In this paper, it is argued that metaphysics, conceived as an inquiry into the ultimate nature of mind-independent reality, is a rationally indispensable intellectual discipline, with the a priori science of formal ontology at its heart. It is maintained that formal ontology, properly understood, is not a mere exercise in conceptual analysis, because its primary objective is a normative one, being nothing less than the attempt to grasp adequately the essences of things, both actual and possible, with a view to understanding as far as we can the fundamental structure of reality as a whole. Accordingly, it is urged, the deliverances of formal ontology have a modal and epistemic status akin to those of other a priori sciences, such as mathematics and logic, rather than constituting rivals to the claims of the empirical sciences, such as physics.