Full Idea
Shoemaker contends that universals concern the way things could be, not merely the way any things actually are.
Gist of Idea
Universals concern how things are, and how they could be
Source
report of Sydney Shoemaker (Causality and Properties [1980]) by Alexander Bird - Nature's Metaphysics 3.2.2
Book Reference
Bird,Alexander: 'Nature's Metaphysics' [OUP 2007], p.53
A Reaction
If you want to retain universals within a scientific essentialist view (and I would rather not), then this seems like the only way to go.