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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, such as science, literature, history, and entertainment. Often, common knowledge does not need to be cited. Common knowledge is distinct from general knowledge.
In broader terms, common knowledge is used to refer to information that a reader would accept as valid, such as information that many users may know. As an example, this type of information may include the temperature in which water freezes or boils. To determine if information should be considered common knowledge, you can ask yourself who your audience is, are you able to assume they already have some familiarity with the topic, or will the information's credibility come into question.
Many techniques 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").
"Conventional wisdom" is a similar term also referring to ostensibly pervasive knowledge or analysis.
Examples of common knowledge:
- "Paris is the capital of France." Many capital cities of countries 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. At various periods in history, it was regarded as common knowledge that the Earth is flat and that the Sun orbits the Earth, although these theories were later found to be false.
- "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.
- "The Fifth Amendment to the United States Constitution grants American citizens the right to refuse to answer any question in a court of law that would engender 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. Thus it may be regarded as common knowledge in the United States.
- 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.