Full Idea
Lewis's multi-purpose ontology seems to have only two kinds: sets and possibilia (actual and possible particulars).
Gist of Idea
There are only two kinds: sets, and possibilia (actual and possible particulars)
Source
report of David Lewis (On the Plurality of Worlds [1986]) by Alex Oliver - The Metaphysics of Properties 3
Book Reference
-: 'Mind' [-], p.7
A Reaction
This is awfully like the ontology of his teacher Quine, but with the wicked addition of modal properties. It is no wonder that Lewis was a bit vague about the concrete boundary, as both of his kinds seem to be abstract. His Achilles' Heel?