Full Idea
If we take mathematics at its word, there are too many mathematical objects for it to be plausible that they are all mental or physical objects.
Gist of Idea
There are too many mathematical objects for them all to be mental or physical
Source
Michael D. Resnik (Maths as a Science of Patterns [1997], One.1)
Book Reference
Resnik,Michael D.: 'Mathematics as a Science of Patterns' [OUP 1999], p.3
A Reaction
No one, of course, has ever claimed that they are, but this is a good starting point for assessing the ontology of mathematics. We are going to need 'rules', which can deduce the multitudinous mathematical objects from a small ontology.