Derek Parfit argues that fission is prudentially better for you than ordinary death. But is having more fission products with good lives prudentially better for you than having just one? In this paper, we argue that it is. We argue that, if your brain is split and the halves are transplanted into two recipients (who both have good lives), then it is prudentially better for you if both transplants succeed than if only one of them does (other things being equal). (...) This upshot rules out, among other things, that the prudential value of standing in the relation that matters in survival to multiple people is equal to their average well-being. (shrink)

The contemporary popularity of semantic externalism has arisen from so-called Twin Earth thought experiments which suggest that the representational content of a natural kind term cannot be wholly determined by processes within a speaker's body. Such arguments depend on the intuition that the extensions of natural kind terms cannot have changed as the result of the scientific investigation of natural kinds' constitutions. I demonstrate that this externalist intuition depends on an assumption about the mentality of isomorphic doppelgangers which has never (...) been questioned but which is nonetheless arguably false. I develop an alternative view of the instantiation of mind which entails a revision of our understanding of the constitution of environmental objects. The picture seems to be fully coherent despite its oddity and I can find no good reason to reject it. The conclusion must be that the case for semantic externalism is thus less compelling than is often supposed. (shrink)