Saul Kripke, a math prodigy and pioneering logician whose revolutionary theories on language qualified him as one of the 20th century’s greatest philosophers, died on Sept. 15 in Plainsboro, New Jersey. He was 81.
His death, at Penn Medicine Princeton Medical Center, was caused by pancreatic cancer, according to Romina Padro, director of the Saul Kripke Center at the City University of New York, where Mr. Kripke had been a distinguished professor of philosophy and computer science since 2003 and had capped a career exploring how people communicate.
Mr. Kripke’s classic work, “Naming and Necessity,” first published in 1972 and drawn from three lectures he delivered at Princeton University in 1970 before he was 30, was considered one the century’s most evocative philosophical books.
“Kripke challenged the notion that anyone who uses terms, especially proper names, must be able to correctly identify what the terms refer to,” said Michael Devitt, a distinguished professor of philosophy who recruited Mr. Kripke to the City University Graduate Center in Manhattan.
“Rather, people can use terms like ‘Einstein,’ ‘springbok,’ perhaps even ‘computer,’ despite being too ignorant or wrong to provide identifying descriptions of their referents,” Devitt said. “We can use terms successfully not because we know much about the referent but because we’re linked to the referent by a great social chain of communication.”
The Pulitzer Prize-winning historian Taylor Branch, writing in The New York Times Magazine in 1977, said Mr. Kripke had “introduced ways to distinguish kinds of true statements — between statements that are ‘possibly’ true and those that are ‘necessarily’ true.”
“In Professor Kripke’s analysis,” he continued, “a statement is possibly true if and only if it is true in some possible world — for example, ‘The sky is blue’ is a possible truth, because there is some world in which the sky could be red. A statement is necessarily true if it is true in all possible worlds, as in ‘The bachelor is an unmarried man.’”
Many colleagues ranked Mr. Kripke (pronounced KRIP-key) with better-known luminaries like Bertrand Russell and Ludwig Wittgenstein.
He fit the profile of a distracted, deep-thinker: white-bearded, rumpled and toting his books and notes on Princeton’s campus and later at City University in a plastic Filene’s Basement shopping bag.
He even became something of a cult figure. He was said to have been a model for the brilliant but flawed philosopher Noam Himmel in Rebecca Goldstein’s 1983 novel “The Mind Body Problem” and a namesake for Barry Kripke, a character on the TV sitcom “The Big Bang Theory.”
But he was not, for the most part, what most people would characterize as a public intellectual.
One reason was that much of his research remained unpublished, surviving in recorded remarks, notes and privately circulated manuscripts. He would lecture extemporaneously without notes for hours, leaving it to others to transcribe his taped remarks, which he would later meticulously edit and only then publish in works like “Naming and Necessity” and “Wittgenstein on Rules and Private Language” (1982).
Even in the academy, fellow polymaths were bedazzled by the breadth of his boundless ruminations into metaphysics, modal logic, recursion theory, identity materialism and the ontological nature of numbers.
“Naming and Necessity” drew such strands together into a groundbreaking work of analytic philosophy.
“Kripke showed how necessity — the same kind of necessity as exhibited by mathematical truths — should be seen as a real feature of how some things are in the real world, and no mere artifact of language,” said Nathan Salmon, a philosophy professor at the University of California, Santa Barbara, who studied with Mr. Kripke and was later his colleague at Princeton and City University.
“Things like chemical elements and compounds, things like tables and ships, even things like ourselves, all exhibit in one way or another the same kind of necessity that arises in mathematics,” Salmon said. “Kripke’s realism about necessity, and his brilliant insights into its logic, led to his important observation that proper names of people and things — words like ‘Einstein’, ‘Charles III’, and ‘water’ — are rigid designators.”
The term “rigid designator,” which has entered the Oxford English Dictionary, defines the type of linguistic expression that refers to the same thing in all possible worlds, as opposed to a descriptive designator, which may not.
Einstein, for example, is always the one and only Einstein in any world. However, “the inventor of relativity theory” is a descriptive designator. Water is a rigid designator, while “the substance that fills the lakes and oceans” is descriptive.
While the definition may seem self-evident to a layman, its impact in the hermetic world of philosophy was seismic.
“Before Kripke, there was a sort of drift in analytic philosophy in the direction of linguistic idealism — the idea that language is not tuned to the world,” the philosopher Richard Rorty said in an interview in 2006, a year before he died. “Saul almost single-handedly changed that.”
Saul Aaron Kripke was born on Nov. 13, 1940, in Bay Shore, New York, on Long Island, the eldest of three children of Dorothy (Karp) Kripke, who wrote children’s books about Judaism, and Rabbi Myer S. Kripke, who lead a Conservative congregation further east on Long Island, in Patchogue.
When Saul was 3, his mother recalled, he walked into the kitchen and asked whether God was everywhere. When she replied yes, he asked if that meant that he was encroaching on God’s space in the kitchen.
“I was startled that Saul already seemed to have an intuitive grasp of the notion that two objects cannot occupy the same space at the same time,” his mother was quoted as saying in The Times Magazine article.
In 1946, the family moved to Omaha, Nebraska, where Myer Kripke became the leader of Beth El Synagogue. Joining the Rotary Club, he befriended a young money manager, Warren Buffett, with whom he invested $67,000 that by the 1990s, after Buffett had become one of the world’s most successful investors, was worth $25 million.
The rabbi’s precocious son had taught himself ancient Hebrew by the age of 6, had finished reading Shakespeare’s complete works by 9 and published his first completeness theorem in modal logic when he was 18.
“Saul once told me he would have invented algebra if it hadn’t already been invented,” Dorothy Kripke said, “because he came upon it naturally.”
After completing high school, he attended Harvard, taught a graduate-level course in logic at nearby MIT during his sophomore year and graduated summa cum laude from Harvard in 1962. His classmates included Laurence Tribe, the future constitutional scholar, and Theodore Kaczynski, who would become a math whiz and the domestic terrorist known as the Unabomber.
“I wish I could have skipped college,” Mr. Kripke told The Times in a 2006 interview. “I got to know some interesting people, but I can’t say I learned anything. I probably would have learned it all anyway, just reading on my own.”
He was awarded a Fulbright, taught briefly at Harvard and was appointed to professorships at Rockefeller University in New York City (1968 to 1976), Princeton (1978 to 1998) and then the City University without ever earning a graduate degree.
In 2007, City University established the Saul Kripke Center at the Graduate Center to archive, study and publish his works. Padro, the center’s director, estimated that as much as 70% of Mr. Kripke’s work remained unpublished.
In 1973, Mr. Kripke delivered the prestigious John Locke Lectures at Oxford. In 2001, he was awarded the Rolf Shock Prize from the Royal Swedish Academy of Sciences, widely regarded as the equivalent of the Nobel in philosophy.
His marriage in 1976 to Margaret Gilbert, a British philosopher, ended in divorce. His sisters, Madeline Kripke, who kept one of the world’s largest private collections of dictionaries, and Netta (Kripke) Stern, died before him.