Knowles uses the literary device of antithesis, or the placing together of opposites, in the opening lines of chapter 3:
Yes, he had practically saved my life. He had also practically lost it for me.
The lines also use parallelism, which occurs when the same grammatical structure is used in two or more consecutive sentences.
Gene uses a cliché when he says he would have "lost face" with Finny if he had refused to jump out of the tree. By "losing face," he means he would have felt diminished or ashamed if he backed out of the exercise. This can also be considered an idiom.
Gene employs a metaphor, a comparison not using the words like or as, when he compares his mind to a straight jacket, saying his thoughts gave him
the maneuverability of a strait jacket.
In other words, he is completely constricted by his need to please Finny.
In the following, Knowles uses the literary devices of dialogue, alliteration, and personification:
"At least it's not as bad as the seniors," I said, handing him the fragile racquet and the fey shuttlecock. "They're doing calisthenics."
Dialogue lends a sense of immediacy, putting the reader directly into the scene. In the quote above, Gene is talking to Finny, who does not like having to play badminton as a summer sport. Gene uses alliteration in the repeated f sounds at the beginning of the words fragile and fey. Fey may also be seen as personifying, or assigning human characteristics to, the shuttlecock: it is a word usually used to describe people.