@J.R. I understand your point of view. In my opinion, though, we can consider "all" uses of the definite article through the concept of "identifiability" no matter whether it's something unique (like
the sun), it's something specific (even though it might not be unique, like
the window), or it's something generic (like
the air, and our
the city), because it's identifiable, i.e., it's "known" to the user, either implicitly or explicitly. It's just my opinion though, and I don't force anyone to understand it the way I do. Then again, I don't think my idea is very far off. —
Damkerng T. 40 secs ago