How many vowel sounds are there in English? David Deterding (2004). Download: http://www.ubd.edu.bn/academic/faculty/FASS/staff/docs/DD/STETS-vowels.pdf British English has 12 monophthong vowel sounds and American English has 10 or 11 monophthong vowel sounds.
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STETS Language & Communication Review, Vol. 3, No. 1, 2004
between the onset and the rhyme. However, if a syllable
starts with any consonant followed by /j/, then the only
vowels that can occur are /υə/ (for some speakers)
and /u /, so for example /kju t/ is a good word of English
but */kjɑ t/ is not. This unexpected restriction between
the /j/ and the following vowel suggests that /j/ belongs
not in the onset, but in the rhyme, and we should then
regard /ju / as a vowel of English.
Furthermore, we might note that /h/ can never be
followed by another consonant, so */hr t/ and */hlp/
are not possible syllables in English. But note that
hue /hju / and huge /hju d / are perfectly good words
of English. If /h/ cannot be followed by a consonant but
/hju / is a good word of English, this again suggests that
/j/ should be part of the vowel and not part of the onset.
However, note that all the other diphthongs in
English are falling diphthongs, with the first part being
the main part of the vowel. So, for example, with /a/, it
is the [a] that is the main part, and the final  is called
an offglide. But if /ju / is regarded as a vowel of English,
it is a rising diphthong, with the second part of the vowel
being the main part and the initial [j] being an onglide.
In consequence, it is the only rising diphthong in English,
and the need to introduce this category to deal with just
one vowel makes this analysis rather unattractive
(Deterding & Poedjosoedarmo 1998:28). As usual, there
is no simple answer.
It is not easy to determine exactly how many vowels there
are in English. American speakers have about sixteen
vowels (though some have fewer), and British speakers
may have about twenty vowels, though there may be more
depending on the analysis adopted.
In fact, there are further issues that could be
considered. For example, one way of representing
American English suggests that there are no diphthongs
at all, for just as /w/ can occur at the start of a syllable,
one could say that a word such as cow ends with /w/, so
we might transcribe it as /kaw/ rather than /kaυ/.
Similarly we might allow /j/ at the end of a syllable and
transcribe buy as /baj/ rather than /ba/. If we allow /w/
and /j/ at the end of syllables, there is no need for
diphthongs (Ladefoged 1999:42) (though this cannot
easily be extended to deal with the centring diphthongs
of British English).
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