Question

what guesses does the poet make about the theme/ subject of the reaper's song?

Answer 1

The poets guessed that it was a sad song but he can't understand the song lyrics which sung by the solitary reaper

Answer 2

Hii thank u so much for such a beautiful and useful question.
Now,
As the poet was the nature lover. Though he would not be able to clarify the words of the song sung a highland girl. So by her songs tuning he made some guesses about the theme. And in the end he thought that the song of a highland girl is sad but melancholic......

Hope this answer will really help u.....