Plagiarism

Common Knowledge

In writing, facts that are common knowledge do not have to be cited. Most writers are familiar with this concept and on the surface it sounds easy to apply. But the difficulty is in identifying what actually is common knowledge. 

The Massachusetts Institute of Technology (MIT) offers this useful breakdown:

"Broadly speaking, common knowledge refers to information that the average, educated reader would accept as reliable without having to look it up.  This includes:

• Information that most people know, such as that water freezes at 32 degrees Fahrenheit or that Barack Obama was the first American of mixed race to be elected president.
• Information shared by a cultural or national group, such as the names of famous heroes or events in the nation’s history that are remembered and celebrated.
• Knowledge shared by members of a certain field, such as "the fact that the necessary condition for diffraction of radiation of wavelength from a crystalline solid is given by Bragg’s law."

"What is Common Knowledge." Academic Integrity at MIT: A Handbook for Students, https://integrity.mit.edu/handbook/citing-your-sources/what-common-knowledge. Accessed on 28 Sept. 2022.

Common knowledge is a concept that depends heavily on audience. Who is the intended audience for a particular piece of writing? Is it a general, educated reader? Is it a reader from the United States? In the same source, MIT adds a helpful question to help you decide: "Will I be asked where I obtained my information?" Another way of thinking about this would be, would my reader have to do research to find this information out?

As noted above, if you are writing to a narrower audience than the general reader, that special group usually has its own set of common knowledge that doesn't require factual citation:

• a readership of nurses and doctors can be assumed to have a much more in-depth knowledge of anatomy than general readers
• a readership of amateur astronomers can be expected to have a good general knowledge about basic astronomy, but not necessarily the complex physics that professional astronomy requires. General readers would be assumed to have only the most basic knowledge of the information.

Because misrepresenting something as common knowledge is a form of plagiarism, it is generally a wise to provide a citation if you have any doubt about the status of a piece of information for your readers.