 These are only some of the fundamental categories and articulations that structure the real world. It is not just the theory of categories, but the theory of strata (“levels of reality”) that distinguishes Hartmann’s ontology. Like everything else, strata of reality are characterized by their categories. By definition, the categories characterizing strata of reality are not general, in the sense that they do not pertain to reality in its entirety, but only to specific domains of real being. On the other hand, fundamental categories are the most general and simple categories, and for this reason they are contained in the special categories of all of the strata (A21b). Strata are the true structuring framework of the real world. While the latter has unity, its unity is the unity of neither a principle nor a center. The unity of the real world is instead provided by the structure and order of the strata (A52a).