We shall never know. It was a time when people moved about without need for passports or visas, when many musicians were itinerant, when the authorship of a tune by a commoner was unimportant.

We do know, however, that when we sing about love, we don't sing about sleeves. And as a dedicated gardener, I can assure you that white sleeves turn brown, not green, after a while. So I lean toward a Celtic origin with the word "Sliabh" in there somewhere. But we all know I could be wrong.