Full Idea
For a predicate to have a referential function is one way, but not the only way, to harbour ontological commitment.
Gist of Idea
Reference is not the only way for a predicate to have ontological commitment
Source
Alex Oliver (The Metaphysics of Properties [1996], §22)
Book Reference
-: 'Mind' [-], p.63
A Reaction
Presumably the main idea is that the predicate makes some important contribution to a sentence which is held to be true. Maybe reference is achieved by the whole sentence, rather than by one bit of it.