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You’ve probably heard you do not need to cite common knowledge sources. Finding a common definition for common knowledge can be hard. It can change depending on the context and that can get confusing.

Broadly speaking, common knowledge is information that an educated reader accepts as reliable without needing to look it up. The first two left-column items in the chart below are the most well-known common knowledge items. The next two entries list less commonly understood common knowledge items. If in doubt, it is better to cite and be certain rather than making assumptions and leaving yourself open to charges of sloppy scholarship or plagiarism.

No Citation Needed:

  1. Information found in reference-based sources broadly distributed by multiple (traditional/scholarly) publishers.
    (ex. word definitions, historical dates and facts, biographies of famous people)
  2. Established principles most people know.
    (ex. water boils at 212° Fahrenheit/100° Celsius)
  3. Knowledge shared by members of a certain group.
    (audience-based relevant to culture, nation, career field, academic discipline, or peer group)
  4. Your own ideas, summaries, or conclusions containing ideas cited previously in the paper/project.

Source Documentation Required:

  1. Data generated by others
    (even if you created the chart or graph containing them).
  2. Statistics obtained from a source.
    (ex. US Census Bureau, Bureau of Labor Statistics).
  3. References to studies or findings by others.
    (qualitative or quantitative research projects)
  4. Reference to specific dates, numbers, or facts the reader would need to research.
    (audience-based relevant to culture, nation, career field, academic discipline, or peer group)

Example (no citation needed):

The Big Bang Theory, developed in the late 1920’s, hypothesized that an enormous explosion started the expansion of the universe 13-14 billion years ago.

Example (needs documentation):

Sir Fred Hoyle, an English astronomer, coined the phrase “Big Bang” during a 1949 radio broadcast to mock the theory originally proposed in 1927 by Georges Lemaitre, a Belgian Catholic Priest, astronomer, and professor of physics. Lemaitre originally called his theory the “hypothesis of the primeval atom” or the “cosmic egg.” Sir Hoyle’s competing theory lost support, but his mock name won and that’s what we call it today.

To deal with the changing landscape of what is or is not common knowledge ask yourself:

  • Who is my audience?
  • What can I assume they already know?
  • Will I be asked where I obtained my information?

When in doubt, cite your source!

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