natural-kind terms

In the SEMANTIC analysis of NOUNS, a type of general term for entities which have an identity in nature (as opposed to artefactual, abstract and other general terms). They include some SORTAL terms (e.g. lion), where a notion of individuation is involved, and some mass terms (e.g. water), where there is no such notion. Their study has been important in the development of theories of DIRECT REFERENCE.