How foolish of you to ask. You're supposed to revise your probability simply based on Will's claim that he has an argument. That is how rational agreement works.

Bwa ha ha. I've already dropped way too many hints here and elsewhere, and I think it's way too awesome for me to reveal given that I didn't come up with it and there is a sharper more interesting more general more speculative idea that it would be best to introduce at the same time because the generalized argument leads to an that is even more awesome by like an order of magnitude (but is probably like an order of magnitude less probable (though that's just from the addition of logical uncertainty, not a true conjunct)). (I'm kind of in an affective death spiral around it because it's a great example of the kinds of crazy awesome things you can get from a single completely simple and obvious inferential step.)