What Is a Diphthong?
The Blue Book of Grammar and Punctuation
What Is a Diphthong?
Communication is as much about sounds we make and interpret with meaning as it is words that are written with thought.
Approximations of dates of origin of human speech have varied from 200,000 years ago to 50,000 years ago. Some recent research suggests our first speech sounds were made around 70,000 years ago.
Unlike nonhuman primates and other animal species with systems of social communication, we distinctly use our tongues, lips, and jaws to form speech.
Central to our speech is the larynx (voice box). Scientists have often emphasized it as the key to what further separates us from other primates and our ancient ancestors. Ours is lower down in the throat, allowing us to produce a range of particular vowels.
As we learn to speak as infants, we become aware of simple, monosyllabic vowel sounds: a, e, i, o, u, and sometimes y. We also grow increasingly adept with short vowel sounds (cat, sit) and long ones (paper, unit).
When simple vowels have one syllable with one sound, they are also known as monophthongs.
When a vowel has two adjacent sounds within the same syllable—i.e., the sound changes within the syllable’s space—we refer to it as a diphthong.
Diphthong Definition
The word “diphthong” originates from the Greek díphthongos (“having two sounds”).
Diphthongs create unique sounds by having two vowel sounds that glide together within a syllable. Because of this movement from the first sound to the second, a diphthong is also referred to as a “gliding vowel.”
Recognizing diphthongs is important for accurate pronunciation of words. When we listen carefully to a word with a diphthong, we can hear its blending vowel sounds.
| steak | fear |
| weight | soil |
| tough | stair |
| dough | enjoy |
In each of these examples, two vowel sounds merge in the space of one syllable to form a combined and changing sound.
Note that not all diphthong sounds consist of only two vowels in typical writing. Some also include consonants (right), and others are represented by a single vowel (sure).
Pronouncing Diphthong Syllables
When we are pronouncing single vowels (monophthongs), our tongue and other mouth parts typically remain in fixed positions (i.e., they don’t move). When we are pronouncing a diphthong, they will move to produce the two close vowel sounds within a syllable.
As a matter of test and comparison, say the world “blah.” Notice how the ah comes out as a single sound without extra mouth movement.
Now say the word “cow.” Note how your lips move to shape the glide from o to w. You have just spoken a diphthong.
Because our speech is typically emitted quickly, neither we nor our listeners may always detect a diphthong, hearing it instead as one sound. The more we focus on the vowels in our speech, the more aware we can become of the diphthongs we pronounce. The nuances can sometimes be highly subtle and only finely perceptible.
The Eight Diphthongs
The number of diphthongs in American English is sometimes debated, but language experts will often agree on at least eight of them.
Diphthongs in language are represented by two vowel symbols that identify the sounds that glide to form the diphthong.
The following are the eight standard diphthongs.
/ aɪ / Like “eye”; common letters: i, igh, y; examples: crime, light, cry
/ eɪ / Like “great”; common letters: ea, ey, ay, ei, ai; examples: break, pray, weight
/ əʊ / Like “boat”; common letters: ow, oa, ough; examples: slow, dough, moan
/ aʊ / Like “ow!”; common letters: ou, ow; examples: crown, hound, now
/ eə / Like “air”; common letters: ai, ea; examples: stair, bear, lair
/ ɪə / Like “ear”; common letters: ie, ee, ea; examples: near, pier, jeer
/ ɔɪ / Like “boy”; common letters: oi, oy; examples: oil, coil, toy
/ ʊə / Like “sure”; common letter: u; examples: fur, lure, pure
Remember: For a sound to be a diphthong, it must have a changing, gliding sound. Words such as you and true are not diphthongs because the two vowels produce fixed single sounds.
Diphthongs: Not Long or Disyllabic Vowels
Because of how some of them sound, diphthongs may at times also be referred to as long vowels. This can often be inaccurate in that although vowel sounds glide and change in a diphthong, they do not always take more time to pronounce than a single-sound monophthong.
For example, say the word “game.” Now say the word “air.” “Game” has a single-sound long vowel (a monophthong). “Air” contains a two-sound vowel glide (a diphthong), but its pronunciation length is the same (a single exhalation).
Diphthongs also are distinct from disyllabic vowel pairings, which are pairs of vowels that occupy separate syllables.
| fluid | two syllables | flu-id |
| reinstall | three syllables | re-in-stall |
| coincidence | four syllables | co-in-ci-dence |
| intuitively | five syllables | in-tu-i-tive-ly |
As we can see, the vowels that are next to each other are separate sounds pronounced in different syllables, not as glided sounds that would make them diphthongs.
With this further insight into what diphthongs are and how you can spot them, you have a stronger skill in your pronunciation of American English.
Related Topic
Clipping Syllables to Sizes We Like
Sibilance: Definition and Examples
Proper Pronunciation: A Sound Policy
Pop Quiz
Identify the words with diphthongs in the following sentences.
1. I would like to get an oil change, please.
2. Did you hear about the billion-dollar donation?
3. Jen is writing with an almost empty pen.
4. The Ahmeds are joining us for dinner tonight.
5. That boat engine sure is loud.
Pop Quiz Answers
1. I would like to get an oil change, please.
2. Did you hear about the billion-dollar donation?
3. Jen is writing with an almost empty pen. no diphthongs
4. The Ahmeds are joining us for dinner tonight.
5. That boat engine sure is loud.
If the article or the existing discussions do not address a thought or question you have on the subject, please use the "Comment" box at the bottom of this page.
What about the word “tour”? So many broadcasters pronounce the word as “tore,” not “two er.” Which pronunciation is correct?
“two er”