Indefinite Articles A and An

Indefinite Articles 

A and an are called the indefinite articles because they do not point out any particular person animal or thing.
e.g.

• I met a friend.

• There is a cat on the table.

Here in these sentences we are not talking about particular friend or cat, so we use ‘a’ as indefinite article before them.

Now I’ll discuss about four important rules to use Articles ‘a’ and ‘an’.

Using A and An

Rule 1

1. We put a or an before the singular form of a countable noun.
For example 

• He was sitting on a chair.

• She was eating an apple.

Here chair and apple are countable so you’ll use ‘a‘ before them.
You cannot use a or an before uncountable nouns.
Like I like an honesty. incorrect.
I like honesty. correct.

Rule 2

2. We use ‘a’ when the following word begins with a consonant sound. You have to be careful while choosing a or an according to the sound not letter.
e.g.

a boy

a pencil

Here boy has ‘b‘ sound and pencil has ‘p’ sound so we’ll use ‘a’ before boy and pencil.

Another example 

a European

This can be little bit confusing for you as E is a vowel letter but when you pronounce European we get ‘y‘ sound at the beginning like ‘yoo‘ and ‘y‘ is a consonant sound.

Let’s take more examples 

a university 

a unique idea

In both the examples above we have vowel letters ‘u‘ but they have consonant sound while pronouncing them that us ‘y‘.
It’s ‘yoo/niversiry‘ not ‘oo/versity‘

a one rupee coin

In one the sound is ‘w’ so use ‘a’ before one.

Rule 3

3. We use ‘an’ before a word beginning with a vowel sound

e.g.
an example
an M.A.
An S.P.
an important meeting
an honest opinion
an honourable man

Some of the given examples can create confusion in your mind like why do we use an before M.A., S.P. or honest.
The reason is very simple and clear as I discussed the rule that we use an before a word beginning with vowel sound. So we have to observe sound not the letter. 
When we pronounce M.A. or S.P., we get vowel sound from the letter M and S as they begin with ‘a’ sound. In the same way when we pronounce honest or honourable, we get ‘o’ sound as letter ‘h’ is silent. That’s why we use ‘an’ before these words not ‘a’.

Rule 4

4. We usually use a or an when we are mentioning someone or something for the first time

• I bought a car.

• She is reading a book.

• I ate an orange.