 The ontology of natural language is intimately linked to compositionality, the chief tenet of natural language semantics. Which entities play a role in the semantic structure of natural language depends very much on what the semantic contribution of occurrences of expressions to the composition of the meaning of the sentence is taken to be. Different compositional semantic analyses of the language may thus go along with different ontologies. This means that the choice of an ontology may depend on the choice of a compositional semantic theory, which in turn may depend on the choice of a syntactic theory. Generally, the contribution of referential NPs is taken to be that of standing for entities and the role of predicates that of expressing properties that are applied to entities. There is a formal alternative, though, on which referential NPs denote higher-level functions (individual concepts) that apply to predicate denotations  (§2.2.1.1).  What is most important is that for the purpose of compositionality the contributions of referential NPs and of predicates are the same in different types of sentences. Sometimes, different syntactic analyses may have significant consequences for ontological issues, such as the analysis of the number of planets is eight as an identity statement about numbers (Frege) as opposed to an analysis of the sentence as a so-called specificational sentence, conveying a question-answer relation  (§1.6).