Unfalsifiability

What it looks like

The supporting evidence and the disconfirming evidence turn out to be the same evidence. Officials deny it, which is what officials would do. No documents exist, which shows how thorough they were. The investigation cleared them, which tells you about the investigation.

What has happened is that the claim has quietly stopped being about the world. Nothing you could go and look at bears on it any more.

Why it works

The structural signature was identified in a 2012 study which found that belief in one account of an event correlated positively with belief in a mutually exclusive account of the same event.1 Controlling for belief that authorities were covering something up reduced that association to nothing. Individual theories were not being held as competing explanations. They were being held as instances of a higher-order belief that officials deceive — and that higher-order belief is what makes the structure self-sealing, because an official denial is precisely what it predicts.

That finding was contested, and the current state is more careful than the original. A 2026 reanalysis using a Bayesian coherence measure across 8,590 participants from eight studies, plus a preregistered study of 469, finds a robust association between conspiracist belief and incoherence, strongest among the strongest believers.2 Cite the 2012 study as the origin and the 2026 one as where the question now stands.

The philosophy needs stating accurately rather than as a slogan. Popper’s falsifiability criterion was a way of separating science from non-science — not a test of meaning, and not a test of truth.3 It comes with serious caveats: no hypothesis is ever tested alone, so a failed prediction does not tell you which assumption failed; real research programmes survive anomalies rather than dying on one counter-example; and Popper himself accepted that a single conflicting observation is never sufficient, given measurement error.

The sharpest caveat comes from philosophers of conspiracy theory. Something close to unfalsifiability is a consequence of the claim, not a trick: if the conspirators are competent and secretive, then genuine absence of evidence really is weak evidence.4 Which means unfalsifiability is a warning about a claim’s epistemic status, and not a refutation of its content. A media literacy site that overstates this is committing the error it is teaching against.

Documented cases

A claim tested, and the test absorbed

In 2016 researchers surveyed 77 atmospheric chemists and geochemists about whether there was evidence of a secret large-scale atmospheric spraying programme. Seventy-six reported finding none.5 On publication one of the authors, Steven Davis, said plainly: "We don’t imagine that we’re going to sway the beliefs of hardcore adherents."

He was right, and the reason is the structure. A survey of experts is exactly the thing the belief predicts will come back negative.

The mechanism, filmed

The 2018 documentary Behind the Curve records flat-earth researchers running their own experiments. One bought a ring-laser gyroscope, which registered a drift of fifteen degrees per hour — precisely what a rotating Earth produces. On camera he says: "Now, obviously we were taken aback by that. Wow, that’s kind of a problem." He then set out to disprove that the instrument was registering the Earth’s motion. A second experiment, using light through aligned holes, also came out against a flat Earth; the response was "Interesting. That’s interesting."6

This is the tactic caught in the act, by its own adherents, on their own equipment. The disconfirming result did not function as a verdict. It became a problem to be neutralised.

What to do about it

• Ask the person making the claim what would change their mind. Get a specific answer before discussing any evidence, so it cannot be adjusted afterwards.
• Distinguish the two failure modes. Either no disconfirming observation exists even in principle, or one exists and was explained away after it arrived. The second is what the gyroscope case shows, and it is the more common.
• Ask the sizing question. How many people would have to keep this secret, for how long, with what incentive to defect? That is a claim about the world, and it can be checked.
• Notice when a denial is being counted as confirmation. If both a denial and an admission would support the theory, no answer was ever going to matter.
• Do not overclaim. "This is unfalsifiable, therefore false" is itself a fallacy. The accurate statement is narrower and stronger: this is built so that evidence cannot bear on it, so evidence is not why anyone believes it.

Sources

Every figure on this page comes from one of these. Each entry names the publisher, the date and the sample size, so you can check it rather than take our word for it.

1. Wood, M. J., Douglas, K. M. & Sutton, R. M. — "Dead and alive: Beliefs in contradictory conspiracy theories"Social Psychological and Personality Science 3(6):767–773 · 2012 · n=137 and n=102https://kar.kent.ac.uk/28566/1/Wood%20et%20al%202012%20SPPS.pdf
2. Miani, A., Cruz, N. & Lewandowsky, S. — "Still very much dead and alive: Incoherence in conspiracism as a departure from Bayesian rationality"PNAS Nexus 5(8):pgag250 · 2026 · 8,590 participants reanalysed, plus preregistered n=469https://doi.org/10.1093/pnasnexus/pgag250
3. Thornton, S. — "Karl Popper"Stanford Encyclopedia of Philosophy · revised 31 July 2026https://plato.stanford.edu/entries/popper/
4. Pauly, M. — "Conspiracy Theories"Internet Encyclopedia of Philosophy · a living page with no publication date shown · checked 2026-09-02https://iep.utm.edu/conspiracy-theories/
5. Shearer, C., West, M., Caldeira, K. & Davis, S. J. — "Quantifying expert consensus against the existence of a secret, large-scale atmospheric spraying program"Environmental Research Letters 11(8):084011 · 2016 · n=77 expertshttps://doi.org/10.1088/1748-9326/11/8/084011
6. Whalen, A. — "Behind the Curve ending: flat earthers disprove themselves with their own experiments"Newsweek · 25 February 2019https://www.newsweek.com/behind-curve-netflix-ending-light-experiment-mark-sargent-documentary-movie-1343362
7. Shahab, L., McGowan, J. A., Waller, J. & Smith, S. G. — "Prevalence of beliefs about actual and mythical causes of cancer"European Journal of Cancer · 2018 · n=1,330 adults in Englandhttps://www.eurekalert.org/pub_releases/2018-04/cru-bif042518.php