  Kaplan (1989a) also says that indexicals are rigid designators. The notion of a rigid designator comes from Kripke (1980), who (roughly speaking) defines a rigid designator to be an expression that designates the same thing with respect to all possible worlds. When Kaplan claims that indexicals are rigid designators, he means that if object \(o\) is the referent of expression \(E\) with respect to context \(c\) and the world of \(c\), then \(o\) is also the referent of \(E\) with respect to \(c\) and any other world. For example, if Mary is the referent of ‘I’ with respect to \(c\) and the world of \(c\), then Mary is also the referent of ‘I’ with respect to \(c\) and any other world.