Full Idea
In the Peano axiomatisation, arithmetic seems primitively to involve the thought that 0 is a number.
Gist of Idea
Peano arithmetic requires grasping 0 as a primitive number
Source
Tyler Burge (Frege on Apriority (with ps) [2000], 5)
Book Reference
Burge,Tyler: 'Truth, Thought, Reason (on Frege)' [OUP 2001], p.385
A Reaction
Burge is pointing this out as a problem for Frege, for whom only the logic is primitive.