Assume you are reviewing a paper and discover that some general definitions therein have been copied from Wikipedia without mentioning the source. Should it be considered plagiarism or can it be considered legit because Wikipedia is freely available and anonymous?

Surely this behaviour shows poor effort in literature research because if something is on Wikipedia it surely is also in some more authoritative document. However, generic definitions of centuries old concepts should now be copyrightless and Wikipedia is as good as any textbook or giving one in your own words.

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    You seem to misunderstand what "free" means in this context. I suggest you read the relevant part of Wikipedia's Terms of Use.
    – user9482
    Commented Aug 8, 2018 at 7:05
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    Even Wikipedia articles have references at the end, so yes they should cite
    – The Hiary
    Commented Aug 8, 2018 at 7:07
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    When you say "some general definitions" are you talking about well known field-specific definitions? generic definitions of centuries old concepts typically don't need to be referenced if they're the sort of thing that would be in every [field] textbook. If someone rattles off the definition of ,say, the speed of light or something that generic then they , typically if being reasonable, don't need to track down whatever textbook they were taught it from as kids. If it's very generic then that definition might be written everywhere including wiki's.
    – Murphy
    Commented Aug 8, 2018 at 10:57
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    "Wikipedia is as good as any textbook" - yeah, so would you not consider it plagiarism to copy an excerpt from a textbook either?
    – Bergi
    Commented Aug 8, 2018 at 18:32
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    "if something is on Wikipedia it surely is also on some more authoritative document" -- in fact, it's worth noting that Wikipedia's policies explicitly state that content on Wikipedia must exist in some other more authoritative document (see WP:V). If they don't, remove them from Wikipedia.
    – Jules
    Commented Aug 8, 2018 at 18:45

6 Answers 6


Copyright for a written work expires some years after the author's death; the length of time under copyright law varies from country to country. Wikipedia and other sites use a variety of licencing models which allow the material to be copied and the conditions that apply to the use of the material.

But regardless of whether something is still copyrighted or not, open source or not, freely available or not, if it is quoted, cited, copied or otherwise repeated in a text, if the source is not cited then yes, it is plagiarism.

When something passes into "common knowledge" then it can be written without having to find a quotable source. But there are also specific situations where something that might normally be considered "common knowledge" needs to be referenced to a source, such as student work where values, definitions, etc., are expected to be researched for accuracy and should also therefore include a reference.

There may also be the case where the value/definition is used in a way that is outside the norm, e.g. a definition that is unusual in the mainstream but is used in a specific way for a specific context, or a value that is based on some work that extends the precision beyond what is considered to be the norm.

The criteria remains, that if someone else wrote it and you copy it then not crediting the original author/source is plagiarism - academic theft.

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    if someone rattles off " generic definitions of centuries old concepts" like say the definition of what a cell wall is or the definition of the speed of light or something similarly universally known within the field it's typically considered unreasonable to call it plagiarism. I just worry that someone will go into automatic bot-like "ah-ha! plagiarism!" mode reading this and some poor students somewhere in the world will get unreasonably accused of plagiarism.
    – Murphy
    Commented Aug 8, 2018 at 11:03
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    If someone does a copy-paste from anywhere then they should cite the source. If it is a generic definition of a well-known concept in a field then they should not need to copy it from somewhere, but if they don't know it well enough to write it themself and thus they copy it from some source, they need to attribute that source.
    – Mick
    Commented Aug 8, 2018 at 12:42
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    @Mark You should cite your source. Citations aren't just about avoiding committing plagiarism. It is more helpful to readers if you provide complete citations, rather than leaving them to wonder where you're getting the content, and where to go to read more. Bear in mind that 'readers' includes you, the writer. Commented Aug 8, 2018 at 14:04
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    @MaxBarraclough I can't imagine a scenario where I'd follow a citation for the first 12 digits of pi, yet I couldn't write them down from memory.
    – Mark
    Commented Aug 8, 2018 at 15:31
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    I would also add that, even if the information has passed into common knowledge, if you copy-paste the text word-for-word, you still need to cite AND QUOTE the text. You can only state common knowledge without citation if you state it in your own words.
    – brendan
    Commented Aug 8, 2018 at 20:41

Yes, that is plagiarism. But even beyond that, it's not true that

Wikipedia is freely available and anonymous

Instead, as you will find on the bottom of every Wikipedia article,

Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply.

That license specifically requires (as by its short summary)

Attribution—You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work.)

Wikipedia has a very lenient understanding of proper attribution – normally, attribution according to the CC licenses is the extreme opposite of anonymous! Traditionally, a CC license would require listing every single contributor to the document used. The revision history of a Wikipedia article (I'll use ‘Eigenvalues and eigenvectors’ as example) is public, and statistics suggest that most of the edits are not anonymous (IPs), but at least pseudonymous (users with named accounts) and several of the main authors have account names that suggest those are their real names. We are permitted to give attribution to “the Wikipedia contributors“ (which is at least somewhat anonymous) instead of that list, but an appropriate mention is still required, such as

Wikipedia contributors. Eigenvalues and eigenvectors. Wikipedia, The Free Encyclopedia. August 3, 2018, 15:11 UTC. Available at: https://en.wikipedia.org/w/index.php?title=Eigenvalues_and_eigenvectors&oldid=853269180. Accessed August 8, 2018.

(In addition, that license means that if someone makes use of a text under this license, for example, using some definition on Wikipedia in their paper, they would have to publish their document under a compatible license!)

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    You might add that the complete edit history of a Wikipedia article is documented in full, and many authors aren't anonymous (e.g. I wasn't anonymous until my employer objected to my name being associated with my Wikipedia edits). Commented Aug 8, 2018 at 19:11
  • I have tried to add it. If you find a better way to phrase it, please edit my aswer.
    – Anaphory
    Commented Aug 10, 2018 at 18:03

Yes, it's plagiarism. Being freely available and anonymous doesn't mean you can copy from it liberally, because it's still written by someone other than yourself.

Note that Wikipedia has its own "cite this page" link (example), indicating it also thinks it should be cited if you take information from it.

  • Makes sense too, couldn't mark it as right solution because someone else was first. Commented Aug 8, 2018 at 7:18
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    When you have more than one acceptable answer, you should accept the one you feel is best, not necessarily the first.
    – WGroleau
    Commented Aug 8, 2018 at 12:00
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    @MarcoStamazza You can change which answer you accept, if you want to. It’s usually a good idea to wait a while before accepting one, in case a better answer comes along. Commented Aug 8, 2018 at 14:15

It seems you are conflating intellectual property rights with plagiarism. The two topics are, for these purposes, unrelated.

Just because a body of work is released to the public and has generous terms of use DOES NOT give you license to claim that work as your own. That is plagiarism. The definition of plagiarism is claiming someone else's work as your own. Generous licensing does not confer ownership of that property, and a citation is required to attribute that work to its original source.

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    That distinction would only be useful if the IP rights to a Wikipedia article were actually permitting use without attribution, but they don't.
    – Anaphory
    Commented Aug 8, 2018 at 15:03
  • i dont understand what youre saying. you as a user, do not own the article on wikipedia. you as an author, must cite the source if its not an original work. it seems that is a good distinction. i think what youre saying is wikipedia's terms of use are stricter than what is mused above. that certainly doesnt change the fact you dont own the article and have to cite your source.
    – user96140
    Commented Aug 8, 2018 at 15:08
  • You are right; I only wanted to highlight that doing what the OP's article does is not only plagiarism, but also violating the IP rights, which are not exactly as “freely available and anonymous” as the OP thinks.
    – Anaphory
    Commented Aug 8, 2018 at 15:13

My general litmus test is thus: Is the definition as-is riddled in textbooks everywhere? Therefore I see no reason to, since it is "common knowledge". If that definition is relatively new and only available in, say, one or two journal articles or some obscure textbook that is the sole authority on a subject (and possibly the wikipedia page), then one references the journal article, if only so that others know where to go learn more about the subject.

Sometimes I discover that I learn a thing from Wikipedia about that definition. But, since Wikipedia disallows original research, that thing is generally reasonably deducible from the definition with a minimum of logic. And, anyhow, you can't copyright ideas. Since the thing is not original research, I generally do not cite the idea. However, since there exist those who would complain about mere phrasing, I reword whatever it is for their sake.

  • Seems dangerous. Do you mean to imply you would copy a definition from a text book without attribution, even though it is explicitly copyrighted? Do text book authors have fewer rights somehow? Their publishers would disagree, of course. You should read the license that Wikipedia puts on all articles. It is quite open, but does require attribution. Sloppy scholarship will only hurt you, actually.
    – Buffy
    Commented Aug 9, 2018 at 15:26
  • My point is that the textbook author almost surely did not devise the definition, and did not bother citing anyone. Therefore, any "copying" that I am guilty of they are as well. Of course, I'm coming from a math/science sort of perspective. This may be different in, for instance, philosophy, where half of the debate is over the definitions of various terms.
    – Him
    Commented Aug 9, 2018 at 16:29
  • In other words, textbook authors have no rights to works that they themselves did not originate. They also cannot copyright them.
    – Him
    Commented Aug 9, 2018 at 16:30
  • Fine. It's your reputation, not mine. My degrees are in math, by the way.
    – Buffy
    Commented Aug 9, 2018 at 16:47
  • I will note, however, that copyright is for words, etc, not ideas. But citation should go beyond copyright.
    – Buffy
    Commented Aug 9, 2018 at 16:50

It isn't necessarily plagiarism: The authors may have written both their manuscript and the Wikipedia article.

The authors may have avoided self-plagiarism in their manuscript by writing it first, the self-plagiarism issue on Wikipedia still remains (I'm unsure what Wikipedia's policy is).

  • Discussion about copyright, preprints and self-plagiarism moved to chat. If you post any further comments along that line, please make specific suggestions how this answer can be improved. Otherwise take it to chat.
    – Wrzlprmft
    Commented Aug 11, 2018 at 15:47

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