The Sun Also Rises: Theme Analysis

The Challenge of Moral Value
This book could easily be described as "immoral." There are many characters doing things that parents would not want their children doing. Perhaps most shockingly, Brett seems to have sex indiscriminately. Jake betrays his friend Montoya by allowing Romero and Brett to disappear together. Cohn abandons his aging fiancee because he thinks he has not had enough experience to marry. Mike is bankrupt, quite cruel when he is drunk, and looks the other way when his fiancee has affairs with other men. Almost all of the characters are tremendous drinkers, and virtually every character gets too drunk to walk at some point in the book.
The key to understanding this is the time period, the mid-twenties in a Europe that had just fought the Great War and wasn't yet aware of the full significance of what had happened. It was difficult for people who had observed the horrors of trench warfare to believe that a benign divinity could allow such an enormous waste of human life. They had seen the use of chemical weapons, battles such as Verdun or the Somme where hundreds of thousands of men might die in a single day with no visible change in positions, and the increased use of machines that kill. For people such as Jake, Mike, and Brett who survived these things, it might mean that the world has lost its innocence, and traditional Christian morality no longer has any relevance. Or it might mean that everything that used to mean something- art, love, peace-has become threatened. What it often meant, in the simplest terms, was that the world changed a great deal as a result of the War, and many people, unsure what the changes meant, started to experiment to find out.
Over the course of the novel, at least four of the five characters who meet in Pamplona for the fiesta (Jake, Cohn, Mike, and Brett) are tested in some way. Cohn must confront Brett's promiscuity, both as a participant and an observer, and he is unable to resolve this challenge to his understanding of morality. For Cohn, beautiful women who are "well-bred" do not do things like what he catches her doing with Romero. If they are, it is something that they need to be rescued from, not something that they should enjoy and refuse to abandon.
Mike, like Cohn, is tested by Brett. Unlike Cohn, though, he tries to destroy himself with alcohol, fails, and meekly sleeps through his rival's final bullfight and then travels back into France without really confronting Brett's abandonment. His relationship with Brett was never about morality or any meaningful commitment, because she regularly had relationships with other men. Mike seems almost proud that he foresaw Brett's interest in Romero, and he is clearly a moral failure and a victim.
Jake, like the others, is tested by Brett, and though his failure seems to take more effort on her part, it is more serious than the others. Brett tells Jake that she loves him, and treats him differently, possibly because of his impotence. She connects with Cohn through him, though he does not know about her trip to San Sebastian with Cohn until afterward. He does know about her intentions with Romero, though, and he not only introduces the two of them, he politely steps out of the way so that they can abscond together. By risking the corruption of Romero, the only really positive male character in the book and the greatest hope for moral clarity, Jake risks despair, something that is conveyed in the last line of the novel-that it might only be a pretty lie that he and Brett could ever really be in love if he wasn't impotent.
Perhaps Brett's decision at the end of the book "not to be a bitch" is the greatest moral choice, and the best example of moral value. She is promiscuous, she is a drunk, and she manipulates Jake in numerous ways, but in the end she convinces Romero to leave her, not because she doesn't care about him and not because she doesn't want to be with him, but because she knows that it would be bad for him. She cares enough about Romero, at least, to let him go, knowing that it is the best thing for him. Romero is very young, innocent, but he has a strength of spirit and courage that Cohn cannot beat out of him with his fists, and that he quickly demonstrates despite his beaten and sore body in the bullfight ring. He is clearly a hero, and though Brett knows that he would be rich and famous and take care of her, she tells him to leave.
It is possible that Romero, through his relationship with Brett, teaches her enough about morality for her to realize that she does not belong with him and that he would be better off without her. If this is true, then Romero becomes the only source of meaningful moral clarity. He does things the right way; he presents a positive model of virtue, through his respect for tradition, history, his sport, his people, himself, and both the animals he kills and the natural world that produces them.