What is the main theme?

The main theme that runs through this book is alienation, whether the book is read as the funny/tragic account of a deeply troubled, rebellious, and defensive teenager or as a commentary on a smug and meaningless social milieu. Phoebe sums up Holden's sense of separateness from and anger at other people when she tells him he doesn't like anything. Holden's red hunting cap, which he dons when he is most insecure, is a continuing symbol throughout the book of his feeling that he is different, doesn't fit into his environment, and, what's more, doesn't want to fit in.