, my, late, go.

Feel that? Your mouth didn’t just make one simple, static sound. It moved. It shifted. Your tongue glided, your lips changed shape, all within a single beat. What you just performed is a bit of linguistic magic known as a diphthong.

If that word sounds like something from a dusty phonetics textbook, don’t worry. Diphthongs are far more common and practical than they sound. In fact, mastering them is one of the fastest ways to improve your pronunciation and sound more like a native English speaker. Let’s break down what they are and how you can say them perfectly.

So, What Exactly Is a Diphthong?

The simplest definition is right in the description: a diphthong is two vowel sounds smashed together into one syllable. The word itself comes from the Greek diphthongos, which means “two sounds.”

Think of it as a “vowel glide.” You start at one vowel sound and smoothly glide to a second one without any pause. The whole thing is treated as a single vowel. This movement is the key feature that separates them from their simpler cousins, monophthongs.

The ‘Pure’ Vowel: Monophthongs

Before we dive deeper into diphthongs, let’s clarify what they’re not. A monophthong (from Greek monos, “single”) is a pure, single vowel sound. When you say one, your tongue and lips get into position and stay there for the duration of the sound.

Consider these words:

• meet (the “ee” sound)
• cat (the “a” sound)
• hot (the “o” sound)
• sit (the “i” sound)

When you say the vowel in each of these, your mouth holds a single, steady position. That’s a monophthong. A diphthong, on the other hand, is all about the journey.

Why Should You Care About Diphthongs?

This isn’t just an academic exercise. For language learners, diphthongs are a high-impact area to focus on for two main reasons:

1. They are a key to sounding natural. A very common feature of a “foreign accent” in English is the tendency to pronounce diphthongs as monophthongs. For example, a learner might say late as “let”, missing the glide from “eh” to “ee.” Nailing the vowel glide makes your speech sound instantly more fluid and native-like.
2. They can change the meaning of a word. English has many “minimal pairs” where the only difference is a monophthong versus a diphthong. Getting it wrong can lead to confusion. For instance:
   • met vs. mate
   • pen vs. pain
   • wok vs. woke
   • rid vs. ride

Clearly, these little glides pack a big punch. So let’s meet the main players in English.

Meet the Diphthongs: A Practical Guide

While pronunciation varies wildly across English accents, these five diphthongs are fundamental to most, especially General American English. We’ll break each one down into its starting point, ending point, and give you plenty of words for practice.

1. The “MY” Sound: /aɪ/

This is one of the most common diphthongs in English.

• The Glide: It starts with an open, relaxed sound like the “ah” in father and glides up to a high front sound like the “ee” in meet. (Ah → ee)
• How to Say It: Start with your jaw dropped and your tongue low and flat for the “ah.” Then, as you continue the sound, raise your jaw and the front of your tongue, and spread your lips slightly to glide into the “ee” position.
• Examples: my, I, high, buy, time, night, find, style, right, ice.

2. The “COW” Sound: /aʊ/

This sound gives English that characteristic “down home” feel in words like town.

• The Glide: It also starts with that open “ah” sound from father, but this time it glides toward a rounded “oo” sound like in boot. (Ah → oo)
• How to Say It: Start with your jaw dropped for “ah.” Then, glide by rounding your lips and raising the back of your tongue to make the “oo” sound.
• Examples: cow, now, how, house, about, town, loud, proud, mouth.

3. The “BOY” Sound: /ɔɪ/

This sound is less common than the first two, but just as distinct.

• The Glide: It starts with a mid-back, rounded vowel like the “aw” in law or caught. From there, it glides up to the high front “ee” sound from meet. (Aw → ee)
• How to Say It: Start with your lips rounded and the back of your tongue raised for the “aw” sound. Then, unround your lips and raise the front of your tongue to glide into the familiar “ee” position.
• Examples: boy, toy, noise, choice, coin, voice, enjoy, loyal, soil.

4. The “SAY” Sound: /eɪ/

This is the sound that distinguishes met from mate. Many learners pronounce it as a single “eh” sound, but the glide is crucial.

• The Glide: It starts with a mid-front vowel like the “e” in bed or dress and, like several others, glides up to the “ee” sound from meet. (Eh → ee)
• How to Say It: Start with your mouth in a relaxed, neutral position for the “eh” sound. Then, raise your jaw and tongue to slide into the “ee” sound.
• Examples: say, day, wait, name, face, late, great, pain, rain, they.

5. The “GO” Sound: /oʊ/ (or /əʊ/ in British English)

This sound is sneakily a diphthong for most native speakers, even if they don’t realize it. It’s what separates not from note.

• The Glide: It starts with a mid-back, rounded “oh” sound and glides into the higher, more rounded “oo” from boot. (Oh → oo)
• How to Say It: Begin with your lips in a relaxed circle for “oh.” Then, make the circle smaller and tighter as you glide toward the “oo” sound. You should feel the back of your tongue rise slightly.
• Examples: go, no, so, boat, coat, phone, joke, slow, know, although.

How to Practice and Master Diphthongs

Knowing what a diphthong is helps, but mastery comes from physical practice. Here are a few techniques to train your mouth and ears.

• Slow It Down: Take a word like time and say it in slow motion: “t-ahhhhh-eeee-m.” Exaggerate the two parts of the vowel. Feel your tongue and jaw moving. Then, gradually speed it up until it becomes one smooth, single sound.
• Use a Mirror: This is especially helpful for diphthongs involving lip rounding (/aʊ/, /ɔɪ/, /oʊ/). Watch your mouth as you say how or go. Do you see your lips changing shape from open to round, or from a relaxed circle to a tighter one?
• Listen and Shadow: Find recordings of native speakers. Websites like Youglish allow you to search for words in YouTube videos. Listen intently to the vowel sound, then try to mimic it exactly—this is called “shadowing.”
• Record Yourself: Use your phone to record yourself saying lists of diphthong words. Then, listen back and compare your pronunciation to that of a native speaker. You might be surprised by what you hear.

The Glide to Fluency

Diphthongs may seem like a small, technical detail, but they are the building blocks of natural-sounding speech. They are the difference between a flat, stilted pronunciation and a dynamic, fluid one.

By understanding that these sounds are movements—glides from one position to another—you unlock the secret to producing them correctly. So the next time you say hello, ask “how are you?”, or simply talk about the time, pay attention to that beautiful linguistic magic. You’re not just speaking; you’re gliding.