We use the Indefinite Article – a or an – when we talk about:
jobs – He is an artist and his wife is a plumber.
beliefs – He is a Buddhist and his wife is an atheist.
nationalities – He is an American and she is a Canadian.
We never use the indefinite article with non-countable nouns:
* I swam in a clean water and ate a pasta.
* an asterisk denotes ungrammatical English
Before a Vowel
A or An? The general rule is that we use a before a consonant and an before a vowel:
a bowl
a car
a dog
but…
an ant
an elephant
an insect
an orange
an urn
But, what is important here is not the way a word is written, but the way it sounds. We choose a or an depending on the sound at the beginning of the word and whether it is a vowel sound or a consonant sound.
For example, take the word uniform. Although it begins with a vowel – u – when we write it, when we say it the first sound is /y/ which is a consonant:
uniform is pronounced /ˈjuːnɪfɔːm/ so we say a uniform
One word which is often confused is hotel. Some people pronounce this word as /həʊˈtɛl/ so they would write:
a hotel
But other people pronounce this word as /əʊˈtɛl/ and so they would write:
an hotel
Useful Links
Articles in English Grammar – a general look at articles in English