When the speaker and the listener both know the referent. A shared or common object or person.
“The dog looks sick.”
The father responds, “Yes, she does. That’s because she chewed up and ate the couch cushions.”
The boy says “the” because the father and the boy both know which dog the boy is talking about.
General vs. Particular
We do not use “the” when we speak about something in general terms. For example:
“Apples are delicious.” This refers to any apple or every apple. Especially, the ones you think of when you hear the word “apples”.
But, when we speak about specific (or particular) apples, we use “the“. For example:
The apples in this picture are red: The apples in this picture are green:
Using “a”, “an” or “some” to introduce. Then, using “the” after the introduction
When we talk about something for the first time, we will use one of these three articles: a, an, some
I have a pen and some paper. The pen is blue and the paper is white.
Look: there is a chipmunk standing on its hind legs at the edge of the table. It’s eating strawberries. It is so cute and furry! Oh no, the chipmunk sees us. I think it’s going to get scared. There it goes – bye bye!