Echoing Eco: From the logic of stories to posterior predictive simulation

“When I put Jorge in the library I did not yet know he was the murderer. He acted on his own, so to speak. And it must not be thought that this is an ‘idealistic’ position, as if I were saying that the characters have an autonomous life and the author, in a kind of trance, makes them behave as they themselves direct him. That kind of nonsense belongs in term papers. The fact is that the characters are obliged to act according to the laws of the world in which they live. In other words, the narrator is the prisoner of his own premises.” — Umberto Eco, Postscript to The Name of the Rose (translated by William Weaver)

Perfectly put. As I wrote less poetically a few years ago, the development of a story is a working-out of possibilities, and that’s why it makes sense that authors can be surprised at how their own stories come out. In statistics jargon, the surprise we see in a story is a form of predictive check, a recognition that a scenario, if carried out logically, can lead to unexpected places.

In statistics, one reason we make predictions is to do predictive checks, to elucidate the implications of a model, in particular what it says (probabilistically) regarding observable outcomes, which can then be checked with existing or new data.

To put it in storytelling terms, if you tell a story and it leads to a nonsensical conclusion, this implies there’s something wrong with your narrative logic or with your initial scenario.

Again, I really like how Eco frames the problem, reconciling the agency of the author (who is the one who comes up with premise and the rules of the game and who works out their implications) and the apparent autonomy of the character (which is a consequence of the logic of the story).

This also connects to a discussion we had a year ago about chatbots. As I wrote at the time, a lot of what I do at work—or when blogging!—is a sort of autocomplete, where I start with some idea and work out its implications. Indeed, an important part of the writing process is to get into a flow state where the words, sentences, and paragraphs come out smoothly, and in that sense there’s no other way to do this than with some sort of autocomplete. Autocomplete isn’t everything—sometimes I need to stop and think, make plans, do some math—but it’s a lot.

Different people do autocomplete in different ways. Just restricting ourselves to bloggers here, give the same prompt to Jessica, Bob, Phil, and Lizzie, and you’ll get four much different posts—and, similarly, Umberto Eco’s working out of the logic of a murder in a medieval monastery will come out different from yours. Not even considering the confounding factor that we get to choose the “prompts” for our blog posts, and Eco picked his scenario because he thought it would be fruitful ground for a philosophical novel. Writing has value, in the same way that prior or posterior simulation has value: we don’t know how things will come out any more than we can know the millionth digit of pi without doing the damn calculation.