How does the dialogue in A Separate Peace add to our understanding of the novel's characters and themes?
Dialogue is one of the most effective tools of characterization. Through a character's words, we can learn much about his/her impressions of self, as well as how others respond. For example, in this novel, Gene shouts at Finny “You see! Kill me! Now you know what it is! I did it because I felt like that! Now you know yourself!” He vents his anger on Finny, which reveals more about him than anything else. We see that he still harbors the same rage that drove him to jostle Finny out of the tree in the first place. While he seems to be justifying his action to Finny, he is really attempting to rationalize his behavior to himself. Lashing out like this to a boy who's bed-ridden (through Gene's own fault) reflects Gene's instability and incoherency.
Others reveal themselves through their words. Edward "Leper" Lepellier uncovers his own madness in his conversation with Gene, & in doing so suggests an experience with the military that contrasts with what the boys expected. He tells Gene "The army has the perfect word for everything, did you ever think of that?...And the perfect word for me…psycho. I guess I am. I must be. Am I though, or is the army? Because they turned everything inside out.” Leper here is trying to come to terms with the way his life turned out, & the changes that have been wrought upon his mind.
Overall, dialogue connects to every theme in the book, allowing the audience to determine each character's perspective. For example, Leper's dialogue suggest that propaganda depicting war as fun and clean is terribly wrong. Gene's dialogue reveals that our true enemies are ourselves, no matter who we project our troubles onto.