Indefiniteness

In the name of Allah, the Most Gracious, the Most Merciful,

Articles a and an. When do we use them? When do we use articles in English?

When do we use the? When don't we use the?

A , just like an, is an indefinite article. The, however, is a definite article.

To help us determine whether we use a definite or an indefinite article, we need to look up the meaning of the word indefinite.

Indefinite adj - not clearly expressed or defined.
definite adj - clearly expressed or defined.

So now it is clear that we should use definite articles when we are defining nouns that are clearly expressed while indefinite articles are used when we are defining nouns that are not clearly expressed or defined.

Example:

I would like an apple please.
Which apple? The apple on the table or the apple in the basket?
I would like the apple which tastes best.

In the first sentence, an is used because the sayer didn't care nor did he clearly express which apple he wanted.
In the third sentence, the is used because it is clearly mentioned which apple the sayer was referring to.
And in the last sentence, it is clearly expressed that the apple mentioned is the apple that tastes best.

Allah knows best.