The upshot of these points is that for Everettian interpretations, including 'many minds' versions, reductionism is a live option: but as for ordinary objects like persons or ships, it will be a difficult task to state, or even sketch, the kind of facts that subvene persistence of branches.
Now, having analysed descriptions of musical experience, we realize that the descriptions of what the subject feels can supervene and subvene on the descriptions of what are true to his or her experiences.
There he is considering mental-to-mental causation, and he asks: how can the instantiation of a mental property cause the instantiation of another taking into account that the instantiation of the second mental property can be explained by the instantiation of a physical property that subvenes it?