 The conclusions of the arguments given above include not only the falsity of descriptivism as a thesis about the reference of natural kind terms, but also the more general truth of semantic externalism. The Earthling in 1750 and their Twin Earth counterpart are supposed to be intrinsic physical duplicates. (There is a problem in that one would expect the twin to have XYZ in its blood stream, etc., not H2O, so the two are not perfect duplicates; but we can take it that this physical difference should not affect the argument.) Although they are duplicates, the terms they use have different extensions; likewise their thoughts have different truth conditions. Consequently, the reference, extension, and truth conditions of a person’s utterances do not supervene on their physical state. These things are fixed, at least in part, by external considerations. We might retain a conception of the psychological such that the psychological still supervenes on the physical; but then one would have to deny that ‘thinking about water’ characterizes a psychological state. Or, we must deny that the psychological state of a subject supervenes upon the physical state of the subject.