Science at a Crossroads: How the Crisis of the 20th Century Gave Birth to the Principle of Falsifiability

1. Introduction

The principle of falsifiability is the idea that a theory is scientific only if there is some way it could be proven false. It is not just a philosophical criterion, but a key filter that separates science from ideology and pseudoscience. To understand the importance of this principle, we need to look back at the crisis that science faced at the start of the 20th century.

2. Historical Context: Why Science Needed a New Criterion

By the early 20th century, the old scientific picture of the world was beginning to show cracks. Newton’s mechanistic approach and positivistic faith in facts seemed solid. But a series of revolutionary discoveries destroyed this sense of stability:

• 1905 – Einstein publishes the Special Theory of Relativity: Space and time were revealed to be non-absolute.
• 1915 – Einstein’s General Theory of Relativity: Gravity is understood as the curvature of spacetime.
• 1925–1927 – Quantum Mechanics (Bohr, Heisenberg, Schrödinger): Particles behaved not as solid objects but as probabilistic waves.
• 1927 – Heisenberg’s Uncertainty Principle: The impossibility of simultaneously measuring the exact position and momentum of a particle undermined deterministic views of the world.

These discoveries shook the foundations of classical materialism and empirical positivism. It turned out that observation alone no longer provided a complete picture of reality—theory now played a key role in defining what counted as fact.

Positivism was built on the idea that knowledge is constructed only from observational facts. But it became clear that:

• Facts do not exist outside theory—their meaning is determined by the framework in which they are interpreted.
• Observational results depend on the chosen methods and theoretical apparatus (especially evident in quantum mechanics).
• Some scientific concepts cannot be directly tested: An electron is not something you can see or touch, but a theoretical construct.

Thus, the foundations of positivism were under threat. Science needed a new criterion—one that could distinguish genuine scientific knowledge from pseudoscience, when observation was no longer the absolute judge of truth.

Amid this intellectual uncertainty and methodological blurring, Karl Popper emerged—a philosopher who would formulate a new foundation for the scientific approach.

3. Karl Popper and the Birth of the Principle of Falsifiability

3.1 The Biography of Karl Popper

Karl Raimund Popper was born on July 28, 1902, in Vienna (then Austria-Hungary)—one of Europe’s intellectual capitals, where philosophy, psychology, and political theory were actively developing.

Vienna at that time was a crossroads of many ideas: German idealism, Marxism, psychoanalysis, and logical positivism, represented by the Vienna Circle, a group of philosophers striving to build a strict scientific philosophy based on empirical verification. Though Popper was not a formal member of the Circle, he interacted with its members and took part in shaping the intellectual environment of the time.

In his youth, Popper was fascinated by Marxism and psychoanalysis,s but soon noticed a common trait: these theories could interpret any event as confirmation of their correctness.

3.2 Marxism: Ideology Disguised as Science

Marxist theory was presented as a strict science of historical laws. It claimed that society inevitably develops through stages, leading to the triumph of the proletariat.

But in practice, the following happened:

• If a revolution began, the theory was right.
• If it didn’t, it meant the masses were still under “false consciousness.”
• If the bourgeoisie gained strength, this was explained as a temporary retreat before historical necessity.

3.3 Psychoanalysis: A Theory that Never Risks Being Wrong

Freud’s psychoanalysis—later Adler’s and Jung’s as well—offered a new picture of the psyche, explaining behavior through unconscious impulses and complexes.

Initially, psychoanalysis was seen as a scientific breakthrough, but upon closer inspection:

• Agreement from the patient confirmed the diagnosis.
• Disagreement also confirmed it—as a sign of “resistance.”

3.4 The General Problem: A Theory that Can’t Be Falsified Is Not Scientific

Both Marxism and psychoanalysis had one thing in common: their theories were immune to being disproven. Everything that happened was seen as confirmation, never as a challenge.

Similar logic appeared in other intellectual systems—from esoteric teachings to various schools of sociology and psychology. Such systems never made mistakes—meaning, in effect, they explained nothing.

This led to a demarcation problem in the philosophy of science: what criterion could separate genuine scientific knowledge from pseudoscience and other non-scientific thinking? Why did Einstein’s General Theory of Relativity look scientific, while Marxism and psychoanalysis did not? Old reference points had vanished, and new ones had not yet emerged.

Popper’s answer was the principle of falsifiability—an idea that later became central to his philosophy of science. He outlined this approach in his landmark book, “The Logic of Scientific Discovery” (1934), which became one of the cornerstones of 20th-century philosophy of science.

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3.5 Verification vs. Falsifiability

It was once believed that a scientific theory becomes more convincing as more observations confirm it — this approach is called empirical verification. For example, if over a hundred years we observe a thousand white swans, we might conclude: “All swans are white.” The more matching examples there are, the more stable the theory appears.

However, Karl Popper pointed out a fundamental limitation of this approach: no matter how many confirmations there are, there is always a possibility that an exception will be found. A thousand white swans strengthen our confidence, but a single black one destroys the rule.

And this is not just a metaphor. Until 1697, it was indeed believed in Europe that all swans were white — no others had ever been observed. Only after a Dutch expedition discovered black swans in Australia did it become clear: all previous observations were just particular cases, not a universal law.

A single clear counter-example is enough to bring down a system built on thousands of confirmations.

Therefore, instead of accumulating confirmations, Popper suggested using the criterion of falsifiability:

Core Tenets:

• A theory is scientific only if it allows for experimental refutation.
• The greater the risk of being falsified, the higher its scientific value.
• The principle of induction (generalizing from experience) is unreliable: no amount of confirming evidence can guarantee truth.

Thus, scientific theories must make predictions that, in principle, can be disproven by empirical evidence.

3.6 Testing Einstein’s General Theory of Relativity

The principle of falsifiability was vividly demonstrated in the test of Einstein’s general theory of relativity. Einstein predicted that the gravity of massive objects (like the Sun) would curve spacetime, causing the path of starlight passing nearby to bend.

In 1919, astronomer Arthur Eddington organized an expedition to observe a solar eclipse. During the eclipse, the Sun could be covered, allowing photographs of stars close to its edge. Comparing these stars’ visible positions to their usual places in the sky, Eddington recorded the deflection predicted by Einstein.

This experiment was risky, not just scientifically but socially. Newtonian mechanics was still seen as unquestionable, and Einstein, a relatively unknown German-speaking scientist in postwar Britain, was viewed with suspicion.

Eddington staked his reputation by backing a theory that contradicted both academic consensus and the political climate. If the prediction had failed, the theory would have been refuted—and it was precisely this testability that made it scientific.

4. The Reaction of Intellectual Currents

The principle of falsifiability provoked a stormy reaction in the scientific and philosophical community. Some accepted it as a revolutionary breakthrough, others as an excessive limitation, and still others as a threat to science itself. Let’s look at how different groups of thinkers responded.

4.1 The Positivists: “Popper Is Destroying Our Methodology!”

By the early 20th century, the philosophy of science was grounded in logical positivism (the Vienna Circle), where verification—confirming facts through experience—was the main criterion of scientific validity. Popper’s criterion of falsifiability was a shock to positivists: it undermined the idea of science as the cumulative confirmation of facts, and transformed scientific work into an endless search for possible disproofs. In their eyes, this looked like excessive skepticism and a threat to their entire methodological tradition.

4.2 Scientists: “What About Complex Theories?”

4.2.1 Classical Physics and Chemistry – Accepted

For scientists working in classical physics and chemistry, experiment had always played a central role. Thus, the idea of falsifiability was seen as a natural extension of scientific practice: a theory should be testable, and it should be possible to refute it. The case of general relativity was a perfect example: a prediction, a risk, an experiment, and the possibility of being wrong. Such cases strengthened faith in Popper’s criterion as a logical and practically useful tool for separating science from non-science.

4.2.2 Modern Physics and Quantum Mechanics: Challenging Falsifiability

But in the second half of the 20th century, the principle of falsifiability lost its unchallenged authority. A number of modern theories—such as string theory, the multiverse hypothesis, and broad concepts of dark matter and dark energy—look elegant, but manage to evade strict experimental tests. Virtually any observation can be interpreted within these hypotheses, making them nearly immune to refutation.

Quantum mechanics is a particularly interesting exception. Unlike the theories above, it displays extraordinary predictive power: its mathematical formalism yields clear, statistically precise results that are empirically confirmed. Lasers, transistors, atomic clocks—all these are not just technological achievements, but evidence of the theory’s empirical reliability.

However, even here, problems arise—not so much with the theory itself, but with its philosophical interpretations. For example, Everett’s many-worlds interpretation, though compatible with the mathematics of quantum mechanics, is itself unfalsifiable. Yet it is often accepted by the scientific community, or at least not rejected. Meanwhile, alternative interpretations (e.g., those where consciousness plays a role in wavefunction collapse) are dismissed almost automatically.

This creates a paradox: the core theory passes the falsifiability test, but the debate over its interpretation often escapes the scientific method and hinges on philosophical preference. Those interpretations that fit the materialist worldview are deemed “scientific,” even if they lack strict testability. Interpretations outside this framework are labeled “metaphysical.” Thus, a tool meant for honest demarcation easily becomes a way to defend the dominant worldview consensus.

4.2.3 When Science Becomes a Hobby Club

If Popper’s principle is a non-negotiable criterion of science, then any refusal to apply it to certain theories turns science into a subjective club, where some ideas are called “scientific” without testing, while others are dismissed outright.

This destroys the foundation of honest methodology. When we stop testing, falsifying, and discarding theories, science becomes a set of conventions, where the status of a theory is determined not by method, but by community consensus.

4.3 Philosophers of Science: “Popper Is Not a Panacea!”

If positivists criticized falsifiability on methodological grounds, among philosophers of science, it sparked a fundamental debate about its limits and applicability. Here, the issue was not “defects” in the principle, but competing philosophical perspectives on scientific knowledge and the process of scientific change.

4.3.1 Imre Lakatos: Trying to Outflank Falsification

Imre Lakatos proposed replacing falsifiability with the more flexible idea of “scientific research programs.” In his model, each program has:

• a “hard core”—principles that are not subject to revision,
• and a “protective belt”—hypotheses that can be adapted or changed when challenged.

For Popper, this was a compromise. The notion that any scientific theory contains “sacred” elements, preemptively shielded from criticism, renders the theory partly unfalsifiable. In effect, this is a return to dogma, just inside a “program.” If the hard core can’t be touched, the scientific process becomes political: the school that survives longest wins.

In Lakatos’s model, Popper’s criterion dissolves—and the risk of replacing science with belief sneaks back in through the back door.

4.3.2 Thomas Kuhn: Paradigms Instead of Disproof

Thomas Kuhn, in his famous book “The Structure of Scientific Revolutions”, showed that in the history of science, theories don’t change through strict refutation, but through paradigm shifts. In his view, the scientific community holds to a prevailing theoretical framework until enough “anomalies” pile up. Then comes a revolution—one paradigm replaces another.

Kuhn argued that old theories are not always falsified—they simply lose authority, while the new paradigm captures the minds. The process, then, looks less like rational testing and more like the social dynamics of belief.

For Popper, this was a dangerous turn: if acceptance of a theory depends on the mood of the scientific community, rather than its ability to be disproved, then the main filter against pseudoscience and dogma disappears. The criterion becomes collective—and thus vulnerable to fashion, ideology, and pressure.

4.3.3 Paul Feyerabend: “Science is Anarchy”

Paul Feyerabend went further than any of Popper’s critics. He rejected the very idea of a universal scientific method, claiming that no criteria, including falsifiability, capture the full complexity of science.

In his book “Against Method”, Feyerabend argued that scientific progress often occurred in spite of the rules, not because of them. His slogan became famous: “Anything goes.”

Feyerabend didn’t just critique Popper—he undermined the very foundation of science as a system with internal logic. In his view, science was a motley mix of traditions, beliefs, methods, and tricks, with no required standards of truth. This was not methodology but philosophical relativism.

4.4 Psychologists and Sociologists: “What About the Humanities?”

The principle of falsifiability is hard to apply to the humanities—history, psychology, sociology. Here, it is impossible to conduct repeatable experiments, isolate variables, or make unequivocal predictions. Cultural processes, human behavior, and collective consciousness do not obey strict physical laws.

Even in scientifically oriented psychology—from behaviorism to cognitive models like those popularized by Sapolsky— theories often rest on the interpretation of observations, not on testing clearly falsifiable hypotheses. Behavior is explained after the fact, not predicted in advance.

Thus, the humanities deal in interpretations, not falsifiable hypotheses. Their value lies in their power to make sense, not in experimental rigor. But for this reason, they are not science in Popper’s sense. This doesn’t diminish their importance, but it means they cannot be equated with the hard sciences.

Science begins where there is a risk of being disproven. Where this risk is absent, a different field of knowledge begins—valuable, but of another kind.

5. Is the Principle of Falsifiability Itself Falsifiable?

The principle of falsifiability is not a statement about the world, but a condition for the possibility of meaningful conversation about it.

This raises a subtle philosophical paradox: if falsifiability is the criterion of science, must this very criterion be falsifiable? After all, if it isn’t, doesn’t it fail its own test?

However, this logic contains a category error. The principle of falsifiability is not a scientific theory and makes no empirical predictions. It is a methodological standard, a philosophical stance, setting the boundaries of scientific discourse. Thus, demanding empirical verification from it makes as little sense as asking logic to prove its own consistency by its own means, which, as Gödel’s theorem shows, is impossible.

Popper’s principle acts as a metalanguage—a language for describing science, not a language for describing reality. Like other foundational assumptions of science (the principle of causality, the existence of an external world, the law of non-contradiction), it cannot be tested by experience, but without it, meaningful scientific discussion would be impossible.

Its metaphysical character is not a flaw but a necessity: it sets the minimum needed to distinguish science from non-science, and so is not required to meet its own criterion, just as a ruler is not required to measure itself.

6. Personal Experience

My first encounter with the principle of falsifiability wasn’t in books, but in conversation. I shared alternative views, hoping for curiosity or dialogue, but immediately got the same question:

“Can you suggest an experiment where your theory would fail?”

If I admitted that I hadn’t thought of such an experiment ahead of time—simply because it wasn’t obvious to me—the verdict followed at once:

“Then it’s not falsifiable. Then it’s not science. Then it’s nonsense.”

The discussion stopped there, with no attempt to understand or discuss the substance. The principle, intended as a tool for testing ideas, became an automatic barrier—a kind of off-switch for thought.

Gradually, I realized that falsifiability is often used not to search for truth, but to defend the boundaries of an accepted worldview. Especially when it comes to materialism.

So, I started to ask a counter-question:

“Can you imagine an experiment that would disprove materialism?”

The answer—silence. Because no such experiment exists.

This is precisely what Popper warned against: a theory that cannot be refuted is not science but metaphysics.

7. Materialism, Idealism, and the Trap of One-Sidedness

The principle of falsifiability was conceived as an impartial tool for distinguishing science from pseudoscience. But when applied honestly and symmetrically, it exposes the vulnerability of worldviews that claim universality, most notably, materialism and idealism.

Materialism builds its monopoly on the assertion: “everything is matter.” Its proponents—especially scientific realists and atheists—have long used Popper’s criterion to dismiss religious, metaphysical, and all alternative concepts as “unfalsifiable,” and thus “unscientific.” On the surface, this looks rigorous, but on closer inspection, it’s a logical trap.

The central axiom of materialism—“everything is matter”—is itself unfalsifiable. Any new phenomenon, no matter how unexpected, can be easily declared by a materialist as:

• a hypothetical or as-yet-undiscovered form of matter (e.g., dark matter, dark energy, unknown physical fields),
• a postulation of extra dimensions, spaces, or even entire universes that cannot be directly observed,
• an explanation of complex phenomena, such as consciousness or meaning, in terms of even more abstract physical models,
• or simply a deferral: “Science will explain it eventually.”

As a result, materialism becomes exactly the kind of closed system Popper called unfalsifiable

: a theory immune to any refutation, automatically degenerating into a form of metaphysics.

At the same time, idealism—“everything is consciousness”—is no better. Here, everything is explained by “features of consciousness,” any contradiction is declared an illusion, and any complexity is a game of imagination. Both materialism and idealism are mirror-image dogmatisms, where everything is neatly “put in its place” ahead of time.

7.2 Who Is Falsifiability Addressed To?

Popper made it clear: the principle of falsifiability is addressed not to “outsiders,” but precisely to those who claim universal explanation. If you say “everything is matter,” you must specify under what conditions you would abandon your theory. If you’re an idealist, same thing.

But neither group ever does. The materialist will always interpret any miracle as a new form of matter. The idealist as just another manifestation of consciousness.

That’s why one-sided doctrines are not science, but disguised dogma. They are not open to genuine refutation; they leave no room for the unexpected.

7.3 Honesty Versus Dogma

Honesty is not believing your system is flawless, but being willing to revise it if reality takes a different turn.

True scientific attitude is not about choosing the “right” system, but about always being ready to test and reconsider your foundations.
Falsifiability is a way to keep the door open to all knowledge and prevent truth from becoming trapped in the next dogma.

8. Conclusion

The principle of falsifiability was one of the greatest methodological shifts of the 20th century. It gave science a new criterion of maturity: not the quest for confirmation, but readiness for refutation. It was a call for intellectual honesty and scientific courage.

When we apply it honestly and symmetrically, it exposes not only pseudoscience but also hidden dogmas, including materialism. Anything that claims to be science but does not allow for the possibility of refutation is not knowledge but faith, just dressed in scientific language.

That is its true purpose: not to defend ready-made truth, but to protect the path to it.

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