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Kawoomba comments on You only need faith in two things - Less Wrong Discussion

22 Post author: Eliezer_Yudkowsky 10 March 2013 11:45PM

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Comment author: Kawoomba 11 March 2013 08:17:13AM *  3 points [-]

Solomonoff induction will quickly be promoted as a hypothesis

Again, promoted how? All you know is "induction is very, very unlikely to work" (low prior, non 0), and "some single large ordinal is well-ordered". That's it. How can you deduce an inference system from that that would allow you to promote a hypothesis based on it being consistent with past observations?

It seems like putting the hoversled before the bantha (= assuming the explanandum).

Comment author: Qiaochu_Yuan 11 March 2013 08:22:09AM 1 point [-]

Promoted by Bayesian inference. Again, not all Bayesian inference is inductive reasoning. Are you familiar with Cox's theorem?

Comment author: Kawoomba 11 March 2013 08:32:32AM 5 points [-]

Only in passing. However, why would you assume those postulates that Cox's theorem builds on?

You'd have to construct and argue for those postulates out of (sorry for repeating) "induction is very, very unlikely to work" (low prior, non 0), and "some single large ordinal is well-ordered". How?

Comment author: ESRogs 12 March 2013 12:42:21AM 2 points [-]

Wouldn't it be: large ordinal -> ZFC consistent -> Cox's theorem?

Maybe you then doubt that consequences follow from valid arguments (like Carroll's Tortoise in his dialogue with Achilles). We could add a third premise that logic works, but I'm not sure it would help.

Comment author: [deleted] 13 March 2013 08:47:10PM 1 point [-]

Can you elaborate on the first step?

Comment author: ESRogs 14 March 2013 01:11:53AM 0 points [-]

Believing that a mathematical system has a model usually corresponds to believing that a certain computable ordinal is well-ordered (the proof-theoretic ordinal of that system), and large ordinals imply the well-orderedness of all smaller ordinals.

I'm no expert in this -- my comment is based just on reading the post, but I take the above to mean that there's some large ordinal for ZFC whose existence implies that ZFC has a model. And if ZFC has a model, it's consistent.