Diphthong

What Is a Diphthong?

A diphthong is two adjacent vowel sounds within the same syllable. For example:

• hound
(In "hound," which is one syllable, the vowel sound starts with an "a" sound and glides to an "oo" sound. In phonetics, this would be written as ɑʊ.)
• jeer
(Here, the vowel sound starts with an "ee" sound and glides to an "uh" sound. In phonetics, this would be written as ιə.)

Diphthongs contrast with monophthongs, which are simple vowels, i.e., ones that do not have a sound change. For example:

• hand
  ,
  pen
  ,
  dinner
  ,
  cottage
  ,
  butter

What Does Diphthong Mean?

The word "diphthong" originates from Greek. It means "two voices" or "two sounds." A diphthong is sometimes called a "gliding vowel" because moving from the first vowel sound to the second is called "gliding."

The 8 Diphthong Sounds

Here are the eight diphthong sounds:

phonetic symbol	common letters	example words
ɑι	i, igh, y	crime , light , byte
eι	ea, ey, ay, ai, a	break , prey , pray , braid , ache
əʊ	ow, oa, ough	slow , moan , dough
ɑʊ	ou, ow	hound , crown
eə	ai, ea	lair , bear
ιə	ee, ie, ea	jeer , pier , near
ɔι	oy, oi	boy , oil
ʊə	u	pure

Notice that not all diphthongs are made up of two vowels in normal writing. Some diphthongs include consonants ("ight," "ough"), and some are represented by a single vowel. When using phonetics symbols, diphthongs are represented by two vowel characters.

Diphthongs Are Not Long Vowels

Do not confuse diphthongs with "long vowels." Even though diphthongs have two sounds, they are not necessarily longer than the other vowels. In spelling, the term "long vowel" is reserved for the sounds "A, E, I, O, U," while the term "short vowel" is used for "a, e, i, o, u."

Diphthong vs Disyllabic Vowel Pairings

Do not confuse diphthongs with disyllabic vowel pairings (i.e., vowel pairings that have two distinct syllables). For example:

Diphthong

The word contains the diphthong "ei," which starts with an "eh" sound and glides to an "ee" sound (eι).

Disyllabic vowel pairing

The vowel pairing "ei" in the word does not contain a diphthong. This word clearly has three syllables (re-in-vent). Sometimes, distinguishing between a diphthong and two syllables is harder. For example, the word also has two syllables (ru-in). So, the "ui" is not a diphthong. The same is true for (2 syllables), (3 syllables), and (4 syllables). When you have a short, stressed vowel followed by an unstressed vowel (like in "ruin"), it can sound like a diphthong (and in some accents might be!), and many such words commonly cause debate among linguistics scholars about their diphthonginess.

Why Diphthongs Are Important

Diphthongs are common. They're everywhere. A diphthong can appear at the beginning of a word, the middle of a word, or the end of a word. For example:

• Beginning.
• out
  ,
  oil
  ,
  ache
• Middle.
• hound
  ,
  boil
  ,
  break
• End.
• slow
  ,
  enjoy
  ,
  prey

And, a word can have more than one diphthong. For example:

• cowboy
  (ɑʊ and ɔι),
  highway
  (ɑι and ɑι),
  mealtime
  (ιə and ɑι)

In any sentence, you are more likely to encounter a diphthong than not. So, knowing just the short and long sounds of the individual letters is not enough when learning to read because a diphthong creates a unique sound as its two vowel sounds glide together. This means that spotting diphthongs is essential for accurate pronunciation.

Key Points

Video Lesson

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