Site Rules.

[Reticulis]

a vs. an
Rule. Use a when the first letter of the word following has the sound of a consonant. Keep in mind that some vowels sound like consonants when they’re sounded out as individual letters.
Examples:
a finger
a hotel
a U-turn (pronounced You-turn)
a HUD program
a NASA study
Rule. Use an when the first letter of the word following has the sound of a vowel. Remember that some consonants sound like vowels when they’re spoken as individual letters.
Examples:
an FBI case (F is pronounced ef here)
an honor (H is silent here)
an unusual idea
an HMO plan (H is pronounced aitch here)
an NAACP convention (N is pronounced en here)
Deciding whether to use a or an before abbreviations can be tricky. The abbreviation for Frequently Asked Questions (FAQ) causes confusion because it can be pronounced as a word (fak), or one letter at a time (F-A-Q). Using the guidelines above, one would say a FAQ when it is pronounced as one word, and an FAQ when it is pronounced one letter at a time.