Articles "a", "an" and "the" are considered as three of the most common adjectives that we usually use in a sentence.

A and an are indefinite articles; they refer to any one of a class of nouns. The, the definite article, refers to a specific noun.

INDEFINITE: a contest, an opportunity
DEFINITE: the winner

The following examples below are pointers that will help us understand how to use these articles in different sentences.

"A" and "AN"

1. a - indefinite article (not a specific object, one of a number of the same objects) with consonants

Examples:

> "She has a dog."
> "I work in a factory."

2. an - indefinite article (not a specific object, one of a number of the same objects) with vowels (a,e,i,o,u)

Examples:

> "Can I have an apple?"
> "She is an English teacher.

"THE"

1. the - definite article (a specific object that both the person speaking and the listener know)

Examples:

> "The car over there is fast.
> "The teacher is very good, isn't he?


** The first time you speak of something use "a" or "an", the next time you repeat that object use "the".

Examples:

> "I live in a house. The house is quite old and has four bedrooms."
> "I ate in a Chinese restaurant. The restaurant was very good."

** DO NOT use an article with countries, states, counties or provinces, lakes and mountains except when the country is a collection of states such as "The United States".

Examples:

> He lives in Washington near Mount Rainier.
> They live in northern British Columbia.

** Use an article with bodies of water, oceans and seas..

Examples

> "My country borders on the Pacific Ocean."

** DO NOT use an article when you are speaking about things in general

Examples:

> "I like Russian tea." > "She likes reading books."

** DO NOT use an article when you are speaking about meals, places, and transport

Examples:

> "He has breakfast at home."
> "I go to university."
> "He comes to work by taxi."