Fides Quaerens Intellectum » C. S. Lewis, Internalist Epistemology, and Plantinga’s EAAN:

"Lewis’s argument presses that naturalism entails epistemic skepticism because it has no basis for internalist (ground-and-consequent) inferences. Plantinga’s own epistemology, however, relies on externalist (cause-and-effect) inferences (though his are based on God, not naturalism), which Lewis as a good internalist would say that this is not a good basis for accepting that a belief is true!"