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What is plagiarism?


Adams State University, Nielsen Library

 [Comments in brackets, like this, were added by the ASU Psychology Department to reflect APA style.] 

Thanks to ASU Psychology for these examples.

Plagiarism is presenting someone else's words, knowledge, or ideas as though they were your own. 

However, information considered to be "common knowledge" does not need to have its source documented.

Plagiarism includes:

  • Quoting someone else's exact words without documenting the source.
  • Modifying someone else's words without documenting the source.
  • Presenting someone else's idea without documenting the source.
  • Presenting information that falls outside of "common knowledge" without documenting the source.


The book "The Aztecs: Gods and Fate in Ancient Mexico" by Cottie Burland and Werner Forman contains the following sentence: "Diseases were thought of as small, insect-like spirits, that were sent among the people for one reason or another, usually by the gods." (p. 32)

If source information is not provided, all of the following are examples of plagiarism:

  • Diseases were thought of as small, insect-like spirits, that were sent among the people for one reason or another, usually by the gods. This is a word-for-word copy of the original. The student should place quote marks around the sentence and document the source of this quote [including page number for APA style].

  • The Aztecs thought diseases were small, insect-like spirits that were sent among the people for a reason. The gods were frequently believed to have sent these spirits. Although not a word-for-word copy, it is obviously just a rewording of the original.  [The student should do a better job of paraphrasing – meaning putting it into their own words – AND document the source.  No page number needed.]

  • Modern humans know that diseases can be scientifically explained. However, ancient peoples, such as the Aztecs, believed that diseases were caused by tiny spirits. This is not a case of copying words, but of copying knowledge. The Aztecs' belief that tiny spirits caused diseases is not usually considered to be "common knowledge". The student should document the source of this information.


What is common knowledge?

Common knowledge may include:

  • Common sense observations.
  • Generally accepted facts.
  • Shared folklore.
  • Facts to be found in most general reference sources.


  • Common sense observations: e.g., most babies cry frequently.
  • Generally accepted facts: e.g., many Americans eat turkey at Thanksgiving. However, the question arises of "generally accepted by whom?"
    • That George Bush was a U.S. President is common knowledge among Americans. That Mwai Kibaki is the current president of Kenya is a similar type of fact, but it is a fact unknown by most Americans. Some professors would consider both of these facts to be common knowledge, while other professors would consider only Bush's presidency to be common knowledge.
    • The medical criteria for Asperger's Disorder is not common knowledge among most Americans, but it may be common knowledge to the people working in the field of counseling. If a student were writing a general composition that included the medical criteria for Asperger's, it would not be considered common knowledge. But if a student were writing a research paper for a psychology class, the professor may or may not consider it to be common knowledge. [The ASU psychology faculty would NOT consider it common knowledge and would expect a reference.]
  • Shared folklore (e.g., Little Red Riding Hood carried a basket of goodies to her sick grandmother).
  • Facts to be found in most general reference sources. This would include general encyclopedias, dictionaries, and almanacs. Although this information is easily locatable by anyone, it may not be well-known information (e.g., a knout is a whip for flogging criminals). Professors vary on whether they consider such information to be common knowledge.  [Faculty in the ASU Psychology Department prefer to see the source cited.]


Each professor has a slightly different interpretation of what constitutes "common knowledge." Students should make sure they understand their professors' standards before writing papers.

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