 The general idea is that you should set your  credences to what you expect your credences to be in the future. More  specifically, your credence in \(X\) should  be the expectation of your future possible credences  in \(X\) over the things you might  learn. Given that, for all the things you might learn in this example  your credence in \(H\) would be the same, you  should have that as your prior credence also. Your prior should be  such that \(P(H) = [0,1]\). So having a  precise prior credence in \(H\) to start with  is irrational. That’s how the argument against dilation from  reflection goes. Your prior \(P\) is not  fully precise though. Consider \(P(H \cap  Y)\). That is, the prior belief in the conjunction is  imprecise. So the alleged problem with dilation and reflection is not  as simple as “your precise belief becomes imprecise”. The  problem is “your precise  belief in \(H\) becomes  imprecise”; or rather, your precise belief  in \(H\) as represented  by \(P(H)\) becomes imprecise.