Kripke Quote on Necessity: Rigid Designation

Quote

"Let's call something a rigid designator if in every possible world it designates the same object, a nonrigid or accidental designator if that is not the case." — Saul Kripke, Naming and Necessity (1980), Preface

Historical Context

When Saul Kripke delivered the three lectures that became Naming and Necessity at Princeton University in January 1970, the philosophy of language was dominated by a picture of reference that had been essentially unchallenged for over half a century. This was the descriptivist theory, traceable to Gottlob Frege's distinction between sense and reference and developed in detail by Bertrand Russell's theory of descriptions. On the descriptivist view, a proper name refers to its bearer by means of a description or cluster of descriptions that the speaker associates with the name. "Aristotle," on this account, means something like "the pupil of Plato who taught Alexander the Great and wrote the Nicomachean Ethics." The reference of the name is fixed by these descriptions, and if the descriptions are all false — if it turns out that Aristotle never studied with Plato, never taught Alexander, and never wrote the works attributed to him — then the name fails to refer.

This descriptivist orthodoxy was part of a broader philosophical framework that connected meaning, knowledge, and necessity in a specific way. Since Immanuel Kant, philosophers had generally assumed that necessary truths are knowable a priori — that what must be the case can be known without empirical investigation — and that a posteriori truths, which require experience to establish, are contingent. On this Kantian picture, the identity statement "Hesperus is Phosphorus" (the Morning Star is the Evening Star), if it is a genuine identity, must be either necessary and a priori or contingent and a posteriori. The standard view was that it is contingent and a posteriori: we had to discover through observation that the Morning Star and the Evening Star are the same planet, and things could have been otherwise.

Kripke's lectures demolished both the descriptivist theory of reference and the Kantian framework in a single, devastating argumentative sweep. The concept of rigid designation, defined in the passage quoted above, was the linchpin. Kripke distinguished between rigid designators — terms that refer to the same object in every possible world — and nonrigid or accidental designators, which may refer to different objects in different worlds. Proper names, Kripke argued, are rigid designators. "Aristotle" refers to the same man, Aristotle, in every possible world in which Aristotle exists — including worlds where he never studied with Plato, never taught Alexander, and never wrote a single philosophical text. The descriptions we associate with the name may be false of its bearer in other possible worlds, but the name still refers to that same individual.

The definition quoted here appears in the Preface to the 1980 Harvard University Press edition of Naming and Necessity. The lectures were first published in 1972 as part of the collection Semantics of Natural Language, edited by Gilbert Harman and Donald Davidson, but the 1980 standalone edition, with Kripke's substantial new Preface and footnotes, became the canonical text. The Stanford Encyclopedia of Philosophy describes Naming and Necessity as one of the most influential philosophical works of the twentieth century, a work that reshaped the philosophy of language, metaphysics, and epistemology in ways that are still being worked out today.

Meaning and Interpretation

The definition of rigid designation is deceptively compact, but its philosophical implications are enormous. To understand why, it helps to see what Kripke was arguing against and what his alternative picture implies.

On the descriptivist view, the meaning of a proper name is given by the descriptions speakers associate with it. When I use the name "Aristotle," what I mean is "the philosopher who studied with Plato, taught Alexander, and wrote the Nicomachean Ethics." If I encounter someone who uses the name "Aristotle" but associates it with entirely different descriptions — say, "the philosopher who founded the Lyceum and was born in Stagira" — we might be talking about the same person, but we could also be talking about different people, depending on whether our descriptions happen to pick out the same individual. Reference, on this view, is mediated by descriptive content.

Kripke's rigid designation thesis overturns this picture. If "Aristotle" is a rigid designator, then it refers to Aristotle — that particular individual — in every possible world in which he exists. This means that the reference of the name is not determined by the descriptions speakers associate with it but by something else: a causal-historical chain that links the speaker's use of the name back to the original naming of the individual. When I use the name "Aristotle," I refer to the ancient philosopher not because I know a set of descriptions that uniquely identify him, but because my use is part of a chain of communication that traces back through my teachers, through books, through the transmission of the name across centuries, to the original baptism of that particular man. The descriptions I associate with the name may be incomplete, inaccurate, or entirely wrong, but the name still refers to the same person.

This has immediate consequences for the modal status of identity statements. If "Hesperus" and "Phosphorus" are both rigid designators, and if Hesperus is Phosphorus (both are Venus), then Hesperus is Phosphorus in every possible world — the identity is necessary. But the discovery that Hesperus is Phosphorus was an empirical achievement, requiring astronomical observation. So the identity "Hesperus is Phosphorus" is both necessary and a posteriori. This shatters the Kantian assumption that necessity and apriority always go together. Some truths are necessary even though they can only be discovered through experience, and some truths that can be known a priori are not metaphysically necessary.

The concept of rigid designation also transformed the debate about natural kinds. Kripke argued that natural kind terms like "water," "gold," and "tiger" are also rigid designators: "water" refers to H2O in every possible world, not just in the actual world. This means that it is a necessary truth that water is H2O — if a substance is not H2O, it is not water, even if it looks and behaves exactly like water. This position, developed independently by Hilary Putnam in his work on semantic externalism, has been called the "new theory of reference" and has had profound implications for the philosophy of science, the metaphysics of essences, and the philosophy of mind.

In the philosophy of mind, Kripke used rigid designation to mount a powerful argument against the identity theory — the view that mental states are identical to brain states. If "pain" is a rigid designator for a particular kind of sensation, and "C-fiber firing" is a rigid designator for a particular kind of neural event, then if pain is C-fiber firing, the identity is necessary. But Kripke noted an asymmetry: we can coherently imagine C-fiber firing occurring without pain (in an automaton, say), but we cannot coherently imagine pain occurring without it feeling like pain. This suggests that pain and C-fiber firing are not identical, because genuine identities between rigid designators should be as inconceivable to deny as the identity of water and H2O. The argument, brief but pointed, has been one of the most discussed challenges to physicalism in the philosophy of mind.

The deeper significance of Kripke's definition lies in its reopening of metaphysical questions that the positivist tradition had declared meaningless. If W.V.O. Quine and the logical empiricists had sought to deflate metaphysical talk of necessity, essence, and possible worlds into logical or linguistic talk, Kripke showed that these metaphysical notions have a rigor and intelligibility that cannot be explained away. Rigid designation is not merely a claim about how language works; it is a claim about the metaphysical structure of reality — about what things are essentially and what they are only accidentally. The definition quoted above, with its economical precision, opened a door through which a generation of philosophers would pass to explore questions of essence, modality, and the nature of reference itself. The Stanford Encyclopedia of Philosophy notes that the consequences of Naming and Necessity are still being worked out across metaphysics, epistemology, and the philosophy of language, and that Kripke's concept of rigid designation remains the starting point for virtually all serious work on reference and modality in contemporary analytic philosophy.