The writing style in A Separate Peace varies based on when in the protagonist Gene's life the story is taking place. The novel is an extended frame story: Gene describes his past to the reader as a series of boyhood flashbacks to his time at the Devon School.
Early in the novel—immediately following the dreamy and almost Gothic introduction—younger Gene’s style is boyish and boisterous. It’s full of short, clipped dialogue between Gene and Finny, which continues almost unchanged throughout the book when the boys are together. The adolescent Gene doesn’t know how to express his feelings about the things going on around him, especially when it comes to Finny. Accordingly, Knowles’s sentences narrating Gene’s thoughts tend to be far longer and more expository than things he says aloud.
The language Knowles uses becomes gradually more mature and refined as the series of flashbacks through Gene’s boyhood progresses. Gene’s younger self speaks self-consciously, but his diction is quite casual. He also often reacts sarcastically when he’s scared or confused. As an older teenager and then an adult, Gene’s language becomes more formal and a great deal more melancholy. In order to express the difficulties of Gene’s complicated adolescence, the novel also makes heavy use of metaphors, similes, and personification. This is particularly notable when it comes to descriptions of the Devon School itself. It feels like a character in its own right, as it so often actively influences the choices Gene and his friends make. It’s an oasis of sameness in a world that is violently changing, a quality that Knowles emphasizes through figurative language linking New England’s natural beauty and the school’s museum-like stillness.