 With metaphysically relevant expressions, there is a general issue whether they may be used as technical terms pertaining to a particular philosophical view, in which case the expressions may be regarded as part of the periphery of language, not displaying an ontological notion that is part of the ontology of natural language  (§4.1).  Nouns such as existence, property, being, event, and number may be candidates since they can be used with particular philosophical notions in mind, unlike the verb exist  (§1.3)  and copula and modal verbs, which do not permit non-ordinary, “philosophical” uses.