Try reading the following words out loud: boy, toy, coin. Do you notice anything about the vowel sound? You should be able to hear two different vowel sounds in one syllable – these are called diphthongs.
This article will introduce diphthongs, provide a list of all the diphthongs in English, explain the different types of diphthongs, and, finally, explain the differences between monophthongs and diphthongs.
Diphthong vowel definition
A diphthong is a vowel that contains two different vowel sounds in one syllable. The word diphthong comprises di, which means ‘two’ in Greek, and phthong, which means ‘sound’. Therefore, diphthong means two sounds.
Diphthongs are gliding vowels, created when a speaker glides from one vowel sound glides into another. The first vowel is usually longer and stronger than the second one in the English language. For example:
In the English word 'house' the vowel sound in the first syllable, /aʊ/ is a diphthong. It starts with the sound of the vowel /a/ and glides to the sound of the vowel /ʊ/. The diphthong is formed by the transition between the two vowel sounds and is thus considered a single vowel sound.
Here is another diphthong example:
/ɔɪ/ is a diphthong. It is the ‘oi’ sound in words such as boy /bɔɪ/, toy /tɔɪ/, or coin /kɔɪn/.
Try saying the previous three words slowly. When creating the vowel sound, do you notice how your lips make both a rounded shape and a spread wide shape? Also, see how your lips don’t touch when changing from one mouth shape to another, demonstrating how one vowel slides glides into another.
Careful! Just because a word has two vowels next to each other does not mean it will produce a diphthong sound. For example, the word feet /fiːt/ doesn't have a diphthong but contains the monophthong /iː/ (the longer e sound).
List of diphthongs
There are eight different diphthongs in the English language. They are:
As you can see, the diphthong examples are represented by two separate symbols, which highlight the two different vowel sounds. We use these symbols (found in the International Phonetic Alphabet or the English phonemic alphabet) to transcribe diphthongs.
The word chair is transcribed as /ʧeə/. We can see that the diphthong /eə/ falls at the end of the word.
Are you struggling to hear the two separate vowel sounds in these words? Don’t worry! Diphthongs might seem new and alien to you because native English speakers tend to shorten diphthongs into singular vowel sounds. Try pronouncing the previous words as if you were the Queen of England. Can you hear the glide now?
Fig. 1 - The words "how now brown cow" all have the diphthong /aʊ/.
Different types of diphthong vowels
Linguists have divided the eight diphthong vowels into different types (or categories) according to the sound they produce and how they are pronounced. These categories are falling and rising diphthongs, opening, closing, centring diphthongs, and wide and narrow diphthongs.
Let’s have a look at these categories of diphthongs and their examples in detail.
Falling and rising diphthongs
Rising diphthongs are the opposite of falling diphthongs. They begin with a lower pitch or volume and end with a higher pitch or volume. The rising diphthong sound is created in English when a vowel follows a semivowel. The semivowels are /j/ and /w/. There are no specific phonemic representations (e.g. /əʊ/) for rising diphthongs, as they are usually analysed as a sequence of two phonemes (e.g. /wiː/). The rising diphthong sound can be heard in words like yell (/jel/), weed (/wiːd/), and walk (/wɔːk/).
Opening, closing, and centring diphthongs
Opening diphthongs have a second vowel sound that is more ‘open’ than the first. An ‘open vowel’ is a vowel sound pronounced with the tongue as low down in the mouth as possible (e.g. /a/ in cat).
An example of an opening diphthong is /ia/ – the ‘yah’ sound in Spanish found in words like hacia. Opening diphthongs are usually rising diphthongs, as open vowels are more prominent than closed vowels.
Closing diphthongs have a second vowel sound that is more ‘closed’ than the first. A closed vowel is pronounced with the tongue in a much higher position in the mouth (e.g. /iː/ in see).
Examples of closing diphthongs are: /ai/ found in time, /əʊ/ found in globe, and /eɪ/ found in late. Typically, closing diphthongs are falling diphthongs.
Centring diphthongs have a second vowel that is mid-central, i.e. it is pronounced with the tongue in a neutral or central position. The mid-central vowel sound is also known as the schwa (/ə/). Any diphthong ending with the schwa sound can be considered a centring diphthong, e.g. /ɪə/ found in dear, /eə/ found in fair, and /ʊə/ found in cure.
Wide and narrow diphthongs
Wide diphthongs require a large tongue movement from the first vowel sound to the second vowel sound. In wide diphthongs, the sound difference between the two vowel sounds will be more prominent.
Examples include: /aɪ/ found in time and /aʊ/ found in cow.
Narrow diphthongs require a smaller movement from one vowel to the other. In narrow diphthongs, the two vowel sounds will sound similar and will be pronounced in a similar way.
Monophthongs and diphthongs
Diphthongs are different to monophthongs, which are a single vowel sound within a syllable.
For example, the /ɪ/ in sit, the /u:/ in cool, and the /ɔ:/ in all.
Monophthongs are also called pure vowels, as their pronunciation is limited to one vowel sound. On the other hand, diphthongs contain two vowel sounds in one syllable and are sometimes called gliding vowels as the pronunciation of one vowel sound ‘glides’ to another.
Remember, just because two vowels appear next to each other in a word doesn’t mean a diphthong is created.
Meat (/miːt/) – Here, two vowels appear next to each other, but they create the single vowel sound /iː/ - a monopthong pronounced like the long ‘ee’ sound.
Time (/taɪm/) – Here, no vowels appear next to each other, but the word is pronounced with the diphthong /aɪ/.
Diphthong - Key Takeaways
A diphthong is a vowel that contains two different vowel sounds in one syllable.
Diphthongs are gliding vowels, as the first vowel sound glides into the next.
In the English language, there are eight diphthongs.
Diphthongs are categorised in terms of how they sound and how they are pronounced. These categories are: rising and falling diphthongs, opening, closing, centring diphthongs, and narrow and wide diphthongs.
Diphthongs are contrasted with monophthongs, which are pure vowel sounds.
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