In A Separate Peace, how do Gene and Finny act as a foil to each other?

A foil in literature is someone that makes another character seem better by contrast. Since A Separate Peace is narrated from Gene's point of view, his insecurities are pitted against Finny's greatest talents. For example, Gene feels insecure because he compares his introverted self and academic achievement with Finny's extroverted personality and athletic abilities. This does not provide the satisfaction he is seeking because it is as if he is comparing the proverbial apples to oranges. As many people do, Gene sees his weaknesses in Finny's strengths. Little did he know, however, that Finny may also harbor some jealous feelings. When Gene asks Finny if he would mind if Gene graduated at the first of the class, Finny says the following:

"'Mind?' Two clear green-blue eyes looked at me. 'Fat chance you've got, anyway, with Chet Douglass around'

'But you wouldn't mind, would you?' I repeated in a lower and more distinct voice.

He gave me that half-smile of his, which had won him a thousand conflicts. 'I'd kill myself out of jealous envy'" (52).

Now, whether or not Finny was serious is arguable, but the physical and mental contrasts between Gene and Phineas are sure. Finny's weaknesses in academics highlight Gene's strengths, whereas Genes weaknesses in athletics help to highlight Finny's strengths in that area. In an ironic twist though, Finny loses his ability to use his athletic strengths when Gene makes him fall out of the tree and he breaks his leg. Doctors say he will never be able to use it for sports again.

As unfortunate as the accidents is, Gene didn't intend to get Finny out of the way by jouncing the tree limb; he was just trying to make Finny look foolish for once during an athletic endeavor because they had just been arguing. Gene didn't want Finny to lose his athletic abilities for good, but once that does happen, Gene is able to become a better person. This is where the true nature of Gene and Finny as foils makes a difference in the story. Finny suffers a traumatic event that spirals him into depression and denial about the war. Gene wrestles with his conscience and how to be a better friend after witnessing and experiencing his own vengeful feelings exposed toward someone who was supposed to be his best friend. Had Finny not broken his leg and declined in his strength of character, though, Gene would not have been able to rise up out of his jealous nature to become a better person. In the end, Gene explains it best as follows:

"I never killed anybody and I never developed an intense level of hatred for the enemy. Because my war ended before I ever put on a uniform; I was on active duty all my time at school; I killed my enemy there" (204).

In summary, Finny seemed to be the strong, more dominant character at the beginning of the story, but he declined physically and mentally in the end. Conversely, Gene seemed to be the weak one at the beginning of the story and ends up being the stronger one. This is the perfect example of foil characters in literature because by contrasting both boys throughout the novel, one seems better than the other at different times and for different reasons.