Full Idea
According to intensionalist semantics the meaning of a proposition is determined by the properties an object possesses.
Gist of Idea
Intensionalists say meaning is determined by the possession of properties
Source
Dale Jacquette (Intro to 'Philosophy of Logic' [2002], §4)
Book Reference
'Philosophy of Logic: an anthology', ed/tr. Jacquette,Dale [Blackwell 2002], p.5
A Reaction
This sounds good to me. Extensionalist don't seem to care what sets they put things in, but if property possession comes first, then things will fall into their own sets without any help for us. We can add silly sets afterwards, if we fancy.