Rules Pertaining to Usage of Article - Part - I

In English there are two types of articles:

(i)   The Indefinite Articles
(ii)  The Definite Article

The Indefinite Articles : A and An (Please note that ‘An’ is a variant of ‘A’.)
'A' and 'An' are to be used with Nouns that are singular.  Singular Nouns are, To simply put, we can put one, two, ... in front of them.
The Definite Article     : The

Notes:

1. The indefinite article ‘a’ is used before: 
 (a) a word beginning with a letter having a consonant sound. 
  Examples:  a book, a man, a dinner.

 (b) a word that begins with a letter (like O) with the sound like ‘wa’ 
 Examples: a one-rupee note, one-eyed man etc.

 (c) a word beginning with ‘u’ or ‘eu’ giving the consonant of ‘yu’.
 Examples: a university, a European.

2. The indefinite article ‘an’ is used before:
 (a) a word beginning with a letter like a, e, i, o, u having a vowel sound.
 Examples:  an apple, an egg,  an umbrella, an idiot, etc.

 (b) a word beginning with ‘h’ but the pronunciation starts with a vowel.
 Examples: an heir, an hour, an honest man, etc.

 (c) an abbreviation, the first letter of which is ‘M’ 
 Examples: an M.L.A., an M.P., an M.Com an S.D.O and F.R.C.S., an X-mas gift etc.


RULES REGARDING THE ARTICLES:
We use a or an:
Rule 1:  If noun is singular countable, article must be used. 
John is teacher (Incorrect))
John is a teacher (correct)

Man came to my house yesterday  (Incorrect)
A man came to my house yesterday  (Correct)

Rule 2:  a or an must be used for noun complement which includes professions. 
He was great man.  (Incorrect)
He was a great man  (Correct)

He is actor  (Incorrect)
He is an actor  (Correct)


Rule 2: If we want to say something about speed or price.
Eg: 
I bought these onions Five rupees kilo.  (Incorrect)
I bought these onions Five rupees a kilo  (Correct)
The speed of the train is fifty miles hour  (Incorrect)
The speed of the train is fifty miles an hour  (Correct)

Rule 4:  In exclamatory sentence before singular and countable nouns
Eg:
What a fine sketch!  (Correct)
What a great shot!  (Correct)

Rule 5:  Before the word ‘most’ when it is used in the sense of very or much or exceedingly.
Examples:Sreedhar is most intelligent student.  (Incorrect)
Sreedhar is a most intelligent student  (Correct)

This is most unfortunate event.  (Incorrect)
This is a most unfortunate event.  (Correct)


Rule 6:  Before a singular countable noun which is used as an example to represent a class.
Examples:
Cow is useful animal  (Incorrect)
 A cow is useful animal  (Correct)

Note : It must be borne in mind that ‘man’ or ‘woman’, when used in a general sense to represent ‘mankind’ as a whole, never takes are article.

Examples:
A man is mortal  (Incorrect)
Man is mortal  (Correct)

A woman is man's better half  (Incorrect)
Woman is man’s better half  (Correct)

Rule 11:  With the words a lot of, a couple, a great many, a good deal of, a good many, a great deal of, a few, a little etc. when they mean 'Some amount' and 'a small number'
Few books were in the library  (Incorrect)
A few books were in the library  (Correct)


Lot of people have attended the party  (Incorrect)

A lot of people have attended the party  (Correct)


Rule 5:  In certain phrases: a cold, a pain, on an average, make a noise, make an effort, make a mistake, a fever. etc.
I've got cold  (Incorrect)

I've got a cold  (Correct)

Rule 6:  With certain numbers : a hundred, a thousand, a million etc.

Rule 7:  ‘A’ can be used before Mr. / Miss / Mrs. + name
Examples:
 a Mr. Bose, a Mrs, Bose etc.
Note : A Mr. Bose denotes a person who is called Bose, and implies that he is a stranger to the speaker.
Mr. Bose, without ‘a’. implies that the speaker knows Mr. Bose, or knows of his existence.

Rule 8:  Before a proper noun to make it a common noun.
Examples:
Mohan is a Newton of our class  (Incorrect)
Mohan is the Newton of our class  (Correct)

Rule 9:  Before certain uncountable nouns preceded by nouns + of
Examples:
 a piece of advice, a bit of news, a drop of water etc.

Rule 10:
After the words many, rather, such, quite etc in certain structures.
Examples:
 1. Many a friend of mine is attending the party.
 2. Such a show cannot be arranged now.
 3. He is rather a fool to take such decisions.

A or An is not used before: 

(a) Plural nouns: a books, a universities etc. (Incorrect)

(b) Uncountable nouns: an advices, an information etc. (Incorrect)

(c) Names of meals:
Examples:
 Let us have a dinner (Incorrect)
 Let us have dinner  (Correct)

Note: An indefinite article can be used before names of meals when these are preceded by an adjective.
Example:
 She gave me a good breakfast at 8 p.m.  (Correct)