What Is Plagiarism? Definition, Types, and Real Examples

The Council of Writing Program Administrators, in its statement on best practices, defines plagiarism as deliberately using someone else's language, ideas, or other original material without acknowledging the source (see the statement). It then separates two problems. Submitting someone else's text as your own is plagiarism. Carelessly or inadequately citing words and ideas you borrowed is what the statement calls misuse of sources. A student who tries to credit a source but gets the citation format or the quotation marks wrong has, in its words, "not plagiarized."

Not every institution draws the line there. The Purdue OWL's plagiarism overview says plagiarism "can range from unintentional (forgetting to include a source in a bibliography) to intentional." Your own school's policy decides which view applies to your work.

For something to count as plagiarism, three things have to line up. The material comes from an identifiable source, you present it in a way that reads as your own original work, and you don't credit that source. Common knowledge and your own analysis don't meet the first condition. Citation marks where someone else's words, data, or argument begin. Passing that material off as your own is more than a formatting lapse. It runs against honesty, the first of the six fundamental values of academic integrity set out by the International Center for Academic Integrity.

Santa Clara University Library's guide names six types of plagiarism. The table below follows it, with paraphrasing folded into the mosaic row and translation in a row of its own. Here is what each type looks like in an actual paper.

Mosaic and patchwork plagiarism have their own guide on paraphrasing plagiarism. Reusing your own work is covered in self-plagiarism.

The sources in these examples are fictional.

Direct plagiarism

A study by Rivera (2021, p. 14) says: "Street trees planted in the 1990s now keep the city's older neighborhoods cooler on summer afternoons."

• Plagiarized: the same sentence in your paper, with no quotation marks and no citation.
• Quoted and cited: Rivera (2021) found that "street trees planted in the 1990s now keep the city's older neighborhoods cooler on summer afternoons" (p. 14).
• Paraphrased and cited: Rivera (2021) links cooler summer afternoons in older parts of the city to street trees from the 1990s (p. 14).

The paraphrase keeps its citation. New wording changes how the idea is expressed, not whose finding it is.

Translation plagiarism

You translate a paragraph of a German study by Keller (2019) into English. Translating it yourself does not make the passage your own. The ideas and the argument are still Keller's, so the paragraph needs a citation. Sheffield Hallam University's policy, for example, says plagiarism includes another person's work "written in one language and then translated into a different language and submitted under your name."

APA Style treats your own translation as a paraphrase. You use no quotation marks and cite the original by author and date. APA also recommends a page number when one is available. The MLA Style Center asks you to add "my trans." to the parenthetical citation.

Source-based plagiarism

A textbook by Morgan (2020) summarizes a 1998 experiment by Lee. If you cite Lee without reading Lee's paper, your reference list claims a reading you never did. APA's advice is to "find the primary source, read it, and cite it directly" (APA Style on secondary sources). If you can't, cite the work you read: (Lee, 1998, as cited in Morgan, 2020). Our guide on how to cite a secondary source shows the format in other styles.

In initial findings presented in 2011, the Citation Project analyzed 164 research papers from first-year composition courses at 15 colleges in 12 states. Of the 1,832 citations the researchers coded, 44 percent fit the description of students cutting and pasting from the Internet. That figure is not a plagiarism rate. The study's exact-copying category counted verbatim text with or without quotation marks. Rebecca Moore Howard, one of the project's two lead researchers, did not put this down to dishonesty. "We don't think we have lazy, fraudulent students," she said, as quoted in Inside Higher Ed's coverage of the findings. She added, "We think we have students working for efficiency and doing efficient writing."

Here is one way it happens. You read a paragraph and understand it. Then you write it down in nearly the source's phrasing, with a word changed here and there. You never notice that your paraphrase has become a close copy. Notes make it worse. A phrase you copied weeks ago without quotation marks looks like your own wording by the time you draft from it.

No. Common knowledge needs no citation. The hard part is deciding what counts. MIT's academic integrity handbook describes it as "information that the average, educated reader would accept as reliable without having to look it up," such as the fact that water freezes at 32 degrees Fahrenheit. The Purdue OWL offers a rough test: information you find "undocumented in at least five credible sources."

What counts also depends on the field and the audience. In MIT's example, a description of the symptoms of Asperger's Syndrome needs a citation in a general writing class, but probably not for graduate students in psychology. Before you leave a fact uncited, ask:

• Would a reader in this course know it without looking it up?
• Could you find it, uncited, in many general sources, or only in the one you read?
• Is it a statistic, a study's finding, or a specific date or number that readers would only know from research? MIT says to cite these.
• Could a reasonable reader dispute it? Then it is someone's argument, and it needs a source.

If any answer points to a source, cite it. Both guides give the same rule: when in doubt, cite.

A similarity report measures how much of a text overlaps with a comparison database. It does not measure intent, and a match is not the same thing as plagiarism. Matches include properly quoted and cited material, shared reference-list entries, and common phrasing, so a high score can appear with no misconduct at all. A low score doesn't prove that a text is free of under-cited paraphrase either. The University of Reading's staff guide to these reports makes the same points.

So no fixed percentage marks the point where plagiarism begins. A score tells a reader where to look. Whether the overlapping text is correctly attributed is a judgment someone still has to make by reading the matched passages, and our guide to reading a similarity report shows how to do that with your own draft.

• As a rule of thumb, quote exactly, with quotation marks, whenever you keep three or more of the source's words in their original order.
• Paraphrase from what you understood, not from the text in front of you. Close the source, write the idea down in your own words, then compare your version with the original.
• Cite paraphrases as well as quotes. A borrowed idea needs credit even when the words are yours. Our guide on how to cite a paraphrase covers the format.
• Put quotation marks in your notes the moment you copy a phrase, while you still know which words are the source's.
• If you reuse your own earlier work, check your institution's policy and disclose the reuse. Our guide on self-plagiarism explains when that applies.