 A problem now arises for de re statements about what is possible or necessary for a particular individual. Since Joe Biden might have had three arms, there should be a world where he has three arms. But if Biden were part of another world, then that world and our world would have a part in common. Lewis denies that different worlds can share parts. Even if we allowed for overlapping worlds, it is hard to see how the other world could have a three-armed Biden as a part, given that this part is also part of our world, where Biden has two arms (compare Lewis 1986e, 199ff.). So ‘Biden might have had three arms’ is not analysed as stating that there is a world which contains a three-armed Biden as part. Rather, it says that there is a world that contains a three-armed representative or counterpart of Joe Biden.