You use “a” and “an” before singular nouns, but the choice depends on sound, not spelling. Use “a” before words that start with a consonant sound: a book, a car, a university Use “an” before words that start with a vowel sound: an apple, an egg, an hour Important detail: it’s about how it sounds, not just the first letter. For example: “a university” (because it sounds like “yoo-niversity,” starting with a consonant sound) “an hour” (because the “h” is silent, so it sounds like “our”) Simple rule to remember: If it sounds smooth with a vowel start, use “an.” If it sounds like a consonant start, use “a.”