Universal Willie

"Willie" is this universal name in folk music, it seems. Willie is everybody from this handsome guy that every lady in the whole castle loves to the fellow who kills pretty Polly. And everything in-between, though I suppose Willie O' Winsbury would fit in the first category. Anyhow, it's like the name "Johnny", only Johnny is mostly a soldier (Johnnie Cope? No exception! The guy was a general! He was also a real person). What's with it? If only the most universal name for women in folk music wasn't Mary. I don't care for that name at all, really...