Thursday, February 2, 2023

Rethinking priors

Suppose I learned that all my original priors were consistent and regular but produced by an evil demon bent upon misleading me.

The subjective Bayesian answer is that since consistent and regular original priors are not subject to rational evaluation, I do not need to engage in any radical uprooting of my thinking. All I need to do is update on this new and interesting fact about my origins. I would probably become more sceptical, but all within the confines of my original priors, which presumably include such things as the conditional probability that I have a body given that I seem to have a body but there is an evil demon bent upon misleading me.

This answer seems wrong. So much the worse for subjective Bayesianism. A radical uprooting would be needed. It would be time to sit back, put aside preconceptions, and engage in some fallibilist version of the Cartesian project of radical rethinking. That project might be doomed, but it would be my only hope.

Now, what if instead of the evil demon, I learned of a random process independent of truth as the ultimate origin of my priors. I think the same thing would be true. It would be a time to be brave and uproot it all.

I think something similar is true piece by piece, too. I have a strong moral intuition that consequentialism is false. But suppose that I learned that when I was a baby, a mad scientist captured me and flipped a coin with the plan that on heads a high prior in anti-consequentialism would be induced and on tails it would be a high prior in consequentialism instead. I would have to rethink consequentialism. I couldn’t just stick with the priors.


Sam Harper said...

But aren't we kind of already in that situation? We're all hard wired to presume certain things about reality, like belief in morality, the external world, induction, etc. If those beliefs are merely caused by the way our brains are, should that be any reason to be skeptical of them? How is that different than if a mad scientist rewired our brains at a young age? In both cases, we would be predisposed to believe things that were not the result of reasoning to conclusions. Our beliefs would be caused.

Alexander R Pruss said...

I think we get skepticism IF we think that this wiring is independent of the facts that the wired beliefs are about. Theists don't think that, for instance.