ARTICLE IN ENGLISH GRAMMAR

English Grammar Articles
(a, an, the)

      What are English grammar articles? An articles is a word that is used before a noun to show whether the noun refers to something specific or not. a, an, and the are articles

      Articles in English grammar are the words "a," "an" and "the." Articles belong to a larger category of words called "determiners," which also includes words such as "this," "some," "my" and "any." Articles and determiners appear before nouns and serve the function of making nouns more specific. Articles are used to signify levels of definiteness or knownness.

The Definite Article
(For example: the box)

"Definite" means "clear, obvious."
The definite article tells us that the noun is specific. The speaker talks about a particular (or known) thing.
The definite article in English is "the."
Examples:
"The car I bought broke down."
"He has a son and a daughter. The daughter is a doctor."
"The actors were really good."
"I remember the day we first met."

"The" can be used before both singular and plural nouns.
Examples:
"The flower he gave her was very beautiful."
"The flowers on the table are nice."

The Indefinite Article
(For example: a box)

"In-" means "not," and "definite" means "clear, obvious."
"Indefinite" means "not clear, not exact."
The indefinite article tells us that the noun is not specific. The speaker talks about any one of that type of thing.
The indefinite articles in English are "a" and "an."
Examples:
"I need a pen."
(The speaker doesn't tell us which pen he needs. He simply needs a pen, any pen.)
"Lisa wants to see a movie."
(The speaker doesn't tell us which movie Lisa wants to see. She wants to see some movie.)
"Joe has a car."
(The speaker doesn't tell us which car Joe has. He has some car.)
"She is a dancer."
(She dances for a living.)

What is the difference between "a" and "an"?

"A" and "an" have the same meaning.

We use "a" before a consonant sount.
Examples:
a dog
a building
a university

We use "an" before a vowel sound.
Examples:
an apple
an umbrella
an eye

Important!

We use "a" and "an" only before a singular noun. We can't use "a" and "an" before a plural noun.

Examples:
Correct: a car.
Incorrect: a cars.

Correct: an orange.
Incorrect: a oranges.

What is the difference between "a" and "the"?

"The" is used to talk about specific or known things. These are usually things that have been mentioned before or that the listener is familiar with.
"A" (or "an") is used to talk about things which are not specific. These are usually things that haven't been mentioned before or that the listener is unfamiliar with.
Let's say I tell you: "I went to see a doctor last week."
Explanation: I went to see some doctor. I didn't mention him before, and you are not familiar with him. Another option is that it is not important who he is. So I use the word "a".
Then I say: "The doctor said I should get more rest."
Now you already know which doctor I am referring to. I am referring to the doctor I went to see. So I use the word "the."
Next I say to you: "Do you remember the movie we watched together?"
I use the word "the" because I mention a specific movie – you know which movie I am talking about.
Then I tell you: "Well, I've seen a better movie since!"
You are not familiar with the new movie, so I use the word "a".
I also tell you: "A man on the street stepped on my foot."
You don't know who exactly stepped on my foot, I've never mentioned him before. So I use the word "a".
Finally, I tell you: "I am a singer."
This sentence simply means that I sing for a living. If I said: "I am the singer", you would understand that I am the singer that was mentioned before.

For example:
- "Wow! I heard a great singer is coming to town."
- "Oh, it's me. I am the great singer."

Now that we understand the general idea of English grammar articles, here are some more specific details:

 Examples:

"I need a chair."

In the sentence above we find the article "a". It shows us that the speaker does not need a specific chair. He can have any chair.

"I want an egg."

In the sentence above we find the article "an." It shows us that the speaker does not want a specific egg. He can have any egg.

"I want the red apple."

 In the sentence above we find the article "the." It shows us that the speaker wants a specific apple.

Spesific Uses of English Grammer Articles

In this case		Example Sentence
Use "a" / "an"	You mention something for the first time.	I have a problem.
	You want to say that something belongs to a certain group.	This is a table.
	You want to say that someone belongs to a certain group.	She is a designer.
	You want to say that something is that kind of thing.	I've built a strong ship.
	You want to say that someone is that kind of person.	He is a nice guy.
Use "the"	You talk about a specific thing.	The feeling I got was very strange.
	It is clear which thing you are talking about.	I passed the test!
	There is only one such thing.	Look at the sun.
No article	You talk about something in general.	Pigs can't fly. Diving can be difficult.
	You talk about cities, countries, streets, etc.	We visited Italy.

Source :
http://www.learnenglish.de/grammar/articlestext.html
http://en.wikipedia.org/wiki/Pattern_grammar
http://www.learnenglish.de/grammar/articlestext.html