sentences:  By this time, he had doubts about fundamental aspects of the work that went back to the earliest versions of the stories, and it seems that he felt the need to resolve these problems before he could produce the "final" version of "The Silmarillion".During this time he wrote extensively on such topics as the nature of evil in Arda, the origin of Orcs, the customs of the Elves, the nature and means of Elvish rebirth, and the "flat" world and the story of the Sun and Moon.In any event, with one or two exceptions, he wrought little change to the narratives during the remaining years of his life.