There are no similarly important systems of organization for the other aspects of novels that matter to readers— happy endings, tearjerkers, books set in Tokyo, or novels that feature firefighters or princesses or nuns. There is no system to indicate whether the style is minimalist, like Hemingway, or more complex like David Foster Wallace. There’s no way of knowing based on how bookstores are arranged if the protagonist is male or female, old or young, or if a story is set in London or Hong Kong.