 Rational intuitions seem relevant to testing proposed definitions of “cube”, but not proposed reference-fixing descriptions of “water”. If someone thought that the correct definition of “cube” is: a three-dimensional solid with six faces all of which are parallelograms with equal sides, we could show it is not a correct definition of “cube” by imagining a “squished” cube that satisfies that definition but, intuitively, is not a cube. None of the properties mentioned in the reference-fixing description for water are either necessary, or taken singly or together, sufficient conditions of a liquid’s being water. So it does not seem that rational intuitions could play much of a role in determining what the essential nature of knowledge is if “knowledge” were a natural kind term whose reference is fixed by some description. People would have to empirically discover the nature of knowledge with the aid of its reference-fixing description, just as they had to empirically discover the nature of water. The same thing would seem to apply to normative terms like “right” or “what there is most reason to do (or believe)” if they were natural kind terms.