2.1.1 The Indefinite Article ‘a/an’:
The form a is used before a word beginning with a consonant, or a vowel with a consonant sound.
Examples: a man a European a university
a hat a one-way street a ewe
The form an is used before words beginning with a vowel (a, e, I, o, u) or words beginning with a mute consonant, or before individual letters spoken with a vowel sound.
Examples: an apple an island an M.P
an yield an egg an hour
Use of ‘a/an’:
1.a/an is used before a singular noun which is countable, when it is mentioned for the first time and represents no particular person or thing.
Examples: I need a pen.
They live in a bungalow.
2.a/an is used before a singular countable noun which is used as an example of a class of things.
Examples: A child needs love. (all children, any child)
A car must be maintained. (all cars, any car)
3. a/an is used in certain expressions of quantity, with certain numbers and in expressions of price.
Examples: a lot of a couple Rs.10 a kilo
a great many a dozen 50ps a dozen
Before half when half follows a whole number. However, a half holiday, a half portion, a half share is possible.
Examples: 1 ½ kilos=one and a half kilos or a kilo and half, but 1/2kg=half a kilo (not a before half)
4.In exclamations before singular, countable nouns.
Examples: Such a long queue!
What a pretty girl!
5.a can be placed before Mr./Mrs./Miss.
Examples: A Mr. Patel, means a man called Patel and implies that he is a stranger to the speaker.
Mr. Patel, would mean that the speaker knows him.
6.a/an are used in the following cases.
Examples: in an assembly of 30 people a breach of peace
to give an assurance lack of a quorum
The indefinite article cannot be used before plurals So,
a man – men (not a men)
an ostrich – ostriches (not an ostriches)