Overview
A and an are the indefinite articles in English. They come before singular countable nouns and signal that you are talking about one unspecified member of a group. The choice between a and an depends on sound, not spelling.
1. The Sound Rule
| Use | Before | Examples |
|---|---|---|
| a | Consonant sound | a book, a car, a university /juːnɪˈvɜːsɪti/ |
| an | Vowel sound | an apple, an egg, an hour /ˈaʊər/ |
Key principle: Listen to the first sound of the next word — not the first letter.
2. Tricky Cases
| Word | Article | Why |
|---|---|---|
| university | a university | Starts with /j/ sound (consonant) |
| European | a European | Starts with /j/ sound (consonant) |
| hour | an hour | H is silent; starts with /aʊ/ (vowel) |
| honest | an honest person | H is silent; starts with /ɒ/ (vowel) |
| MBA | an MBA | Starts with the vowel sound /em/ |
| SMS | an SMS | Starts with the vowel sound /es/ |
| uniform | a uniform | Starts with /j/ sound (consonant) |
3. When to Use A / An
Use 1 — First mention (introducing something new)
- I saw a dog in the park. (first time mentioning it)
- She bought an umbrella.
Use 2 — Describing someone's job or role
- He is a teacher.
- She is an engineer.
Use 3 — Saying what something is (classification)
- A whale is a mammal.
- An oak is a tree.
Use 4 — Expressing quantity "one"
- I need a pen. (= one pen)
- Give me an apple.
Use 5 — With prices, speeds, and frequencies
- £5 a kilo
- 80 km an hour
- Three times a week
4. When NOT to Use A / An
| Situation | Example |
|---|---|
| Plural nouns | ~~a cats~~ → cats / some cats |
| Uncountable nouns | ~~a water~~ → water / some water |
| Before adjective + plural | ~~a nice days~~ → nice days |
5. A / An vs. The
| A / An | The |
|---|---|
| First mention | Second mention (already known) |
| Non-specific | Specific |
| One of many | The only one / already identified |
| I saw a dog. | The dog was brown. |
6. Common Mistakes
| Mistake | Correction | Explanation |
|---|---|---|
| an book | a book | /b/ is a consonant sound |
| a apple | an apple | /æ/ is a vowel sound |
| a hour | an hour | H is silent; vowel sound |
| a university | correct! | /j/ is a consonant sound |
| She is teacher | She is a teacher | Need article before job title |
| I drink a water | I drink water | Uncountable — no article |
7. Real-World Examples
- A nurse works long hours. An engineer designs buildings.
- It takes an hour to drive there — about 80 km an hour.
- He is a European working at an NGO in London.
- I need a USB drive and an HDMI cable.
Summary
| Rule | Example |
|---|---|
| Consonant sound → a | a car, a house, a university |
| Vowel sound → an | an egg, an hour, an MBA |
| First mention | I saw a dog. |
| Job / classification | She is an architect. |
| Quantity "one" | a pen, an apple |
| Not with plural / uncountable | cats, water (no article) |