Johns Hopkins University Secondary Support Initiative (JHUSSI)  

Why and When To Cite Sources

In this section you will explore why and when we need to cite sources in further detail. You will then view a video related to common knowledge to learn about instances when you do not need to cite a resource. 

In this section you will learn:

  • Why we need to cite sources

  • When we need to cite sources

  • What constitutes common knowledge for which you do not have to cite a resource

"A plagiarist should be made to copy the author a hundred times." --Karl Kraus

Why do I need to cite sources?

  • Cite to avoid plagiarism
  • Cite to demonstrate academic scholarship

In academic writing, we must cite the source of each idea or item of information we use, whether we are quoting, paraphrasing, or summarizing. Citations not only prevent plagiarism, but they also demonstrate our academic scholarship.

In APA style, the use of In-text and reference page citations give proper credit, allow readers to follow the path of our research, and lend credibility to our arguments. Additionally, citations show respect for those whose ideas have fostered our own research.

When do I need to cite sources?

  • Credit must be given when the words or ideas are not our own.
  • If the words or ideas originated elsewhere you must give credit where it is due.

We need to cite when:

  • Using or referring to somebody else's words or ideas from an article, book, newspaper, song, TV program, webpage, letter, advertisement, or any other source;
  • Using information gained through interviewing another person;
  • Copying exact words or unique phrases;
  • Reprinting any diagrams, illustrations, charts, and pictures;
  • Using ideas that others have given us in conversations or over email.

We do not need to cite when we are:

  • Writing from our own experiences, observations and  expressing  our own conclusions about a topic;
  • Using common knowledge--folklore, common sense observations;
  • Compiling generally accepted fact.


Stolley, K., Brizee, A., & Paiz, J. (2013, February 13). Is it plagiarism yet? Retrieved from

Video Library


Examples of Common Knowledge

It is important that you also recognize when you do not need to cite a resource. You do not need to cite a resource for what is considered common knowledge. Please reveiw the examples below as well as the video to the right to learn more about what is considered to be common knowledge.

Easily observable information:

  • The First Amendment concerns freedom of speech;

  • Rush hour traffic tends to be worse in urban populations.

Commonly reported facts:

  • Cigarette smoking can cause health problems;

  • Jackie Robinson was the first Black player in the major leagues.

Common Sayings:

  • “Look before you leap”;

  • “He who hesitates is lost”. 

If you have any questions, consult with individual faculty members. 

After you have completed this section, please go to the APA Formatting Style section.