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.