Full Idea
Armstrong takes properties to be universals, and believes there are no 'uninstantiated' universals.
Clarification
Something is 'instantiated' if examples of it exist
Gist of Idea
Properties are universals, which are always instantiated
Source
report of David M. Armstrong (A Theory of Universals [1978]) by John Heil - From an Ontological Point of View §9.3
Book Reference
Heil,John: 'From an Ontological Point of View' [OUP 2005], p.91
A Reaction
At first glance this, like many theories of universals, seems to invite Ockham's Razor. If they are always instantiated, perhaps we should perhaps just try to talk about the instantiations (i.e. tropes), and skip the universal?