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Prevention of plagiarism

Are you working on your Bachelor's or Master's thesis, your doctoral thesis or another academic paper and are uncertain whether you are doing everything right when it comes to citations? We are happy to support you in plagiarism prevention. After all, knowledge of the different types of plagiarism and how to avoid them through correct citation and paraphrasing is essential in academic writing.

The Download ETH Zurich Citation Guidelines (PDF, 65 KB) provides a compact overview of the most important definitions and rules for dealing with third-party sources.

Check every academic paper for correct citation before submitting it. You can find the most important aspects you should consider in a Download checklist (PDF, 98 KB).

We have compiled detailed information for you below.

Why is citation necessary?

Both in your studies as well as in scientific research, the fundamental values and principles of scientific integrity must be adhered to when writing scientific papers and texts.

Citing is an essential part of this: it shows that your text or research is related to other texts, sources and research results and is part of a broader academic discourse. Your own and other people’s results are interlinked, and it becomes clear where you position yourself in the research landscape. Accordingly, you must select the information you integrate into your own text in a sensible and targeted manner.

By referencing third parties, you can support your own scientific argumentation with the ideas of other people and with evidence. At the same time, you make it transparent which information comes from which other authors. This allows readers to use the information provided to efficiently locate the sources you have used, to look them up themselves and to follow up on the ideas of others.

The obligation to cite a source correctly is also enshrined in external page Copyright Law (Art. 25). Sources include, for example, texts, images, interviews, code, research data from other researchers, blog posts, blueprints, etc. The form or medium in which the source is published is irrelevant.

When is citation required?

The following graphic will help you decide whether or not you need to include a source citation in your scientific paper.

Muss ich zitieren?

What are citation styles?

A citation style specifies in detail how the references are to be formatted. These include the short references in the text as well as the complete references in the bibliography. Although there are hundreds of citation styles, some are used particularly frequently, such as APA, Chicago, Harvard, IEEE, MLA, etc.

The citation styles help to format references in a standardised way. This ensures that all authors publish according to generally applicable rules in a scientific field or a journal. Before writing your academic paper, find out which citation style is used in your department or academic field or is required for publications by publishers and journals. If no citation style is specified for Bachelor's or Master's theses, please contact your supervisor.

There is a distinction of three systems within which there are different citation styles, each with different rules:

In these citation styles, the paraphrase is followed by the author's surname and the year of publication in round brackets. In the case of a direct quote, the page number on which the quotation is found is also included. The complete references are listed in alphabetical order in the bibliography.

The advantages of this system are that the name of the author and the publication date of the source are visible in the text and the reading flow is not interrupted by looking up the source.

Example of the Harvard citation style:

In-text citation: This article (Darr, 2019) shows...

Or: Darr (2019) explains in his article...

Bibliography: Darr, T. (2019) Combating plagiarism: A hands-on guide for librarians, teachers, and students. Santa Barbara, California: Libraries Unlimited.

The reference in the text is simply a number in square brackets. The numerical system is chronological, and all references are listed in the bibliography at the end of the text in the order in which they are cited. This system results in a more compact text body (compared to the author-date system).

Example of the IEEE citation style:

In-text reference: Darr [1] explains in his article...

Or: This article [1] shows...

Bibliography: [1] T. Darr, Combating plagiarism: A hands-on guide for librarians, teachers, and students, Santa Barbara, CA, USA: Libraries Unlimited, 2019.

Footnotes are mainly used in the humanities. The reference is followed by a superscript number corresponding to the footnote. The footnote contains a short reference with details about the source, including the page number from which a paraphrase, a summary or a direct quote originates. If it is not a direct quote, the author's name is often preceded by the abbreviation "cf." for "compare". The footnote always ends with a full stop. The complete references are listed in alphabetical order in the bibliography at the end of the text.

In German-speaking countries, an adapted version of the Chicago Notes and Bibliography Style is often used. You should therefore always enquire how this style is used in your academic field.

Example for Chicago Notes and Bibliography Style:

In-text reference: Darr1 explains in his article...

Footnote: 1 Darr, Combating plagiarism, p. XY.

Bibliography: Darr, Terry, Combating plagiarism: A hands-on guide for librarians, teachers, and students, Santa Barbara, CA, USA: Libraries Unlimited, 2019.

Correct citation thanks to reference management software

A reference management software helps you maintain an overview when searching for scientific information and thus avoid plagiarism. How does it work? A reference management software

  • helps you organise your literature and keep track of what you have already read or do not want to read,
  • generates fully formatted bibliographic information with a single click,
  • automatically creates the references in the text and the bibliography in the citation style you use, which contributes significantly to the prevention of plagiarism,
  • allows you to take notes on the managed literature.

Important to know: Check the references anyway – especially if it is not a common source. If you want to look up if a source is referenced correctly, use external page Cite Them Right.

Detailed information can be found in the self-study course Find your reference management programme! on the Moodle platform.

The role of the bibliography

To support the argumentation in your scientific text, you draw on sources from other scientists. These sources – both published and unpublished – are listed completely, clearly and uniformly in a bibliography. Readers are thus provided with indications to the topic and content of your work. At the same time, your supervisor and your readers are able to determine whether you have dealt with the sources relevant to your subject area.

Thanks to the bibliography, the sources you have consulted can be clearly identified. It contains only those publications that you have actually consulted and appear in your text.

How the sources are formatted depends on the citation style you use. Since a reference management programme automatically creates the bibliography correctly – in accordance with the selected citation style – changes made in the reference management programme are also automatically updated in the bibliography.

In addition, you should clarify which requirements your department or journal has regarding the bibliography.

What are sources?

There are three different types of sources. Before you include information in your own work, you should first verify that the source is trustworthy.

There are three different types of sources:

  • Primary sources contain information about an event that is documented for the first time and recorded by persons directly involved, such as scientists or witnesses (e.g. in the case of a historical event). Primary sources include, for example, studies, articles, interviews, photographs or letters.
  • Secondary sources describe, analyse or interpret primary sources or compile content from other specialist literature. Examples of secondary sources include lecture notes, specialist and non-fiction literature, or review articles.
  • Tertiary sources do not contain any new information, but rather reproduce existing information from other sources in a concise form. Examples include dictionaries or encyclopaedias, as well as textbooks.

For a source to be used in a scientific context, it must be citable and worth citing.

The decisive factors for citability are that a source is

  • published and therefore available over a longer period of time,
  • identifiable,
  • accessible and
  • verifiable.

There are citable sources that have not yet been published, such as preprints. These are manuscript versions of scientific publications that have not yet undergone a peer review process. Whether these may be used as a source depends on the scientific field. Therefore, you should check with your supervisor whether you are allowed to use preprints or not.

If you use other sources that have not (yet) been published, you must describe them in detail and possibly include them in the appendix (e.g. interview).

For a source to be worth citing, it must fulfil certain characteristics and scientific quality criteria. In addition to those already mentioned above, the source must be

  • peer-reviewed,
  • written by scientific experts,
  • relevant to the scientific field,
  • and of high scientific quality (e.g. article in a renowned scientific journal or publication by a renowned publisher).

This also applies to literature that is available through open access.

Do Wikipedia articles fulfil these criteria? Since they can be written or edited by anyone, they are not considered reliable sources. However, they can be useful for gaining an initial, cursory overview of a topic.

Of course, the credibility of sources also depends on other factors. Reflect on the following questions:

  • Who are the authors? What is their professional background? Which institutions do they represent?
  • Do the authors argue objectively, verifiably and validly?
  • What is the source’s context? (Who is the target group? Who is behind a publication? What interests are being pursued? Which partners are listed?)
  • What type of source (text genre) is it?
  • Are specialised vocabulary and scientific language used (correctly)?
  • In the case of a scientific journal: How high is the journal’s impact factor?

Citing and referencing in times of generative artificial intelligence 

What does the use of generative artificial intelligence mean with regard to citation and plagiarism? How must the use of generative AI tools be declared?

  • On our website Plagiarism and generative Artificial Intelligence, we have compiled some useful information.
  • Please also refer to the website AI in Teaching and Learning, which contains ETH Zurich's guidelines on the use of generative AI tools. You will also find an overview of common tools, background information on how they work, information on maintaining scientific integrity and on further training opportunities.
  • Publishers and research funders have issued guidelines on the use and declaration of generative AI tools. Please refer to their websites for further information.
  • The use of generative AI tools raises many other legal questions: Can content from licensed scientific sources be entered into AI tools? Is it allowed to share full texts, journal articles, books, book chapters or other data licensed by the ETH Library with these platforms? We have summarised the conditions in the ETH Library handbook under the heading Artificial Intelligence: Use of Licensed Full Texts in Generative AI Tools.

What is plagiarism?

Plagiarism occurs when information from a third-party source is incorporated into one's own text without citing the source and the copyright holders. Sources include, for example, text, illustrations, interviews, code, research data from other researchers, blog posts, construction or blueprints, etc. The data may be available in print, online as open access or provided by a publisher or in another media form.

The following examples are considered plagiarism:

  • A text or content is taken from a source (third-party intellectual property) without identifying the source.
  • Internet sources lack a DOI or URL.
  • A foreign-language text is translated without indicating the source of the original.
  • References in the text are missing and for direct quotes are lacking quotation marks.
  • Parts of the text are copied from the writer’s own previous work without this being clearly declared (so-called self-plagiarism).
  • Submitting the work of another author under one’s own name, even with the permission of the original author (a.k.a. collusion), is not permitted and will result in consequences for both parties.

A special form of plagiarism is ghostwriting, where a person submits a work under their own name that was written by a third party as a commissioned work.

Generative artificial intelligence

Output created by generative artificial intelligence cannot be attributed to any author. Because the output is not reproducible or reliable, it does not constitute a citable or citation-worthy scientific source. If tools based on artificial intelligence are used, they must be declared or identified transparently. Failure to declare the use of such tools amounts to ghostwriting.

Authors of Bachelor’s, Master’s and doctoral theses must sign a declaration of originality stating whether generative artificial intelligence tools were used in their work. In this context, an individual agreement with the supervisor is decisive as to whether AI must be declared or not.

Consequences of plagiarism

Plagiarism, ghostwriting, and the unauthorised, undeclared use of generative artificial intelligence technology constitute deception of the readership with regard to the origin of the text and may invoke disciplinary proceedings as per the ETH Zurich Ordinance on Disciplinary Measures  of 10 November 2020 (SR 414.138.1). Detailed information on these proceedings and their jurisdiction can be found on the Disciplinary affairs website.

Obvious types of plagiarism

The most frequent form of plagiarism that occurs is copying without specifying where the information used comes from. This type of plagiarism ranges from copying a few passages (copy-paste plagiarism) to copying an entire paper and submitting it under one's own name (so-called full plagiarism).

Another common way in which plagiarism can occur is through inaccurate work:

  • References for quotations, paraphrases or summaries are missing.
  • A source is not listed in the bibliography.

Therefore, always make sure to work diligently and check for the issues listed above before submitting your text.

Less obvious types of plagiarism 

In addition to these more obvious types of plagiarism, there are some other, lesser-known forms of plagiarism:

An author uses a citation that they have found in a source without looking up the original citation.

Ways to avoid

  • Always consult the original reference/source and paraphrase or quote directly from it.
  • Always make sure that the original citation is a) correct and b) fits into the context of your own work.
  • If you cannot find the original source, look up how to cite "secondary citations" (or secondary reference) in your citation style guide.

It is considered plagiarism if you use existing code without referencing it. This also applies to code that is available open access.

Ways to avoid

  • Always provide a reference for code in the text and list the complete source in the bibliography.
  • If you extend or supplement existing code with your own code, refer to the original source in an annotation line within your code. Alternatively, you can make a complete reference in the readme-file accompanying your code.

Depending on the discipline, subject-specific rules may apply as to how to deal with code from another source and how to cite it. Your supervisor will be able to advise you if you are unsure.

Image plagiarism occurs when an image, graphic, illustration, photograph, etc. is used without referring to the original source and without indicating the source in the text using an in-text reference and listing it in the bibliography.

Ways to avoid

  • Always refer to the original source with a short reference in the text and a complete reference in the bibliography.
  • Also indicate if it is your own work. This can be done as follows:
    E.g.: graphic by the author, own photograph, etc.
  • If you have been inspired by an illustration and then create your own illustration, also refer to the original. This can be done as follows:
    Example 1: Own illustration, idea for the illustration orignates from [SOURCE XY].
    Example 2: Own illustration, based on ...
  • If you are working on your doctoral thesis or on a publication for a journal and would like to use an image from another source, you must obtain written authorisation to do so. To request this, contact the publisher of the source. Many publishers have corresponding forms online. If the publisher is unable to grant you permission due to a lack of rights, contact the author of the original source. In the event of a negative decision, you may not use the illustration under any circumstances, as this would constitute an infringement of copyright and would have serious consequences. This applies to both original and modified images (see also the Federal external page Copyright Act).

Creative Commons licences allow the limited use of third-party works. Detailed information on CC-BY licences can be found in the manual of the Research Collection.

The entire content, namely the idea of a source, is taken and reproduced in the author's own words, but no reference is made to the original source and no other sources are used.

Ways to avoid

  • If you use a source multiple times, cite it multiple times.
  • Additional sources should also be consulted.
  • The best way to avoid plagiarism of ideas is to extract one point from the main source and examine it. Support your argument with other sources. This changes the focus of the original source, and the additional sources turn the work into a new, independent piece of work.

Mosaic plagiarism occurs when entire paragraphs are copied and reassembled in a different order. In most cases, the source is missing.

Ways to avoid

  • Whenever you copy something, always include an in-text reference and list the source in the bibliography.

An author reuses the content of their own published work (this can be a term paper, thesis or journal article) in another work without clearly declaring this. All written work you have submitted over the course of your studies is considered published.

Ways to avoid

  • The good news is that you are allowed to reuse information from previously published work.
  • Indicate that parts of the content have already been published in a scientific paper or journal article and include a reference to the title of the work, the university and the date of submission or information about the journal in which it was published.
  • This also applies to graphics, illustrations, photographs, etc.

Depending on the subject area, the reference to your own previously published content is handled differently. Therefore, you should clarify with your supervisor how you should proceed.

An author copies the entire structure of a scientific paper one-to-one, including its outline (incl. titles and subtitles) and complete bibliography. Scientific papers in technical and scientific fields are characterised by a "uniform" structure:

  • Table of content
  • Abstract
  • Introduction
  • Methods and Materials
  • Results
  • Discussion
  • Bibliography
  • Appendices

These "structures" are not a problem. However, everything that goes beyond this "standardised" structure is individual, which is why it can be problematic if obviously foreign structures are adopted.

Ways to avoid

  • Do not use the complete structure of a source as a reference point, but rather its content, and extract the information you need for your work. This way, you avoid the risk of adopting someone else's structure or ideas.
  • Consult several sources to support your argument.

An author translates a text from a foreign language without indicating that the relevant passage is a translation and without providing a reference to the original source.

Ways to avoid

  • Clearly identify passages that you have translated yourself and include a reference to the original source.
  • Paraphrase the original text, provide an in-text reference and list the original source in the bibliography.

What is general knowledge?

Information is considered general knowledge if it is publicly available in at least five trustworthy sources and is neither new, controversial nor unusual. Here are two examples:

  • Einstein studied at ETH Zurich.
  • The Second World War ended in 1945.

There is also general knowledge in the respective subject areas. This is usually referred to as knowledge that is acquired in the first foundation year of the degree programme. General knowledge increases over the course of one’s studies, so a Bachelor's thesis requires more comprehensive citations than a Master's or doctoral thesis.

The problem with general knowledge in academic writing is that there is no clear boundary as to what counts as such and what does not. If in doubt, think about who will read your work – colleagues with a comparable level of knowledge should have the same general knowledge as you. If you are still uncertain, you have two options on how to proceed:

  1. Ask your supervisor whether a certain piece of information counts as general knowledge.
  2. Or simply cite the source. It is never wrong to state where information comes from.

Direct quote

A direct quote is when content is taken from a source verbatim – including outdated forms of spelling or spelling mistakes.

When should you incorporate a direct quote into your text? This is recommended in the following cases:

  • Your argument is decisively supported by the addition of an important piece of evidence.
  • An expert makes a certain statement and you want to emphasise that you have noticed it.
  • An author encapsulates something precisely and you cannot say it better in your own words.
  • The exact wording is crucial.
  • It will stylistically improve your text.
  • For definitions and standards.

The following is an example of a direct quote, using Harvard Style for the in-text reference and the bibliography:

The novel begins with explaining the arrival in Petersburg and that there was “[…] a cold northern breeze […]” (Shelley, 2015, p. 15) in the air.

Bibliography entry for this source:

Shelley, M. (2015) Frankenstein, or, the Modern Prometheus. London: The Folio Society.
 

A direct quote should always be enclosed in "quotation marks". Please note that there are different types of «quotation marks» depending on the citation style. Make sure that you use the "correct" characters.

In addition to the quotation marks, it is mandatory to refer to the source at the end of the direct quote. For better readability, an abbreviated form is used. This contains the following information:

  • Name of the author (unless mentioned in the sentence)
  • Publication year of the source
  • Page number on which the original quotation appears

The full details of the source are listed at the end of the paper in the bibliography. How the abbreviated reference and the bibliography are structured also depends on the citation style used. Knowing and applying the correct citation style is therefore an essential part of academic writing.

Mark longer quotations

Quotations longer than approximately three lines are highlighted by indenting the left and right margins and optionally by using a smaller font and narrower line spacing. In this case, the quotation marks can be omitted. The abbreviated form of the reference must be used.

  • Spelling mistakes and emphasis: Use [sic] to indicate spelling mistakes. It comes from Latin and means "exactly so". This shows that you are aware of the mistake, but that this is actually how it appears in the original.

    In the case of emphasised words, use square brackets to indicate that this is how they appear in the original:

    Example: "Things important to virtue [italics in the original] are the phollowing [sic]"

  • Omissions: If you omit parts of the original, you must indicate this with three dots in square brackets: [...]. This applies if you omit the beginning or the end, but also if you omit a part of the direct quotation in the middle:

    Example: "[...] customer friendliness, flexibility of the organisation [...] technological developments and their conceptual implementation."

  • Additions: To insert an original quotation into your own sentence, grammatical additions may have to be made. These must also be enclosed in square brackets:

    Example: Eco notes that “to cite a book […] means to have paid one’s depts [off]” (Eco, 2010, p. 213).

    Example from TUM Citation guide, Technical University of Munich, version dated September 2024, external page https://mediatum.ub.tum.de/doc/1236069/1236069.pdf, last accessed: 09.10.2024.

    In the same way, short additions can be inserted to make the quotation easier to understand.

    Example: [Text, author's note]

If the original quotation is in a different language to your text, you must reproduce the direct quotation in the original language. Add the translation in a footnote – even if you do not otherwise use footnotes. Remember to mention whether the translation was made by you or by a AI-based tool.

A secondary citation is a citation that another author reproduces in their text. If you also want to use this exact quotation, proceed as follows: Find the original and check whether the citation is correct and whether it was understood correctly by the author in the textual context. It is also important that the original citation fits into the context of your work. If so, cite the original. If you cannot find the original citation, follow the procedure for secondary citations in the guidelines for the citation style you are using.

Paraphrase

Paraphrasing is the method you mainly need when writing your introduction, in which you provide an overview of the current state of research. This serves to situate your work in its scientific context: you show what other researchers have achieved in a particular field, highlight how your work fits into the scientific context and why it is important for research. By paraphrasing, you can elegantly borrow ideas and thoughts from others – a legitimate practice in academic writing.

A paraphrase is the analogous reproduction of another person's text in your own words. Information and ideas are thus formulated in a new way, but the meaning of the original text is retained, and no information is added that is not in the original text. However, relevant information must not simply be omitted either.

For paraphrases created using generative AI tools, check whether the content has been reproduced correctly and whether the core statements correspond to the original.

Just like direct quotations, paraphrases must be labelled as such by indicating the source at the end of the paraphrase. Here, too, an abbreviated reference is usually sufficient, which is noted in such a way that the reader can find the full reference in the bibliography. What this looks like depends on the citation style which you must be familiar with when writing a scientific paper.

To write a good paraphrase, you should always take notes on what you have read during the reading process. Note down key words or fixed terms that you will use in the paraphrase.

It is advisable to read a sentence or section more than once before writing the paraphrase. This allows you to engage more deeply with what you have read, which in turn will help you to understand the content of a text even better.

To avoid staying too close to the original, it helps to completely change the structure of the sentence. For example, place a key word that occurs at the end of the sentence in the original at the beginning. This means you will inevitably have to structure the sentence differently. You can also use synonyms to express the same thing in different words.

It is also helpful to begin a paraphrase with introductory words. This could look like this:

The scientist XX describes / explains / differentiates / emphasises... etc.

"Announcing" a paraphrase in this way also helps the reader to distinguish between your ideas and those of others, which is essential in academic writing.

Here is an example of a paraphrase:

Original text

The principles of designing out waste and pollution, keeping products and materials in use and regenerating natural systems is defined as the circular economy (Macarthur, 2020).
 [AE, Academic English UK, exercise 5: external page https://academic-englishuk.com/improve-your-paraphrasing-skills/ [consulted on 18.12.2024].

And here follows a possible paraphrase:

Macarthur (2020) defines the circular economy as the method of eliminating waste and pollution, the continual use of resources and the restoration of physical and biological materials.
[AE, Academic English UK, exercise 5: external page https://academic-englishuk.com/improve-your-paraphrasing-skills/ [consulted on 18/12/2024].

If you would like to practise paraphrasing, simply enter "paraphrasing exercises" into a search engine. Recommended websites include:

Diligence is key

Note down the following information while searching for information and reading:

  • Full title including subtitle
  • Publication year of the source
  • Page numbers in the case of an article, books, etc.
  • Full name of the author (first and last names)
  • Document in which the article is found, including the name of the publisher and place of publication
  • Title of the journal, including issue number and year, publisher and place of publication
  • For electronic resources: the DOI (permanent link) or URL and the date of last access
  • For code: date of last access and URL as well as information about the author
  • For generative AI tools: the prompts and the date when they were created
  • Full details of the generative AI tool used, including version, date of last access and the use case

Make sure that you carefully record all this information about the sources you use right from the start. A reference management programme such as Zotero, EndNote, Mendeley, Citavi or Bibtex can help you to gather the relevant information and keep track of it.

Cite Them Right

For detailed information on the subject of citation, paraphrasing and, above all, citation styles, please consult external page Cite Them Right. The platform, which is licensed by ETH Zurich, offers in-depth information on the topic of citation and lists the citation styles that are most frequently used across disciplines. You will also find information on how to cite output from generative AI tools in the various citation styles.

external page Quick guide to using Cite Them Right

Further reading

Many university libraries have compiled extensive information on the topics of plagiarism, citation and artificial intelligence, for example:

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