@Fuego Most of the "skeptics" I've met take the null hypothesis to illogical extremes; I feel like they think that if something can't be proven true, it must be false, rather than allowing for the possibility that we just don't -- and possibly can't -- know.
@Fuego I don't think we need to go into socraticism; we can say "our knowledge is based on these sets of assumptions which we can or can't test and here's our criteria for evaluating new evidence" but at some point all systems of understanding are rooted in the assumptions those systems must make in order to be able to say anything definitive at all.
A priori reason can really only get you as far as "I exist, I have sense data, and I know I'm thinking." After that, you have to assume stuff.