Full Idea
It is part of the concept of an axiom that it can be recognised as true independently of other truths.
Gist of Idea
The truth of an axiom must be independently recognisable
Source
Gottlob Frege (On Euclidean Geometry [1900], 183/168), quoted by Tyler Burge - Frege on Knowing the Foundations 4
Book Reference
Burge,Tyler: 'Truth, Thought, Reason (on Frege)' [OUP 2001], p.348
A Reaction
Frege thinks the axioms of arithmetic all reside in logic.