Vowel Diagram
In the previous section, we learned that there are about 15 vowel phonemes in standard American English. Our goal is to learn all these sounds so that we can say words correctly. So, in this section, we aim to find a way to study them systematically.
Since vowel sounds are produced without any obstructing part in the mouth, it can be hard to describe how to pronounce vowel sounds. Some methods suggested are the shape of the mouth and the distance between the lips. These methods are limited however since they do not explain what is really going on inside of the mouth.
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| Vowel diagram with lips and tongues |
Tongue height
To describe the production of vowel sounds systematically, linguists employ two measures: the height of the tongue and the originating location of the sound in the mouth. The way we move and shape our tongue plays a big part in giving each vowel its own sound. When we pronounce a vowel, even a small change in the position of the tongue can make a difference in the way the vowel sounds. The height of the tongue means how high the tongue is placed in the mouth. The vertical position of the tongue can be high, middle, or low.
The high position means that the tongue is raised toward the top of the mouth. Mechanically speaking, to raise the tongue, the lips will have to be close to each other. Vowels that are produced high are /i/, /ɪ/, /ʊ/, and /u/. We call these four vowels high vowels.
The middle position is where the tongue is placed in the middle of the mouth. The lips are a little apart from each other. Vowels that are produced in the middle, called middle vowels, are /ɛ/, /ʌ/, /ə/ and /ɔ/. Also occurring in the middle are /e/ and /o/, which are the beginning sounds of diphthongs: /eɪ/ and /oʊ/. /e/ and /ɛ/ are pronounced in proximity, but /e/ occurs a little higher than /ɛ/, so /e/ is viewed as a high-medium vowel, and /ɛ/ as low-medium vowel. Likewise, /o/ and /ɔ/ occur in proximity, but /o/ occurs higher than /ɔ/, so /o/ is a high-medium vowel and /ɔ/ is a low-medium vowel.
The low position of the tongue means that the tongue is farther down. To do this, the jaw should open wide. Low vowels are /æ/ and /ɑ/.
Advancement
The other way to categorize the vowel sounds is to consider where the sound originates in the mouth. This measure is called advancement. Vowel sounds can originate at the front of the mouth, in the middle of the mouth and in the back of the mouth. Vowels that occur at the front of the mouth are the following four: /i/, /ɪ/, /ɛ/ and /æ/. These four vowels are called the front vowels. Vowel sounds that originate in the center of the mouth are /ə/ and /ʌ/. Vowels that occur at the back of the mouth are the following four: /u/, /ʊ/, /ɔ/ and /a/. These are called the back vowels.
Vowel diagram
Now that we classified vowles based on the tongue height and advancement, we can create the vowel diagram, where the x coordinate is the advancement and the y coordinate is the tongue height.
Vowels that are high and front are /i/ and /ɪ/. Compared with /i/, /ɪ/ is lower and less frontal. /ɛ/ is a middle front vowel, and /æ/ is a low front vowel. /u/ and /ʊ/ are high back vowels. Compared with /u/, /ʊ/ is lower and central. /ɔ/ is a mid back vowel and /a/ is a low back vowel. The center middle vowels are /ə/ and /ʌ/, which are essentially the same sound except for the emphasis. In standard American English, /e/ and /o/ do not occur as pure phonemes, but as part of diphthongs as in /eɪ/ and /oʊ/. Also, the high and mid back vowels (/u/, /ʊ/, /o/ and /ɔ/) are called round vowels since they are produced with the lips rounded.
Tenseness
The vowel diagram provides us with a rough idea of how vowels should sound. But it does not help us pronounce them precisely since some vowels share the same coordinate points. /i/ and /ɪ/, for example, are high and front vowels. Since they are produced in close proximity, these two vowels can be hard to distinguish and thus hard to pronounce correctly for us non-native English speakers. So we need a way to distinguish them. Linguists distinguish /i/ and /ɪ/ by the tenseness. To say /i/, we need to make the muscles in the vocal tract work hard. The lips are pulled back and the tongue is tense. But when we say /ɪ/, the vocal tract is relaxed. So for example, ‘beet’ and ‘bit’, ‘peach’ and ‘pitch’ are contrasted by the vowel sounds being tense in the first words but lax in the second. Similarly, in ‘kook’ and ‘cook,’ the first word has a tense vowel /u/, and the second has a lax vowel /ʊ/. Vowels that are located at the peripheral regions of the vowel diagram, except /æ/, are called tense vowels because the pronunciation of these sounds requires some muscular effort. Vowels that occur in the center region including /æ/ are called lax vowels, by contrast.
Similar sounding vowel pairs
Vowels that are near each other in the vowel diagram are produced with tongue
positions that are close to each other and thus sound similar. In other words, vowels that occur in proximity can be more difficult to differentiate than those that are farther apart in the vowel diagram. For this reason, we first learn individual vowels and then compare vowels in close proximity. Among the 10 pure vowels, (/i/, /ɪ/, /ɛ/, /æ/, /u/, /ʊ/, /ɔ/, /ɑ/, /ə/, /ʌ/), the proximal vowel pairs are these:
/i/ and /ɪ/
/ɛ/ and /æ/
/u/ and /ʊ/
/ɔ/ and /ɑ/
/ə/ and /ʌ/
We’ll learn these vowel pairs. In particular, to differentiate the proximal vowels, we will use the minimal pair technique. A minimal pair is a pair of words that differ in a single phoneme. Minimal pairs are often used to demonstrate that two sounds (or phones) are two separate phonemes in the language. For example, we can demonstrate that /s/ and /z/ contrast in English by adducing minimal pairs such as bus and buzz. Since the only difference in these words is the /s/ vs. /z/, we can conclude that they belong to distinct phonemes.
In addition, we will also learn the five diphthongs of standard American English. They are /eɪ/, /aɪ/, /ɔɪ/, /aʊ/ and /oʊ/. The diphthongs can be divided into two groups based on the final vowel sound, /ɪ/ or /ʊ/. Those ending with /ɪ/ are /eɪ/, /aɪ/ & /ɔɪ/, and those that end with /ʊ/ are /aʊ/ and /oʊ/. Regarding /eɪ/ and /oʊ/, the first sounds in these diphthongs, /e/ and /o/ do not occur on their own as vowel phonemes in American English. As you can see in the vowel diagram, /e/ and /ɛ/, /o/ and /ɔ/ are pronounced in proximity, meaning that /e/ and /ɛ/ sound similar, and /o/ and /ɔ/ also sound similar. Compared with /ɛ/ and /ɔ/, /e/ and /o/ occur at higher position.