Kesey’s decision to make Chief Bromden the narrator of One Flew Over the Cuckoo’s Nest was simply a brilliant idea. Chief can't speak, so instead he’s sitting back, observing the ward, and taking stock of everything. They know he’s watching, but the men don’t know how perceptive he is. In making Chief an intelligent, calm, and sharp narrator, Kesey is able to depict the men and the asylum in an insightful, logical, and detailed way. Chief tells us what’s going on – he’s our eyes and ears in the asylum – and we feel like we can trust him completely.
As for the dialogue, Kesey lets his characters go wild. He lets the men hoot, holler, and carry-on as they see fit. McMurphy’s vernacular tells us a lot about him – how smart he is, how he approaches life, the way he communicates with the men, and the way he deals with Nurse Ratched. His speech also captures a colloquial way of speaking that was characteristic of the era.
Look at this telling passage, about half-way through the book:
McMurphy doesn’t know it, but he’s onto what I realized a long time back, that it’s not just the Big Nurse by herself, but it’s the whole Combine, the nation-wide Combine that’s the really big force, and the nurse is just a high-ranking official among them.
The guys don’t agree with McMurphy. They say they know what the trouble with things is, then get in an argument about that. They argue till McMurphy interrupts them.
“Hell’s bells, listen at you,” McMurphy says. “All I hear is gripe, gripe, gripe. About the nurse or the staff or the hospital. Scanlon wants to bomb the whole outfit. Sefelt blames the drugs. Frederickson blames his family trouble. Well, you’re all just passing the buck.”
Here we see that Chief is on top of his game. He’s smart. He’s observant. He has opinions and theories. Take a look at McMurphy’s language – it situates him in history and location, but it also shows how he’s honest and upfront with the guys and is not afraid of being rough or crass. One of the most impressive things about One Flew Over the Cuckoo's Nest is how masterfully Kesey uses dialogue and narration.