Definite and indefinite articles

Other Rules for Indefinite Articles

We might choose to use an indefinite article in English for one of two reasons:

1. 
   We are introducing a noun for the first time in a story. When a joke starts out, “A man walks into a bar,” the indefinite article “a” is used for both the man and the bar because this is the first mention of both nouns.
   
2. 
   We don't care which one exactly. If you're going to the store and your husband says, “Pick up a bottle of Chardonnay and some olive oil,” he doesn't care which bottle or which olive oil you get.
   

In either case, the noun is understood as being very general. There are millions of men, bars, and bottles of Chardonnay in the world, and there are millions of gallons of olive oil. When you use an indefinite article, you are beginning to narrow things down a bit, but you're not into specifics just yet.

Definite Articles

We have only one definite article in English, and it's “the.” We use “the” for singular, plural and uncountable nouns when the reader or listener clearly understands which thing we're talking about in particular. This could be for three different reasons.