Lars Eighner's Homepage Writers' Workshop FAQ: Q. We pronounce "an" before an acronym or a set of initials that begins with a vowel sound like MD, but how should it be written?

Q. We pronounce "an" before an acronym or a set of initials that begins with a vowel sound like MD, but how should it be written?

A. My rule of thumb is how the sentence would be pronounced if read aloud. I would say "em dee." I cannot imagine anyone reading "Lt." as "el tee." Even though they both begin with "M" (pronounced "em" by most people) you should write "Bill is an MD," but "there is a Mr. Smythe to see you" because no one would pronounce "Mr." as "em-are." Likewise, write "a NATO round" because "NATO" is pronounced "nay-toe" beginning with the consonant sound of "n," but write "an NAACP spokesperson because "NAACP" is pronounced "en-double-aye-sea-pea," beginning with the vowel sound "eh."