 Kripke presents rigidity first as an alethic notion but there is also a temporal interpretation, as we’ve seen. There are other interpretations too, which is not surprising if rigidity is fundamental to all our modal talk: and it seems reasonable to say, with Føllesdal, that it is. “All our talk about change, about causation, ethics and knowledge and belief, as well as about the other modalities, presupposes that we can keep our singular terms referring to the same objects. To the extent that we fail, these notions become incoherent” (Føllesdal 1986, p. 111). 