 Distinguishing different branches of metaphysics goes hand in hand with the view according to which there is not a single ontology, but several, at least apparent, ontologies, ontologies pertaining to language, to cognition, and to fundamental reality. But there is also the question whether there is in fact a single ontology of natural language. When natural language has been used to clarify metaphysical intuitions, the presupposition was that metaphysical intuitions do not show interpersonal inconsistencies, which means that there is a unique ontology reflected in the relevant ways in natural language. There are reasons to be skeptical of that presupposition. It is not necessarily the case that there is a single ontology implicit in all natural languages, just as there may in fact be interpersonal differences among intuitions, which have now become the subject of experimental philosophy (see entry on  experimental philosophy).  The proper subject matter of natural language ontology should thus be the ontologies of natural languages. The possibility of interlinguistic ontological differences touches touches upon the Sapir-Whorf hypothesis and the controversy surrounding it (Pinker 1994; Hespos &amp; Spelke 2004; Pelletier 2011). Of course, it may turn out that the ontologies of natural languages are in fact the same or at least that there are constraints on how the they may differ from each other and what linguistic phenomena (of the lexical or functional part of grammar) such differences may pertain to. Assuming a distinction between core and periphery, clearly, if there is a universal ontology shared by human languages, it should pertain to the core only. Generative linguists may furthermore be interested in such constraints, or a universal ontology, as a way of explaining how the grammar of a language with the ontology that goes along with it can be learned.