Full Idea
The number-concepts just cannot be got by concentrating on the number and abstracting from the kind of things being counted.
Gist of Idea
We can't acquire number-concepts by extracting the number from the things being counted
Source
Peter Geach (Mental Acts: their content and their objects [1957], §8)
Book Reference
Geach,Peter: 'Mental Acts: Their content and their objects' [RKP 1971], p.28
A Reaction
This point is from Frege - that if you 'abstract away' everything apart from the number, you are simply left with nothing in experience. The objection might, I think, be met by viewing it as second-order abstraction, perhaps getting to a pattern first.