rationalskepticism.org

I merely mean that Mathematician B is making the kind of statement about possibility that Plantinga thinks he can intuitively justify: people can phrase that as they want. I mean that Mathematician B is actually asserting the equivalent of the possibility premise in Plantinga's argument. Mathematician B could have simply said "I have no idea" - and we might infer from this that he thinks it is possible that the answer is "Yes" and possible that the answer is "No" - but what I am saying here is that Mathematician B is not just relying on uncertainty to say that something is possible - which would be the default position in the absence of certain knowledge one way or the other. He is doing something stronger: he is actually asserting a possibility premise in modal logic. Now, it is not my job to sort that out and decide whether it is a meaningful thing to do - but Plantinga's argument relies on a distinction between the kind of possibility we may say to apply because we can't prove something to be otherwise and the kind of possibility that you can, somehow, know something to have that is a stronger sort of possibility that justifies statements about possible worlds.