Diphthongs  

A diphthong is a single-syllable vowel sound in which the beginning of the sound is different from the end sound—that is, the sound glides from one vowel sound to another. For this reason, diphthongs are often referred to as gliding vowels. A “pure” vowel sound that doesn’t glide is known as a monophthong. It’s also possible (though less common) to have a single syllable that glides between three vowel sounds; this is known as a triphthong, which we’ll look at in another section.

There are eight vowel sounds in American English that are generally agreed upon as being diphthongs. We already encountered four of these when we looked at “traditional” long vowels (vowel sounds that are pronounced the same way as the names of the letters), but there are also a few others that occur. Let’s start by reviewing the diphthongs that make up the traditional long vowels, and then we’ll move on to the rest.

With the exception of long E (/i/), all of the traditional long vowel sounds are diphthongs. These most predictably occur when the vowel letter is followed by a single consonant and a silent “e”:

(*Note that the traditional transcription for long U is /juː/. The triangular colon [ ː ] represents the elongation of the vowel sound. However, in most American dictionaries, this colon is omitted because the elongation of /ju/ is implied. This guide follows the convention of omitting the triangular colon so that the IPA pronunciations match what would be found in an American dictionary.)

The silent “e” rule is not the only instance when these long-vowel diphthongs occur. For more information on when a vowel creates the traditional long sound, go to the section overview on Vowels.

In addition to the four diphthongs listed above, there are two other diphthongs that regularly occur in American English pronunciation. There are also two others that are sometimes articulated (but aren’t always included in IPA transcriptions).

Below, we’ll look at each diphthong individually, listing common vowel digraphs that form the sound, along with example words and their full IPA pronunciations.

This diphthong is pronounced “au-ee”—it begins with the /ɔ/ sound (as in dawn or door) and glides to the /ɪ/ sound (as in pit). It generally only occurs with the vowel combinations “OY” and “OI.”

This diphthong is pronounced “ah-oo”—the vowel glides from the /æ/ sound (as in bat) to the /ʊ/ sound (as in pull). It generally occurs with the digraphs “OU” and “OW.”

Be careful, though, because many words that have “OU” or “OW” spellings will make the long O (/oʊ/) vowel sound, as in:

Finally, some words that are spelled with “OW” can be pronounced either way, which alters the meaning of the word altogether. Let’s look at some common examples:

There are two other diphthongs that sometimes occur in American English: /ɪə/ and /ɛə/. These can be found in certain instances where a vowel sound is followed by an “r.” However, it is very common in General American pronunciations to omit the schwa sound before the “r” in /ɪər/ and /ɛər/, and the standard transcription in (most) American dictionaries is often simply /ɪr/ or /ɛr/, respectively. While the IPA transcriptions used in this guide generally favor the trends of American dictionaries (and do not include the schwas as a result), we’ll have a quick look below at when they might occur.

When this diphthong is articulated, it is pronounced “ih-uh,” quickly gliding from the short I sound /ɪ/ (as in tip) to an unstressed schwa (/ə/). It usually occurs with the digraphs “EE,” “EA,” and “IE” when they are followed by an “R.”

(*Note that “-ier” is often used to create the comparative form of adjectives that end in “y,” as in happier, fussier, busier, etc. In this case, “-ier” is pronounced “ee-er,” and its IPA notation is /iər/. This is not a diphthong, however, because it is stressed as two separate syllables.)

When this diphthong is articulated, it is pronounced “eh-uh,” quickly gliding from the short “E” sound /ɛ/ (as in set) to an unstressed schwa (/ə/). (In some dialects, the “E” sound sometimes raises up slightly to sound more like “ei”; for this reason, some dictionaries transcribe the diphthong as /eə/ instead.)

This diphthong usually occurs with the letter combinations “ARE” and “AIR,” but be careful: it also sometimes occurs with “EAR,” which is often pronounced /ɪər/. All of the root “EAR” words that have the /ɛər/ pronunciation are listed below.

*The most notable exception to this rule is the short word are, which is pronounced “ahr” (/ɑr/).

It’s also important to note that verbs ending in ARE keep this pronunciation even when they are made into a gerund or present participle, in which case the final “e” is replaced with “-ing.” For example: