Beyond Falsifiability: The Origins of Critical Rationalism
Karl Popper is best known for proposing that scientific theories should be ‘falsifiable’ — that they should, in principle, be refutable by experience. And although falsifiability dominated Popper’s early writings, it was never the crux of his philosophy; it was primarily a critique of the widespread positivism that was so influential during his early career. Positivism held that ‘scientific’ statements are those that are ‘verifiable’ by experience, and that all other statements are either nonsense or true by definition, and so tell us nothing about the world. Popper saw that positivism was fatally flawed. For one thing, ‘verifying’ the truth of a statement would require that that statement, as well as its accompanying verification statement, be expressed in a perfectly precise language — which cannot exist. And even if it could, we would still be left with an infinite regress of statements about statements about statements, etc.
Popper, disagreeing strongly with positivism, proposed falsifiability during the 1930s as a practical criterion to solve the problem that the positivists had raised, but not solved, of how to distinguish ‘scientific’ statements from other kinds of statements. ‘Scientific’ statements, he suggested, are those with empirical content — not because these statements are verifiable by experience, but because they can be falsified or criticized by experience. Crucially, falsifiability was unlike positivism in that it was not by itself intended as a comprehensive explanation of scientific knowledge. It was intended only as a useful rule to distinguish between different types of theories that exposed themselves to different types of criticism.
Yet falsifiability was derived from Popper’s philosophical tour de force, so-called ‘critical rationalism’. Critical rationalism differs radically from positivism and from all traditional epistemological theories. It explains that there is only one process, even in principle, that can systematically generate new knowledge: variation and criticism of already existing knowledge. The crucial feature of this theory — namely, the use of criticism to correct errors in pre-existing knowledge — grew out of Popper’s deep-rooted appreciation of human fallibility: our ability to make mistakes. And although Popper eventually developed critical rationalism into a sophisticated philosophical theory, his interest in our fallibility and its consequences was not only intellectual. It was also deeply personal. It arose, fittingly, from a momentous mistake that he himself made, many years before proposing falsifiability, as a 16-year-old boy growing up in postwar Vienna. It was there, during the spring of 1919, that Popper, albeit briefly, became a Communist.
That spring, the atmosphere in Vienna was electric. Six months earlier, the Allied victory in World War I had vanquished the half-millennia-old Habsburg monarchy, leaving Vienna under the control of a feeble and vulnerable interim government. This rump state almost immediately came under threat when two of Austria’s neighbors, Bavaria and Hungary, succumbed to Communist revolutions. Hungary’s new Communist leader swiftly dispatched an emissary to Vienna to initiate a coup by using Austrian troops just returning from the war. The Hungarians aimed to topple the interregnum Austrian government and create a belt of Communist states locking arms across Central Europe.
The Hungarians were entering a Vienna utterly transformed from its prewar glitz and glory. In addition to ending the old Habsburg dynasty, World War I had devastated Vienna’s economy, and the 16-year-old Popper was upset by the ruinous poverty he saw afflicting the city’s lower classes, and especially by its contrast with the opulence of Vienna’s high society. Popper’s disgust at the economic consequences of the war matched his disgust at its savage and apparently pointless bloodshed. The world appeared to him as a cruel and unfair place, and he longed for it to become more just and peaceful. By early 1919, he had joined a socialist student group, and “peace propaganda” converted him into a Communist by that spring.
In developing Communism, Marx had claimed to discover fixed laws of history that he could use to ‘scientifically predict’ humanity’s historical destiny. Specifically, Marx held that humanity’s long-term historical development obeyed certain unbreakable economic laws, and that according to these laws, capitalism was an inevitable yet reassuringly transient phase of human history — a mere detour en route to the ultimate destination of Communism, which the theory predicted would be a stateless paradise of peace and equality.
The peacefulness and egalitarianism of Marx’s envisioned Communist society greatly appealed to the disillusioned Popper, and Marx’s characterization of Communism as ‘scientific socialism’ gave his predictions about the future of civilization an aura of supreme confidence — like using Newton’s Law of Universal Gravitation to predict a projectile’s forward motion. And besides the impressive sophistication of Marx’s ‘scientific’ theory of economics, his writings also conveyed to Popper a deeply felt, sincere concern for the wretched conditions of the poor that Marx had witnessed during his life. Marx’s combination of erudition and humaneness attracted the brilliant and idealistic young Popper, who remained horrified by the violence of the war and by the suffering poor he saw filling up the streets around him in postwar Vienna.
Post-conversion, Popper regarded himself as a serious Communist, and on June 15, 1919, he participated in a large street demonstration of unarmed Communist students and workers. Popper, like most of the marchers, did not know that this demonstration was connected to the treacherous Hungarian-backed coup attempt. On the previous night, after an influential socialist politician whom the Communists had solicited to join their plot warned the authorities of the imminent insurrection, police had detained Communist leaders throughout Austria. The demonstrators learned of these arrests while still in the streets, and some of them marched on Vienna’s central police station, which held the detained Communist leaders; Popper marched among them. In reaction to the incoming wave of demonstrators, police fired into the crowd. They killed twelve and wounded eighty.
Popper was deeply shaken by this experience of violence, and he felt partially responsible for it. He had worked since his conversion to proselytize for Marxism, arguing to convince other young people that Communism was a scientifically proven theory, and that efforts to advance society toward the Communist utopia were key to its revolutionary political program. He now realized that by convincing other young people to become Communists, and by dogmatically confirming their views just as other Communist activists had confirmed his, he shouldered some of the responsibility for this tragic loss of innocent lives. In this realization, Popper’s persistent yearning for a more peaceful and equitable world would cause him to interrogate his Marxist beliefs.
After the killings, Popper expressed his dismay to some of the more experienced Communists and was surprised by their lack of concern. When Popper asked why they were so unfazed, they referenced Communist theory. Communism’s economic laws of history predicted growing conflict between the upper and lower socioeconomic classes — a crucial element of Communist theory known as ‘the intensification of the class struggle’. The theory prophesied that this inevitable intensification of class conflict would eventually lead the proletariat to initiate a revolution against the capitalists, which the proletariat would ultimately win, thus making way for the Communist utopia. In reviewing these elements of Communism with Popper, the more senior Communists explained to him that the June 15 killings had merely been an inevitable component of the intensification of the class struggle, and that in the final analysis, they would prove to be a moral good: they would help to accelerate society toward the goal of Communism.
Popper, who had converted to Communism in search of a more just and peaceful world, was troubled by this response. The killings were obviously a tragedy, and yet Popper’s comrades, his fellow concerned Communists, seemed not only callous but also content. Their attitudes puzzled Popper at first. But he came to understand that the Communists were in a sense possessed — possessed by a dogma that they failed to look upon critically. They took for granted the truth of Marx’s theory, and in doing so automatically dismissed any contrary political, historical, or moral theories that would make the June killings seem tragic. They simply knew the political, historical, and moral meanings of their comrades’ deaths, and in that understanding they were apparently unperturbed and even sanguine. It was then that Popper decided he would reexamine Marxism with a critical mindset, seeking to determine whether ‘scientific socialism’, with its historical predictions and moral implications, was in fact true. When he did, the theory appeared to him very differently than it had before: he saw within it many inadequacies, all of which he had previously missed.
This marked a turning point in Popper’s intellectual development. He was disturbed to realize that despite his formerly intense and heartfelt Communist convictions, he had been dangerously mistaken. More disturbing still, he realized that he had recklessly spread those mistakes — with tragic consequences — all while firmly believing that he knew an unshakeable scientific truth, and that he was acting righteously by helping to rescue humanity from its state of cruelty and injustice.
These realizations affected Popper for the rest of his intellectual life and profoundly influenced the development of critical rationalism. It was because of these realizations that Popper became a fallibilist. Reflecting on how blind he had previously been to his errors, he concluded that proving any idea to be error-free was impossible — that no matter how certain he or anybody else felt that an idea was true, nobody could ever prove definitively that the idea was free of any misconceptions, or that it came from an infallible authority; and that for this reason, no matter how vast humanity’s knowledge ever becomes, no theory should ever be considered sacred or above criticism. He came to recognize that certainty is unachievable: that we are fallible, and that therefore all of our knowledge is conjectural. But this conclusion did not cause Popper to despair, because he realized that just as error is inevitable, progress is possible: we can decide to apply criticism to our ideas, just as Popper had done to Marxism and would later do to positivism. In doing so, we may detect and correct some of the errors in our knowledge.
This last point was impressed upon Popper quite dramatically during that same period of 1919, when he learned of astronomical observations made by Arthur Eddington on an oceanic expedition just two weeks before the June 15 killings in Vienna. The Eddington crew had measured the celestial positions of several distant stars appearing around the sun during a full solar eclipse. The expedition aimed to test a surprising prediction derived from Albert Einstein’s theory of General Relativity. Contrary to the classical Newtonian picture of space and time as background entities within which physical events unfold, General Relativity proposed that space and time form a unified, pliable manifold: a dynamic physical object that warps in the presence of matter, with more matter causing more warping.
This theory of Einstein’s predicted that, when light from distant stars passed around the sun on its way toward our observation equipment here on Earth, it would bend as it passed through the warped spacetime around the sun, causing the positions of those distant stars in the sky, as viewed from the Earth, to appear shifted from their usual locations. Crucially, although both General Relativity and Newton’s Law of Universal Gravitation accounted equally well for many of the same phenomena, Newton’s theory — considered incontrovertible for centuries — could not predict the displacement of starlight predicted by General Relativity. For this simple reason, Eddington’s observations not only pitted each of the two theories against observational results, but also, and even more critically, pitted the two theories against each other.
When Einstein realized that his theory predicted phenomena contradictory to Newton’s laws, it was he who proposed the crucial observation to test his theory. The boldness of Einstein’s risky proposal to test his own theory against Newton’s impressed Popper immensely, but it was Einstein’s public statement that he would abandon his theory if it was contradicted by the proposed observation that impressed Popper the most. He was “struck by the tremendous difference” between Einstein’s critical attitude toward his own theory of General Relativity, and the Communists’ dogmatic, quasi-religious attitude toward Communism. Whereas the Communists searched everywhere for confirmations of their theory — even going so far as to contentedly accept the killings of young activists as fulfillments of Communist predictions — Einstein intrepidly searched for refutations of his theory. He criticized his own brainchild for the sole purpose of figuring out whether it was in fact true.
Eddington’s observations vindicated Einstein’s theory against Newton’s, and this too emphasized to Popper the pervasiveness and inevitability of human error. For Newton’s gravitational theory had been considered scientific gospel for centuries, yet it had been mistaken all along. It had taken Einstein to produce an astoundingly creative theory, and to propose a crucial test of his theory against Newton’s, for humanity to finally discover this mistake. It was Einstein’s critical attitude, his searching for errors — what we might call ‘the fallibilist mindset’ — that Popper would later apply in criticizing the positivist effort to empirically ’verify’ certain theories. He proposed instead his negative method of criticizing or falsifying our theories in order to detect in them any lurking errors. That way, we can try to correct them and thus grow our knowledge.
‘Falsifiability’ was never intended as a recipe for discovering truth, as positivism was; it simply recommended that we seek evidence contradicting the theories that we create in an attempt to identify errors in those theories, which we might then try to correct. And the paramount value of error and of its systematic elimination to the growth of knowledge, as Popper realized, is a straightforward consequence of our fallibility. This is the core insight of critical rationalism, and it is arguably Popper’s greatest contribution to philosophy. Philosophers for centuries had obsessively sought ways to prove that some of our knowledge must be true, by reference to ultimate foundations or infallible authorities, such as gods, reasons, senses, or persons such as Marx. But Popper, unlike those other philosophers, learned to reject authority. He grappled with ideas directly. And in doing so, he corrected some errors and deepened his knowledge about knowledge, and about how it grows. He showed that by criticizing our ideas, we might discover and eliminate some of our errors, and thereby learn more about the world. And he taught that, in pursuing knowledge, we should abandon once and for all the search for ultimate foundations or infallible authorities: for we cannot have them, but we do not need them.
Lucas Smalldon is a science writer based in Gettysburg, Pennsylvania. You can follow him on Twitter @reason_wit_me.
Further Reading/Viewing
Malachi Hacohen, Karl Popper: The Formative Years, 1902–1945 (Cambridge University Press, 2000); pages 77–86.
Karl Popper, Unended Quest (Routledge, 2002; first published in 1974); pages 30–39.
Karl Popper, The Open Society and its Enemies, Volume Two: Hegel and Marx (Routledge, 2003; first published by Routledge & Kegan Paul Ltd in 1945); pages 89–232.
“Interview Karl Popper Open Universiteit” (https://www.youtube.com/watch?v=7plyg2CebKE).
“Philosopher Karl Popper — A Portrait” (https://www.youtube.com/watch?v=_5J3cne5WEU&t=238s)
