Natural Kind Fundamentalism

This paper defends Natural Kind Fundamentalism (NKF), the view that the ontological category of natural kind is fundamental. I develop a primitivist account of categorial fundamentality based on the Complete Categorial Basis (CCB) criterion, which requires that fundamental categories form a complete and minimal system irreducible to other categories through ontological dependence relations. I argue against bundle-theoretic reductions and in favour of the view that natural kinds are substantial universals serving as principles of unity for property clusters. This framework distinguishes between the metaphysical ‘why’ question (answered by substantial universals as unifiers) and the empirical ‘how’ question (concerning specific unification mechanisms). I demonstrate that natural kinds and properties exhibit mutual but asymmetric dependence: properties depend generically on kinds for instantiation, while kinds depend rigidly on their essential properties. The resulting formal ontological structure satisfies the CCB criterion and explains why certain property clusters are non-arbitrary without reducing kinds to properties or vice versa.