My question is similar to Is verbatim copying several paragraphs of text with citation considered plagiarism?, but I want to ask about very short, concise wordings. As an example, I read a paper in which the author uses the following sentence:

While in the above description we have specified a local algorithm as a function that maps local neighbourhoods to local outputs, we could equally well […]

Now, instead of copying the exact sentence with its grammatical structure, I want to point the reader to this paper and briefly mention one of the conclusions made in this paper. Consider the sentence

author et al. [citation] show that a local algorithm is a function that maps local neighborhoods to local outputs.

The wording "function that maps local neighborhoods to local outputs" is a verbatim copy from the original source. Of course, I could replace this wording with something else that expresses the same, but I find the original citation very concise and I could not come up with a completely different and equally concise sentence.

I always use quotes in addition to a citation to tell the reader that not only the conveyed ideas and concepts, but also the wording, is not my own intellectual achievement. But in this case, one might argue that a person that has understood the ideas described in the original paper might come up with the exact same wording, hence the wording is not a result of the original author's linguistic style, but rather a direct conclusion of the idea he wants to explain.

Is it acceptable to use this wording with a citation and no quotations, or should you always use quotes for verbatim-copies?

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    When you quote the words of another, you need quotation marks. Always.
    – Bob Brown
    Mar 15, 2016 at 14:14
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    "Depends" "on" "the" "size" "of" "the" "quote" "and" "the" "likelihood" "of" "that" "sentence" "appearing" "in" "the" "literature". Mar 15, 2016 at 14:36
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    @Helios35 I am not in the expert in your topic. If that sentence regularly appears in the literature, if it's a standard formulation used in equivalent form virtually everywhere in the relevant literature (say: "A group is a set G together with a map f:GxG -> G with following properties ...." or whatever) one wouldn't quote it. However, if this formulation is very specific to this author or has been introduced by them, you must quote. In mathematics, concept trumps wording, so sometimes citation is sufficient where quotes would make it cumbersome. Ask your advisor. Mar 15, 2016 at 14:47
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    Generally, math is quite special about these things. Simple (for the given community) to obtain reformulations are not considered your own idea and, if not common knowledge, need citations; while identical formulations where either common knowledge, or properly cited, are typically not expected to be quoted. In language-heavy topics, however, the precise formulation counts. In that case, the rule-of-thumb I gave earlier is a useful guideline. However, if in doubt, ask your advisor. Mar 15, 2016 at 14:52
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    Beware that your reuse of those words is making a claim that doesn't come from the source. They said they chose to use a particular definition; that is not the same that showing that particular definition is the most correct one, which is the thought you are attributing to them.
    – Ben Voigt
    Mar 15, 2016 at 19:12

5 Answers 5


I disagree with the two existing answers (gerrit and Patric).

In mathematical writing, it is not necessary to put quotation marks around very short fragments of descriptive text where that text is the obvious and natural way to express the idea. For example, if Smith has written a paper whose main result is

Theorem. Every even number is divisible by two.

then it is perfectly acceptable to write

Smith [cite] shows that every even number is divisible by two.

without quotation marks and without clumsy rephrasings such as

Smith [cite] shows that all even numbers have two as a factor.

The significant intellectual contribution of the work you're citing is the theorem itself, not the obvious wording that they used to express it. As you say, anybody who understood the concept would probably choose to phrase it in that way, even if they'd never seen the paper you're citing. Mathematical writing would be completely unreadable if every phrase that had ever appeared before was put in quotation marks. After all, Smith was hardly the first author to talk about even numbers – are we going to accuse him of plagiarism for not acknowledging that the phrase "even number" is a quotation from somebody else?

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    People whose academic background is different from math or TCS may find this quite bizarre, suspect, and unbelievable. If that applies to you, try it yourself. Open your favorite search engine, enter "showed that" or "proved that" plus some word that occurs exclusively in math and TCS, say, "epimorphism", "holomorphic", "abelian", "noetherian", "bipartite", "manifold", or "differentiable". You'll find hundreds or thousands of papers where some mathematician cites a result of another mathematician. You'll find virtually no quotation marks.
    – Uwe
    Mar 15, 2016 at 23:59
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    @Uwe For people whose academic background is math, it seems unbelievable to consider using quotation marks. Aren't math papers hard enough to read already? Mar 16, 2016 at 3:51
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    @BenWebster Right. And that applies not only to one line summaries of results, but also to cited definitions and theorems. Imagine a lengthy theorem copied from another paper, where the notation has to be adapted because the original paper uses a different typographic convention to distinguish vectors and scalars. What should one do? Quote the entire text, but unquote every variable? That would be ridiculous. The theorem is attributed to the original paper; that's sufficient.
    – Uwe
    Mar 16, 2016 at 8:14
  • I don't think I have seen quotation marks used in a mathematical paper or book, ever. At least not to, you know, mark a quotation, only as scare quotes or whatnot.
    – tomasz
    Mar 17, 2016 at 4:57
  • @tomasz: I've seen it. But never for theorems or definitions. May 7, 2016 at 17:17

At our Physics Department we would not consider such a sentence without quotation marks as plagiarism, due it is below a threshold of originality. In technical writing words are less important than in humanities. Of course it is not allowed to copy whole paragraphs, but single sentences and phrases, which describe technical terms or lab procedures are too trivial and too standardized concerning the wording so there is no need for quotations marks.


Hm. Well... when determining whether something is plagiarism - or really, whether you are going to suffer the consequences of plagiarism - what matters is not your opinion, and not ours, but the opinions of the people who are in a position to impose those consequences. So you should ask them, if you can. ;-)

The message I've always gotten is that this particular example would qualify as plagiarism. There is some threshold of genericity below which you don't have to identify a quote as a quote, but for a lot of people, the phrase you consider quoting doesn't fall below that threshold. I've heard stories of grant proposals being rejected due to instances of plagiarism on the same scale you are talking about. I think that's rather silly, but again, it's not my opinion that matters.

  • 1
    Well, I talked to colleagues today, two of the from an other University here in Germany and for Physics and for Germany, such sentences are not considered plagiarism in a thesis or publication. In other fields this might be different.
    – tf2016
    Mar 16, 2016 at 18:44
  • I think it depends on the specific people involved more than the country or field.
    – David Z
    Mar 16, 2016 at 18:49
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    Well, for the mathematicians above it seems to be quite strange to add quotation marks in their field for such sentences, and so do we at our department. I think the field is very important in this case, because mathematics and physics is not about the words, it is about the facts (as mentioned above, it is not allowed to copy whole paragraphs, etc.).
    – tf2016
    Mar 16, 2016 at 19:02
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    I'm also in physics. And the cases I mentioned, in which short phrases were considered plagiarism, come from grant applications for physics research projects, reviewed (and rejected for plagiarism) by physicists. My point is that the argument that mathematicians and physicists don't care about small amounts of copied text doesn't hold, because some of them do.
    – David Z
    Mar 16, 2016 at 19:05
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    Well ok, then I agree to your suggestion, the initial author of this question should ask the people, who are responsible for his case, because the way we others would handle the case won't help him. Thanks for your input.
    – tf2016
    Mar 16, 2016 at 19:14

While in the above description we have specified a local algorithm as a function that maps local neighbourhoods to local outputs, we could equally well […]

You can quote like this:

author et al. [citation] show that "a local algorithm is a function that maps local neighborhoods to local outputs".

If you do changes to the wording due to grammatical necessities, mark them with within the quote and if you leave out parts of their wording, mark it with [...]

  • So should you mark the as -> is?
    – Bergi
    Mar 16, 2016 at 11:02
  • I didn't see that, sorry, but I assume it's a typo of the asker. If not: Mistakes inside a quote are normally marked with [sic]. Mar 16, 2016 at 12:23
  • No, it's not, both sentences are completely grammatical, and would even be wrong with the opposite word.
    – Bergi
    Mar 16, 2016 at 12:28
  • I don't think you'd need quotes even if "is" were "as" here, as per D. Richerby's answer. One issue is that the OP seems to be using the original's working definition as if it were some sort of proof, but that's not really germane. Mar 16, 2016 at 12:32

I know that many physicists, mathematicians, and computer scientists don't like to use quotations, because they assume they are dealing with truth and of course that transcends any sort of ownership of the ideas (although the expression of the idea could be quite original). I think it comes down to how much and how often one is copying text. I find a 5-word phrase here or there to not be problematic if it is clear who is speaking here. But when paragraphs and paragraphs are taken, entire proofs (including the mistakes), page after page: it is no longer acceptable. There is no "legal" amount to copy. Just do your best to make it clear what is from you and what is from others. Be very careful not to interpret things into what they published that they did not say, as above.

Why not

Author et al. specify a local algorithm to be a function that maps local neighborhoods to local outputs (2014). In this thesis, a local algorithm will be used as .....

This makes it clear that the local algorithm definition comes from Author et al. and the year closes out the use of their text/ideas nicely.

For computer scientists I say: ( ) -> is how you quote: Where does it begin, where does it end, where did you get it from? If you make all three clear, you are on the safe side.

  • I don't think this is really relevant. Nobody's talking about taking "paragraphs and paragraphs ..., entire proofs (including the mistakes), page after page". Indeed, I've never seen a computer science paper do anything like that. Apr 10, 2016 at 5:09
  • Just because you haven't encountered it, doesn't mean that it does not exist. Check out mathematik.uni-marburg.de/~gumm/Plagiarism/index.htm for a documentation of such a case. I blogged about the case in 2010 copy-shake-paste.blogspot.de/2010/05/…. There have been others, but this one is publicly documented. Apr 10, 2016 at 13:56
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    Of course plagiarism where many pages were copied exists in math and computer science. But that's not what the OP was asking about. Apr 11, 2016 at 2:35
  • I don't understand the downvotes. Using the formula "Author + phrase + citation" seems intuitive for me.
    – Ooker
    Jan 2, 2017 at 10:05
  • @Debora Weber-Wulff : The reason it's irrelevant here is because the question posed to this site specifically asks about short phrases (about one sentence or less) only. It's about these troublesome borderline cases where that overt malice is not in play and yet it seems to skirt the rules while never quite being blatant "enough". Feb 2, 2019 at 12:50

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