Plagiarism, crediting and good citation practice – short version

All researchers are, to some extent or other, standing on the shoulders of their predecessors. It is therefore quite normal and necessary for researchers to include something which others have written in their works. In such a case it is vital that your references are accurate. Otherwise you risk being accused of plagiarism and research misconduct.

The world of research is frequently shaken by allegations of plagiarism. These are cases where an author publishes a work which turns out to contain something which the author has taken from others without an adequate reference.

Plagiarism can have major and unfortunate consequences for those involved. As a researcher you can ultimately be demoted or lose your job. It is therefore vital for researchers to know what plagiarism is and where not to cross the line when it comes to using work created by others.

What is plagiarism?

The word plagiarism can be traced back to a poem by the Roman epigram poet, Martial (approx. 40-104 AD). Martial compared his epigrams with freed slaves and the imitation of them with ”plagium”. That was the crime of kidnapping people and selling them into slavery. You can read more about the concept of plagiarism (in Danish) in Morten Rosenmeier’s guide to copyright, Ophavsret for begyndere – en bog til ikke-jurister, chapter 2.

The modern understanding of plagiarism is to take something that others have created and publish it as if you had made it yourself. For example it is  plagiarism if a researcher publishes a book, and then it turns out that some of the pages have been copied from another book without a clear reference to the source. Another example is to publish a scientific paper which appears as if it is based on your own research, but which is actually stealing other people’s research.

Why is plagiarism not acceptable?

There are several reasons why you should not plagiarise. The three main reasons are:

First, because plagiarism is against some basic universal human notions that you should not ”reap where others have sown”, ”free-ride on the work of others”, ”cut corners” or ”strut in borrowed feathers”. When it comes to plagiarism committed by researchers, there is the added notion that researchers have an ethical obligation to ensure that their research is ethical and fair. If you, as a researcher, are caught in plagiarism, you may risk being ostracised by your peers. There will be rumours and whispering. You are no longer part of Society.

Secondly, plagiarism conflicts with the legal rules that stipulate that researchers should act in accordance with the ethical standards of good research practice etc. If a researcher plagiarises, it will very often be contrary to the so-called good scientific practice. This may lead to criticism from the code of practice committees set up under a number of universities. In more serious cases, plagiarism may also reflect so-called scientific dishonesty and trigger criticism from one of the Danish Committees on Scientific Dishonesty (”DCSD”) under The Danish Agency for Science, Technology and Innovation. Examples include

Finally, plagiarism may sometimes constitute an infringement of the Danish Copyright Act. In short, this is the case if

  • what you have taken from a work reflects originality per se, that is, creative, aesthetic choices. The originality can be found in the specific wording or in a creative way of putting the fabric together.
  • What you have taken from a work is concrete. However, it is not an infringement of copyright to take over the purely abstract elements of a work, for example its method, its style or its theories etc.

You can read more (in Danish) about the difference between the concept of plagiarism in terms of copyright and the ethics of science in Morten Rosenmeier’s guide to copyright, Ophavsret for begyndere – en bog til ikke-jurister, chapter 8

The typical penalty for copyright infringement is that you have to pay a fee to the aggrieved party, as well as any compensation and damages. In addition, copyright infringement may constitute a criminal offence. Finally, the party who has been plagiarised, may intervene with injunctions etc., and have the plagiarist – or his publisher – ordered to withdraw the infringing publication. You can read more (in Danish) about sanctions against copyright infringement in Danish law in Ophavsret for begyndere – en bog til ikke-jurister, chapter 12.

When is it a case of plagiarism?

It may sometimes be difficult to determine when plagiarism has taken place. Although there are clear-cut cases, for example if an author publishes a book that is largely made up of transcripts from another book. But some cases may constitute a legal grey area. These cases are the tricky ones. Many plagiarism cases actually arise because the plagiarist unwittingly crossed the line. The following outlines a few of these cases.

Copying text

Many plagiarism cases occur in the situation where someone has copied text, which others have written, without acknowledgement of the source. This sort will usually constitute plagiarism in terms of the ethics of science as well as copyright. It will for example normally be considered plagiarism if an article contains half a page from another article without acknowledgement of the source, or if you publish a book which contains sections which in reality is a translation of something in a foreign book.

However, there are grey areas. Among other things it is difficult to decide what to think of cases where someone just copies individual sentences  or other quite short passages. This is especially true if what is copied  is banal and bland and not an expression of linguistic autonomy. But it is hard to say where to draw the line.


Right now you are looking at an article about plagiarism from If you upload the entire article to your own website and pretend that you wrote it yourself, it is plagiarism for which others may criticise you. It would also be plagiarism if any of you should get the idea to upload just one section of the article and pretend to have made it. For example by writing:

Example #1: Plagiarism ”The world of research is frequently shaken by instances of plagiarism. Typically cases where an author publishes something which turns out to contain something which the author has taken from others without an adequate reference. Plagiarism can have major and unfortunate consequences for those involved. As a researcher you can ultimately be demoted or lose your job. It is therefore vital for researchers to know what plagiarism is as well as the threshold for the use of work created by others.”

But what if you just capture some of the section, and for example just write:

 Example #2: Plagiarism ”Cases of plagiarism can have major and unfortunate consequences for those involved. As a researcher you can ultimately be demoted or lose your job. It is therefore vital for researchers to know what plagiarism is as well as the threshold for the use of work created by others.”

Or what if you only take one sentence, for example this sentence:

Example #3: Plagiarism ”Cases of plagiarism can have major and unfortunate consequences for those involved.”

In terms of copyright it will constitute an infringement as long as you can say that the text that has been copied by its own virtue reflects some, maybe minimal, linguistic originality. It would probably mean that there is no copyright infringement in example #3. However, it is quite possible that there is an infringement of copyright in example #2. And there is little doubt that there is infringement of copyright in example #1.

In terms of science ethics the question is more difficult. Most would probably agree that in terms of science ethics, reprehensible plagiarism has been committed in example #1 as opposed to in example #3. Example #2, on the other hand, is in the grey area. Even when you only copy quite small, bland statements from others, it is probably a question of how often you do it. If an author of a book for example copies individual, bland phrases from the works of others 25 different places in the book, many will probably characterise the book as a whole as reprehensible plagiarism.

If you want to be on the safe side, you should not copy text from others without citing the sources. That is our advice.

In addition, see DCSD’s decision of 2 December 2014, p. 15:

The Committee does not think that there is a clearly defined line between what constitutes plagiarism and what does not, but considers the following wording by S. Dutch, Professor of Natural and Applied Sciences at the University of Wisconsin, a constructive guideline:”Obviously copying 1000 words verbatim without attribution is plagiarism… Is 100 words plagiarism? Almost certainly. 10? Maybe.” [Footnote omitted].

Taking over theories, methods, etc.

Plagiarism cases can also include situations where you have taken over someone else’s theories, principles, methods, and the like. The basic principle under copyright law is that you can have no copyright to purely abstract ideas, only to more concrete subject matters. Therefore, taking someone’s theories and opinions etc. will not normally constitute copyright infringement. However, in terms of science ethics  this would often be a completely different matter. When it comes to science ethics, theft of other people’s theories and methods, etc. will often be regarded as highly reprehensible.

Example: Einstein’s theory of relativity, which we remember from our physics class, is almost certainly not protected by copyright because, as already mentioned, copyright does not extend to abstract theories. In contrast, it would be most unfortunate from a science ethics perspective  if a researcher represented the theory of relativity as if it were something he had made up himself.

Therefore: Do not take other people’s theories and the like without acknowledgement of the source.

Using the literature references of others

Copyright protects only subject matters that reflect originality. Which does not often apply to literature references found in a book. If, for example, a book about copyright says

”Please refer to Koktvedgaard, Immaterialret p. 53f, Koktvedgaard/Levin, Immaterialret p. 75f, Schønning, Ophavsretsloven med kommentarer p. 198, Hygum Jacobsen/Schelin, Ophavsretten er din, p. 26. Differing in part, Fromm/Nordemann, Urheberrecht p. 63”

It is probably doubtful to claim that these references are so original per se that they are subject to copyright protection.

If another book therefore takes these references and copies them all it is probably not a copyright infringement. But when it comes to science ethics you must be more careful about using references made by others. If, in a scientific book on copyright, you systematically take other authors’ references instead of making your own, you can quickly reach a point where your peers will think that you have cut corners and strut in borrowed feathers. In any case, if you do it more than once in an article or book, you risk being accused of plagiarism.

Having studied the sources yourself is not enough to avoid criticism. What gives rise to criticism when using  the acknowledgements of others is not  – or not limited to – the lack of source studies. It may, in terms of science ethics, be somewhat inherently reprehensible to systematically take the literature references of others, even if you have looked up all the sources yourself. If you overdo it things will go wrong.

This area also has some difficult grey areas. For example, it may be a matter of how many references you are using, and how often you do it. If in a book about copyright you borrow one of the literature references above and for example write

”Please refer to Hygum Jacobsen/Schelin, Ophavsretten er din p. 26”

you cannot rightly say that it is plagiarism. If, however, you take all the references mentioned above you are getting close to the outer boundary of that grey area. And if you are taking a significant part of other people’s literature references in a book or an article you are virtually asking for a plagiarism case.

But it is hard to determine exactly where the boundary is. Beware of using the source references of others without loyally crediting them for it.

Using the quotes of others

As a researcher, it may be hard to resist the temptation to use other people’s quotes.

Example: A statesman says something in a private letter. Later the statement is quoted in a biography about that person, written by author A, who had access to the statesman’s private archive. Then author B also writes a biography about the statesman. In the biography, author B uses the quotation from the private letter without reading the letter himself and without reference to author A.

This is not an infringement of author A’s copyright. Copyright applies only to the parts of a text that is created by an author as a product of his creativity, and in this example, you cannot rightly say that author A has ”created” the quotation from the statesman. After all, it is the statesman who made up the statement, not author A. Therefore B’s taking the quote from A is not an infringement of A’s copyright.

But within the context of science ethics it is a completely different ballgame. According to science ethics you must be careful about using the quotations of others. In the example above, author B should explicitly state that he has taken the quote from author A’s book. For example, author B might write that this statement is ”quoted from” author A.  If, however, you quote someone else’s quotes from a source, without referring to anything other than the original source, it may be a case of plagiarism.

There are complicated grey areas here too. All things being equal, it may be a matter of whether the quotes you are using are generally known or not. If so, borrowing the quotes may not be an act of plagiarism. In contrast it may be plagiarism if the quotes you borrow from others are not generally known, but the result of research, for example in archives.

Example #1: A researcher wants to quote Neil Armstrong’s first words on the moon, that is, ”One small step for man, one giant leap for mankind” in a book.  He finds the quote in an article on space travel on Wikipedia but refers in his book directly to Neil Armstrong, not to the Wikipedia article.

Is that plagiarism? Most will undoubtedly agree that it is not.

Example #2: A researcher is writing an article about Apple founder Steve Jobs. In doing so, he takes a number of quotes by Steve Jobs from Issacson’s biography, ”Steve Jobs”. The latter book is based on numerous interviews with the main character, conducted by Isaacson himself. Would it be all right for the researcher in this case to refer directly to Steve Jobs without mentioning Isaacson’s book?

Most people would probably think that the answer is no, and that the researcher should make it clear where he quotes from. The number of quotes you take from others may also play an important role. If, for example, the researcher in example #2 takes only one quote from someone else, some might say that it is trivial. In contrast, using more than 25 quotes is asking for criticism.

Use of factual information

Everybody builds on the work of their predecessors, and therefore it may happen that researchers take factual information from the works of others. The use of factual information without acknowledging the source may in some cases cause problems.

Basically, there is no copyright  to factual information in isolation. You cannot claim that people who write about the facts “create” them in a creative way. As a rule it will therefore not constitute an infringement of copyright to use the facts of a work, even if you do not cite the work.

However, there may well be copyright to a number of  the facts contained in a work whose author has selected and/or compiled the information in a creative way. In the media you sometimes find cases of whether you are allowed to make films about historical events without the permission of the authors who have written non-fiction about them. In the ’80s Danish newspapers were writing about whether a planned recording of a film about Peter von Scholten – the Danish Governor-General, who on his own initiative freed slaves in the Danish West Indies in 1848 – would require permission from the author Thorkild Hansen, who had portrayed the events in the book ”Islands of Slaves”. The real answer is that Thorkild Hansen could have a case if the film in one way or another took the original selection, structure and composition of his book, for example by focusing on the same events as the book and leaving out the same things. On the other hand, it would not be an infringement to take some individual facts from the book without taking over the structure.

The general rule is that there is no copyright to facts in isolation, because the author did not make them in a creative way. But copyright does not tell the whole story. In terms of science ethics, it is also questionable to what extent you can use facts without acknowledging the source. The answer is that the use of factual information provided by others may well be unethical and reprehensible in some cases. In this context, it probably matters whether the facts are common knowledge or not, and how many times in a work you use them.

Example # 1Use of factual information  In a non-fiction book, you write that man first set foot on the moon on 21 July 1969. You have that information from an encyclopaedia, but do not refer to the encyclopaedia.

Example #2: Use of factual information  You would like to tell a little about the background of the explosion of the space shuttle “Challenger” in 1986 in a non-fiction book. Therefore you use various information about it from Claus Jensen’s book about Challenger, ”No Downlink”, 1993, without referring to it. The information is not generally known, but only mentioned in Claus Jensen’s book and in some U.S. reports etc.

Example #3: Use of factual information  You would like to tell a little about the background of the Challenger accident in a non-fiction book. So you just use one piece of information about it from Claus Jensen’s book without referring to it.

Anything objectionable here in terms of science ethics? Most would probably agree that nothing is wrong in example #1, and probably not in example #3. The author in example #2, however, may be subject to criticism for having behaved unethically. The difference is that the information used in example #1 is common knowledge, and that in example #3 only a single piece of information has been used. The question is, how much generally known information you can use before you go from the acceptable to the reprehensible. It is difficult to give a definite answer.

If you want to be on the safe side, our advice is: Do not use other people’s factual information without acknowledgement of the source. In addition, see DCSC’s decsion of 2 December 2014

”The Committee is of the opinion that general knowledge can be described without a source reference without constituting plagiarism. General knowledge may be defined as knowledge that everybody in a particular group or a regional, institutional or academic community can be expected to possess. This includes facts about geography, history, physics, language, literature, etc. [note omitted].

The Committee is also of the opinion that verbatim or almost verbatim quotes from other authors’ texts containing background knowledge should be properly credited to the author(s) concerned”.


As a researcher you may sometimes get the urge to repeat yourself. If you have already written about something once, it may for example be reasonable to use the same words the next time you deal with it.  If you do not refer to yourself in such cases, it is a kind of so-called ”self-plagiarism”.

Basically, self-plagiarism is not a copyright infringement because you cannot infringe your own copyright. However, self-plagiarism may well be contrary to copyright law, namely in cases where a researcher has published a text and made an agreement with a publisher to share the copyright to the text.

Example: A researcher publishes an article in a scientific journal and they agree that the journal should have an exclusive right to print the article. Afterwards, the researcher publishes the article in another journal without asking anyone. This would constitute an infringement of the rights of journal #1.

Self-plagiarism also has an ethical aspect. It should be taken seriously. If you publish the same article twice, you are dealing with are so-called “double publishing”. It is a common research ethics notion that you should clearly state if you double publish. In other words, in article 2 you should clearly indicate that the article has been published before. If you fail to do so, you run the risk of criticism for breach of good scientific practice.

But what are the rules if the researcher reuses own work without citing the source in other cases? That is a grey area.

According to section 3.1 of the Danish Code of Conduct for Research Integrity,  researchers must mention any reuse the of “results”, “primary material”, “data”, “interpretations”, etc. Thus section 3.1 states:

ii. Publishing the same results in more than one publication should only occur under particular, clearly explained and fully disclosed circumstances.

iii. Recycling or re-use of primary materials, data, interpretations or results should be clearly disclosed.

v. When using one’s own work […] in a publication, appropriate and accurate references to such work should be provided.

However,  in terms of this point it is evident that the code of conduct is primarily written for the purpose of scientific research.

On the other hand, it may sometimes be unclear what not being allowed to repeat your own “results” and “interpretations” etc. in other areas, for example law and the humanities, actually entails. Here researchers are constantly echoing views and perceptions, etc. which they have already expressed before, without referring to themselves. This is for example the case when lawyers account for the way legal rules should be interpreted, or when researchers in the humanities explain the content of literary schools of thought, etc. Sometimes these are views held by people other than themselves. And sometimes they reflect common knowledge. For example: All textbooks about copyright has a section explaining that copyright to mere ideas is never granted. Some of the books mention the example that neither the mood of a film nor the moral of a novel are given copyright protection. Should a lawyer who has written this legal banality in a textbook remember to refer minutely to himself if he repeats it in an article?

When leaving the realm of science, it is also completely unclear what means that you are not allowed to reuse “data” without making a reference. In legal literature you derive results from rulings and legal texts etc.  If taken literally, section 3.1 of the Code of Conduct would mean that if you as a lawyer refer to a ruling in an article, you cannot refer to the same ruling in another article without referring to the first article. But if you assumed this, researchers of law would not be able to do anything but to refer to themselves. So clearly you must interpret section. 3.1 of the Code of Conduct in a fair, balanced way that takes into account that there are different traditions in various scientific fields.

It is doubtful what applies in cases where researchers reuse small pieces of text  from earlier works without citing the source.

Example: An author writes a 20-page article. Some years later he is writing a textbook, and wants to include a short section of 2 pages on the same topic as the one the researcher has previously discussed in the article. The researcher cuts and pastes parts of the article to the textbook while at the same paraphrasing it a bit. He also finds it embarrassing and self-absorbed to refer to himself, and therefore he does not mention in the textbook that the text has actually been reused.

Would you say that the researcher has acted unethically in this example? Probably not. But the issue of self-plagiarism is open to question and a grey area, and you should be careful with it. To be on the safe side as a researcher, you should always mention explicitly when reusing material that you have already published once. You may choose to have an introductory chapter where you neutrally specify that the following section is “based on and repeats text from” such and such earlier works.

A question that calls for special attention is what applies in cases where a researcher reuses material from his or her own publications that are not traditional research publications. For example, can a PhD student reuse material from his or her unpublished thesis? This question was addressed by the Danish press media in the autumn of 2015. The question of whether the PhD dissertation of the Danish Minister of Science, Esben Lund Larsen, was ethically reprehensible was all over the media, among other things because the dissertation did not have any references to the minister’s earlier dissertation on the same subject.

But it is important to note that within law and social sciences etc it is quite normal for PhD students to write a PhD dissertations on the same subject as the one they have written about in their master’s thesis without referring to it. At any rate, when it comes to law students, you would find it outright strange if they referred to a master’s thesis in a scientific dissertation.

However, there are not really any clear ethical rules here. You just have to make do with the loose reflections on self-plagiarism available above. Consequently, as a researcher you should watch out for self-plagiarism. Also, people who have been given the task to determine whether their fellow human beings have committed self-plagiarism which is reprehensible in terms of research ethics, should restrain themselves somewhat instead of just letting go of condemnation.

How to avoid criticism?

Plagiarism cases are unfortunate for those involved. It can be devastating to a researcher’s career to become entangled in a plagiarism case. However, as stated above, there are many grey areas. The question is what to do to be on the safe side. The answer to that is very simple. You merely have to cite the source. If in doubt about whether to cite a source, cite it. If not in doubt, cite just as a precaution. It is better to be safe than sorry. If you want to avoid being accused of plagiarism, cite, cite and cite again. That is the answer. 

How accurate do your references have to be?

Your references must be precise and clear. That is, you have to clearly specify exactly what it is you have borrowed and exactly where you took it from. Thus it does not suffice that you , for example after using more than 10 lines of text from a source, insert a reference to the source after the first line and leave it up to the reader to figure out that you have also taken the next 9 lines from that source. Nor does it suffice that you mention the works that you have taken something from in the bibliography. Nor does it not help to write in the preface that you are indebted to this or that author, and that your own work would never have been possible without them.

As a researcher you should make clear and precise references so that there is no doubt about exactly what you have taken and where you have used it. Then you are on the safe side.

Are popular presentations subject to less stringent requirements?

It is a widespread belief that authors of popular literature need not make as many references as authors who write about real research. Well, this might be the case to some extent.

As we have seen above, it may often be difficult to draw the line between authorised use of other people’s work and unacceptable plagiarism. And when drawing that line, it may possibly make a difference if it is used for research purposes or for mere dissemination of knowledge. Perhaps the author of a book providing popular knowledge can afford to use quotes from others more so than the author of, say, a science article. But this does not imply that you are allowed to plagiarise in popular presentations.

Also when it comes to dissemination of knowledge, it may be reprehensible to use someone else’s facts, quotes, etc. Tread carefully here. In many plagiarism cases the plagiarist has unsuccessfully tried to excuse himself by alleging that his work was purely dissemination of information. And to no avail in so many cases.

You should also be aware of the following: Although slightly less strict reference requirements apply to popular representations, they are usually not applicable  if you are taking actual text from others. The fact that it is a popular presentation might mean that you can use other people’s quotes and ideas etc. without acknowledgement of the source to a slightly greater extent than in the case of research. But you should stay away from their wording. If an author of a popular article just transcribes the sentences from articles he or she has found on the internet there will be no mercy. It will not help to argue that it is just dissemination of information.

Our advice: Do not use other people’s work without acknowledging the source, no matter if you write popular presentations or for research purposes.

See also

If you want to know more about the difference between the concept of plagiarism in terms of copyright and the ethics of science, please refer to

  • Morten Rosenmeier’s guide to copyright, Ophavsret for begyndere – en bog til ikke-jurister, 3rd edition 2014, chapter 8. You can download this freely as an e-book from the website of the UBVA (
  • The Norwegian report ”Good skikk Om bruk av litteratur og kilder i allmenne, historiske framstillinger. Utredning fra et utvalg oppnevnt av Den norske Forleggerforening (DnF), Den norske historiske forening (HIFO) og Norsk faglitterær forfatter- og oversetterforening (NFF), 2006.” It is abbreviated ”Kildebrukutredningen” – and is about the proper use of literature and sources in general historical presentations. It is located in different places on the internet, and the easiest way to find it is by using Google.
  • About plagiarism in student papers, see
  • Lectures, articles and filmed interviews about plagiarism on UBVA’s symposia on plagiarism. Available as Web cast on The topics addressed include:
    • How widespread is plagiarism?
    • The distinction of plagiarism within copyright law and science ethics.
    • Plagiarism of patents, designs and trademarks
    • Why does plagiarism occur?
    • How does it feel to be plagiarised?
    • The history of plagiarism