Full Idea
I deny the absolutism of a unique system of ontological categories and the essentialist view of membership in ontological categories as necessary features. ...I regard ontological categories as similar to axioms of formalized theories.
Gist of Idea
Ontological categories are like formal axioms, not unique and with necessary membership
Source
Jan Westerhoff (Ontological Categories [2005], Intro)
Book Reference
Westerhoff,Jan: 'Ontological Categories' [OUP 2005], p.3
A Reaction
The point is that modern axioms are not fundamental self-evident truths, but an economic set of basic statements from which some system can be derived. There may be no unique set of axioms for a formal system.