Full Idea
I propose a unified theory which is a version of ZF or ZFC with urelements, where the urelements are taken to be the abstracts.
Clarification
ZF is standard set theory. Urelements are members of sets which aren't themselves sets
Gist of Idea
We can combine ZF sets with abstracts as urelements
Source
Kit Fine (Replies on 'Limits of Abstraction' [2005], 1)
Book Reference
-: 'Philosophical Studies' [-], p.368