 Forbes argues that, in order to avoid this (and similar) consequences, we should suppose that (contrary to the second assumption used in setting up the ‘reduplication argument’ sketched above) the oak tree does have a non-trivial individual essence consisting in some of its intrinsic properties, and his favoured candidate for its essence is one that includes the tree’s coming from the particular acorn from which it actually originated. If the tree does have such an ‘intrinsic’ individual essence, then, if w2 and w3 are both possible, each of them must contain a tree that has (in that world) intrinsic properties that are guaranteed to be sufficient for identity with the original tree, in which case (as a matter of logic) there can be no world such as w4 that contains intrinsic duplicates of both of them. (See Forbes 1985, Ch. 6, and, for discussion, Mackie 1987; Mackie 2006; Robertson 1998; Yablo 1988; Chihara 1998; Della Rocca 1996; further discussions by Forbes include his 1986, 1994, and 2002.)