One simple rule: Read it aloud, then use the appropriate indefinite article.
Acronyms (a new and complete word formed from initial letters or initial parts of other words) are read as a word (and not read by reading the letters). So…
Scuba mask is read aloud as (scu’-bah) mask. Not Ess see ewe bee ay mask. So, it is a scuba mask.
[ Trivia ]Self contained underwater breathing apparatus – J. Costeau[ /Trivia ]
The same holds true for a NATO general, a laser beam, a MADD pamphlet, an Interpol criminal. You don’t say the letters of an acronym – ever. You read the word it spells.
Abbreviations are trickier because sometimes the abbreviation is pronounced by its letters, and sometimes the abbreviation is pronounced by the full, unabbreviated title of the thing being abbreviated.
For example, in the phrase Senator from NJ, the state is always read aloud as New Jersey, and never as enn jay even if it is abbreviated in print, and you’re reading that abbreviation aloud. And so, you’d write, a NJ Senator, because you’d say it (out loud or in your mind) as a New Jersey Senator.
However, some abbreviations are read aloud as the letters of the abbreviation, since we say the abbreviation out loud as well as write it that way. In the sentence I didn’t trust the nurse, so I got an M.D. to look at it, the abbreviation is read (aloud and in one’s head) as an emm dee.
So, it’d be proper to write an M.D. from a MD city.
The really tricky part comes from some abbreviations that can go both ways, or newly coined abbreviations where there has been no clear pattern established.
So, when you read my S.O. (or SO) got me a Valentine’s Day gift, do you read it aloud as ess oh or as significant other? Whichever is the norm, or the intent of the author, will determine whether to use a or an.
Peace.
A m. posting.
