Use "a" before a singular noun that starts with a consonant sound:
- He wants to buy a car.
- I need a pen to write this down.
- She ordered a sandwich for lunch.
- I saw a boy running in the park.
- We need a hammer to fix the shelf.
- I want to eat a hamburger.
- A hungry dog will eat anything.
Use "an" before a singular noun that starts with a vowel sound:
- She has an umbrella for the rainy days.
- He is an actor in the new movie.
- An elephant is a big animal.
- I had an idea for the project.
- She wore an orange dress to the party.
- An herbivore is an animal that only eats plants.
- Can you wait for me for an hour?
- An honest person always tells the truth.
Remember that sometimes the first letter of a word may be a vowel, but the sound it makes is a consonant sound. In that case, we use "a" instead of "an":
- A knife is a useful tool for cooking.
- ¿Do you live in a European coutry?
- She is a university professor.
- A unicorn is a mythical creature.