Full Idea
Frege thought that the relations of epistemic justification in a science mirrors the natural ordering of truths: in particular, what is self-evident is selbstverstandlich.
Clarification
'selbstverstandlich' means self-standing, or foundational
Gist of Idea
Justifications show the ordering of truths, and the foundation is what is self-evident
Source
report of Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884], §02) by Robin Jeshion - Frege's Notion of Self-Evidence 1
Book Reference
-: 'Mind' [-], p.944
A Reaction
I'm not sure that I can accept a 'natural ordering of truths'. Is there a natural ordering of the facts of the world? The most I can see is a direction to causation. Maybe inferences have a direction, but humans intrude on those.