 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 categories in terms of what relations of dependence a purported entity has or lacks on mental states (and a second dimension is distinguished in terms of what relations of dependence a purported entity has or lacks on spatio-temporally located objects), so that the law of the excluded middle alone ensures mutual exclusiveness and exhaustiveness of the categories distinguished. (Dummett’s method of distinguishing categories provides another route for guaranteeing mutual exclusivity – see §2.3 below).