A and An - Indefinite Articles
We use indefinite articles a and an when referring to living creatures and things that we talk about for the first time or do not know too closely.
A — we use it with nouns beginning with a consonant:
- a car
- a table
An — we use it with nouns beginning with a vowel:
- an apple
- an elephant
- an injury
Articles a, an mustn't be used with plural nouns:
- There are an elephants in the zoo.
Plural nouns appear alone or are preceded by words such as some or any.
some— used in positive sentences
any — used in questions and negative sentences
- I've got a pen.
- Have I got a pen.
- I haven't got a pen.
- I've got (some) pens.
- Have I got (some) pens.
- I haven't got (any) pens.