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Is this true that in American English a is pronounced aey to rhyme with ace and major, and in British English it is pronounced with long aah sound as in are and father?
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Do you mean the letter name (A,B,C) or the letter sound (how it is used within words) or the word a (as in 'a' cat)?

In British English the letter sound a is pronounced in different ways depending on the word.

The word a is pronounced in two ways. Either a as you mention above in ace or major, or an 'uh' sound (not as in are or father, more of the schwa sound).

The name of the letter A is pronounced as in ace or major.
Is this true that in American English a is pronounced aey to rhyme with ace and major, and in British English it is pronounced with long aah sound as in are and father?

No. It's not true.

Both American and British English contain many different pronunciations of a, depending on the word in which the a occurs. apple, mass, ape, wash, war, spinach, about, said, ..., and there are differences between the two, but these differences
cannot be summarized in such a simple way.

CJ
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The letter "a" is pronounced ay, as in hay or gay. It is pronounced aaah, as in barn or father, by children when learning the alphabet.
Here is a tip about "a" in AmE.

Assuming that a word is syllabized properly, here are various scenarios.

CaC and stressed: CAT vowel (cactus)

CaC and unstressed: CAT vowel ("fan" in fantastic)

Ca~CVV and stressed: MAY vowel ("ra" in voracious, "na" in pugnacious)

CaC~CVV and stressed: CAT vowel (fractious, anxious)

Ca~CVC and unstressed: shwa

~ = syllabic boundary

CAT vowels can become BET vowels before nasal stops.
What is Ca~CVV?
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NL888What is Ca~CVV?
Consonant - "a" - syllabic boundary - consonant - vowel - vowel.

Is that what you were asking?

CJ
Yes thanks.
how can a be the syllabic boundary? Is a served just as a symbol or as an abbreviation of some word?
NL888how can a be the syllabic boundary
Nothing there says that "a" IS the syllabic boundary.

The syllabic boundary occurs after "a" and before the next element. The syllabic boundary is considered an element in that series of symbols just the same as "a" is another symbol in the series.

CJ
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