Today I will be making up another new literary term: major arcs. I was learning about major arcs in Honors Geometry (basically, more than half the circumference along the outside of a circle) when I realized that the concept could be brought into writing. Draw a circle, label the top with one trait, such as "Good", label the bottom with an opposing trait, such as "Evil", and shade along the circle from the top to the bottom and beyond. This is a major arc in which a character underwent a full transformation, but later drifted back toward his original condition.
Few books that I can think of use major arcs. Sometimes characters appear to have changed when they really haven't, which in some ways is a major arc, at least to the readers. Massive weight loss is a decent real-world example. You lost two hundred pounds and then gained fifteen of them back. A swimmer might steadily become less afraid of water from infancy, only to become terrified of it after nearly drowning.
While most books probably wouldn't benefit from having major arcs, the concept is pretty cool. I might give it a try some day.