View source for Common knowledge

{{Short description|Statement widely known to be true}}
{{Distinguish|Common sense|General knowledge}}
{{Other uses}}
{{more footnotes|date=August 2019}}
'''Common knowledge''' is [[knowledge]] that is publicly known by everyone or nearly everyone, usually with reference to the [[community]] in which the knowledge is referenced.<ref name=":2">{{Cite journal|last1=Halpern|first1=Joseph Y.|last2=Moses|first2=Yoram|date=1990-07-01|title=Knowledge and common knowledge in a distributed environment|url=https://doi.org/10.1145/79147.79161|journal=Journal of the ACM|volume=37|issue=3|pages=549–587|doi=10.1145/79147.79161|issn=0004-5411|arxiv=cs/0006009|s2cid=52151232 }}</ref>  Common knowledge can be about a broad range of subjects, such as science, [[literature]], history, or [[entertainment]].<ref name=":2" /> Since individuals often have different knowledge bases, common knowledge can vary and it may sometimes take large-scale studies to know for certain what is common knowledge amongst large groups of people.<ref name=":1">{{Cite journal|last=Geanakoplos|first=John|date=1992-11-01|title=Common Knowledge|url=https://pubs.aeaweb.org/doi/10.1257/jep.6.4.53|journal=Journal of Economic Perspectives|language=en|volume=6|issue=4|pages=53–82|doi=10.1257/jep.6.4.53|issn=0895-3309|url-access=subscription}}</ref> Often, common knowledge does not need to be [[citation|cited.]]<ref name=":0">{{Cite journal|last=Shi|first=Ling|date=2011|title=Common Knowledge, Learning, and Citation Practices in University Writing|url=https://www.jstor.org/stable/40997768|journal=Research in the Teaching of English|volume=45|issue=3|pages=308–334|doi=10.58680/rte201113468 |jstor=40997768 |s2cid=140445118 |issn=0034-527X|url-access=subscription}}</ref> Common knowledge is distinct from [[general knowledge]].

In broader terms, common knowledge is used to refer to information that an agent{{what|reason=What kind of agent?|date=November 2024}} would accept as valid, such as information that multiple users may know.<ref name=":1" /> Assigning something the label of common knowledge requires certain considerations about the involved community, group, society and/or individuals, the time period, and the location.<ref name=":2" />

== Variation ==
Defining something as common knowledge can differ based on circumstances because there are variations in what is considered common knowledge amongst different groups.<ref name=":0" /> The variation can come from the time period, culture, population, class, age, demographic, and other circumstances. For example, the [[Fifth Amendment to the United States Constitution]] might be considered common knowledge among people residing in the United States of a certain age, but cannot be considered common knowledge when considering the general population of other countries.

=== Instability ===
Common knowledge is not always stable, and can shift over time to create new common knowledge. Knowledge that was once considered common knowledge amongst a group, society, or community might later become known as false. For example, for centuries it was common knowledge in Europe that the Sun revolved around the Earth, but after years of arguments, it is now common knowledge that the Earth revolves around the Sun.<ref>{{Cite journal|last1=Theodossiou|first1=E.|last2=Danezis|first2=E.|last3=Manimanis|first3=V.N.|last4=Kalyva|first4=E.M.|date=2002|title=From Pythagoreans to Kepler: the dispute between the geocentric and the heliocentric systems|url=https://adsabs.harvard.edu/pdf/2002JAHH....5...89T|journal=Journal of Astronomical History and Heritage|volume=5|pages=89–98|doi=10.3724/SP.J.1440-2807.2002.01.07 |s2cid=256562413 |via=University of Athens}}</ref>{{clarify|reason=Should this section refer to a common belief that the Sun revolved around the Earth?|date=November 2024}}

=== Large scale ===
On a larger global scale, it is not possible to define almost any knowledge as common knowledge because it is difficult to know how far a fact has spread in global populations without large-scale global population studies.<ref name=":1" /> For example, the current president of the United States might be considered common knowledge in much of the world because of the power associated with that position, but one cannot assume that there is global recognition of this fact as common knowledge without further research into the knowledge of global populations.

=== Common belief ===
It is hard to distinguish fact from belief and thus there are scholars{{who|date=December 2024}} who prefer to separate common knowledge from common belief. Common belief is something that is more easily defined because the requirement is only that a majority of people within a specific group, community, or society believe something to be true whereas common knowledge must meet this requirement and also prove that the belief is a fact.

=== Examples ===
* "[[Paris]] is the capital of [[France]]." Many capital cities of developed countries are considered common knowledge by most people, but one cannot claim this as common knowledge for global populations without further research. 
* "It is dangerous to mix [[ammonia]] and [[bleach]]." Though both common household chemicals, accidents involving the mixing of ammonia and bleach are rare, because the potentially lethal danger in their chemical reaction is a widely circulated cautionary tale amongst some American families and so could possibly be considered common knowledge in those populations, but may not extend to wider populations.

== Other settings ==
Many techniques have been developed in response to the question of distinguishing truth from fact in matters that have become "common knowledge". Techniques for how to shape common knowledge can vary through professional settings.

=== Legal ===
In legal settings, [[rules of evidence]] generally exclude [[hearsay]], which may draw on "facts" someone believes to be "common knowledge".<ref name=":3">{{Cite journal|last1=Levi|first1=Ron|last2=Valverde|first2=Mariana|date=2001|title=Knowledge on Tap: Police Science and Common Knowledge in the Legal Regulation of Drunkenness|url=https://www.cambridge.org/core/journals/law-and-social-inquiry/article/abs/knowledge-on-tap-police-science-and-common-knowledge-in-the-legal-regulation-of-drunkenness/627A2C657344E82DD867785D0EF5F6B8|journal=Law & Social Inquiry|language=en|volume=26|issue=4|pages=819–846|doi=10.1111/j.1747-4469.2001.tb00325.x|s2cid=144058223 |issn=0897-6546|url-access=subscription}}</ref> The use of common knowledge in law varies between countries.<ref name=":3" />

==See also==
* [[Commonsense knowledge]]
* [[Consensus reality]]
* [[Conventional wisdom]]
* [[Factoid]]
* [[Knowledge falsification]]
* [[List of common misconceptions]]

==Further reading==
* R. Fagin, J. Y. Halpern, Y. Moses, and M. Y. Vardi. ''Reasoning about Knowledge'', The MIT Press, 1995. {{ISBN|0-262-56200-6}}
* [[David Kellogg Lewis|Lewis, David]]. ''[https://books.google.com/books?id=UHADV9OkdeIC Convention]: A philosophical study''. [[Harvard University Press]], 1969.
* J-J Ch. Meyer and W van der Hoek ''Epistemic Logic for Computer Science and Artificial Intelligence'', volume 41, Cambridge Tracts in Theoretical Computer Science,  Cambridge University Press, 1995. {{ISBN|0-521-46014-X}}
* [[Robert Stalnaker|Stalnaker, Robert]]. "Assertion". Pages 315–322 in P. Cole (ed.). ''Syntax and Semantics'' '''9''': Pragmatics, 1978.

==References==
{{Reflist}}

{{DEFAULTSORT:Common Knowledge}}
[[Category:Consensus reality]]
[[Category:Sociology of knowledge]]
[[Category:Social epistemology]]
[[Category:Consensus]]
[[Category:Concepts in epistemology]]
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