Full Idea
We can trace the chains of inference backwards, …and the circle of theorems closes in more and more. ..We must eventually come to an end by arriving at truths can cannot be inferred, …which are the axioms and postulates.
Gist of Idea
Tracing inference backwards closes in on a small set of axioms and postulates
Source
Gottlob Frege (Logic in Mathematics [1914], p.204)
Book Reference
Frege,Gottlob: 'Posthumous Writings', ed/tr. Hermes/Long/White etc [Blackwell 1979], p.204
A Reaction
The rival (more modern) view is that that all theorems are equal in status, and axioms are selected for convenience.