"a vs. an"
A lot of people learn to put a before words that star with consonants and an before words that start with vowels, but it’s actually more complicated than that. The actual rule is that you use a before words that start with a consonant sound and an before words that start with a vowel sound.
- Tom waited for an hour.
- Monica was on a historic expedition.
An hour is correct because hour starts with a vowel sound. People seem to most commonly get tripped up by words that start with the letter h and u because sometimes these words start with vowel sounds and sometimes they start with consonant sounds. For example, it is a historic expedition because history starts with an h sound, but it is an honorable fellow because honorable starts with an o sound.
- Tom had a Utopian idea,
- Monica reminded him it’s an unfair world.
The letters o and m can be tricky too. Usually you put an before words that with o, but sometimes you use a. For example, you would use a if you were to say, “She has a one-track mind,” because one-track starts with a w sound.
- Tom wants to work as a missionary.
- Monica wants to get an MBA.
REMINDER: The sound governs whether you use a or an, not the first letter of the word. (Fogarty 6).