Paul Simon learned it in 1965 in London from Martin Carthy and set it in counterpoint with “Canticle”, a reworking of Simon’s 1963 song “The Side of a Hill” with new, anti-war lyrics. Wikipedia
Riddles Wisely Expounded. The Elfin Knight. The False Knight Upon the Road. Lady Isabel and the Elf Knight. Et cetera the Scandanavian versions of the Child Ballads as lore, quests, and riddles.
Apply The Elfin Knight to interbreeding as the Falmer fell, and the herbs illiterate Nedic/Nordic women took to avoid it; and Canticle to the genocide which collapsed their civilization and eradicated their culture. (Video of a nicely haunting version with minimal parts and accompaniment.)
Religious Version
Find the S&G version sung at the Feast of the Dead. By verse, a duet sing the first and last together; a woman sings the Scarborough Fair lyrics in the middle three verses; and a man sings the Canticle lyrics.
The Scarbarrow is a hill which would open on certain nights of the year and the fairyfolk would steal the souls of the dead. Parsley, sage, rosemary, and thyme are herbs to shield the graveyard inhabitants from the charms of the fae.
Scarbarrow Fae, fairyfolk, Falmer. Nords lay impossible charges on them to keep them from the souls of their ancestors. This remembers desparate Falmer raiding Nord barrow-wights in their binding rituals. Desecrating these honored dead was the last decision the banshee made before Kyne cursed her with the screaming thu’um.
Folk Version
Find the circa 1610 version A recited by an ancient Nord lady (mentioned in version B), from clear memories of her youth (she’s not so good at remembering the present). This version is more intimate, describing the contest of wills around the seduction.