Just a couple of bits of information. Sweet William's Ghost (Child #77) is based on the superstition that if one dies with an unfulfilled commitment, he/she cannot rest in peace. In this case, William has left unfulfilled his promise to marry Lady Margaret, his death having prevented it. He returns as a ghost to ask Margaret to release him from the promise. She does this symbolically by smiting him across the breast with a cross. He then returns to his grave to eternal rest.

The other superstition evident in this ballad is the requirement that ghosts must retreat from the world of the living at dawn - signalled by the crowing of the cock.

Regards,
John