Full Idea
To solve the Julius Caesar problem, Frege requires explicit definitions of the numbers, and he proposes his well-known solution: the number of Fs = the extension of the concept 'equinumerous with F' (based on one-one correspondence).
Gist of Idea
Frege solves the Caesar problem by explicitly defining each number
Source
Penelope Maddy (Naturalism in Mathematics [1997], I.1)
Book Reference
Maddy,Penelope: 'Naturalism in Mathematics' [OUP 2000], p.5
A Reaction
Why do there have to be Fs before there can be the corresponding number? If there were no F for 523, would that mean that '523' didn't exist (even if 522 and 524 did exist)?