When writing a paper, I usually face the problem of deciding whether a sentence is cite-able or not. Let's say I am writing about optimization of an algorithm. And I used Java to implement it. So, in the introduction, I would say something like "Java is a class based object oriented language..." This information is available in many java books and online tutorials. Does the ubiquity of the sentence make it un-citeable? Or do I cite that fact. I have read many prominent papers that simply use that sentence without quoting a source.

Or do we only cite numerical facts that go like "Java is x times slower/faster than c++". I once read an article that says "when writing a paper, you should cite every sentence that you happen to read some where." But this is unrealistic; and we might have almost as many citations as the number of sentences in the paper.

Is there any rule that dictates on what is quotable or not?

  • 2
    I suggest you change the question to say, "How to decide whether a statement requires citing a reliable source." May 18, 2013 at 14:59
  • It ultimately depends on the community you are submitting to, but Wikipedia has a rule that says "cite if >50% likely to be challenged" en.wikipedia.org/wiki/Wikipedia:LIKELY which could serve as a heuristic for you. It's unlikely your first example would be challenged whereas the second one would be highly likely in my opinion. May 18, 2013 at 15:05

3 Answers 3


Yes, there are rules on what requires citation.

Generally, publicly-known information (widely known, common knowledge, etc.) does not need to be cited. Your sentence about Java being class-based would fall under this category.

Information which is based on someone else's work (analysis, research, pictures, etc.), whether quoted or paraphrased, should always be cited. Your sentence about Java being x time slower/faster than C++ would fall under this category.

If you are unsure, cite it to be safe.

  • 1
    Wikipedia has specific rules about what is "likely to be challenged" which could be an interesting heuristic to keep in mind: en.wikipedia.org/wiki/Wikipedia:LIKELY May 18, 2013 at 15:01
  • Also you have to consider how important is the truth of that statement for your results. "C++ is a high level language" may be challenged (depends if you compare it to Assembly or Python), but doesn't affect the results of your computation.
    – Davidmh
    Mar 14, 2014 at 21:09

These are not rules but the way I think about it:

  1. if the information is basic introductory text book material, you may not need to cite it.

  2. If the information can be found in advanced text books (not intro-level), cite a book that you are familiar with and that supports that statement.

  3. If the informaiton is only found in research papers obviously those are what you reference.

If yu are uncertain, you simply quote a higher level: uncertain if it goes into (1.) then do (2.) etc. It is worse to miss referencing than providing a citation/reference "too much". In the worst case someone might suggest removing the refence/citation.


It depends of the audience at which is aimed the article.

In theory, in a scientific document you must explicitly list the basis for all your assumptions, and defend them. If the correctness of the thesis described in your article depends on fact $A$, then you either prove $A$ or give a reference to someone who proved $A$. In practice scientific reports skip some references assumed to be common (e.g. definition and properties of the logarithm): it used to be important to save printing space (not so true now with electronic proceedings), it stays important to keep the article uncluttered. Given the reasons for skipping some references, there cannot be any absolute rule about which ones to skip: the decision depends of the audience you are aiming at, and in particular of your evaluation of the knowledge in common between you and them: put references when they are necessary to your audience (and do not clutter your article when they are not).

For instance, your sentence about Java being class-based would be unwelcome (in addition of unnecessary) in an article aimed at researchers in computer science, because this fact is supposed to be well known (and agreed upon). But it might be welcome in an article aimed at students (in computer science or not), or researchers in other fields than computer science (e.g. biologists). On the other hand, the fact that Java is slower than C++ might evolve in time (e.g. java compilers getting better), or be argued against (different type of applications): you should always give a reference for this kind of statement if you did not argue or prove it yourself.

Hope it helps!

  • +1 for explaining the "audience" thing. That might explain the inconsistencies I see in well written famous papers. I have seen the same fact cited in some of the papers, presented without citation in the others. May 18, 2013 at 10:53

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