 Although the argument as presented so far concerns the reference of ‘water’ and other natural kind terms, it is natural to extend it to mental content as well (McGinn 1977; Burge 1979, note 2). Not only does Twin Oscar not refer to water when he uses the term ‘water’, he does not have beliefs about water either. To be sure, he has beliefs that play the same role in his mental life that Oscar’s water-beliefs play in his. But in Twin Oscar’s case, those beliefs are not about water. In particular, while Oscar believes that water is wet, Twin Oscar does not. Since Oscar and Twin Oscar have identical intrinsic properties, yet Oscar believes that water is wet while Twin Oscar does not, mental content cannot be determined solely by intrinsic properties.