English — Indefinite article a/an
English has one indefinite article with two forms: a and an. The choice depends on the sound that follows, not the spelling. Use it before a singular countable noun mentioned for the first time or one of many, and to state someone's job.
How it works
Use a before a consonant sound and an before a vowel sound. Judge by the sound, not the letter: a car, a university (the u sounds like "you"), but an hour (the h is silent) and an apple. The article marks a singular countable noun that is new to the listener or one among many, and it introduces a job: she is a nurse, he is an engineer.
Examples
| Example | Why this form / use |
|---|---|
| a car | Consonant sound /k/ → a; a first-mentioned object. |
| an apple | Vowel sound /æ/ → an; one of many, not a specific one. |
| a university | Starts with a vowel letter but sounds like /juː/ → a. |
| an hour | Starts with h but the h is silent /aʊə/ → an. |
| She is a nurse. | Job/classifier use: a + profession after be. |
| He is an engineer. | Job after be; engineer begins with a vowel sound → an. |
Good to know
A common mistake is choosing the form by spelling. It is a university and an hour, not "an university" or "a hour". Also, a/an never goes with plurals or uncountable nouns (say cars or water, not "a cars" or "a water"), and it is dropped after be with a job in the plural: they are nurses.