= 27d567bc2d48d9f40e9ccc20ea370b15)
lmm comments on Skepticism about Probability - Less Wrong
You are viewing a comment permalink. View the original post to see all comments and the full post content.
= 783df68a0f980790206b9ea87794c5b6)
Loading…= b715d02e85f7b3b4ae65ca3d3e450868)
Subscribe to RSS Feed
Powered by Reddit
= f037147d6e6c911a85753b9abdedda8d)
You are viewing a comment permalink. View the original post to see all comments and the full post content.
Comments (129)
I think De Finetti's justification is fine as far as it goes, but it doesn't go quite as far as people think it does. Here's a couple dialogues to illustrate my point.
Dialogue 1
A: I have secretly flipped a fair coin and looked at the result. What's your probability that the coin came up heads?
B: I guess it's 50%.
A: Great! Will you accept a bet against me that the coin came up heads, at 1:1 odds?
B: Hmm, no, that doesn't seem fair because you already know the outcome of the coinflip and chose the bet accordingly.
A: So rational agents shouldn't necessarily accept either side of a bet according to their stated beliefs?
B: I suppose so.
Dialogue 2
A: I believe the sky is green with probability 90% and also blue with probability 90%.
B: Great! I can Dutch book you now. Here's a bet I want to make with you.
A: No, I don't wanna accept that bet. The theory doesn't force me to, as we learned in Dialogue 1.
In Dialogue 1 I adjust my probability estimate as the bet is offered, no?
That's a reasonable thing to do, but can you obtain something like De Finetti's justification of probability via Dutch books that way?
The obvious steelman of dialogue participant A would keep the coin hidden but ready to inspect, so that A can offer bets having credible ignorance of the outcomes and B isn't justified in updating on A offering the bet.