When to Cite a Source in a Paper

And What Is Common Knowledge?

Student thinking about an essay he’s writing

Echo/Cultura/Getty Images

"Write an essay and back it up with facts."

How many times have you heard a teacher or professor say this? But many students might wonder what exactly counts as a fact, and what doesn't. That means they don't know when it is proper to cite a source, and when it's OK not to use a citation.

Dictionary.com states that a fact is:

  • Something demonstrated to exist or known to have existed.

"Demonstrated" is a hint here. What the teacher means when she/he tells you to use facts is that you need to back up your claims with some evidence that supports your claims (sources). It's one trick that teachers use to make sure you actually use some references when you write a paper, instead of simply offering a list of your opinions.

This may sound easy, but it's actually tough sometimes to know when you need to back up a statement with evidence and when it is fine to leave a statement unsupported.

When to Cite a Source

You should use evidence (citations) any time you make a claim that is not based on a well-known fact or common knowledge. Here's a list of situations when your teacher would expect a citation:

  • You make a specific claim that could be challenged--like London is the foggiest city in the world. 
  • You quote somebody.
  • You make a specific claim that is not common knowledge like the Indian Ocean is the youngest of the world's major oceans.
  • You paraphrase information from a source (give the meaning but change the wording).
  • Offer an authoritative (expert) opinion--like "germs cause pneumonia."
  • You got an idea from somebody else, even through email or conversation.

Although there may be interesting facts that you have believed or know for many years, you will be expected to provide proof of those facts when you're writing a paper for school.

Examples of Claims You Should Support

  • Hot water can freeze faster than cold water.
  • Poodles are friendlier than Dalmatians.
  • American Chestnut trees are nearly extinct.
  • Eating while driving is more dangerous than talking on the cell phone while driving.
  • Thomas Edison invented a vote counter.

When You Don't Need to Cite a Source

So how do you know when you do not need to cite a source? Common knowledge is basically a fact that practically everyone knows, like the fact that George Washington was a U.S. president.

More Examples of Common Knowledge or Well-Known Facts

  • Bears hibernate in the winter.
  • Fresh water freezes at 32 degrees F.
  • Many trees shed their leaves in the fall.
  • Some trees do not shed their leaves in the fall.
  • Bears hibernate.

A well-known fact is something that many people know, but it is also something that a reader could look up easily if he/she didn't know.

  • It's best to plant flowers in the early spring.
  • Holland is famous for its tulips.
  • Canada has a multilingual population.

If you're not really certain about something being common knowledge, you could give it the little sister test. If you have a younger sibling, ask him or her the subject you're pondering. If you get an answer, it could be common knowledge!

A Good Rule of Thumb

A good rule of thumb for any writer is to go ahead and use a citation when you're not certain whether or not the citation is necessary. The only risk in doing this is littering your paper with unnecessary citations that will drive your teacher crazy. Too many citations will give your teacher the impression that you are attempting to stretch your paper to a certain word count!

Simply trust your own best judgment and be honest with yourself. You'll get the hang of it soon!

mla apa chicago
Your Citation
Fleming, Grace. "When to Cite a Source in a Paper." ThoughtCo, Apr. 5, 2023, thoughtco.com/when-to-cite-a-source-1857338. Fleming, Grace. (2023, April 5). When to Cite a Source in a Paper. Retrieved from https://www.thoughtco.com/when-to-cite-a-source-1857338 Fleming, Grace. "When to Cite a Source in a Paper." ThoughtCo. https://www.thoughtco.com/when-to-cite-a-source-1857338 (accessed June 5, 2023).