In Fahrenheit 451, a possible theme for the novel is in the third part of the book, what is it?It's toward the end of the third part of the book.
After the quick and devastating war that destroyed the city, Montag, Granger, and the other book people begin moving upstream. Granger tells Montag about the Phoenix, the mythological bird that every few hundred years would burn itself up only to rise again out of the ashes. He says the cities will do that because man perseveres. He also tells Montag to remember that he is unimportant; it is his task of remembering and of trying to make the world a better, more enlightened place that is important. He continues saying that man has been making the same mistakes for eons and that maybe, someday, if people keep trying and don't give up or give in, they will finally learn and stop repeating their mistakes. That serves as a theme for the book. Montag makes the comment to his wife in an earlier part of the book that maybe books can help them stop repeating the "same damn mistakes". Faber talks about his own, and others', meek attempts to stop the current trend. He says they gave up too easily. Clarisse and Beatty both talk about how things are now in their society versus how they used to be and Beatty, especially, tells us how the change came about. It was mostly due to people forgetting about the past rather than learning from it. Much in the story has to do with the idea of not repeating mistakes and not giving up because the cause of enlightenment is more important than anything else.