Full Idea
The Axiom of Reducibility states that every propositional function is extensionally equivalent to some predicative proposition function.
Gist of Idea
Axiom of Reducibility: propositional functions are extensionally predicative
Source
Penelope Maddy (Naturalism in Mathematics [1997], I.1)
Book Reference
Maddy,Penelope: 'Naturalism in Mathematics' [OUP 2000], p.11
Related Idea
Idea 18168 'Propositional functions' are propositions with a variable as subject or predicate [Maddy]