Chisholm extends the example. He points out that what has happened to Adam and Noah could happen to anyone. Let us say that a person’s “role” in a world is defined by the set of qualitative properties he has there. We can say that a possible world, ws, is a “role swapping world” of the actual world, w1, just in case the roles being played in ws are precisely the same as the roles being played in w1, but at least some of those roles are being played in ws by someone other than the person who plays the role in w1. Role swapping worlds will therefore be indiscernible from each other and from the actual world except for the bare identities of the individuals playing the roles. Chisholm says: