One of the central theses of this ontology is that the world contains four distinct irreducible ontological strata, the organic (biological) realm being one of them. Combined with his general theory of categories, this thesis entails that there is a different set of categories for every stratum. In Philosophische Grundfragen der Biologie (1912) and Philosophie der Natur (1950), Hartmann gives an account of the set of categories belonging to the organic realm — the “organological categories”. We think his views on these matters are well worth to be reconsidered and contrasted with the reductionism and nominalism that dominates contemporary analytic metaphysics.