I can't believe there have been all these posts about this song, and while the authorship of Sandy Denny has been mentioned nobody has uttered the words Fairport Convention, or mentioned that their original version of the song, sung by Sandy who was one of their primary singers from 1968-1970, is by far the best version of the song ever recorded. Quite an original too, that band... Sandy was on their 2nd, 3rd and 4th albums: What We Did on our Holidays, Unhalfbricking, Liege and Lief... I think Who Knows is on Unhalfbricking. This music is a bit like what early joni would sound like if she were british and had electric backing.
