To set the stage, by using the Cartesian demon I'm playing devil's advocate. For the sake of argument, I'm assuming a far more skeptical viewpoint than I myself endorse. But I'm doing that because I'm responding to Scripturalists on their own grounds.
Mind you, I don't mention the Cartesian demon purely for the sake of argument. Thought-experiments like that demonstrate the limitations of proof. But that's only a problem if we equate knowledge with proof.
To a great extent I think Ryan's argument is less with me than his fellow Scripturalists.
I also like Steve. He’s always answered my questions, writes a lot of interesting material, and been nice to me.
I appreciate the concession, but in my experience, that's not garden-variety Scripturalism. Not even close. Unless Scripturalism can falsify the Cartesian demon, how can they prove that most of what they deem to be knowledge isn't delusive belief? How can they be certain? How do they know there's no Cartesian deceiver who's messing with their minds? Unless they can rule that out, precious little of what they believe rises to the level of the indubitable or indisputable. And if they can't, how is their position any signal improvement over the alternatives which they disdain? To say they that know it even though they don't know how that's the case is quite a comedown from the Scripturalism I'm acquainted with–past and present.
Scripturalism is a form of foundationalism. It views knowledge as an axiomatic system. You isolate and identify certain indubitable, irrefragable truths. You then draw logical inferences on the basis of these first truths. You relate them to other truths in a system of mutual entailments.
Problem is, the data-base for indubitable, indisputable truths is very thin. Abstract "laws of logic." Abstract mathematical formulas. Self-presenting states like "I feel pain." Psychology and modal metaphysics.
You can't extract Christian theology from that data-base. You can't extract Bible history from that data base. It doesn't yield contingent truths. Yet that eliminates the concrete created order.
Cartesian skepticism isn't synonymous with global skepticism. Global skepticism is self-refuting. But you can't get much mileage out of that. Although it doesn't take much to refute global skepticism, the exercise doesn't leave you with much to build on. It simply eliminates the utmost extreme.
Ryan is welcome to take issue with where his fellow Scripturalists characteristically assign the burden of proof. He's reversing the onus. When the dust settles, I don't see that Ryan's position is different in kind from non-Scripturalist alternatives. Rather, it seems to be an eclectic synthesis of the best that the alternative positions have to offer. I don't say that as a criticism. I'm not the audience he needs to persuade. Perhaps he'll have more success with the up-and-coming generation of Scripturalists.