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Avoiding Plagiarism:  What is Common Knowledge?

What is NOT common knowledge? What needs to be cited?

  • All statistics, data, figures.

  • References to studies done by others.

  • References to specific facts the average reader would not know about unless he or she had done the research.

What is common knowledge?

Common knowledge is any information that the average, educated reader would accept as reliable without having to look it up.

This includes:

  • General information that most people know, such as: water freezes at 32 degrees Fahrenheit.

  • Information shared by a cultural group, such as the dates of national holidays or names of famous heroes.

  • Knowledge shared by members of a certain field, such as the fact that the necessary condition for diffraction of radiation of wavelength λ from a crystalline solid is given by Bragg’s law.

This situation can be tricky, however. What may be common knowledge in one culture - or in one specific group of people - may not be common knowledge in another. For example, the following would be considered common knowledge to an audience educated in the United States:

  • The American Space Shuttle Challenger exploded shortly after taking off, killing all its crew and passengers.
  • Global warming has become a concern of scientists all over the world; in response, many nations have sought to introduce policies to reduce the emission of greenhouse gasses.

  • Patrick Henry’s statement, “Give me Liberty, or Give me Death!” became a rallying cry for the American Revolution.

The specific dates, facts and trends referred to above comprise information the average, educated reader would know. It is highly unlikely that anyone would challenge these statements. Thus, they do not need to be cited.

Deciding what to cite may also depend on the audience.  An engineering student writing for an engineering audience could write the following and assume that the information would be common knowledge to his or her peers:

  • The development of structural steel and the invention of the elevator made it possible for tall office buildings to be built.  Before that time, large buildings had to be supported by their own walls.

However, the same student writing for a general audience should cite his or her source, as this information would not be common knowledge to the average reader.

The following are examples of statements that need citation:

  • Between 1990 and 2002, the United States was the recipient of $1.27 trillion in direct foreign investment. This amount is more than the combined total received by the United Kingdom, France, Germany and Japan.

Thurow, L. (1993) Fortune Favors the Bold (p. 199).
New York: Harper Collins. 2003.

  • In the last thirty years, discussion has focused on the possible link between overhead power lines and cancer in children. Researchers have investigated whether a connection exists between the low magnetic fields produced by power lines and childhood leukemia, but the evidence remains inconclusive.

Power lines and cancer. (2005. June 4). The Economist Online.
Retrieved June 4. 2005 from

  • The free energy of mixing per site for a binary polymer blend with differing degrees of polymerization can be described through the Flory-Huggins equation.

Flory, P.J. (1953). Principles of Polymer Chemistry.
Ithaca. NY: Cornell University Press.

Each of these statements contains information that would not be known to the average reader. The last equation is specific to the thermodynamics of macromolecular mixtures and would not be considered common knowledge by many scientists or engineers. Therefore, the best advice is: When in doubt, cite your source.

For additional information about common knowledge, please refer to:
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This guide has been adapted from one produced at MIT entitled Academic Integrity at the Massachusetts Institute of Technology:  A Handbook for Students.  We are grateful for their permission to use and revise the work for students at the University of Pennsylvania.

Written by Patricia Brennecke, Lecturer in English Language Studies
Edited by Professor Margery Resnick, Chair of the Committee on Discipline, and Joanne Straggas, Office of the Dean for Undergraduate Education.  Prepared with the support of Professor Robert P. Redwine, Dean for Undergraduate Education at MIT.

Adapted in Fall 2006 for use by graduate students at the University of Pennsylvania and published as the Handbook for Students, Ethics and Original Research by Professor Barbara Fuchs, Romance Languages, Dr. James B. Lok, Professor of Pathobiology, School of Veterinary Medicine, Linda Meiberg, graduate student and Karen Lawrence, Assistant Director of Education.

This edition edited, amended and produced by:

The University Honor Council and the
Office of Student Conduct
University of Pennsylvania
Fall 2008