Saul Kripke (1940-2022), the renowned American philosopher, was a trailblazer in the fields of logic and language. He revolutionized prevailing philosophical views on naming and necessity, creating new theories and insights in these areas. Born in Bay Shore, New York in 1940, Kripke displayed prodigious talent, publishing his first paper on modal logic at the age of 17 while still in high school. He went on to earn a bachelor’s degree from Harvard, and his lifelong journey of philosophical inquiry culminated in numerous influential contributions to logic, language, and metaphysics. Kripke’s groundbreaking work has had a profound impact on contemporary philosophy, solidifying his status as one of the most important and influential philosophers of the 20th century.
Nathan Salmón, an American philosopher, is a leading figure in the fields of analytic metaphysics, the philosophy of logic, and the philosophy of language. Born in Los Angeles in 1951, Salmón received his Ph.D. from UCLA and went on to teach at various universities, including Princeton, UC Santa Barbara, and the CUNY Graduate Center. He has made numerous contributions to contemporary philosophy, particularly in the areas of semantic content, modal logic, and existence. His influential works include Reference and Essence (1981), Frege’s Puzzle (1986), Metaphysics, Mathematics, and Meaning (2005), and Content, Cognition, and Communication (2007), among others. Salmón’s rigorous and innovative approach to philosophy has had a significant impact on the field, making him an essential figure in contemporary philosophical discourse.
Simply Charly: How did you first become interested in the philosophy of Saul Kripke, and what aspects of his work do you find most compelling?
Nathan Salmón: In the spring of 1972, I was a 21-year-old junior at UCLA when on the recommendation of my teacher in introductory modern logic I enrolled in an undergraduate course taught by Saul Kripke, a 31-year-old philosophy phenomenon. Although I was not eligible to take Kripke’s graduate seminar that same term, I attended the class anyway. The undergraduate course focused on Gottlob Frege’s and Bertrand Russell’s competing theories in the philosophy of semantics, from Kripke’s perspective, as well as on some of the critical secondary literature. Meanwhile, the graduate seminar was centered on Kripke’s just-published lengthy article, “Naming and Necessity,” which strongly critiqued both Frege’s and Russell’s theories. This work which would later be repackaged as a book and become Kripke’s signature masterpiece, consisted of transcriptions of his groundbreaking lectures at Princeton two years prior.
Kripke’s philosophical prowess and sheer genius were awe-inspiring. It would be an understatement to describe his two courses at UCLA in the Spring of 1972 as first-rate university courses in the philosophy of semantics. They were spectacular academic events. In these courses, Kripke—a philosophical genius in the strictest sense—was at the top of his game, offering phenomenal insight into a variety of topics in metaphysics, epistemology, philosophy of mind, philosophy of logic, philosophy of mathematics, and more. The undergraduate course was a tour de force. The graduate seminar, which attracted participation from several senior figures, was undoubtedly one of the best university philosophy courses ever taught since Russell led discussions at Cambridge with the likes of Ludwig Wittgenstein and G. E. Moore. Kripke’s two courses provided my introduction to the Saul Kripke Experience, and I have been an avid follower ever since.
SC: One of Kripke’s most famous contributions to philosophy is his theory of modal semantics, which attempts to explain how we reason with modal concepts like necessity and possibility. Can you provide an overview of this theory?
NS: Kripke was largely a philosopher of modality. Like other mathematically-inclined philosophers—Plato, Descartes, Leibniz, and others—Kripke focused on the kind of necessity possessed by mathematical truths. In contrast, empirically-oriented philosophers of the past found this kind of necessity unscientific and tried to deflate it by depicting it as a misleading result of our language-based representation of the world, or even by dismissing it as meaningless. Kripke tackled the issue of necessity during high school, developing its logic in a strikingly creative way that built on Leibniz’s insight that necessity equates with truth in all possible worlds and possibility equates with truth in some possible worlds. He extracted modal logic from the classical logic of “all” and “some” and showed how the properties of modal logic could be captured by specific axioms, depending on what those properties are.
In Kripke’s landmark work, Naming and Necessity, he brought about a philosophical revolution by demonstrating how necessity—the same kind of necessity as exhibited by mathematical truths—should be viewed as a real feature of how some things are, not merely an artifact of language. Things like chemical elements and compounds, things like tables and ships, and even things like ourselves, all exhibit in one way or another the same kind of necessity that arises in mathematics.
SC: Kripke is often associated with a type of anti-descriptivism about proper names, which holds that names do not have a descriptive meaning or sense. Kripke’s theory of reference has been enormously influential in philosophy. How would you summarize this theory?
NS: Ostensibly, Naming and Necessity has a central thesis regarding certain designating expressions. Previous philosophical geniuses, Frege and Russell, argued that proper names of people and things—words like ‘Einstein’, ‘Charles III’, and even the word ‘water’—are descriptive designators, similar in meaning to phrases like “the inventor of the theory of relativity and discoverer of the equation ‘E = mc2’”, ‘the king of the Commonwealth’, or ‘the clear liquid that fills the lakes and oceans’. This account was instrumental in resolving philosophical puzzles that arise when names occur in various psychological attributions, especially attributions of belief, and also when a name fails to designate anything. However, the central thesis of Naming and Necessity is that proper names and similar devices are not descriptive in the manner that Frege and Russell believed and that the prevailing wisdom regarding the philosophical puzzles was mistaken. In fact, Kripke shows that proper names are fundamentally different from descriptive designators, echoing John Stuart Mill’s view that proper names are non-descriptive or, in Mill’s terminology, non-connotative. Indeed, Frege and Russell may be seen as arguing against Mill’s anti-descriptivism about proper names by means of the very puzzles that their theories appear to resolve. Kripke goes a good deal further than Mill. To begin with, Kripke extends his anti-descriptivism to terms for natural kinds, such as ‘water’ and ‘tiger.’ This is in contrast to Mill’s view that all general terms are descriptive designators.
SC: One of Kripke’s most significant contributions to the philosophy of language is his notion of a rigid designator. What is the special significance of this notion?
NS: Kripke’s realism about necessity and his insights into the logic of necessity paved the way for an important observation about proper names: Since names are non-descriptive designators, they are also rigid designators. The notion of a rigid designator arises out of Kripke’s possible-world semantics for modal logic. In that framework, semantic concepts such as truth and designation are relative to a possible world.
For example, the descriptive designator “the inventor of the theory of relativity” designates Einstein with respect to the actual world, but it designates someone else with respect to a possible world in which someone other than Einstein invented the theory of relativity. Roughly, to say that proper names are rigid designators is to say that even in discourse about counterfactual situations, these names obstinately continue to designate the very same things as in ordinary discourse about reality. Thus, even with respect to a possible world where someone other than Einstein discovered relativity theory, the name “Einstein” still designates Einstein. This observation challenges the orthodox view of names received from Frege and Russell, which depicted names as non-rigid. Whereas proper names are rigid designators; descriptive designators typically are not.
SC: Can you explain this theory of reference in more detail and discuss some of the main arguments for it?
NS: As I showed in my doctoral dissertation, Kripke’s arguments against the descriptive theories of Frege and Russell fall into three broad categories: modal, epistemological, and semantic. The modal argument starts by assuming, with Frege and Russell, that the name “Einstein” means something like the inventor of the theory of relativity and discoverer of the equation ‘E = mc2’. If this is correct, then the sentence “Someone is Einstein if and only if he invented the theory of relativity and discovered the equation ‘E = mc2’” is analytic. That is, in that case, it is like the sentence ‘All bachelors are unmarried’—true “by definition”, or more accurately, true solely as a logical consequence of what it means. Insofar as the sentence is analytic, it therefore expresses a necessary truth. However, Kripke points out that this is simply incorrect. Einstein might not have invented either of these things. Furthermore, someone else might have done so instead. These observations both support and are supported by Kripke’s thesis that proper names are rigid designators.
The epistemological argument also starts by assuming with Frege and Russell that ‘Someone is Einstein if and only if he invented the theory of relativity and the equation ‘E = mc2’ ’ is analytic. This has the consequence that the same sentence expresses an a priori truth, i.e., a fact knowable in something like the manner of a mathematical theorem: entirely through reflection on, and reason from, the concepts expressed. Kripke shows that this is also incorrect since we could discover empirically that Einstein didn’t discover either of these things. What is more, we could discover empirically that someone else did instead.
The semantic argument has a somewhat different flavor. Here we suppose that Einstein hadn’t invented the theory of relativity or discovered the equation ‘E = mc2’. To make the case even more compelling, suppose further that an obscure theoretical physicist, Schmidt, invented both of these and was soon murdered, and that Einstein, as a patent clerk, took credit for Schmidt’s theory and equation. Under these circumstances, to whom would our use of the name ‘Einstein’ refer? To Schmidt, as the Frege-Russell theory claims? Clearly not! Under these circumstances, the sentence “Einstein invented the theory of relativity and the equation ‘E = mc2’” isn’t a true sentence about Schmidt; it is a false sentence about Einstein, the very man who actually achieved these remarkable results.
SC: One of Kripke’s most cited articles is called “A Puzzle about Belief.” What is Kripke’s puzzle, and why did it create such a buzz?
NS: Kripke followed up Naming and Necessity with several penetrating sequel pieces, including a book on names that fail to designate anything and his highly influential article posing a philosophical puzzle about belief. One of the most important considerations that led Frege and Russell to their view that proper names are descriptive designators was that the Frege-Russell view yields resolutions to difficult puzzles that otherwise arise about names. These puzzles flow organically from a couple of familiar facts about names. First, some names don’t designate anything at all. Suppose with Mill that proper names are non-descriptive designators, mere labels. What content is then expressed by sentences, like those that arise in the context of a fictional story, sentences that invoke a non-designating name like ‘Harry Potter’? How can such sentences even have content? The Frege-Russell view that names are descriptive designators provides a plausible and satisfying answer to these questions. Even if a name like ‘Harry Potter’ fails to designate anyone, because there is, in reality, no one who answers to the name’s descriptive content, still that descriptive content figures into the content of sentences from fiction like ‘Harry Potter is a student at Hogwarts School’, and even for sentences that the stories might not settle, like ‘Harry Potter is right-handed’.
Second, a single individual might have more than one name. For example, though many of his readers are completely unaware, Lewis Carroll, who wrote the Alice in Wonderland stories, was in fact a mathematician by the name of ‘Charles Lutwidge Dodgson’. ‘Lewis Carroll’ was his pen name. Consider now someone, Smith, who knows Dodgson as their mathematics instructor, and who has also read Alice’s Adventures in Wonderland, but who believes that the mathematician and the fantasy author are different people. As we would normally put it, Smith doesn’t realize that Carroll is Dodgson. Yet Smith knows that Carroll is Carroll. Frege’s philosophy of semantics takes as its starting point a simple question: How, then, can the informative sentence ‘Carroll is Dodgson’ differ at all in content from the utterly uninformative sentence ‘Carroll is Carroll’? That is known as Frege’s puzzle. More pointedly, assuming that names are non-descriptive, how can the attribution ‘Smith believes that Dodgson is exacting’ be true while ‘Smith believes that Carroll is exacting’ is false? This is known as the problem of substitution failure. Here again, the Frege-Russell account provides a satisfying answer. Although the names ‘Carroll’ and ‘Dodgson’ designate the same writer, if they differ in their descriptive content, then Smith’s belief that Dodgson is exacting invokes the concept of being a mathematician, whereas the hypothesis that Carroll is exacting instead invokes the concept of being a fantasy author. The two hypotheses cannot differ in their truth-value, but someone ignorant of Carroll’s double life can believe one of the hypotheses without believing the other.
Whereas Naming and Necessity makes a fairly decisive case against the Frege-Russell account of proper names as descriptive designators, it leaves wide open the resulting question of how then Frege’s puzzle, the problem of substitution failure, and the problems raised by non-designating names are properly resolved. While Naming and Necessity persuaded many readers that the Frege-Russell account is mistaken, many of us also felt frustrated because Kripke did nothing to resolve these remaining problems. In “A Puzzle about Belief” Kripke directly addresses the problem of substitution failure. Here he considers a radical version of Mill’s non-descriptive account. According to what Kripke calls ‘Millianism’, the semantic content of a proper name is simply the person or thing that the name designates, nothing more. According to Millianism, ‘Carroll is Dodgson’ semantically contains just the information that Carroll is Carroll (himself), and the sentence ‘Smith believes that Carroll is exacting’ is in fact true, even though Smith sincerely dissents from ‘Carroll is exacting’. Kripke did not endorse Millianism (as I do). In fact, he implicitly argued that the Millian resolution to his puzzle about belief is incorrect. Instead he argued brilliantly in “A Puzzle” that it is a serious mistake to take apparent substitution failure to be a problem specifically for Millianism. The problem is significantly more widely applicable than that, and apparently arises from entirely innocuous-seeming principles governing language and belief, quite independently of the question of whether names are descriptive designators, or even of whether they are Millian designators. Kripke strongly suggested that attributions of belief in cases where a single person or thing has two names subject the principles governing language and belief to so much strain that the whole apparatus of attributing belief might simply break down.
SC: Kripke’s work on Wittgenstein is also well-known. In your view, what were some of the most important insights that Kripke provided in his interpretation of Wittgenstein’s later philosophy?
NS: Kripke offered a new interpretation of the later work of Wittgenstein. On Kripke’s interpretation, Wittgenstein was primarily concerned with a particular skeptical paradox of his own invention about language and thought. The problem is basically that there do not appear to be sufficient facts about anyone that make it the case that they have the particular concepts and thoughts that we take them to have, not even for basic concepts like that of simple addition in arithmetic. For their past usage, past experiences, and the like do not suffice to determine which concepts they grasp or whether those concepts apply to various unexperienced cases, and if so, how.
Kripke’s interpretation is at best controversial among Wittgenstein scholars. It is important to see the controversy in the proper context. Kripke set very high standards for philosophy, or let’s say more demanding standards. Like Frege and Russell before him, Kripke consistently endeavored to hold the discipline as a whole to his stringent standards. Unsurprisingly, the discipline has been less than enthusiastic about adopting such different standards. Kripke’s interpretation casts Wittgenstein as tacitly meeting a very demanding standard. Specifically, Kripke depicts Wittgenstein as implicitly offering quite forceful arguments for a definite albeit astonishing conclusion about human thought—in sharp contrast to merely gesturing toward some extremely obscure arguments for rather dubious conclusions. If this interpretation does not correspond closely to the man himself, then one should think of it as what Kripke felt a philosopher of Wittgenstein’s preeminent stature might have been up to, and maybe indeed should have been up to.
SC: How does Kripke’s third book Reference and Existence figure in his overall philosophy of language?
NS: Reference and Existence is an important sequel to Naming and Necessity. It is basically a transcription of lectures Kripke presented at Oxford in 1973, where the transcript
was made available to interested scholars, but was first published some forty years later. In those lectures, Kripke addressed the other nest of problems with the non-descriptive account of proper names that emerges in Naming and Necessity: problems that arise in connection with sentences involving non-designating names. Kripke made a compelling case that the characters that populate fictional stories, characters like Harry Potter, exist in reality, not as flesh-and-blood human beings, but as abstract objects created by the storyteller. Harry Potter is not a real person, to be sure, let alone a real wizard, but a fictional wizard created by writer J. K. Rowling. Kripke distinguished between two very different alleged uses of a name like ‘Harry Potter’. On its alleged primary use, the name is utterly non-designating. This, according to Kripke, is the use it has in telling the story. At a later stage, in reflection upon the fiction, the name takes on a secondary use whereby it designates the fictional character created by the storyteller.
One serious problem on Kripke’s account is that the original problems that arise from sentences with non-designating names—problems that Frege and Russell used their descriptive account to resolve—remain unresolved. My own view is that Kripke’s alleged primary use is a myth, that names from fiction have their so-called secondary use right from the start and simply don’t have any relevant use on which they fail to designate anything. But this too only pushes the puzzle back without resolving it. For what about genuinely non-designating names?
SC: Kripke has been a major influence on the development of analytic philosophy more broadly. In your view, what are some of the key ways in which his work has shaped the direction of the field over the past several decades?
NS: Kripke used his revolutionary discoveries about names and the logic of necessity to argue compellingly in Naming and Necessity that some statements that exhibit the same kind of necessity as mathematical truths are in fact unknowable in anything like the way mathematical truths are discovered. The necessary truths of mathematics are discovered by a peculiarly mathematical technique: proof. By contrast, Kripke argued, many necessary truths about substances, about physical objects, and even about people, are discoverable only by empirical methods, like sensory observation. This result, which by now is nearly universally accepted by philosophers, meant that the previous attempts by empiricists to deflate necessity, were fundamentally misguided. Kripke also used his logical insights about names and the logic of necessity to argue, albeit less compellingly, that some truths that are not necessary in the way that mathematics is, can nevertheless be known in a manner not unlike mathematical proof, with no need for experiential observation. This aspect of Naming and Necessity remains controversial, and Kripke subsequently modified his arguments in this connection.
SC: Kripke is widely regarded as one of the most important philosophers of the 20th century. In your view, what do you think will be his lasting legacy, both within philosophy and beyond?
NS: The disciplines of philosophy and logic attract many remarkably intelligent people. Some are genuinely brilliant. Few show signs of authentic genius. Among philosophers of the second half of the 20th Century, Kripke was in a class by himself, an authentic phenomenon. He ranks with Bertrand Russell, arguably the greatest philosopher of the first half of the 20th Century. Although some would rank Wittgenstein above Kripke, this seriously underrates Kripke. Kripke had one of the greatest minds in the history of philosophy.
Many of the great philosophers of the past—figures like Descartes, Hume, and Kant—were creative, coming up with brilliant, novel ideas, with new important insights into the nature of their subject. Some philosophers were creative but excessively audacious intellectually. Exceptional philosophers temper their novel ideas with a certain degree of intellectual caution, a healthy dose of what Russell called ‘a robust sense of reality’. Kripke was unusual in that he had both philosophical virtues. He was amazingly creative, but his rich ideas were invariably insightful, often very penetratingly so. Firmly grounded in reality, and with an unwavering common sense, Kripke would not take a controversial position without offering a forceful argument in its support. He was so brilliant, though, that his intellectually cautious nature never held back his philosophical creativity. The two operated in tandem. He also had a vibrant curiosity about anything and everything, and would often digress before continuing with his line of argument. Hearing one of Kripke’s lectures was a humbling experience for all but the most self-confident of philosophers in the audience, and those few who were not humbled would have done well to reconsider Kripke’s thoughtful and forceful arguments more carefully.
The background context of Naming and Necessity includes Kripke’s pioneering work as a teenager on modal logic, as well as the dominance at the time of Frege’s and Russell’s competing philosophies of semantics. But Naming and Necessity is peppered throughout with numerous penetrating insights and observations on any number of themes in metaphysics, epistemology, philosophy of language, philosophy of mind, and more. The work has a kind of irresistible energy. It bears the unmistakable markings of authentic genius. Above all, it is a great joy to read and to re-read. It is philosophy at its very best.
I’m very glad that I took the opportunity to participate in a small conference with Kripke in Hudson, NY in July 2022 looking back over 50 years of his masterpiece. That was just eight weeks before his sudden and unexpected death at 81, so it turned out to be our last opportunity to engage with him, intellectually and socially, and to show our appreciation for his highly valuable contributions to philosophy, logic, and beyond. If any works of contemporary philosophy will be read and studied beyond the 22nd Century, Naming and Necessity and its sequels will be among them—if not indeed the only ones, since much of philosophy in the 21st Century seems to have lost its way. Kripke also left behind a trove of unpublished material, some of which is ready for prime time or nearly so. Unfortunately, it currently appears that none of that material will be published. Most of it is supposed to be available to researchers through the Saul Kripke Center at the Graduate Center of the City University of New York. Kripke’s death is an enormous loss and marks the end of a golden era. It is difficult to imagine philosophical excellence without Saul Kripke among its guardians. Philosophy will go on without Kripke, but it will be much impoverished, likely for very many years to come.