Common knowledge is knowledge that is known by everyone or nearly everyone, usually with reference to the community in which the term is used. Common knowledge need not concern one specific subject, e.g., science or history. Rather, common knowledge can be about a broad range of subjects, including science, literature, history, entertainment etc. Often, common knowledge does not need to be cited. Common knowledge is distinct from general knowledge. The latter has been defined by differential psychologists as referring to 'culturally valued knowledge communicated by a range of non-specialist media', and is considered an aspect of ability related to intelligence.  Therefore there are substantial individual differences in general knowledge as opposed to common knowledge.
The assertion that something is "common knowledge" is sometimes associated with the fallacy argumentum ad populum (Latin: "appeal to the people"). The fallacy essentially warns against assuming that just because everyone believes something is true, it is. Misinformation is easily introduced into rumours by intermediate messengers.
Many techniques have had to have been developed in response to the question of distinguishing truth from fact in matters that have become "common knowledge". The scientific method is usually applied in cases involving phenomena associated with astronomy, mathematics, physics, and the general laws of nature. In legal settings, rules of evidence generally exclude hearsay (which may draw on "facts" someone believes to be "common knowledge").
Examples of Common Knowledge:
- "Paris is the [current] Capital of France." Many capital cities of states are considered common knowledge by most people.
- "The Moon orbits the Earth." Observation of the moon shows us that this happens. In addition, scientific findings give confirmation.
- "It is dangerous to mix Ammonia and Bleach." Though both common household chemicals, accidents involving their combination are rare relative to the frequency of their proximal and often simultaneous usage, because the potentially lethal danger in their chemical reaction is a widely circulated cautionary tale.*
- "Fifth Amendment to the United States Constitution Of The United States Constitution grants American Citizens the right to refuse answering any question in a court of law that would endanger incriminating themselves." "Pleading the Fifth" is a phrase commonly used in American colloquial speak, and even in such popular media as the sketch comedy series Chappelle's Show.*
See also 
- Common knowledge (logic)
- Common sense
- Consensus reality
- Conventional wisdom
- Cyc, an attempt to capture common sense in a computer system
- Obliteration by incorporation
- Rule of thumb
- Social constructionism
- Judicial notice
Further reading 
- Cambria, E., Song, Y., Wang, H., Hussain, A. (2011) "Isanette: A Common and Common Sense Knowledge Base for Opinion Mining". Proceedings of ICDM11
- R. Fagin, J. Y. Halpern, Y. Moses, and M. Y. Vardi. Reasoning about Knowledge, The MIT Press, 1995. ISBN 0-262-56200-6
- Lewis, David. 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
- Stalnaker, Robert. "Assertion". Pages 315–322 in P. Cole (ed.). Syntax and Semantics 9: Pragmatics, 1978.
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