Full Idea
It must surely be true that a man who has completely mastered arithmetic knows all numbers? Because there are pieces of knowledge covering all numbers in his soul.
Gist of Idea
We master arithmetic by knowing all the numbers in our soul
Source
Plato (Theaetetus [c.364 BCE], 198b)
Book Reference
Plato: 'Complete Works', ed/tr. Cooper,John M. [Hackett 1997], p.219
A Reaction
This clearly views numbers as objects. Expectation of knowing them all is a bit startling! They also appear to be innate in us, and hence they appear to be Forms. See Aristotle's comment in Idea 645.
Related Idea
Idea 645 If two is part of three then numbers aren't Forms, because they would all be intermingled [Aristotle]