When do you use an versus a?

The choice between "an" and "a" depends on the sound of the following word, not its spelling.

Here's the rule:

* Use "an" before words that start with a vowel sound. This includes words that begin with a silent "h", or with a consonant that makes a vowel sound (like "u" in "university").

* Use "a" before words that start with a consonant sound. This includes words that begin with a vowel that makes a consonant sound (like "y" in "yacht").

Examples:

* An apple (vowel sound)

* A banana (consonant sound)

* An hour (silent "h")

* A unicorn (consonant sound)

* An umbrella (vowel sound)

* A useful tool (consonant sound)

Remember: It's the sound of the word that matters, not the letter it begins with.