Full Idea
A deeper justification for believing in [mathematical] propositions [apart from pragmatism] lies in finding their place in a logicist proof structure, by understanding the grounds within this structure that support them.
Gist of Idea
We come to believe mathematical propositions via their grounding in the structure
Source
Tyler Burge (Frege on Knowing the Foundations [1998], 3)
Book Reference
Burge,Tyler: 'Truth, Thought, Reason (on Frege)' [OUP 2001], p.345
A Reaction
This generalises to doubting something until you see what grounds it.