[Galadriel55]

Hm. I always thought that the first theme was neither Eldar nor Edain - just a theme. Maybe of Ainur. Eru brought in both Children.

At least, that's what I thought before I actually had the question written in front of me.

Now I begin to think that the third theme could be the future of Elves and Men, and possibly the beginning of the Second Song.

It's a posibility that the Ainr would sing "both" songs in one if Melkor didn't cause troubles. But the song ended - and quite abruptly - and everything had to be resolved before it could continue, or before you could bring in more themes...