The fact that there are any stories to tell means that something has survived. In a way, these aren’t end-of-the-world stories at all, because the world doesn’t really end—or rather, the world ends, but humanity carries on. These are post-apocalyptic stories, and their focus is not on destruction, but rebuilding. That hopefulness sneaks its way into most stories in the subgenre... The overriding narrative in most post-apocalyptic fiction is the emergence of order from chaos.
That optimism is at the core of David Brin's novel The Postman-- best-known to most as the basis of a not-too-well-received film adaptation* in the late '90s, but don't let that dissuade you. The novel is a fine example of what post-apocalyptic fiction is all about, and, on a larger scale, of what SF as a genre strives to do.
The book tells the story of Gordon Krantz, a drifter struggling to survive in a post-WWIII landscape sparsely populated with insular settlements, savage survivalists, and heartless bandits. Krantz stumbles across the body of a mail carrier in a pre-war delivery truck, and takes his clothing and mailbag for purely practical reasons: they'll keep him warm through the cold nights ahead. But at the next settlement he encounters he finds that people see the old uniform as an emblem of anteapocalyptic stability. So he turns it into a con: he'll pretend he's a real mailman, establishing routes for the "Restored United States," as a way to score free food and shelter in towns that would otherwise refuse him entry. But the con works a bit too well: those mail routes he's pretending to set up turn into a well-functioning communications network, and within a few years he's trapped in the middle of a conflict between these accidentally-united farming communities and a strong, violent, feudal society of survivalists. Krantz, a once-honorable man forced by circumstances into dishonesty, regains his honor by taking responsibility for the survival of democracy in northern Oregon.
The lie of the Restored United States, and Krantz's guilt over his dishonesty, are central to the story of the Postman. Krantz feels he is cheating the poor, simple folk of Oregon by selling them false hope that they can regain something that is lost forever. What he doesn't realize, though, is that the hope can create the reality. Prior to the lie, the communities he encounters were isolated and stagnant, unlikely to survive for more than a generation or two. But given the idea that they could be reunited into a larger culture, they quickly set about to make that idea a reality. Krantz may be lying when he says that the government is regaining strength in the East and has plans to reconnect with the West-- or he may not be; he has no knowledge of the status of the world east of Minnesota. But the idea of the "Restored United States" is ultimately not a lie, because the people of Oregon have made it real for themselves. In Oregon, the United States really is restored, as a direct result of Krantz's dishonesty. In the Postman, faith has a concrete result; faith makes its object real. The lie is not a lie-- it is a myth; it is a fiction that shapes reality.
At one point in the story Krantz is recounting his experiences in the immediate aftermath of the war, when his National Guard unit, assigned to protect granaries against raiding survivalists, fell apart, symbolizing the final collapse of government, stability, and order. But in telling the story to his listeners, he alters the truth to reflect his desires:
The cavalry came. The granaries were saved at the last minute. Good men died.. but in his tale their struggles were not for nothing. He told it the way it should have ended, feeling the wish with an intensity that surprised him.
This embellishment and invention bolsters a more useful image of the world: a picture of a society that has not completely collapsed. And that image, in turn, shapes the real society which Krantz is now creating. Just as importantly, the myth he creates stands as a bulwark against the novel's survivalist villains, totalitarian despots who want nothing more than to see the dream of a resurgent democracy snuffed out. "If America ever stood for anything," Krantz tells one group, "it was people being at their best when times were worst." Which isn't entirely the truth, of course. But in the post-apocalyptic crucible, that's what the ideal of America has become, and that's the version of the American myth that can produce the best result. There's much to say about the myth and the reality of America in this novel, but I'll leave it at this: the America Krantz speaks of is not the America that was, but the America he hopes will come to be. His apparent idealization of the past is really the communication of a prophetic hope for a golden age to come.
And that kind of prophetic fabulation is an important aspect of SF. Whether SF is predicting wonders to come or painting bleak pictures of dystopian wastelands, it always strives to have an impact on the real world. It can inspire either excitement or repentance, and Brin's novel does both: it hopes to create a world in which nuclear war and survivalist gangs will not come to be, and that a compassionate and thoroughly honorable society will. The Postman idealizes its narrative to show us both the best and the worst of ourselves, so that we may choose the right path to a better future.
*Which, for the record, I kind of liked. At the very least it's better than Waterworld.