Most distinctive features of American English pronunciation 48
Vowels. American English is commonly described as having lax vowels, tense vowels, and wide diphthongs. Lax vowels are lower and made with less oral tension; they do not usually end syllables. Vowel length in American English is generally considered to be conditional by phonological environment, so the long/short distinction in BBC English is not usually present, though they have retained the length mark on the tense vowels [i: ɑ: ɔ: ɜ: u:] in order to mark their relationship lo the English long vowels. Since the diphthongal movement in [eı] and [oʊ] is small in American pronunciation, these are treated as tense vowels.
Vowels preceding /r/ are notably influenced by rhotic colouring. Word spellings such as bird, word, earth, jerk, which now rhyme with [ɝ] in American English, at one time in history had differing vowels. The retroflexed vowels [ɝ] and [ɚ], stressed and unstressed, are among those features that noticeably distinguish American English from BBC English. All vowels occurring before [r] within a syllable are likely to become "r-coloured" to some extent.
• lax vowels: ı e æ ʌ ʊ ə
• tense vowels: i: ɑ: ɔ: ɜ: u: eı oʊ
• wide diphthongs: aʊ aı ɔı
• retroflexed vowels ("r-coloured") ɚ ɝ
There is an issue in the symbolization of the diphthong in the word home. This has for many years been represented as [əʊ]. [oʊ] is the preferred transcription for the American English diphthong, though it can be argued that the latter symbolization would be suitable for both.
The American [æ] vowel is somewhat closer than BBC [æ], and seems to be evolving into an even closer vowel in many speakers. It is used in the same words as BBC [æ] and also in most of the words which in BBC have [ɑ:] when there is no letter “r” in the spelling, e.g. pass, ask.
American [ɔ:] is more open in quality than BBC [ɔ:]. It is used where BBC has [ɔ:] (e.g. cause, walk), and also replaces BBC short [ɒ] in many words, e.g. long, dog;. American [u:] is similar to BBC [u:], but is also used where BBC has [ju:] after alveolar consonants (e.g. new, duty).
Consonants. There are numerous phonetic and phonological differences between British and American English, as there are within regional and social varieties within the two political entities. Two differences receive sufficient attention and have attained sufficient generality within the two varieties. One is phonetic: the "flapped" medial [t] (as in butter) is transcribed as [t̬]. The other is phonological: the presence (in American English) of postvocalic [r] (as in farmer ['fɑ:r.mɚ]).
It should also be noted that the difference between "clear" and "dark" [l] is much less marked in American than in the BBC accent, so that even prevocalic [l] in American pronunciation sounds dark to English ears.
The accent used for British English is classed as non-rhotic - the phoneme [r] is not usually pronounced except when a vowel follows it. The American pronunciations, on the other hand, do show a rhotic accent, and in general in the accent described, [r] is pronounced where the letter “r” is found in the spelling.