Full Idea
David Lewis has produced an important theory of properties as sets of actual and possible objects.
Gist of Idea
Lewis says properties are sets of actual and possible objects
Source
report of David Lewis (New work for a theory of universals [1983]) by John Heil - From an Ontological Point of View §12.2
Book Reference
Heil,John: 'From an Ontological Point of View' [OUP 2005], p.128
A Reaction
The notion that a property is an 'object' sounds wrong, as it is too passive. It also seems to allow for the possibility of uninstantiated properties existing, where properties are presumably always 'of' something.