Indefinite article has two forms: a and an.
a – we use before a noun or noun phrase beginning with a consonant
He’s a teacher.
We have a small garden.
It’s a nice dog.
an – we use before a noun or noun phrase beginning with a vowel
[example]Would you like an orange?
She’s an electrician.
An egg for me, please.[/example]
We use indefinite article a / an only when we say about something first time, and described object or person is a countable noun [tooltip/link] in the singular [tooltip/link].
[example]He’s got a game
Can you give me an address?[/example]
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We never use indefinite article a / an before countable noun [tooltip/link] in the plural [tooltip/link] and before uncountable nouns [tooltip/link]. In such situations, we can use e.g some
[example]There’s some milk in the fridge.[/example]
When we say about something second time (e.g in the next sentence), we have to use a definite article the.
[example]She’s got an umbrella. The umbrella is red.[/example]
We use indefinite article a / an only when we say about professions and nationalities in the singular [tooltip/link].
[example]Tomas Carlsen is a Frenchmen.
My brother is a doctor.
He’s a driver.[/example]
If professions and nationalities are in plural we don’t use indefinite article a / an.
[example]Tom and Mark are Englishmen.
My sisters are dancers.[/example]
If a noun is defined by an adjective (or few), we put an article at the front of it (or them)
[example]He’s a handsome boy.
It was a long, tiring journey.[/example]
We use indefinite article a / an in phrases like a lot of, a few, a couple, a little.
[example]I’ve got a lot of video games.
I have a couple of biscuits to share.
There are a few people in the cinema.[/example]