Full Idea
Foundationalists suppose we need not only basic beliefs, but also principles of inference to move to the more sophisticated superstructure. We may understand what justifies the basic beliefs, but what about the inference principles?
Gist of Idea
Foundationalists must accept not only the basic beliefs, but also rules of inference for further progress
Source
Jonathan Dancy (Intro to Contemporary Epistemology [1985], 8.3)
Book Reference
Dancy,Jonathan: 'Introduction to Contemporary Epistemology' [Blackwell 1985], p.118
A Reaction
Very nice question. Of course, you can't justify everything, but each part of a system can be scrutinised in turn by the other parts (with scrutinising principles tested pragmatically).