Full Idea
Modest ontologies are Nominalism (Goodman), admitting only concrete individuals; and Extensionalism (Quine/Davidson) which admits individuals and sets; but Intensionalists (Frege/Carnap/Church/Marcus/Kripke) may have propositions, properties, concepts.
Gist of Idea
Just individuals in Nominalism; add sets for Extensionalism; add properties, concepts etc for Intensionalism
Source
Alex Orenstein (W.V. Quine [2002], Ch.3)
Book Reference
Orenstein,Alex: 'W.V. Quine' [Princeton 2002], p.44
A Reaction
I don't like sets, because of Idea 7035. Even the ontology of individuals could collapse dramatically (see the ideas of Merricks, e.g. 6124). The intensional items may be real enough, but needn't have a place at the ontological high table.
Related Ideas
Idea 7035 God does not create the world, and then add the classes [Heil]
Idea 6124 I say that most of the objects of folk ontology do not exist [Merricks]