Bayesian Inference atop the Cliffs of Insanity

It appears I haven’t updated my priors since 1987. When Vizzini, Inigo, and Andre the Giant stand at the top of the Cliffs of Insanity and see the Man in Black below them slowly ascending, Vizzini claims against the evidence of his own senses that such effort is “inconceivable.” In one of the more oft-quoted lines of the film, Inigo retorts “you keep using that word–I do not think it means what you think it means.”

When I first watched the film as, gosh, I guess I was 13 at the time, I interpreted it as a dig at Inigo’s lack of sophistication. To me, it was a simple pun: “inconceivable” can also mean “unable to conceive [a child].” Ha ha, snare drum, cue curtain, and scene.

The more apt interpretation wouldn’t have occurred to a 13 year old me: Inigo was criticizing Vizzini’s Bayesian processing. “Inconceivable” means that the mind is incapable of imagining the outcome. Well, clearly the evidence presented refutes Vizzini’s prior beliefs about the Man in Black’s abilities. It’s not “inconceivable” unless Vizzini is unwilling or unable to update his beliefs given the currently available evidence. To Inigo, “inconceivable” means that the posterior probability is 0. To Vizzini, “inconceivable” means that the prior probability is 0. The difference in opinion over the use of the word contrasts the simple (Hayekian) humility portrayed beautifully by Mandy Patinkin against the technocratic arrogance portrayed (again, beautifully) by Wallace Shawn.

And a few scenes later [spoiler alert], Vizzini’s hubris leads to his untimely demise. Is The Princess Bride a paean to libertarianism? Eh, probably not. But the political intrigue is catnip for public choice scholars, for sure.

Why is this relevant to Sweet Talk? Well, the unfortunate truth about people is that they tend to be pretty awful Bayesians. In some circumstances, they have resolutely, irrationally immobile priors. In others, they update too much based on weak or misleading evidence. This intemperate tendency should favor biasing institutions towards robustness against the vagaries of popular opinion. Presume Chestertonian fences.

And never go up against a Sicilian when death is on the line.


4 thoughts on “Bayesian Inference atop the Cliffs of Insanity

  1. Great post. To some extent rhetorical persuasion or sweet talk is about increasing *practical* certainty (“social” confidence) in the face of ever present *epistemology* uncertainty. Vizzini’s dialogue with himself, where he is scaling the infinite regress of switcheroos, is a hilarious example of how often the object of sweet talk is ourselves: Self-persuasion, daily affirmations, “talking yourself into it”. I suppose hayekian humility is therefore about being able to mentally subvert your own self-confidence, as it were.

  2. Jessica

    Hit “post” accidentally. This entry reminds me of how narrow-minded I was about environmentalism until I actually studied the subject in college and had to eat my words. Embarrassing, but my willingness to change my mind is something I’m proud of. Thanks for shining a light on unconscious processes. 🙂

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