The Nicene Creed was hammered out at two councils under imperial pressure to settle whether Christ was of the same substance as the Father or merely similar — a distinction that in Greek was one letter (homoousios versus homoiousios), which is where the phrase "not one iota of difference" comes from, ironically inverted. It is recited by Catholics, Orthodox, Anglicans, Lutherans, and many Reformed churches, which makes it the broadest point of Christian agreement — except for one clause. The Western addition of "and the Son" (filioque) to the Spirit's procession was a principal cause of the 1054 schism and remains unresolved.