 Railton’s view is that normative concepts are hybrid concepts, somewhat like the concept of ruby as a red gemstone with such-and-such chemical structure (see  example 15)  or of an ice cube. “Ice” is a natural kind term, or at least its definition as “frozen water” is partly given by the natural kind term, “water”. But, as we have seen, “cube” is not a natural kind terms. So “ice cube” is partly a natural kind term and partly not.