Saul Kripke

Quick Facts

• Full name: Saul Aaron Kripke
• Lived: 1940-2022
• Born: Bay Shore, New York; raised mainly in Omaha, Nebraska
• Main fields: logic, modal logic, philosophy of language, metaphysics, philosophy of mind
• Main tradition: Analytic Philosophy
• Academic homes: Harvard, Rockefeller University, Princeton, CUNY Graduate Center
• Best known for: Kripke semantics, rigid designators, causal-historical reference, necessary a posteriori truth, and "Kripke's Wittgenstein"
• Major works: Naming and Necessity, Wittgenstein on Rules and Private Language, "Outline of a Theory of Truth"

The Big Question

How do words stay attached to things, and what makes a truth necessary rather than just actually true?

Kripke saw that these two questions meet in ordinary names. If "Aristotle" just means "the teacher of Alexander," then it sounds impossible to say "Aristotle might never have taught Alexander." But that sentence is perfectly meaningful. We are talking about Aristotle himself and asking what else could have happened to him.

Kripke's answer was that names are not usually hidden descriptions. They point to things across different ways the world might have been.

In One Minute

Saul Kripke was one of the most important analytic philosophers and logicians of the late twentieth century. He made modal logic clearer, changed the philosophy of language, and helped bring metaphysics back into serious analytic debate.

His most famous idea is the rigid designator. A rigid designator is a word or phrase that picks out the same thing in every possible situation where that thing exists. The name "Aristotle" still picks out Aristotle in a possible situation where he never taught Alexander. The description "the teacher of Alexander" might pick out someone else, or no one.

From that point, Kripke separated three ideas that philosophers had often run together: necessity, knowability without experience, and truth by definition. Some truths are necessary but discovered by experience. "Water is H2O" is the standard example. Chemistry discovered it, but once we know what water is, it could not have been a different chemical stuff.

What They Taught

Kripke taught that language can hook onto the world more directly than many philosophers had thought. Older theories often treated a proper name as a disguised description. On that view, "Moses" might mean "the man who led the Israelites out of Egypt," or "Einstein" might mean "the discoverer of relativity."

Kripke argued that this cannot be the normal story. A person can use a name correctly while knowing very little about its bearer. I can refer to Feynman even if all I know is that he was a physicist. I might even associate a false description with someone and still refer to the right person. A name is not the same thing as the bundle of descriptions in my head.

His alternative is the causal-historical picture of reference. A name is first fixed by some act of naming, introduction, discovery, or public dubbing. After that, later speakers inherit the name through a chain of communication. I can refer to Einstein because my use of "Einstein" belongs to a public history that traces back to Einstein himself.

This matters because names are rigid designators. A possible world is a complete way things could have been. In Kripke's use, possible worlds are tools for logic and metaphysics, not places we can visit. A rigid designator picks out the same object in every possible world where that object exists. "Aristotle" picks out Aristotle even in a world where Aristotle becomes a doctor. "The teacher of Alexander" is not rigid, because in another world Alexander could have had a different teacher.

Kripke then used naming to rethink necessity. A necessary truth is one that could not have been false. A contingent truth is true but could have been false. An a priori truth is knowable without checking the world through experience. An a posteriori truth is learned through experience. Before Kripke, many philosophers expected necessary truths to be a priori. Kripke broke that link.

Some truths are necessary a posteriori. "Hesperus is Phosphorus" means that the evening star and the morning star are the same planet, Venus. People had to discover that by astronomy, so it is a posteriori. But once the names both pick out Venus, the identity could not have failed. Venus could not have been other than Venus.

The same pattern applies to natural kinds. A natural kind is a real type found in nature, such as water, gold, tiger, or human being. "Water is H2O" was discovered by science. Still, Kripke argued that being H2O is not just an accidental feature of water. It is part of what water is. A world with a clear drinkable liquid that is not H2O would contain a water-like liquid, not water.

This reopened talk about essence. An essence is what makes a thing the thing it is, as opposed to a feature it happens to have. Aristotle could have failed to teach Alexander, but he could not have been a completely different person. A particular table might have had a different scratch, but Kripke argued that it could not have originated from a wholly different block of wood and still been that very table.

Kripke also changed logic. Modal logic studies statements about necessity and possibility: "It must be true that..." and "It could be true that..." Kripke semantics explains those statements with possible worlds and relations among them. Roughly, a claim is necessary at a world if it is true in all the relevant worlds; it is possible if it is true in at least one relevant world. That made modal reasoning much more precise.

In Wittgenstein on Rules and Private Language, Kripke gave a famous reading of Ludwig Wittgenstein. The problem is rule-following. Suppose you have always used "plus" in ordinary addition. What fact about your past use guarantees that you meant addition rather than a strange rule that matches addition so far but changes later? Kripke's Wittgenstein treats this as a skeptical challenge. Meaning is not secured by a hidden private mental item. It is stabilized by public practice, correction, and shared standards of use.

Key Ideas With Examples

• Rigid designator: a term that picks out the same thing in every possible world where that thing exists. "Aristotle" still names Aristotle in a world where he never becomes a philosopher.

• Descriptivism: the view that a name gets its meaning or reference from a description associated with it. Kripke attacks the idea that "Aristotle" simply means "the teacher of Alexander."

• Causal-historical reference: names keep referring through a public chain of uses. A child learns "Einstein" from teachers and books, and those uses trace back through a community to Einstein himself.

• Possible world: a complete way things could have been. "There might have been no internet" means that at least one possible world has no internet.

• Necessity: truth that could not have been otherwise. "Two plus two equals four" is necessary because it is not just accidentally true.

• Contingency: truth that could have been otherwise. "Kripke taught at Princeton" is true, but he could have had a different job.

• A priori: knowable without checking experience. Once you understand the terms, "all bachelors are unmarried" does not require a survey.

• A posteriori: knowable through experience. "The morning star is the evening star" required astronomical discovery.

• Necessary a posteriori: a truth that had to be so, but that we discover empirically. "Water is H2O" is learned by science, yet water could not have been a different chemical kind.

• Contingent a priori: a truth fixed by stipulation but not necessary. If a stick is used to set the length of "one meter" at a time, one can know by stipulation that the stick is one meter then, even though the stick could have been longer or shorter.

• Natural kind: a real kind in nature, not just a category we made for convenience. Gold is not whatever looks yellow and shiny; it is the element with atomic number 79.

• Rule-following problem: the worry that no finite record of past behavior fixes one rule rather than another. Past correct additions do not by themselves prove which rule "plus" meant for all future cases.

• Skeptical solution: Kripke's Wittgenstein does not find a private fact that fixes meaning. Instead, he explains meaning through public patterns of use, training, agreement, and correction.

Major Works

• "A Completeness Theorem in Modal Logic" (1959): Kripke's teenage work on modal logic. It helped show how formal systems for necessity and possibility could be matched with precise semantic models.

• "Semantical Considerations on Modal Logic" (1963): a central paper for Kripke semantics. It explains modal claims by looking at truth across possible worlds connected by an accessibility relation, meaning a formal relation that says which worlds count as relevant from another world.

• Naming and Necessity (lectures 1970, book 1980): Kripke's most famous work. It attacks descriptivist theories of names, introduces rigid designation, separates necessity from a priori knowledge, explains natural kinds, and applies these ideas to identity and mind-body debates.

• "Outline of a Theory of Truth" (1975): Kripke's influential work on the liar paradox, the sentence "This sentence is false." He proposes a partial theory of truth in which some sentences are true, some are false, and some never get a settled truth value.

• "A Puzzle about Belief" (1979): a paper about belief reports. Kripke shows how a rational person can seem to believe and disbelieve the same thing when names, translation, and contexts shift.

• Wittgenstein on Rules and Private Language (1982): Kripke's controversial interpretation of Wittgenstein's rule-following remarks. It presents the "plus" and "quus" style skeptical problem and a communal solution.

• Philosophical Troubles (2011): a collection of essays, including work on truth, belief, identity, and philosophical puzzles. It matters partly because much of Kripke's influence came through lectures and unpublished material.

• Reference and Existence (2013): lectures on names, fictional objects, myths, and existence. It asks how we can talk meaningfully about Sherlock Holmes, Zeus, or other things that do not exist in the ordinary way.

Why It Matters

Kripke matters because he changed the map of analytic philosophy. After him, philosophers could no longer casually say that names are just descriptions, that necessity is the same as a priori knowability, or that modal logic is too unclear to be useful.

His work gave philosophers a cleaner way to talk about identity. If "water is H2O" is necessary but discovered, then science can reveal essences. The same point shaped debates about mind and body. If "pain" and "C-fiber firing" rigidly name the same thing, then their identity would be necessary. Kripke argued that pain is different from ordinary scientific identities because pain's felt character is not just an appearance we can peel away. This became a major challenge to simple mind-brain identity theories.

He also helped make metaphysics respectable again in analytic philosophy. Metaphysics asks what reality is like at the most general level. Kripke showed that questions about essence, identity, possibility, and necessity could be argued with logical discipline rather than grand speculation.

His logical work traveled beyond philosophy. Kripke-style models became standard tools in modal logic and related areas that reason about necessity, knowledge, time, proof, and possible states of a system.

Proponents, Critics, and Opponents

Kripke belongs to Analytic Philosophy, but he pushed it away from suspicion of metaphysics. He argued against descriptivist theories associated with Gottlob Frege and Bertrand Russell. Frege and Russell are more subtle than the simple textbook view, but Kripke's target is the idea that ordinary names work by being equivalent to descriptions in the speaker's mind.

Kripke also pushed against W. V. O. Quine's suspicion of quantified modal logic and essentialism. Quine worried that modal talk smuggled in unclear commitments. Kripke helped make that talk precise enough that many later philosophers treated modality as a central tool rather than a mistake.

Hilary Putnam is a close ally on reference and natural kinds. Putnam's slogan that meaning is not only "in the head" fits the same broad shift away from private descriptions. Direct-reference theorists such as David Kaplan, Nathan Salmon, Scott Soames, and Michael Devitt developed related views.

David Lewis is both an ally and a major contrast. Both use possible worlds, but Lewis treats possible worlds as concrete realities, while Kripke uses them as semantic and metaphysical tools without taking that Lewisian step.

Critics argued that Kripke's causal picture can be too simple. Names can shift through mistakes, translations, colonial naming, or social changes. Gareth Evans, John Searle, and later two-dimensional semantic theorists defended more complicated roles for descriptions, context, or cognitive significance.

Kripke's Wittgenstein is also controversial. Some readers think it brilliantly exposes the rule-following problem. Others think it creates "Kripke's Wittgenstein," a powerful but distorted version of Ludwig Wittgenstein's own view. David Chalmers later used Kripkean distinctions between necessity, apriority, and conceivability in arguments about consciousness.

Related Pages

• Analytic Philosophy
• Gottlob Frege
• Bertrand Russell
• Ludwig Wittgenstein
• Hilary Putnam
• W. V. O. Quine
• David Lewis
• David Chalmers