Full Idea
Neo-Fregeans have thought that Hume's Principle, and the like, might be definitive of number and therefore not subject to the usual epistemological worries over its truth.
Clarification
Hume's Principle defines 'equinumerous' by one-to-one mapping
Gist of Idea
If Hume's Principle can define numbers, we needn't worry about its truth
Source
Kit Fine (Precis of 'Limits of Abstraction' [2005], p.310)
Book Reference
-: 'Philosophical Studies' [-], p.310
A Reaction
This seems to be the underlying dream of logicism - that arithmetic is actually brought into existence by definitions, rather than by truths derived from elsewhere. But we must be able to count physical objects, as well as just counting numbers.