 To avoid this result without giving up on externalism about mental content, one might say that what matters in the theory of rationality the naturalness of concepts rather than properties, and say that concepts jade and turquoise are equally natural despite the fact that the properties they correspond to are not. But for this to be illuminating, one will need to provide some picture of what concepts are, and how naturalness for them relates to naturalness for properties (see  §3.3).