Full Idea
Frege developed a formal system to make sure that he hadn't employed unnoticed assumptions about arithmetic.
Gist of Idea
Frege developed formal systems to avoid unnoticed assumptions
Source
report of Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884]) by Shaughan Lavine - Understanding the Infinite VIII.2
Book Reference
Lavine,Shaughan: 'Understanding the Infinite' [Harvard 1994], p.252
A Reaction
It is interesting that Frege seems to have had far more influence on analytic philosophy than he ever had on mathematics.