Common Knowledge

Common knowledge includes facts that are well-known and not widely disputed. They are often historical.


Examples of well-known facts

Periodic Table of the Elements

  • The Declaration of Independence was signed in 1776.
  • Barack Obama is the 44th President of the United States.
  • Disney World is located south of Orlando, Florida.
  • Thanksgiving is celebrated on the 4th Thursday in November in the United States.
  • The chemical symbol for carbon is C.


Periodic Table of the Elements

Figure 1. Image of the periodic table. Reprinted from Torrone, P. (2005, August 19). Periodictable [Image]. Retrieved from Used under a Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic license.


Experts do not always agree on what else is included in common knowledge.

Stolley and Brizee (2010) of the Purdue Online Writing Lab, a widely used and highly regarded source on citation, suggest, "Generally speaking, you can regard something as common knowledge if you find the same information undocumented in at least five credible sources ("Deciding If Something Is," para. 1)."

Many sources such as Kirszner and Mandell's (2011) Wadsworth Handbook include "familiar sayings and well-known quotations" and "information most readers probably know" (p. 223).

Keep in mind though that information your readers already know may be context-dependent, i.e. it may vary based on which class you are in, who the other students are, which discipline (English, Math, Biology, etc.) is involved, etc.

When in doubt, cite. It is better to have some unnecessary citations than to neglect needed ones.