What were the reasons that Bradbury choose the first-person narrator in "Fahrenheit 451"? For example why example why did he choise the third person narrator?
Your questions are contradictory. There is only one narration style in the book and it's third person limited. The story is told through the eyes of an observer who is not a character in the story and this observer is not all-knowing. This observer gives us Montag's thoughts, but no one else's thoughts. The narrator gives us a great deal of detailed description, too. By using this sort of narrator, the reader gets a vivid view of Montag's world, but in a somewhat dispassionate manner. The world in which Montag lives is dispassionate and people are not close to one another, we are told life doesn't hold great value; it is an impersonal, isolated world and this type of narration helps to give that impersonal feeling to the reader to some degree. We don't even get fully into Montag's head until the last section of the book when he is drifting down the river and his mind is filled with memories and images. At that point, he is leaving behind this cold, isolated world and moving into one where fire is warming and people are friendly, so it's fitting that we get to know his thoughts more.