Full Idea
Concept Nominalism says different things have the same property, or belong to the same kind, if the same concept in the mind is applied to different things.
Gist of Idea
'Concept Nominalism' says a 'universal' property is just a mental concept applied to lots of things
Source
David M. Armstrong (Universals [1995], p.503)
Book Reference
'A Companion to Metaphysics', ed/tr. Kim,Jaegwon/Sosa,Ernest [Blackwell 1995], p.503
A Reaction
This is more appealing than Predicate Nominalism, and may be right. Our perception of the 'properties' of a thing may be entirely dictated by human interests, not by nature.