Arguably, the main theme of Fahrenheit 451 is censorship. According to Beatty, censorship came into being as a result of the majority who, over a period of time, chose entertainment over the pursuit of knowledge:
School is shortened, discipline relaxed, philosophies, histories, languages dropped…Life is immediate, the job counts, pleasure lies all about after work.
But this pursuit of pleasure created a society filled with ignorance and technology. We see this most clearly through the character of Mildred. While she has the constant company of the parlour walls, she is miserable and isolated, as demonstrated by her suicide attempt in Part One.
In addition, censorship has created a group of social outsiders, like Clarisse and Faber, who question the status quo and then find themselves ostracised. These individuals have a great impact on Montag and their desire for knowledge contributes to his change from fireman to social outsider. It is the dangers of censorship, however, which provides the impetus for Montag, after he witnesses a woman give her life for her books:
There must be something in books, things we can't imagine, to make a woman stay in a burning house; there must be something there, you don't stay for nothing.