Full Idea
A theory of abstraction is any account that reconstructs mathematical theories using second-order abstraction principles of the form: §xFx = §xGx iff E(F,G). We ignore first-order abstraction principles such as Frege's direction abstraction.
Clarification
'Second-order' principles involve predicates as well as objects
Gist of Idea
Abstraction theories build mathematics out of second-order equivalence principles
Source
R Cook / P Ebert (Notice of Fine's 'Limits of Abstraction' [2004], 1)
Book Reference
-: 'British Soc for the Philosophy of Science' [-], p.791
A Reaction
Presumably part of the neo-logicist programme, which also uses such principles. The function § (extension operator) 'provides objects corresponding to the argument concepts'. The aim is to build mathematics, rather than the concept of a 'rabbit'.