Imagine that you’re at a cafe with a friend. You see three men walk in, one of them young and the other two old. Imagine also that you (believe that you) know something that (you believe that) your friend doesn’t, viz. that the young man is a famous chess player. You may point in the direction of the three men and say: “The young man is a famous chess player.” Pointing in that direction narrows down the possible referent(s) of the subject of the utterance to just those three men, and the category “young man” narrows down the possible referent(s) further: The only possible referent is now just that one man.

In saying that “the young man is a famous chess player,” first you (1) establish joint attention on the referent, in this case “the young man,” and then you (2) say something about that referent, in this case “is a famous chess player.”

But it’s also possible to flip it around. Instead of saying that “the young man is a famous chess player,” which uses the fact that he’s a young man as (perhaps) nothing more than just a way of establishing joint attention on him, you can say that “the famous chess player is a young man,” which makes the fact that he’s a young man into the point that you’re making about him.