An Introduction to the Philosophy of Karl Popper

Karl Popper SelectionsKarl Popper, a 20th century Austrian-British philosopher and professor, has the distinction of being lesser-known among the general population (compared to thinkers of lower caliber) while simultaneously being recognized by many philosophers and scientists as the greatest philosopher of the 20th century.

Sir Peter Medawar, winner of the Nobel Prize for Medicine, said, “I think Popper is incomparably the greatest philosopher of science that has ever been.” Sir Hermann Bondi, the mathematician and astronomer, stated, “There is no more to science than its method, and there is no more to its method than Popper has said.” Popper’s influence is also just as strongly felt today, as the physicist David Deutsch recently wrote a book titled The Beginning of Infinity: Explanations That Transform the World, which is essentially an extension of Popper’s ideas.

Popper’s ideas are revolutionary and eminently practical, and extend beyond the realm of science into the nature of knowledge and the structuring of society. This post will attempt to provide a brief summary of Popper’s ideas that will serve as a starting point for further reading for those interested in becoming better acquainted with perhaps the greatest philosopher of the 20th century.

In tackling Popper’s philosophy, the best place to start is with the problem of induction.

The problem of induction

To understand Popper’s philosophy, you first have to understand the problem of induction. As with much else, it was David Hume who first articulated the problem that all subsequent philosophers of science had to deal with. Hume certainly had the habit of introducing unresolved problems that would set the agenda for all subsequent philosophy.

The problem of induction is simple. Using the example that Popper used, say that, based on your experience, you’ve only ever encountered white swans, and you know of no one else who’s seen differently. You would be tempted to move from the particular instances of seeing white swans to the general statement that “all swans are white,” via the process of induction (deriving general truths from particular instances). This is of course how all scientific laws are formulated: based on a set of particular observations, universal laws are established.

What Hume pointed out was the logical impossibility of proving universal, general statements (like all swans are white) by referencing specific instances (seeing white swans). No matter how many white swans you’ve encountered, it’s always possible that you will encounter a black swan in the future, and it would only require one instance of seeing a black swan to disprove the assertion that “all swans are white.” The statement “all swans are white” can’t be proven after one observation any more than it can be proven after two observations, three, one hundred, or one million, in the context of an infinite amount of possible future observations.

Reflecting on the problem, you’ll realize that all scientific knowledge is like the statement “all swans are white.” That means that no number of observations can ever logically prove a scientific law because 1) there is no logical reason to suppose the future will follow the past, and 2) there is always the possibility that a contradictory observation will be found.

Rescuing science from the problem of induction

The problem of induction is no small problem, as it calls into question the very logical foundations of the entire scientific enterprise. This was an especially concerning problem before Popper, as science was largely seen as the pursuit of establishing certain truth about the world, particularly after Isaac Newton and the fact that Newtonian laws worked so well.

The reason so many practicing scientists hold Popper in such high regard is that Popper provided an adequate solution to the problem of induction, putting science back on solid footing. This solution, among other ideas, is captured in his masterpiece in the philosophy of science titled The Logic of Scientific Discovery.

Popper solved the problem by first noticing an asymmetry between verification and falsification. Using the swan example, no number of observations could verify conclusively the statement “all swans are white,” as the problem of induction shows.

But, one single observation of a black swan could falsify the statement “all swans are white.” So, while general scientific statements can never be verified conclusively, they can be tested by systematic attempts to refute them.

This has several implications:

  1. We now have an appropriate criteria for the line of demarcation between science and pseudoscience. Scientific claims are specific enough to be tested and falsified, whereas pseudoscientific claims are either too vague or else immune from testing and refutation.
  2. All scientific knowledge is provisional and subject to refutation and refinement. For example, Einstein did not replace Newtonian physics, but he did refine it to account for additional phenomena. All scientific knowledge can be described as our best (but not final) explanations according to the evidence we have. (Einstein’s theory will likely be replaced or refined in the future.)
  3. Any claim is strengthened—not necessarily by confirming evidence or experiments—but by the survival of attempts to refute it.
  4. All knowledge grows by this process—the best theories are the ones that survive the attempts at refutation or are otherwise refined to include additional phenomena, with the understanding that all of our knowledge is provisional, and permanently so.

This practical solution adequately resolves the problem of induction, aligns with the history of the evolution of scientific knowledge, and provides a compass for practicing scientists to orient their theories towards a more precise formulation that can be tested with greater degrees of precision.

To elaborate on this point, here’s an example used by the philosopher Bryan Magee. Take the scientific law which states that water boils at 100 degrees Celsius. Abiding by the scientific principle of verificationism, you would test this general law by increasing the temperature of water to 100 degrees Celsius on successive occasions and noting whether or not it boils. Of course, with the problem of induction, you could never prove the law, and your knowledge would remain stagnant if this is the only experiment you ever ran.

Using the principle of falsification, however, could lead to expanded knowledge. Instead of simply increasing the temperature of the water, you would attempt to refute the law in any way possible. In this case, you may heat the water to 100 degrees Celsius at higher altitudes or in closed vessels, in which case you would note that the boiling point was not 100 degrees Celsius.

In this case, in your attempt to refute the general law, you’ve refined your knowledge of the underlying physics and your knowledge of the phenomena has advanced. This process of proposing a hypothesis and attempting to refute it is the process of “conjecture and refutation” that Popper claimed was responsible for the evolution of all knowledge. We can’t ever prove our theory to be true, but we can show that it is preferable to all earlier theories. In other words, science is about finding the best current explanation. It is also about making sure our theories are ever more specific, are making increasingly detailed predictions, and are subject to increasingly detailed testing.

The other implication of this, as pointed out by David Deutsch, is that this process never concludes. As we establish new knowledge, we encounter new problems, which require further refinements, which spawns new problems, and so on, indefinitely. This process is the basis for the title of Deutsch’s book, The Beginning of Infinity. Here’s Popper on the topic:

“The game of science is, in principle, without end. He who decides one day that scientific statements do not call for any further test, and that they can be regarded as finally verified, retires from the game.”

This also provides a workable criteria for the line of demarcation between science and pseudoscience. When confronted with a claim, such as, for example, that we are all part of a single collective consciousness of the universe, we can confidently dismiss the claim as not only wrong, but not even worthy of consideration, as it is not specific enough to test or refute. In addition to not being able to prove this claim—as with all scientific claims—we can’t even show that it is wrong, and something that can never be proven wrong is also probably not right.

The larger point is that, when confronted with a theory that is too vague to be refuted, you should have less confidence in its truth rather than more. This mindset I believe would eradicate a lot of problematic beliefs.

From science to society

In addition to writing about science and the advancement of knowledge through a process of error correction, Popper also wrote about politics, democracy, and the open society. His most important work in this area is The Open Society and Its Enemies, and as we’ll see, Popper’s political philosophy is entirely consistent with his philosophy of science.

If you remember, Popper noticed an asymmetry between verification and falsification in terms of scientific knowledge, which led to his prioritization of the principle of falsification. Similarly, in terms of society, Popper noticed an asymmetry between policies that made people happier or better off and policies that reduced unnecessary suffering. The question of what makes people happy or better off is difficult to impossible to answer, but the question of how to reduce suffering is a much easier one to address.

Therefore, the guiding principle behind The Open Society and Its Enemies is the minimization of avoidable suffering. The idea is not to build a Utopia or create a perfect society (as with Communism), but to reduce suffering, promote liberty, and remove the barriers toward the pursuit of individual happiness. This of course would require active state intervention in the provision of healthcare, education, and social security programs, but as Popper wrote:

“The attempt to make heaven on earth invariably produces hell…It is our duty to help those who need help; but it cannot be our duty to make others happy, since this does not depend on us, and since it would only too often mean intruding on the privacy of those towards whom we have such amiable intentions.”

Of course, it’s one thing to say “reduce suffering” and “promote liberty” and another to actually devise policies that do so. Popper recognized that, first of all, one person’s liberty is another person’s subjugation, and that the absolute maximization of liberty is the best way to destroy it. Popper wrote:

“The so-called paradox of freedom is the argument that freedom in the sense of absence of any constraining control must lead to very great restraint, since it makes the bully free to enslave the meek.”

In the absence of any laws or constraints, a stronger group will always rise to subjugate a weaker group when liberty is allowed to operate completely unabated. At the same time, too many or too restrictive of laws will reduce liberty across the board. In between these extremes of anarchy and totalitarianism is the middle position of responsible reform that improves on the policies that came before while striving for the optimal amount of liberty.

So who has this knowledge of the best policies to implement to maintain this balance? The answer is that no single authority or person does or can have this knowledge. For democracy to work, an open society must be maintained where all ideas and policies can be debated, tested, and revised, to account for the unintended consequences inherent in any policy implementation. In this way, political and moral knowledge can grow in the same way as scientific knowledge, without the monopolization of one person or single group calling the shots.

Popper did recognize the problem of majorities, in particular the problem of a majority voting to abandon the institutions supporting an open society. In this Popper maintained that an open society need not be entirely tolerant, and is justified in using force against those groups that seek to replace the democratic institutions and processes themselves. As Popper said:

“Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them….We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.”

In the absence of such existential threats to the institutions of an open society itself, democracy functions best by ensuring the nonviolent transition of power and by removing ineffective leaders. The vital question of political philosophy, for Popper, is not “who should rule,” but rather “how can we minimize misrule.” This minimization is accomplished by the separation of powers, checks and balances, and recurring popular elections, which do better at removing ineffective leaders than electing good ones.

There is much more to Popper’s theory of social democracy and to his critique of the enemies of an open society, but I’ll save that for those interested in pursuing the recommended reading below.

Principles for reasoning

Popper’s output was vast and his teachings much more detailed than I can provide, so I’ve added some books for further reading below. However, I can leave you with a few overriding principles to keep in mind as you explore his philosophy further, or if you simply want to abide by the spirit of his overall philosophy:

  1. Reject your notions of certainty and absolute truth. It is logically impossible to conclusively prove any theory via induction.
  2. Embrace instead the idea that all knowledge represents the best current explanations, based on available evidence, and that this knowledge is provisional and subject to refutation or refinement.
  3. Remain skeptical of any idea that is immune from falsification. Prefer ideas that are stated in detail, make specific predictions, and can be subjected to testing and refutation.
  4. Recognize that all public policies are subject to unintended consequences, and demand that politicians test and refine their own ideas and policies, rather than stubbornly pursue them despite evidence that they aren’t working.
  5. Understand that all knowledge is the culmination of the continual process of hypothesis generation, testing, and refinement, and that the fate of most ideas is replacement by something better.

And finally, keep in mind Popper’s own definition of a rationalist:

“A rationalist, as I use the word, is a man who attempts to reach decisions by argument and perhaps, in certain cases, by compromise, rather than by violence. He is a man who would rather be unsuccessful in convincing another man by argument than successful in crushing him by force, by intimidation and threats, or even by persuasive propaganda.”

Further Reading

Philosophy and the Real World: An Introduction to Karl Popper by Bryan Magee

At 132 pages, this is the best short introduction to the philosophy of Karl Popper I’ve come across.

The Beginning of Infinity: Explanations That Transform the World by David Deutsch

A modern continuation of the work of Karl Popper, arguing that “explanations have a fundamental place in the universe—and that improving them is the basic regulating principle of all successful human endeavor.” This book takes the reader through every field of science and through the history of human civilization and political and moral concerns.

Popper Selections

Thirty selections taken from Popper’s writings that demonstrate the originality and profundity of his ideas, by a leading scholar of Popper’s work.

And here are Karl Popper’s four most important books:

The Logic of Scientific Discovery by Karl Popper

The primary source of Popper’s philosophy of science, including falsificationism and the evolution of knowledge.

The Open Society and Its Enemies by Karl Popper

Popper’s defense of liberal democracy and an attack on the intellectual foundations and origins of totalitarianism.

Conjectures and Refutations: The Growth of Scientific Knowledge by Karl Popper

Explains how our knowledge, aims, and standards grow by perpetual process of trial and error.

The Poverty of Historicism by Karl Popper

A critique of the notion of fixed or deterministic laws guiding history down a predetermined course.



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