Robin writes:
> As best I can understand it, you complain that it is wrong to
> infer something from the fact that you exist at all, because existing
> is already implied by the fact that you have a certain birth rank.
Not exactly. I try to explain it again below.
> But in my example I rigorously derive posteriors from priors, so
> there can't possibly be any double counting of information. Since
> priors are prior to information, arguments for or against them
> have to be of a different sort.
I'm not sure our disagreement is best described as being about priors. It is rather about what is and what isn't a random sample, and from what sampling population. (see below)
That is true, but then they would not have been you.
> I find
> it quite possible that I could have never existed.
That is also true, but it doesn't imply that you could have been a rock.
> >> Note also that Nick's rule doesn't specify what the prior
> >> is for the universe *, ...
> >I'm not sure what "Nick's rule" is. ...
>
> I meant the rule that worlds have equal probability conditional
> on your existing. What prior would you assign to world * in
> my example?
That depends on such things as simplicity etc. If the three worlds are equal in these repects, I would say P(*) = 1/3. This would be the absolute prior. Then you take account of the fact that you exist, and you rule out world * (though I'm not sure what do about the monkeys). Then you renormalize and get P(#) = P(@) = 1/2.
And yet you to want to reason like this:
Both these arguments seem equally wrong to me.