 Formal ontologies are theories that attempt to give precise mathematical formulations of the properties and relations of certain entities. Such theories usually propose axioms about these entities in question, spelled out in some formal language based on some system of formal logic. Formal ontology can been seen as coming in three kinds, depending on their philosophical ambition. Let’s call them representational, descriptive, and systematic. We will in this section briefly discuss what philosophers, and others, have hoped to do with such formal ontologies.