comments and notes on the flesl.net ipa vowel chart
The chart lists the vowel sounds of standard North American English, the type of of English that is spoken in the north central United States and in central and western Canada.
The sounds are written using the notation of the International Phonetic Alphabet the 'IPA.' In each row of the chart, the IPA symbol for a vowel sound is given in the left-hand column; a common word that includes that sound is given in the central column, and a "transcription" of that word into the IPA is given in the right-hand column.
IPA symbols and transcriptions of English words into IPA symbols are written inside "square brackets." It is important to emphasize this when introducing students to the IPA because many of the IPA symbols are ordinary Latin letters used in the IPA for a special purpose. As a result, without the square brackets, IPA transcriptions can be mistaken for English words. (For example, the transcription of the word "boot" is [but].)
The two upper sections of the chart list the one-sound vowels or "monophthongs." ("Phthongas" is the Greek word for "vowel.") The vowels in the upper left-hand section are pronounced near the front of the mouth, the vowels in the upper right-hand section, near the back. In each section, the upper vowels are pronounced with the tongue close to the top of the mouth and the lower ones with the tongue closer to the bottom of the mouth.
Twenty of the twenty-two symbols on the list represent "phonemes." In other words, they represent an "abstraction" that may include two or more "concrete" speech sounds, or "allophones" that are "heard" as identical by native speakers. (That the sound [i] is a phoneme is indicated, for example, by the fact that if the vowel [i] in the word "feet" were replaced by any of the other vowel sounds on the list, the result would either be a different word such as "fit" [fɪt] or "fade" [fed], or nonsense such as "fow" [fɑw].)
"Phonemes" and "allophones" are sometimes distinguished from one another by writing phonemes in "slash marks" and allophones in square brackets. In the flesl.net chart, however, only square brackets have been used. This seems to be the best policy when using the IPA in ESL instruction. In fact, in that context it may be best to ignore the phoneme/allophone distinction: the idea of a phoneme is subtle, abstract (and apparently controversial among professional phoneticians); introducing it in an ESL classroom my create more confusion than clarity. (Teachers, however, should understand the concept and be ready to use it and discuss it with their students when the occasion arises.)
Two pairs of sounds that seem not to be distinct phonemes but rather allophones of the same phoneme appear on the chart. The first of these pairs includes the stressed vowel [ʌ] and the unstressed vowel [ə]. These two sounds are phonetically different, but they can be interchanged without changing one word into another word or producing meaningless nonsense. That shows they are only allophones, not phonemes.
Second, in standard North American English, the vowel [ɔ] and the more common vowel [ɑ] could be interchanged in the same way. For example, for speakers of standard North American English, the words "caught" and "cot" (a small bed) are "homophones"; they are both pronounced [kɑt]. However, if either or both of these words is pronounced as [kɔt] speakers of standard North American English will understand what is being said and regard it as acceptable speech. This shows that the two sounds, [ɑ] and [ɔ] are allophones of a single phoneme. In standard British English, however, these two sounds are distinct phonemes: "caught" is pronounced [kɑt] and "cot" is pronounced [kɔt], and if the sounds were exchanged a speaker of British English would not understand what was being said.
NOTES ON [ə]/[ʌ] AND [ɔ]/[ɑ]
[ə] and [ʌ]
There is no important difference between the sound represented by the "schwa" symbol, [ə] the vowel sound of the first and third syllables of the word "banana" and the sound represented by the "open 'o' " symbol [ɑ], the vowel sound in the word "but." The first, [ə], is unstressed and the second, [x] is stressed, but the actual sounds are identical or nearly identical. This means that there are no English words which would change their meaning or become nonsense if [ə] were replaced with [ʌ] or [ʌ] with [ə] and that shows the two sounds are not separate phonemes but allophones of the same phoneme.
However, it seems wise for ESL teachers is to treat the unstressed vowel [ə] as an independent speech sound. It is both the most common English vowel and the one that behaves in the most unusual way; it must be understood by anyone who hopes to speak clear, natural-sounding English. Having a special symbol to represent the sound will make easier for teachers to explain the schwa sound to their students and easier for students to understand what they are being taught.
Being aware of "schwa" as a distinct sound should help students in at least two ways. First, spelling should be improved when students come to understand that all the letters normally used to represent the stressed vowels 'a,' 'e,' 'i,' 'o,'and 'u' can also be used to represent schwa. Second, the schwa symbol is extremely useful in teaching English prosody because strong contrasts between stressed and unstressed syllables are a such a distinctive feature of English.
[ɔ] and [ɑ]
The sounds represented by the symbols [ɔ] and [ɑ] were originally separate phonemes in standard North American English as they still are in standard British English; during the 1800s, however, the two sounds "merged" into one in many parts of North America and the words like "caught" and "cot," which had been pronounced differently, came to be pronounced in the same way. (They became "homophones" in other words.) The sound [ɔ] still occurs in standard North American English, in such words as "call," and "cloth," but only as an allophone of the phoneme [ɑ]. In standard British English, and in some varieties of American English, there are still two phonemes [ɔ] as in "caught" and [ɑ] as in "cot".
Despite being only an allophone in isolation, he sound [ɔ] is a part of two phonemes of standard North American English the "r-coloured diphthong" [ɑɚ] that occurs in such words as "store" and "floor," and the "ordinary" diphthong [ɔj] that occurs in such words as "boy" and "toy." So although the sound is not a phoneme, it is necessary to use it in describing phonemes and this seems to be a good reason for including [ɔj] in the flesl.net list of standard North American vowels.
The "diphthongs" vowel phonemes that include two sounds have been divided into two charts, one for the "ordinary" diphthongs that are common to all standard English accents, and another for the r-coloured or "rhotacized" vowels that are used in most parts of Canada and the United States, parts of western and northern England, Scotland, Ireland, Barbados and parts of New Zealand. (The "r-letter" in the Greek alphabet is called "rho.")
notes on the "ordinary diphthongs"
Only three ordinary diphthongs, [ɔj], [ɑj], and [ɑw] have been listed. Often in lists of English vowels, the sounds [e] and [w] appear as parts of the diphthongs [eɪ] and [oʊ]. This seems to be an unnecessary complication and one that could detract from the value of the IPA as a tool for teachers and students of English. It is certainly true that the vowels [e] and [o] are seldom if ever pronounced in a pure way and that, when they appear in "final position," in words such as "say" and "go," they include two noticeably distinct sounds. On the other hand, when they appear in non-final position in words such as "take" and "boat" they seem to be as pure as the vowels [u ]and [i] which are never written as diphthongs. So the logical choice for the purposes of ESL instruction seems to be to treat all vowel sounds, apart from[ɔj], [ɑj],[ɑw] and the r-coloured diphthongs, as pure (or "non-diphthongic.")
This does not mean, of course, that the diphthongic qualities of [eɪ] and [oʊ] should be ignored in teaching English pronunciation. But perhaps they are best dealt with in the context of instruction in prosody and presented as the natural effects of lengthening and stressing certain syllables.
note on the r-coloured (rhotacized) diphthongs
Although they are extremely common in "rhotic English," the r-coloured diphthongs are not common in other languages. So, as with the [θ] and [ð] consonants, learning how to use them in English generally involves the "extra" job of learning how to make an unfamiliar sound.
In teaching the correct pronunciation of the r-coloured vowels, it seems wise, first, to emphasize the fact that they are unusual sounds, and second, the fact that they are diphthongic vowels. This second fact can could easily be missed because the final sound in all seven r-coloured vowels is an allophone of the "r-phoneme" and is often represented in phonetic "transcriptions" by the same symbol, [ɹ] that is used when the "r-phoneme" appears at the beginning of a syllable.
If the diphthongic quality of the sounds is not emphasized and the "r-part'" of the diphthong is represented with the same symbol that is used for the consonantal "r," then students who are using phonetic notation as a guide to pronunciation can easily get the impression that the r-element of the diphthong is in fact the same sound as the consonantal "r." This fact seems to be a good reason for not using a [ɹ] to symbolize the "r-part" of an r-coloured diphthong and using a special IPA symbol, [ɚ], the "rhotacized schwa," instead.
A further possible source of confusion and inefficient learning is the fact that there is a large variation in the way the r-coloured vowels are represented in phonetic notation not only in ESL materials but also, it seems, in standard dictionaries and in the writing of professional phoneticians. This fact provides another good reason for using a special symbol of some sort for the second part of the r-coloured diphthongs. And, beyond that it provides a good reason for using an IPA symbol in particular in the hopes that the confusion resulting from representing one thing with many symbols could be reduced if everyone adhered to an international standard.