What is Common Knowledge?

Common knowledge is generally understood to be any information that the average, educated person would know or accept as true without needing to look it up.

The Yale Poorvu Center for Teaching and Learning defines common knowledge as information that "most educated people know or can find out easily in an encyclopedia or dictionary."

Purdue OWL says that common knowledge refers to information that can be found uncited in at least 5 reliable sources.

Types of Common Knowledge

In keeping with the definitions of "common knowledge" above, there are three main categories that common knowledge could fall into:

• General Information known by the majority of people
  • This includes, but is not limited to, basic facts, geographical locations/features, and long-established theories or equations, etc. 
    Examples:
    • A tomato is a fruit.
    • Seoul is the capital of Korea.
    • Einstein's theory of relativity is E=MC² (energy = mass x the speed of light squared)
• Cultural-Specific Information shared by people within a particular country or cultural group
  • This includes historical people and events
    Examples:
    • The Declaration of Independence was signed in 1776.
    • Martin Luther King Jr. delivered the famous "I Have a Dream" speech in Washington D.C.
    • Kamala Harris was the first woman to be elected Vice-President of the United States.
• Discipline-Specific Information shared by members of a specific field
  • This includes information that may be generally known and accepted by students or experts within a field-of-study, but not widely known outside it
    Examples:
    • In astronomy, it is widely known that black holes are the result of stars that go supernova.
    • In psychology, it is common knowledge that chimpanzees recognize themselves in a mirror.
    • In literature, it's common knowledge that Frankenstein is not the name of the monster, but the name of the scientist who created the monster.

(inspired from What is Common Knowledge? | Academic Integrity at MIT)

Questions to Consider

Since the concept of "common knowledge" is so broad, consider the following questions when deciding whether to cite something that could be considered common knowledge in your work:

• Did I know this information before doing research?
  • If yes, the information might be considered common knowledge.
  • If no, the information is likely not considered common knowledge and should be cited.
• Who is my audience and what can I assume they know?
  • If you're writing for an audience of experts in the field, you might be able to consider a basic piece of discipline-specific information common knowledge.
  • If you're writing for a general audience, you should not consider discipline-specific information common knowledge and cite your source.
• Could my reader ask me to back up this statement with evidence?
  • If the information is considered foundational in your field it can likely be considered common knowledge.
  • If your reader might be surprised by your statement or it could be refuted by other sources, it's probably not considered common knowledge and you should cite your source.

(adapted from What Is Common Knowledge? | Definition & Examples (scribbr.com))