Full Idea
If universals are to ground similarities, it is hard to see why one should admit universals which only happen to be instantiated once.
Gist of Idea
If universals ground similarities, what about uniquely instantiated universals?
Source
Alex Oliver (The Metaphysics of Properties [1996], §11)
Book Reference
-: 'Mind' [-], p.32
A Reaction
He is criticising Armstrong, who holds that universals must be instantiated. This is a good point about any metaphysics which makes resemblance basic.