Quote:
For the sake of convenience, many teachers tell their students that the indefinite article a is used before consonants, while an is used before vowels. In most cases, this is true:
* A cat
* A dog
* A house
* A man
* A woman
* An apple
* An elephant
* An ice-cream
* An orange
* An umbrella
However, the choice between a and an actually depends on pronunciation, not spelling. Thus, a is used before a consonant sound, even if it is written as a vowel, and an is used before a vowel sound, even if it is written as a consonant:
* A uniform
* A one-sided game
* An hour
* An NCO
Some people say an, not a, before words beginning with h when the first syllable is not stressed:
* An hotel (a hotel is more common)
* An historical novel (a historical … is more common)
When an abbreviation takes an article, it depends on the pronunciation of the first letter of the abbreviation:
* An NCO
* A UN spokesman.
yep, an open case