http://www.english-test.net/lessons/16/index.html
Articles — both definite and indefinite
Indefinite — a, an
Uses
- Before a singular noun which is countable when it is mentioned for the first time and represents no particular person or thing.
"A horse is a noble animal." - Before a singular countable noun which is used as an example of a class of things.
"A book is something you read." - With a noun complement, including names of professions.
"She is a doctor, he became a famous actor." - In certain numerical expressions.
"a dozen, a hundred" - In expressions of price, speed, ratio.
"60 miles an hour, 4 hours a day, 30p a box" - With "few" and "little"
"a few people, a little sugar" - In exclamations before singular, countable nouns. "What a pity! What a sunny day!"
- It can be placed before Mr., Mrs, Miss, Ms + surname.
"a Mr. Brown phoned today."
Not Used
- Before plural nouns.
"Horses are noble animals." - Before uncountable nouns
"Milk is good for you." - Before abstract nouns.
"Fear is natural." - Before names of meals except when preceded by an adjective.
"We had a late breakfast and decided to miss lunch."
Definite — the
Uses
- Before nouns of which there is only one.
"The earth is round." - Before a noun which has become definite as a result of being mentioned a second time.
"We saw a good film last night. It was the film you recommended." - Before a noun made definite by the addition of a phrase or clause.
"The woman dressed in black." - Before a noun which, by reason of locality, can represent only one particular thing.
"There’s a bee in the kitchen." - Before superlatives and "first", "second" and "only"
"The longest river in the world." - Before singular nouns used to represent a class of objects.
"The donkey is a very obstinate animal." - Before an adjective used to represent a class of persons.
"That tax hurts the rich." - Before names of seas, rivers, chains of mountains, groups of islands and plural names of countries.
"the Pacific Ocean, the Thames, the Andes, the West Indies, the Netherlands" - Before musical instruments.
"She plays the piano"
Not Used
- Before countries, towns, proper names.
"Charlie lived in Chicago in America" - Before abstract nouns.
"Jealousy can be dangerous." - Before parts of the body and articles of clothing — these normally prefer a possessive adjective.
"Lift your left arm."
"He removed his hat."
