Full Idea
It is no surprise that we should be able to reason mathematically about many of the things we experience, for they are already 'abstract'.
Gist of Idea
Mathematics isn't surprising, given that we experience many objects as abstract
Source
George Boolos (Must We Believe in Set Theory? [1997], p.129)
Book Reference
Boolos,George: 'Logic, Logic and Logic' [Harvard 1999], p.129
A Reaction
He has just given a list of exemplary abstract objects (Idea 10489), but I think there is a more interesting idea here - that our experience of actual physical objects is to some extent abstract, as soon as it is conceptualised.
Related Idea
Idea 10489 We deal with abstract objects all the time: software, poems, mistakes, triangles.. [Boolos]