August 4, 2023. What’s the difference between legitimate science and pseudoscientific bullshit like astrology, psychoanalysis and multiverse theories? The former makes predictions precise enough to be tested and possibly disproved, or falsified. The latter, not so much. Philosopher Karl Popper, 1902-1994, gets credit for this so-called falsification principle, which I have found quite useful. I also appreciate Popper’s opposition to dogmatism in politics as well as science. But my take on this complicated thinker, whom I interviewed in 1992, is complicated, as you’ll see when you read this updated excerpt from The End of Science. –John Horgan

I begin to discern the paradox lurking at the heart of Karl Popper's career when, prior to interviewing him in 1992, I ask other philosophers about him. Queries of this kind usually elicit dull, generic praise, but not in Popper’s case. Everyone says this opponent of dogmatism is almost pathologically dogmatic. There’s an old joke about one of Popper’s books: The Open Society and its Enemies should be titled The Open Society by One of its Enemies. 

When I call Popper at his home outside London, a woman with an imperious, German-accented voice answers: Mrs. Mew, housekeeper and assistant to “Sir Karl.” She orders me to fax her a sample of my writing, and she gives me a long list of Sir Karl’s books, must-reading for an interview. Finally, after more calls and faxes, she sets a date. I ask her for directions from the local train station, but she assures me that all the taxi drivers know where Sir Karl lives. “He’s quite famous.”

“Sir Karl Popper's house, please,” I say as I climb into a cab at the train station. “Who?” the driver asks. Sir Karl Popper? The famous philosopher? Never heard of him, the driver says. He knows the street where Popper lives, however, and we find Popper's house, a two-story cottage surrounded by a neatly trimmed lawn, with little difficulty.

A tall, handsome woman answers the door: Mrs. Mew. She is only slightly less forbidding in person than over the telephone. Guiding me to a table in the kitchen, she tells me that Sir Karl is tired. He just turned 90 and has endured many interviews and congratulations related to that milestone; he has also been toiling over an acceptance speech for the Kyoto Prize, known as Japan's Nobel. I should expect to speak to him for only an hour at most.

I am trying to lower my expectations when Popper bursts into the kitchen. He is stooped and surprisingly short; I assumed the author of such autocratic prose would be tall. Yet he is as kinetic as a bantamweight boxer. He brandishes the article I faxed him, which reports on how quantum mechanics is challenging conventional scientific objectivity. “I don’t believe a word of it,” he growls with a German accent, “subjectivism” has no place in physics. “Physics,” he exclaims, grabbing a book from a table and slamming it down, “is that!”

He keeps jumping up from his chair to forage for books or papers that can buttress a point. Striving to dredge a name or date from his memory, he kneads his temples and grits his teeth as if in agony. At one point, when the word "mutation" eludes him, he slaps his forehead repeatedly with alarming force, shouting, “Terms, terms, terms!”

Words gush from him with such force that I cannot ask my prepared questions. “I am over 90, and I can still think,” he says, as if I doubt it. He knew all the titans of twentieth-century physics: Einstein, Schrodinger, Heisenberg… Popper blames Bohr, whom he knew “very well,” for having introduced “subjectivism” into physics. Bohr was “a marvelous physicist, one of the greatest of all time, but he was a miserable philosopher, and one couldn’t talk to him. He was talking all the time, allowing practically only one or two words to you and then at once cutting in.”

As Mrs. Mew turns to leave, Popper asks her to find one of his books. She disappears and returns empty-handed. “Excuse me, Karl, I couldn't find it,” she reports. “Unless I have a description, I can't check every bookcase.”

“It was actually, I think, on the right of this corner, but I have taken it away maybe...” His voice trails off. Mrs. Mew rolls her eyes without really rolling them and vanishes.

He pauses a moment, and I blurt out, “I wanted to ask you about...”

“Yes! You should ask me your questions!  I have wrongly taken the lead.”

I note that he seems to abhor the notion of absolute truths. “No no!” Popper replies, shaking his head. He, like the logical positivists before him, believes that a scientific theory can be “absolutely” true. In fact, he has “no doubt” that some current theories are true (although he refuses to say which ones). But he rejects the positivist belief that we can know a theory is true. “We must distinguish between truth, which is objective and absolute, and certainty, which is subjective.”

Science cannot be reduced to a formal, logical system or method, Popper says; a scientific theory is an invention, an act of creation, based more upon a scientist's intuition than upon pre-existing empirical data. “The history of science is everywhere speculative,” Popper says. “It is a marvelous history. It makes you proud to be a human being.” Framing his face in his outstretched hands, Popper intones, “I believe in the human mind.”

For similar reasons, Popper opposes determinism, which he sees as antithetical to creativity and freedom. “Determinism means that if you have sufficient knowledge of chemistry and physics, you can predict what Mozart will write tomorrow,” he says. Popper doesn’t need quantum mechanics or chaos theory to tell him that determinism is “ridiculous.” Waving at the lawn outside the window, he says, “There is chaos in every grass.”

Popper is proud of his strained relations with other philosophers, including Wittgenstein, with whom he had a famous run-in. Popper was lecturing at Cambridge in 1946 when Wittgenstein interrupted to insist on the “nonexistence of philosophical problems.” Popper retorted that there are many such problems, such as establishing a basis for moral rules. Wittgenstein, who was sitting beside a fireplace toying with a poker, thrust it at Popper and demanded, “Give me an example of a moral rule!” Popper replied, “Not to threaten visiting lecturers with pokers,” whereupon Wittgenstein stormed out of the room. [For other accounts of this episode, see the book Wittgenstein’s Poker.]

Popper also disdains so-called postmodernists who argue that “knowledge” is just a weapon wielded by people vying for power. “I don't read them,” Popper says of the postmodernists, waving his hand as if at a bad odor. He adds, however, that he “once met Foucault.”

I suggest that postmodernists describe how science is practiced, whereas he, Popper, stipulates how it should be practiced. To my surprise, Popper nods. “That is a very good statement,” he says. “You can't see what science is without having in your head an idea what science should be.” He admits that scientists invariably fall short of his ideal. “Since scientists got subsidies for their work, science isn't exactly what it should be. This is unavoidable. There is a certain corruption, unfortunately. But I don't talk about that.” 

Then Popper talks about it. “Scientists are not as self-critical as they should be,” he asserts. “There is a certain wish that you, people like you”--he jabs a finger at me—“should bring them before the public.” He stares at me a moment, then reminds me that he did not seek this interview. “Far from it,” he says.

Popper plunges into a technical critique of the big bang theory. “It's always the same,” he sums up. “The difficulties are underrated. It is presented in a spirit as if this all has scientific certainty, but scientific certainty doesn't exist.” I ask if Popper still doubts Darwin's theory of natural selection, which he has suggested is unfalsifiable and thus pseudo-scientific. “That was perhaps going too far,” Popper says, waving his hand dismissively. “I'm not dogmatic about my own views.” Abruptly he pounds the table and exclaims, “One ought to look for alternative theories!”

Popper scoffs at scientists’ hope that they can achieve a final theory of nature. “Many people think that the problems can be solved, many people think the opposite. I think we have gone very far, but we are much further away.” He shuffles off and returns with his book Conjectures and Refutations. Opening it, he reads his own words with reverence: “In our infinite ignorance we are all equal.”

I launch my gotcha question: Is your falsification concept falsifiable? Popper glares at me, then his expression softens, and he places his hand on mine. “I don't want to hurt you,” he says gently, “but it is a silly question." Peering searchingly into my eyes, he asks if one of his critics urged me to pose the question. Yes, I lie.

“Exactly,” he says, looking pleased. “The first thing you do in a philosophy seminar when somebody proposes an idea is to say it doesn’t satisfy its own criteria. It is one of the most idiotic criticisms one can imagine!” His falsification concept, he says, helps distinguish between empirical and non-empirical modes of knowledge. Falsification itself is “unempirical”; it belongs not to science but to philosophy, or “meta-science.” Popper asks if I understand his response, and I nod. He squeezes my hand, murmuring, “Yes, very good.”

Emboldened, I say a former student accuses Popper of not tolerating criticism. “It is completely untrue!” he cries. “I was happy when I got criticism! Of course, not when I would answer the criticism, like I have answered it when you gave it to me, and the person would still go on with it.” In that case, Popper would eject the student from his class.

The late afternoon light bathes the kitchen in a ruddy glow. Mrs. Mew appears to inform us that we have been talking for over three hours. How much longer, she inquires peevishly, do we expect to continue? Perhaps she should call me a cab? I look at Popper; he has broken into a bad-boy grin but does appear to be drooping.

I slip in a final question: Why in his autobiography does he say that he is the happiest philosopher he knows? “Most philosophers are really deeply depressed,” he replies, “because they can’t produce anything worthwhile.” Grinning, Popper glances at Mrs. Mew, who looks horrified. Popper’s smile fades. “It would be better not to write that,” he says to me. “I have enough enemies.” He stews a moment and adds, “But it is so.”

I ask Mrs. Mew if I can have the speech Popper plans to give at the Kyoto Prize ceremony. “No, not now,” she says curtly. “Why not?” Popper asks. “Karl,” she replies, “I've been typing the second lecture nonstop, and I'm a bit...” Plus she does not have a final version. What about an uncorrected version? Popper asks. Mrs. Mew stalks off.

She returns and shoves Popper’s lecture at me. “Have you got a copy of Propensities?” Popper asks her. She purses her lips and stomps into the room next door, while Popper explains the book’s theme: quantum and even classical physics reveal that nothing is determined; there are only “propensities” for certain things to occur. For example, Popper says, “in this moment there is a certain propensity that Mrs. Mew may find a copy of my book.”       

“Oh, please!” Mrs. Mew exclaims from the next room. She returns, no longer trying to hide her annoyance. “Sir Karl, Karl, you have given away the last copy of Propensities. Why do you do that?”

“The last copy was given away in your presence,” he says boldly.

“I don't think so,” she retorts. “Who was it?”      

“I can't remember,” he mutters sheepishly.

My cab arrives. I thank Popper and Mrs. Mew for their hospitality and take my leave. As the cab pulls away, I ask the driver if he knows whose house this is. No, someone famous, is it? Yes, Sir Karl Popper. Who? Karl Popper, I reply, one of the greatest philosophers of the 20th century. “Is that right,” murmurs the driver.

When Popper dies two years later, the Economist hails him as having been “the best-known and most widely read of living philosophers.” The magazine notes, however, that the anti-dogmatist did not take criticism well.

Can a skeptic avoid self-contradiction, or what might be called the Popper paradox? And if he doesn’t, if he preaches but fails to practice intellectual doubt and humility, does that negate his work? Not at all. Such paradoxes corroborate the skeptic’s point, that the quest for truth is endless, twisty and riddled with pitfalls, into which even sharp-eyed seekers tumble. In our infinite ignorance we are all equal.

Further Reading:

See my profiles of philosophers Thomas Kuhn and Paul Feyerabend.

Philosophy: What’s the Point?

My Controversial Diatribe Against “Skeptics”

What’s the Point of the Humanities?

Advice to Aspiring Science Writers: Remember Marx

Conservation of Ignorance: A New Law of Nature