Falsifiability
Also known as: Refutability
Falsifiability is the property of a claim being capable, in principle, of being shown false by some observation or experiment.
The criterion was made central to philosophy of science by Karl Popper in The Logic of Scientific Discovery (1934). Popper was responding to a problem in early 20th-century philosophy: theories like astrology, Marxist historiography, and Freudian psychoanalysis seemed to explain everything that happened, but never made specific predictions that could fail. A theory that cannot fail, Popper argued, is not a scientific theory — it is a story compatible with any data.
A claim is falsifiable when there is some conceivable evidence that, if observed, would count against it. "All swans are white" is falsifiable: a single black swan refutes it. "There is an invisible, intangible, undetectable dragon in my garage" — Carl Sagan's example — is not falsifiable, because every property that would let you detect the dragon has been removed by stipulation. Popper's criterion is not a test for whether a claim is true or even useful; it is a test for whether it counts as a scientific hypothesis at all.
Falsifiability shows up constantly in religious epistemology. Many religious claims ("God answers prayer through whatever happens, including silence"; "the resurrection is a spiritual reality not subject to historical disproof") are unfalsifiable in Popper's sense. Critics argue this places them outside the domain of science; defenders argue the criterion is too narrow and that historical, ethical, and theological claims are evaluated by other standards. Either way, asking what would have to be true to refute a claim is one of the most useful tools in philosophy of religion.
Falsifiability has been refined heavily since Popper. Pierre Duhem and W. V. O. Quine pointed out that no scientific claim can be tested in isolation — a failed prediction can always be saved by adjusting auxiliary assumptions. Imre Lakatos and Thomas Kuhn argued that mature sciences protect their core commitments through exactly this kind of move, and that this is rational rather than disreputable. The criterion remains a useful first-pass filter even though it is not, by itself, a complete philosophy of science.
Sources
- Stanford Encyclopedia of Philosophy — Karl Popper
- Karl Popper, The Logic of Scientific Discovery (1934)
Related terms
- Methodological naturalismMethodological naturalism is the working principle that scientific inquiry should look only for natural causes — not because the supernatural is ruled out as impossible, but because invoking it would prevent the inquiry from going anywhere.
- Russell's teapotRussell's teapot is Bertrand Russell's analogy that the burden of proof for an unfalsifiable claim lies on the person making it, not on the person doubting it.
- Sagan standardThe Sagan standard is the principle that the strength of evidence required to accept a claim should scale with how surprising the claim would be if true.