"An" or "A" with acronyms which sound like they start with a vowel? [duplicate]

It depends on whether the abbreviation is an acronym or an initialism. As "fubar" and "scuba" are usually pronounced as a word (making them acronyms), it would make sense to say "a fubar" and "a scuba diver". "FAQ" is a bit harder, because I have heard people say it like an initialism: "‹f›‹a›‹q›", while others pronounce it as an acronym /fæk/. Therefore, one should write either "a FAQ" or "an FAQ" depending on how that person pronounces it, ie, whether it is an acronym or an initialism.

The important point to remember is the following:

Written language is a representation of the spoken word.

Thus, the answer is "If the word following the indefinite article begins with a vowel sound, use an; if it begins with a consonant sound, use a."

In the case of initialisms and acronymns, use the exact rule above. For initialisms (e.g. "US"), the individual letters are pronounced. With what sound does the first pronounced letter begin? In the example "US", the first sound is /j/ (or "y"). This is a consonant sound, despite the letter "U" being a vowel; thus, you use a, as in a US dollar.

Contrast this with the initialism "RPM", which begins with the consonant "R" but is pronounced starting with /a/; thus, you use an, as in an RPM counter.

The rule about the usage of a and an as indefinite articles is that an is used before a vocal sound.

• A warranty (/ˈwɑːrənti/)
• A user (/ˈjuːzər/)
• A one-way (/ˈwən ˌweɪ/)
• A man (/mæn/)
• An angel (/ˈeɪnʤəl/)
• An information (/ˌɪnfərˈmeɪʃən/)

When used before an acronym, the rule is still valid, but which article to use depends from how the acronym is pronounced (letter by letter, or as a word).

• An MP3 (/ɛm pi θri/)
• An RPG (/ɑːr pi ʤi/)
• An FBI agent (/ɛf biː aɪ/)
• A GPS device (/ʤi pi ɛs/)
• A NASA employee (/ˈnæsə/)