I can't see how the explanatory power could be greater?
For example, a B-theory, or the PSR could potentially explain the existence of the Universe, including your mind, while a purely Idealistic model may have some problems explaining what you see, and why.
That's a good way of pointing out the problem of coherentism, but what assumptions are you making with regard to your axioms? Simply an external world in the sense of avoiding solipsism? Admittedly I'll likely have to read more about foundationalism, classical or otherwise, to get a true conception of where you are coming from.
The only assumptions I'm making in regard to my axioms are that they are by default true unless they are proven false, my personal axioms are usually the ones most people have: existence of other minds, existence of the external world, the truth of logical and mathematical axioms, and the such. Think of knowledge like a tree, the base are the axioms. Idealism can be constructed based in both coherentism or foundationalism, of course, since those are epistemologically neutral model ( and, if we ignore infinitism, are by force the three possible ways one may go ), however whatever epistemological ground you take, an Idealist cannot attack an externalist position unless they find a common ground from where the Idealist can point into a contradiction in the externalist worldview (since logical axioms are usually regarded as foundational or vital in both the coherentism and Foundationalism ). For example, the externalist may hold a scientific way of figuring out the truth, and the Idealist also. From there, the Idealist may point a scientific study that contradicts the externalist view, thus, showing that an sub-epistemological part on the externalist view leads to a contradiction of the other axiomatic belief in the external world.
Hmmm, we may have to go over Feser's commentary on proofs of God sooner rather than later! But I need to check out more on reformed epistemology.
Feser is more (IMHO) well versed in Thomistic philosophy rather than in reformed epistemology, but we can start there if you wish. I've personally studied in depth many arguments from God, with the help of many theists and atheist in a very popular forum that is the ownership of a philosopher and apologist of christianity. We can pick anyone you wish, and I'll explain you my insights into them. My personal favorites, in advance, are the Kalam argument, the Leibnizian argument, the Modal Ontological Argument, and a few forms of Trascendental Arguments, although I've also always been quite interested in the Evolutionary Argument Against Naturalism, and the such.
Thanks! I find hard agnosticism leads one to interesting places. :)
Indeed :)