Full Idea
In Frege's view axioms are basic truth, and basic truths do not need proof. Basic truths can be (justifiably) recognised as true by understanding their content.
Gist of Idea
Basic truths of logic are not proved, but seen as true when they are understood
Source
report of Gottlob Frege (works [1890]) by Tyler Burge - Frege on Knowing the Foundations 1
Book Reference
Burge,Tyler: 'Truth, Thought, Reason (on Frege)' [OUP 2001], p.337
A Reaction
This is the underpinning of the rationalism in Frege's philosophy.