Full Idea
Mathematicians abstract properties which are conceptually separable from the world of change. It makes no difference if you treat them as separate, in the sense that it does not result in error.
Gist of Idea
Mathematicians study what is conceptually separable, and doesn't lead to error
Source
Aristotle (Physics [c.337 BCE], 193b33)
Book Reference
Aristotle: 'Physics', ed/tr. Waterfield,Robin [OUP 1996], p.36
A Reaction
This strikes me as a crucial point to make against Frege (if Aristotle is right). Frege hates abstractionism precisely because it is psychological, and hence admits subjective error, instead of objective truth. Does 'pure' abstraction avoid error?