A rigid designator is a term that refers to the same object in every possible world where that object exists. The concept was introduced by Saul Kripke in Naming and Necessity (1980) and stands as one of the most influential ideas in the philosophy of language.
The central claim is that proper names work differently from definite descriptions. “Richard Nixon” refers to the same person in every possible world — even worlds where Nixon never became president, never entered politics, or pursued an entirely different life. The name tracks the individual, not any set of properties. By contrast, a description like “the 37th president of the United States” is non-rigid: in a world where someone else won the 1968 election, that description would pick out a different person.
This distinction matters because it reshapes how necessity and identity work. If “water” rigidly designates H2O, then “water is H2O” is necessarily true — true in every possible world — even though it took empirical investigation to discover this. The necessity is metaphysical, not epistemic: we had to learn that water is H2O, but once discovered, the identity holds across all possible worlds.
Kripke argued that rigid designation undermines the descriptivist theory of names, which held that a name is equivalent to a cluster of descriptions associated with its bearer. If names were just abbreviations for descriptions, they would be non-rigid — their referent would shift across possible worlds as the descriptions are satisfied by different objects. The rigidity of names shows they function through a causal-historical chain of reference rather than through descriptive content.
Natural kind terms like “water,” “gold,” and “tiger” also function as rigid designators on this account. They refer to the same natural kind in every possible world, fixed by the actual-world sample that anchors the term.
Related terms
- extension — the actual referent of a term in a given world
- intension — the rule or criterion that determines reference
- primary intension — the epistemic route to reference
- secondary intension — the metaphysical dimension of reference