Editing Falsifiability (section)

{{Short description|Property of a statement that can be logically contradicted}}
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[[File:Black and white swans on a lake.jpg|thumb|alt=Three swans swimming, two white and one black|The belief that "all swans are white" can be falsified by observing a single black swan.<ref name=Popperonstateofaffairs group="upper-alpha"/>]]

'''Falsifiability''' (or '''refutability''') is a [[deductive]] standard of evaluation of scientific theories and hypotheses, introduced by the [[Philosophy of science|philosopher of science]] [[Karl Popper]] in his book ''[[The Logic of Scientific Discovery]]'' (1934).{{refn|group=upper-alpha| name=faithfultranslationofLoSD}} A [[Scientific theory|theory]] or [[hypothesis]] is '''falsifiable''' if it can be logically contradicted by an [[empirical test]].

Popper emphasized the asymmetry created by the relation of a universal law with basic observation statements{{refn|group=upper-alpha|name="basicstatementsbreakthesymmetry"|The falsifiability criterion is formulated in terms of basic statements or observation statements without requiring that we know which ones of these observation statements correspond to actual facts. These basic statements break the symmetry, while being purely logical concepts.}} and contrasted falsifiability to the intuitively similar concept of [[Verifiability (science)|''verifiability'']] that was then current in [[logical positivism]]. He argued that the only way to verify a claim such as "All swans are white" would be if one could theoretically observe all swans,{{refn|group=upper-alpha|name="blackswanimpossible"}} which is not possible. On the other hand, the falsifiability requirement for an anomalous instance, such as the observation of a single black swan, is theoretically reasonable and sufficient to logically falsify the claim. 

Popper proposed falsifiability as the cornerstone solution to both the [[problem of induction]] and the [[demarcation problem|problem of demarcation]]. He insisted that, as a logical criterion, his falsifiability is distinct from the related concept "capacity to be proven wrong" discussed in [[#Falsificationism|Lakatos's falsificationism]].{{refn|group=upper-alpha|name=cleardistinctioncomplete}}{{refn|group=upper-alpha|name="twomeanings"}}{{refn|group="upper-alpha"|name="somecontradiction"}} Even being a logical criterion, its purpose is to make the theory [[predictive power|predictive]] and [[Testability|testable]], and thus useful in practice.

By contrast, the [[Duhem–Quine thesis]] says that definitive experimental falsifications are impossible{{sfn|Mayo|2018|loc=Sec. 2.3}} and that no scientific hypothesis is by itself capable of making predictions, because an [[Empirical method|empirical]] test of the hypothesis requires one or more background assumptions.{{sfn|Harding|1976|p=X}}

Popper's response is that falsifiability does not have the Duhem problem{{refn|group="upper-alpha"|name=falsifiabilityasfalsificationproblems}} because it is a logical criterion. Experimental research has the Duhem problem and other problems, such as the problem of induction,{{refn|group=upper-alpha|name=inductionisalogicalfallacy}} but, according to Popper, statistical tests, which are only possible when a theory is falsifiable, can still be useful within a [[Critical rationalism|critical discussion]].

As a key notion in the separation of science from [[non-science]] and [[pseudoscience]], falsifiability has featured prominently in many scientific controversies and applications, even being used as legal precedent. However, falsifiability is not a [[Necessity and sufficiency|sufficient]] condition for demarcating science as theories have to actually be tested in order to eliminate theories that are wrong. In scientific practice, this can cause theories to change from being falsified back to unfalsified, such as when the once-falsified [[Geocentric model|geocentric]] world view was restored as a viable reference frame within [[special relativity]]. There is ambiguity surrounding the status of theories that cannot currently be tested.<ref>{{Cite web |last=Hansson |first=Sven Ove |orig-date=2021 |editor-last=Zalta |editor-first=Edward N. |title=Science and Pseudo-Science |url=https://plato.stanford.edu/entries/pseudo-science/ |website=The Stanford Encyclopedia of Philosophy (Fall 2021 Edition)}}</ref>