Teacher working with a group of students

Citing Sources: Common Knowledge

If information is common knowledge, a source does not need to be cited. That sounds straightforward but determining exactly what is and is not common knowledge can be complex.

The issue raises some interesting questions for writers: who are their readers and what can they assume about them? What constitutes common

Questions to Consider

  • Who is the specific audience I am writing for?
  • What information can I safely assume they already know? Do at least five other reliable sources share the same assumption?
  • Will reasonable people want to know where the information is coming from to confirm it or to understand more?
  • Will many people find what I am saying controversial and want to verify and/or challenge it? 

In addition to the above questions, here are some general principles, with examples, to keep in mind. 

Do Not Cite Sources When

  • Facts are easily verified and already known. For example, “Toni Morrison was born on February 18, 1931.” This can be easily looked up, and there is no real controversy or debate surrounding it.
  • Non-controversial opinions are shared to specific groups. For example, “Toni Morrison was one of the most influential American writers of the last fifty years.” This is common knowledge to writers and people in the literary field.
  • At least five other credible sources do not think it is necessary to cite. For example, “There have been multiple attempts to ban Toni Morrison’s The Bluest Eye from high school classrooms.” This might not be known by the audience, but a quick survey of credible sources shows that people in the field believe it to be commonly understood.

Do Cite Sources When

  • Statistics and numerical data are used to demonstrate the credibility of the source and reliability of the information. For example, “The week after Morrison’s death, 84,000 copies of The Bluest Eye were sold.
  • Controversial opinions held by some experts are shared to specific groups in the field. These should be cited because they are not commonly held. For example, “The Bluest Eye should be removed from high school classrooms, not because of its graphic content, but because it lacks effective plot development.” Readers who care about Morrison probably want to know the source of this criticism and read it for themselves.
  • Information that is not commonly known to a specific group is shared. For example, while widely known in the literary field, the claim, “Toni Morrison was one of the most influential American writers of the last fifty years,” might not be as generally understood by Biology or Business majors.

When in Doubt, Cite the Source

Better to over cite sources than under cite them because we do not want to plagiarize, even accidentally. For more information about plagiarism, visit the College of DuPage Library.

Contact Information

Learning Commons
Student Resource Center (SRC), Room 2102
Call: (630) 942-3940
Email: learningcommons@cod.edu 
Hours of Operation

Mathematics Assistance
(630) 942-3339
Email: math-assist@cod.edu

Writing, Reading, Speech Assistance
(630) 942-3355
Email: wrsa@cod.edu

Tutoring Services
(630) 942-3686
Email: tutoring@cod.edu