The  determiners a/an and the are called "articles". They are the most common of all determiners. They come at the very beginning of a noun phrase. We divide them into "indefinite" and "definite" like this:

 indefinite
articles
definite
article
 a/anthe
use withsingular countable nouns onlyall nouns
use fora non-specific person or thing (singular)specific people or things (singular or plural)

We use indefinite  to mean non-specific. Indefinite  is general. We use definite  to mean specific. Definite  is particular. When we are talking about something in general, we use a or an. When we are talking about something in particular, we use the.

Think of the sky at night. In the sky we see MILLIONS of stars and ONE moon. So normally we would say:

  • I saw a star last night.
  • I saw the moon last night.

Look at some more examples:

a/anthe
I was born in a town.

John had an  omelette for lunch.

James Bond ordered a drink.

We want to buy an umbrella.

Have you got a pen?
The  capital of France is Paris.

I have found the  book that I lost.

Have you cleaned the car?

There are six eggs in the fridge.

Please switch off the  TV when you finish.

Of course, often we can use a/an or the for the same word. It depends on the situation, not the word. Look at these examples:

  • We want to buy an  umbrella. (Any umbrella, not a particular umbrella.)
  • It's raining! Where is the  umbrella? (We already have an umbrella. We are looking for our umbrella, a particular umbrella.)
This little story should help you understand the difference between a/an and the:
A  man and a  woman were walking in Oxford Street. The  woman saw a  dress that she liked in a  shop. She asked the  man if he could buy the  dress for her. He said: "Do you think the  shop will accept a  cheque? I don't have a  credit card."

Articles with Countable and Uncountable Nouns

Notice that we use the indefinite article a/an ONLY with singular countable nouns:  a dog, an egg, a very big man, an extremely delicious meal

By contrast, we can use the definite article the with ALL nouns: the dog, the eggs, the big men, the music, the food, the red wine

It is sometimes also possible to have no article at all—the so-called ZERO article. This can happen with all nouns (but normally not singular countable nouns): dogs, eggs, hot meals, music, red wine

The following table shows how we usually use articles with countable and uncountable nouns, but see EnglishClub Tip below for more about this.

 a/antheZERO
countablesingulara dogthe dogdog
plurala dogsthe dogsdogs
uncountablea musicthe musicmusic
In English, a singular countable noun usually needs an article (or other determiner) in front of it. We cannot say:
  • I saw elephant yesterday.

We need to say something like:

  • I saw an elephant.
  • I saw a pink elephant.
  • I saw the elephant.
  • I saw your elephant.

But see ZERO Article for cases when no article or other determiner is needed.

sources : Original Link