Full Idea
Armstrong thinks universals play two roles, namely grounding objective resemblances and grounding causal powers.
Gist of Idea
Universals explain resemblance and causal power
Source
report of David M. Armstrong (A Theory of Universals [1978]) by Alex Oliver - The Metaphysics of Properties 11
Book Reference
-: 'Mind' [-], p.30
A Reaction
Personally I don't think universals explain anything at all. They just add another layer of confusion to a difficult problem. Oliver objects that this seems a priori, contrary to Armstrong's principle in Idea 10728.
Related Idea
Idea 10728 A thing's self-identity can't be a universal, since we can know it a priori [Armstrong, by Oliver]