Full Idea
For Lewis, we can see the purpose of physics as being to discover what universals there actually are.
Gist of Idea
Physics aims to discover which universals actually exist
Source
report of David Lewis (New work for a theory of universals [1983]) by A.W. Moore - The Evolution of Modern Metaphysics Intro
Book Reference
Moore,A.W.: 'The Evolution of Modern Metaphysics' [CUP 2013], p.18
A Reaction
It seems that Lewis uses the word 'property' to mean predicates, which consist of a multitude of sets, while universals are the properties that naturally exist and cut nature at the joints . Infuriating, because the other way around seems better.