Common knowledge

Not to be confused with Common sense or General knowledge.

For the logical concept, see Common knowledge (logic). For the American game show, see Common Knowledge (game show). For the book about Wikipedia, see Common Knowledge?

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. Common knowledge can be about a broad range of subjects, such as science, literature, history, or entertainment. "Conventional wisdom" is a similar term also referring to ostensibly pervasive knowledge or analysis. Since individuals often have different knowledge bases, it can be difficult to know for certain what is common knowledge amongst large groups of people. 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 an agent would accept as valid, such as information that multiple individuals may know. Assigning something the label of common knowledge requires certain considerations about the involved community, group, society and/or individuals, the time period, and the and the location.

Establishment difficulties

It can be difficult to define something as common knowledge because there are variations in what is considered common knowledge amongst different groups. For example, The Fifth Amendment to the United States Constitution, might be considered common knowledge amongst people residing in the United States of a certain age, but cannot be considered common knowledge when considering the general population of other countries.

Another issue that must be considered is that of the time period. 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 not common knowledge that the Earth revolves around the sun.

On a larger global scale, it is difficult to define almost any knowledge as common knowledge because it is difficult to know how far a fact has spread in global populations. 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 define fact from belief and thus there are scholars who prefer to separate common knowledge from common belief. Common belief is something that is more easily defines because the requirement is only that a majority or 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. For example, if a mayor of a city gets up in front of a crowd and announces that he is resigning, it could be considered common belief that he is going to resign but common knowledge within the present group that he has made an announcement about his potential pending resignation. Not all scholars seem to make the distinction between common knowledge and common belief.

Examples

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.

See also

• Common knowledge (logic)
• Common sense
• Consensus reality
• Conventional wisdom
• Cultural heritage
• Cultural practice
• Cyc, an attempt to capture common sense in a computer system
• Obliteration by incorporation
• Rule of thumb
• Social constructionism
• Judicial notice
• List of common misconceptions
• Factoid

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
• 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.