An Ontology of Meta-Level Categories

We focus in this paper on some meta-level ontological distinctions among unary predicates, like those between concepts and assertional properties. Three are the main contributions of this work, mostly based on a revisitation of philosophical (and linguistic) literature in the perspective of knowledge representation. The first is a formal notion of ontological commitment, based on a modal logic endowed with mereological and topological primitives. The second is a formal account of Strawson's distinction between sortal and non-sortal predicates. Assertional properties like red belong to the latter category, while the former category is further refined by distinguishing substantial predicates (corresponding to types like person) from non-substantial predicates (corresponding to roles like student). The third technical contribution is definition of countability which exploits the topological notion of connection to capture the intended semantics of unary predicates.