Full Idea
Every proposition, no matter what subject matter it may have, is entirely about being.
Gist of Idea
Every proposition is entirely about being
Source
David Lewis (Things qua Truthmakers [2003], p.26), quoted by Trenton Merricks - Truth and Ontology 4.VI
Book Reference
Merricks,Trenton: 'Truth and Ontology' [OUP 2007], p.91
A Reaction
Since Lewis's propositions are sets of possible worlds, I presume this claim is made because proposition relates to all of the possible worlds, which therefore presumably embody Being.