Idea
Falsifiability
Popper argued you can never prove a general theory true, since no number of confirming cases rules out a future exception. You can prove one false with a single solid counterexample. So the mark of a scientific theory is not how much evidence supports it, but whether it makes risky predictions that could fail. A theory that can absorb any outcome, contradiction included, explains nothing. Good science courts its own refutation.
Karl Popper developed falsifiability in the 1930s as a “demarcation criterion,” a line between science and non-science, most fully in The Logic of Scientific Discovery. He was reacting to theories he felt could explain any observation whatsoever, contrasting them with Einstein's relativity, which made a specific, checkable, and potentially fatal prediction.
You cannot prove a theory true by piling up confirmations, but one clean contradiction can prove it false.
Trust the model that dares to be wrong and isn't, not the one that can never be wrong.
Where it breaks down
Strict falsifiability is too clean for real science: theories are rarely abandoned on a single failed test, because any experiment involves auxiliary assumptions that might be blamed instead. Later thinkers like Kuhn and Lakatos showed that theories are held, patched, and replaced in messier, more social ways. Falsifiability is an ideal that clarifies, not a rulebook scientists literally follow.
The everyday version is useful anywhere: ask of any confident claim, “what would change your mind?” If the honest answer is “nothing,” you are not looking at a theory. You are looking at a faith.
How it connects
Karl Popper's answer to what separates science from everything that merely sounds scientific: a real theory sticks its neck out.
This idea appeared in A model that survives attempts to kill it, the Involves connection for August 16, 2026, which asked: What makes an idea scientific rather than just convincing?
Check yourself
According to Popper, what makes a theory scientific?
It forbids some observations: there are results that would prove it wrong.. Right. A scientific theory takes risks: it rules things out, so reality can contradict it. What explains everything predicts nothing.
What the sources establish
Popper proposed falsifiability, the capacity to be contradicted by observation, as the criterion distinguishing scientific theories from non-scientific ones.
Sources
Karl Popper (Encyclopaedia Britannica, 2024), Sections on falsifiability and the demarcation of science