(2023-09-21) Davies Probability By Stories A Four Point Scale

Dan Davies: probability by stories, a four point scale. I probably ought to do an occasional series of “ideas for novels that will never be written”. Among the works from which my finance career has saved the reading public is a science fiction murder mystery, set in a world in which time travel is in wide use.

In such a world, obviously, there is no fixed set of historical facts, so conventional techniques of deduction don’t work. Consequently, society has had to gradually abandon the whole concept of causation and explanation. The detectives investigating the case are actually literary critics – their job is to find the person whose guilt makes the most satisfying narrative.

I actually quite like the idea of “narrative probability”, and would defend its use in a lot of applications.

These would be cases where you’re trying to express subjective probabilities

if you have more than two or three options, you’ll almost always get a set of probabilities that doesn’t add up to 1. People don’t think about probabilities in this way

reformulating the question. “What is the subjective probability?” in a lot of important contexts means “to what extent is this consistent with your information set?” or roughly “how much sense would this outcome make to you?”.

If you ask the question “how much sense does this make?”, I’d argue that there’s roughly a four point scale:
“This version of events makes no sense”
“This version of events makes sense”
“This version of events makes more sense than any of the others”
“No other version of events makes sense”.