One reader has asked a question that a lot of people probably would like the answer to:
When using acronyms such as FTP, HTTP, and ASP it sounds weird to use "a" in front of "FTP". Are acronyms an exception to the rule of preceding a word beginning with a vowel with "a" and preceding any word beginning with a consonant with "an"? For example: "I have a FTP server" sounds better like "I have an FTP server."
Well, he is right. An acronym that begins with a vowel sound is treated like a word that begins with a vowel sound: it takes "an," not "a".*
Whether one uses "an" or "a" is determined entirely by the sound that follows the article, because the only reason for using "an" is to prevent the vowel sound of "a" from eliding into the vowel sound that begins the next word. That is why we use "a," not "an" before a word beginning with a long "u," because the word sounds as though it begins with a "y":
a U.S. decision in favor of a unilateral strike
On the other hand, if the word begins with a short "u", then that is a vowel sound, so the word would be preceded by "an":
an unlikely story
an unworthy opponent
*Those who are aware that in American usage periods and commas "always" go inside the quotation marks may not be aware that there is actually an exception to this rule. If the item enclosed in quotation marks consists of letters or figures, then the period or comma goes outside the quotation marks. For more examples of this, see "Quotation Marks: Where Do the Periods and Commas Go--and Why?"