 is necessary. A name such as ‘Jack the Ripper’, Kripke argued, is rigid: it picks out the same individual across possible worlds; the description, on the other hand, is non-rigid. Kripke used such reference-fixing stipulations to argue for the existence of contingent a priori truths—(1) being an example. Reference-fixing stipulative definitions can be given not only for names but also for terms in other categories, e.g., common nouns.