'A' and 'an' are both indefinite articles used before nouns or before adjectives that modify nouns.
To determine if you should use 'a' or 'an' before a word, you need to listen to the sound the word begins with.
Use 'a' if the word begins with a consonant sound and use 'an' if the word begins with a vowel sound. Below are some examples.
- a book
- an apple
- a card
- an upside down picture
- a perfect circle
It is important that you listen to the sound, and not only look at the letter. For example, 'unicorn' begins with /j/ (the y sound)
so you should use 'a' before it. The word 'honor' begins with /ɑ/ so you should use 'an' before it. Below are some examples.
- I drive a blue car
- They have an old house.
- They saw a cat in the alley.
- They opened an arcade in the mall.
- I bought a used car.
- The name 'Matt' starts with an M.
- She wore a unique dress to the party.
- He was an honorable man.
- He needed a USB charger.
- My TV has an LCD screen.
Just remember: listen to the first sound of a word to determine if you should use 'a' or 'an' before it.