Full Idea
Ontology is not empirical, but ontologists do make discoveries; empirical investigation won't discover that holes exist; we see that two things are the same colour, but a philosopher must resolve whether one universal is present in both.
Clarification
'Ontologists' study what exists
Gist of Idea
Empirical investigation can't discover if holes exist, or if two things share a colour
Source
Trenton Merricks (Objects and Persons [2003], Pref)
Book Reference
Merricks,Trenton: 'Objects and Persons' [OUP 2003], p.-6
A Reaction
This is one of the best, simplest and clearest statements I have encountered of the autonomy of philosophy. One may, of course, respond by saying 'who cares?', but then who cares about quarks, or the economy of the Spanish Empire?