If someone claims that “there exists at least one mermaid in the world” or “there exists a being in the world that turns copper into gold by touch,” what position would science take?
Kabul 24: In his book The Logic of Scientific Discovery, Popper draws a sharp distinction between two types of statements: those that speak as “laws” with a claim of universal scope about all possible cases, and those that merely report the “existence of at least one instance.”These two types of statements differ in form, role, and—most importantly—their relationship to empirical testing and the possibility of falsification.
For this reason, Popper argues that if we want to understand how science progresses and how it separates itself from pseudoscience, we must precisely distinguish these two kinds of statements and determine the place of each in the scientific method.
First, the strictly universal statement is what science typically calls a “law,” “principle,” or “general proposition.” Such a statement claims that in all times and places, and for all cases falling under a certain condition or class, a specific relationship holds.
It does not speak only about a limited group of observed cases; rather, its scope is potentially infinite—it encompasses cases we have seen today, cases that may occur tomorrow, and cases that are not yet accessible to observation.
Examples include: “All individuals infected with HIV will develop AIDS within ten years,” or “All metals expand when heated,” or “All workers go on strike in protest after an increase in working hours.”The key feature of these statements is that they “say a lot” and, precisely for that reason, take risks.
If even one valid counterexample is found that contradicts what the law claims, the law is damaged.This is the point on which Popper relies: the epistemic value of a scientific law lies in exposing itself to the possibility of failure.
That is, the world can reject it with a single unfavorable observation.For instance, if a person is found who does not develop AIDS ten years after HIV infection, or a metal is discovered that does not expand when heated, or a worker does not strike after increased hours, the aforementioned universal statements are falsified.
Thus, the strictly universal statement, from the perspective of scientific method, is a tool for prediction, explanation, and—most importantly—for subjecting itself to the rigorous judgment of experience.
Second, the strictly existential statement is one that, instead of laying down universal laws, simply says “such a thing exists” or “at least one case of this type has occurred.”
Examples: “There exists at least one mermaid in the world” or “There exists a flying mountain in the world.”An existential statement does not claim that it is always and everywhere the case. It only announces that at least once, or at least somewhere, such a case exists.
According to Popper, the strictly existential statement by itself is not a central pillar of science, because it lacks the kind of risk present in universal laws.
That is, it “says so little” that the world cannot easily reject it with a clear and decisive blow.The main reason for this difference lies in the issue of falsifiability.
The strictly universal statement is falsifiable because a single valid counterexample suffices to call it into question.
That one case is logically sufficient to undermine the universal claim. But the strictly existential statement is not like this.If someone says “such a thing exists,” to refute it we must show that “nowhere and at no time” does such a thing occur.
And this is practically impossible, because no researcher or scientific institution can search the entire world and all times to prove absolute non-existence.
Therefore, the existential statement is, on the one hand, “verifiable” (if an instance is demonstrated, it is accepted), but on the other hand, it is not “falsifiable” (because its non-existence cannot be proven with limited observations).
This is where Popper speaks of a fundamental asymmetry: a universal law can be refuted by a single observation but cannot be finally proven by infinitely many observations.In contrast, an existential statement can be confirmed by a single observation but cannot be definitively refuted by any finite set of observations.
Popperian science is built precisely on this asymmetry and therefore regards “the falsifiability of universals” as the core of scientific method, not the accumulation of evidence for existential claims.
For this reason, Popper concludes that strictly existential statements alone are not scientific. Not in the sense that they are meaningless or entirely worthless, but in the sense that the central criterion of science—the possibility of being rejected by experience—is not directly available in them.
When expressed in isolation and without connection to a theoretical framework, such statements resemble claims that can evade rigorous testing indefinitely.
Whenever we ask the claimant to demonstrate absolute non-existence or provide a clear way to falsify it, they can say “maybe it’s somewhere else” or “maybe we haven’t found it yet.”Nevertheless, Popper explains that in actual sciences, we often see apparently existential statements being accepted:
for example, “a new element exists,” “a new particle exists,” “an unknown mechanism exists,” or “a therapeutic effect has been observed in a certain group.”The secret of this acceptance is that in science, these statements are rarely isolated and independent; they are quickly placed within a network of theory and law-like structure.
That is, they come with specific predictions: if such a thing or mechanism really exists, it must produce certain effects under defined conditions, it must have certain signs, it must be reproducible in independent tests, and it must compete with rival laws or theories.
In this case, the existential statement effectively becomes a “piece” of a broader falsifiable system.
And because that overall system can be exposed to falsification, the existential statement indirectly enters the scientific arena. Thus, an existential statement becomes scientific when it contributes to generating testable consequences and clear criteria for refutation, not when it is merely an unsupported announcement of existence.
Ultimately, science and scientific observation can never prove a strictly existential statement in the sense of “final proof.” Science can provide evidence, show instances, examine reproducibility, and make intersubjective judgments about the reliability of observations.
But an existential claim is not the kind that can be “definitively proven” like a mathematical theorem.
For this reason, the burden of providing evidence and instances—that is, what is practically called “empirical confirmation”—falls on the person making the existential claim.If they provide no instance, science has no direct tool to prove absolute non-existence.
And if they do provide an instance, science accepts it only to the extent that the presented observation is reviewable, reproducible, and consistent with critical scrutiny.
Therefore, in Popper’s framework, science is not a device for proving existences, but a device for rigorously testing claims. What advances science is not saying “it exists,” but having the courage to say “if this is the case, these consequences must follow, and I am willing for my claim to collapse if a contrary observation appears.”I wrote this discussion because yesterday there was a debate over an existential statement.
However, I cannot write anything about that particular existential statement or its logical examination.
Jamshid Mehrpour — Kabul
