Thanks to Rapaire for including Yeats' "Host of the Air." I remined me of a thing I have experienced in Muscoge folk lore, known and loved by some as "those damnable dualities." In the realm of ritual, it's carried to the 4th power (2 to the 4th) which is itself another duality. I am personally inclined, beyond ritual applications, to see the value in dualities as carrying the cultural wisdom that there is always an "on the other hand." They are also useful heuristic and pnemonic (sp?) devices.