Full Idea
We may say that indispensability is a pretty strong argument for the existence of at least predicative sets, and a pretty strong, but not as strong, argument for the existence of impredicative sets.
Gist of Idea
Indispensability strongly supports predicative sets, and somewhat supports impredicative sets
Source
Hilary Putnam (The Philosophy of Logic [1971], p.346), quoted by Penelope Maddy - Naturalism in Mathematics II.2
Book Reference
Maddy,Penelope: 'Naturalism in Mathematics' [OUP 2000], p.105
Related Ideas
Idea 18135 If mathematics rests on science, predicativism may be the best approach [Bostock]
Idea 8747 Realists are happy with impredicative definitions, which describe entities in terms of other existing entities [Gödel, by Shapiro]
Idea 18134 Predicativism makes theories of huge cardinals impossible [Bostock]