The law of the excluded middle alone ensures mutual exclusiveness and exhaustiveness for categories defined by presence or absence of a relation.

The specific worries about (1) guaranteeing the mutual exclusiveness and joint exhaustiveness of the categories, and (2) whether or not any single system of categories could purport to be uniquely correct, can, however, be met by certain ways of formulating ontological categories. The first sort of worry can be met by ensuring that categories (of the same level) are defined in ways that guarantee mutual exclusiveness and exhaustiveness. Thus, e.g., Thomasson (1999, chapter 8) distinguishes categ