ontologist

noun

1. A scholar or theorist of ontology, or an adherent of a particular ontological doctrine.

   “On the other hand, nominalists and parsimonious ontologists who do not believe in the existence of properties, facts and abstract entities do stick to these colloquial usages of ‘property’ and ‘fact’ grounded in principles as platitudinous as [i]–[iii] without apparent problems.”