Wikipedia:Citing sources

This guideline is a part of the English Wikipedia's Manual of Style.

It is a generally accepted standard that editors should attempt to follow, though occasional exceptions may apply. Any substantive edit to this page should reflect consensus. When in doubt, discuss first on the talk page.

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[[:|WP:CITE
WP:REF]]

This page is a style guide, describing how to write citations in articles.

The ability to provide sources for edits is mandated by Wikipedia:No original research and Wikipedia:Verifiability, which are policy. Attribution is required for direct quotes and for material that is challenged or likely to be challenged. Any material that is challenged and for which no source is provided may be removed by any editor. For information about the importance of using good sources in biographies of living persons, see Wikipedia:Biographies of living persons, which is also policy.

If you don't know how to format the citation, provide as much information as you can, and others may fix it for you.

Why sources should be cited

To credit a source for providing useful information and to avoid claims of plagiarism.
To show that your edit isn't original research.
To ensure that the content of articles is credible and can be checked by any reader or editor.
To help users find additional reliable information on the topic.
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To reduce the likelihood of editorial disputes, or to resolve any that arise.
To ensure that material about living persons is reliably sourced and complies with Wikipedia:Biographies of living persons.

Note: Wikipedia articles may not be cited as sources.

When to cite sources

When you add content

All material that is challenged or likely to be challenged needs a source.

The need for citations is especially important when writing about opinions held on a particular issue. Avoid weasel words such as, "Some people say ..." Instead, make your writing verifiable: find a specific person or group who holds that opinion and give a citation to a reputable publication in which they express that opinion. Remember that Wikipedia is not a place for expressing your own opinions or for original research.

Because this is the English Wikipedia, English-language sources should be given whenever possible, and should always be used in preference to other language sources of equal calibre. However, do give references in other languages where appropriate. If quoting from a different language source, an English translation should be given with the original-language quote beside it.

When you verify content

You can add sources even for material you didn't write, by using a source to verify the material. Adding citations is an excellent way to contribute to Wikipedia. See Wikipedia:Forum for Encyclopedic Standards and Wikipedia:WikiProject Fact and Reference Check for organized efforts to add citations.

Material that is, or is likely to be, challenged

Think ahead. Try to imagine whether people might doubt what you wrote, or need more information about it. Supporting what is written in Wikipedia by referring to a clear and reliable source will add stability to your contribution.

Facts that are fully sourced in text need not be further cited; this will most often apply to sources with a well-established and traditional citation system ("Mark 16:48"; Lycidas, l. 135); but other cases are possible: "In the preamble of Magna Carta", "on the first page of the Washington Republican for February 6, 1824".

Say where you got it

It is improper to copy a citation from an intermediate source without making clear that you saw only that intermediate source. For example, you might find some information on a web page which says it comes from a certain book. Unless you look at the book yourself to check that the information is there, your reference is really the web page, which is what you must cite. The credibility of your article rests on the credibility of the web page, not on the book, and your article must make that clear.

When adding material to the biography of a living person

Biographies of living persons should be sourced with particular care, for legal and ethical reasons. All negative material about living persons must be sourced to a reliable source. Do not wait for another editor to request a source. If you find unsourced or poorly sourced negative material about a living person — whether in an article or on a talk page — remove it immediately. Do not leave it in the article and ask for a source. Do not move it to the talk page. This applies whether the material is in a biography or any other article.

When you quote someone

You should always add a citation when quoting published material, and the citation should be placed directly after the quotation, which should be enclosed within double quotation marks — "like this" — or single quotation marks if it's a quote-within-a-quote — "and here is such a 'quotation' as an example". For long quotes, you may wish to use Template:Quotation.

How to cite sources

The following are different citation systems you can use to insert references into Wikipedia articles:

All three are acceptable citation systems for Wikipedia. Do not change from Harvard referencing to footnotes or vice versa without checking for objections on the talk page. If there is no agreement, prefer the style used by the first major contributor.

When writing a new article or adding references to an existing article that has none, follow the established practice for the appropriate profession or discipline. An article's previous content contributors usually know the established practice; follow their lead if the article already has references.
If the established practice is unavailable or disputed, contributors should decide on a style that they believe strikes an appropriate balance between preserving the readability of the text and making citations as precise and accessible as possible.
If contributors differ as to the appropriate style of citation, they should defer to the article's main content contributors in deciding the most suitable format for the presentation of references. If no agreement can be reached, the citation style used should be that of the first major contributor.
When sources are mentioned within the body of an article, it is helpful to identify them clearly on the first mention. For example, this would mean including the first name and surname, that is, the full name the person usually uses. Even better is to include some information about the person's relevant background, such as, "John Smith, a history professor at Yale University, writes that ..."
It is helpful to briefly mention in the footnote what claim it is that is being referenced. This allows later editors to tell whether it's a phrase, sentence or paragraph that's being documented, and also to find undocumented claims sneaking into paragraphs that were otherwise referenced.
If you are unclear as to which system or style to use, remember: the most important thing is to provide all the information one would need to identify and find the source. If necessary, put this information in the talk page, or in a comment on the main page, and ask others how to format it correctly for that article.

Embedded HTML links

Web pages referenced in an article can be linked to directly by enclosing the URL in square brackets. For example, a reference to a newspaper article can be embedded like: [http://media.guardian.co.uk/site/story/0,14173,1601858,00.html], which looks like this: [1]

In the References section, you should also list a full citation:

*Plunkett, John. [http://media.guardian.co.uk/site/story/0,14173,1601858,00.html "Sorrell accuses Murdoch of panic buying"], ''The Guardian'', October 27, 2005, retrieved October 27, 2005.

which appears as:

Plunkett, John. "Sorrell accuses Murdoch of panic buying", The Guardian, October 27, 2005, retrieved October 27, 2005.

Harvard referencing

The Harvard referencing system places a partial citation — the author's name and year of publication within parentheses — usually at the end of the sentence, within the text before the punctuation, and a complete citation at the end of the text in an alphabetized list of "References". According to The Oxford Style Manual, the Harvard system is the "most commonly used reference method in the physical and social sciences" (Ritter 2002).

For one author, add the author's surname and the year of publication in parentheses (round brackets) after the sentence or paragraph, and before the period: for example (Smith 2005).
For two authors, use (Smith & Jones 2005); for more authors, use (Smith et al. 2005).
If the "References" section contains two or more works by the same author but published the same year, use a letter after the year to distinguish the different sources (for example, (Smith 2005a) and (Smith 2005b). Make sure that the in-text citations use the correct letters that correspond to the full citation in the "References" at the end of the article.

If the date of publication is unavailable, use "n.d." (meaning, no date)

Many times authors use an edition of a book that was published long after the original publication. In such cases, many people put the original date of publication in square brackets followed by the date of publication of the edition used by the author who is making the citation. For example, a citation might be

(Marx [1867] 1967)

And the complete reference would be:

Marx, Karl. [1867] (1967). Capital: A Critique of Political Economy Vol. I. Edited by Frederick Engels. New York: International Publishers. ISBN 1-899235-74-4

When providing a page number, the convention is (Smith 2005:73).
For a quotation that is within the text and marked by quotation marks, the citation follows the end-quotation mark ("), and is placed before the period (.), "like this" (Smith 2005).
For a quotation that is indented, the citation is placed after the period, like the following. (Smith 2005)
When the author of the reference is named as part of the text itself, put the year in parentheses; for example "Smith (2005) says..."

Note: Harvard referencing is not complete without the full citation at the end of the page (article) in the References section, as described next.

Complete citations in a "References" section

Complete citations, also called "references", are collected at the end of the article under a ==References== heading. Under this heading, list the comprehensive reference information as a bulleted (*) list, one bullet per reference work. Try to make sure that whichever citation system you choose is used consistently throughout the article. Note that citation templates are not required, though they may be used at the discretion of individual editors.

References typically include: the name of the author, the title of the book or article, and the date of publication. Different professions, academic disciplines, and publishers have different conventions as to the order in which this information should be arranged, or whether additional information is required. Usually, the list is in alphabetical order by the author's surname. The name of the publisher and its city is optional. The ISBN of a book is optional. Journal articles should include volume number, issue number and page numbers, if available.

Typical references would be:

McDougall, Dan. "Trauma of quake's shattered children", The Observer, October 23, 2005.
Smith, J. How to cite your sources, Random House, 2005. ISBN 1-899235-74-4

or using a template:

* {{cite journal | author=L. Hussein ''et al.'' | title=Nutritional quality and the presence of anti-nutritional factors in leaf protein concentrates (LPC) | journal=International Journal of Food Sciences and Nutrition | year=1999 | volume=50 | issue=5 | pages= 333–343}}

which results in:

L. Hussein; et al. (1999). "Nutritional quality and the presence of anti-nutritional factors in leaf protein concentrates (LPC)". International Journal of Food Sciences and Nutrition. 50 (5): 333–343. {{cite journal}}: Explicit use of et al. in: |author= (help)

For more templates to assist formatting, see the citation templates.

Citations for newspaper articles typically include the title of the article in quotes, the byline (author's name), the name of the newspaper in italics, date of publication, and the date you retrieved it if it is online.

Some books have been reprinted several times over the course of the years. Sometimes they have gone through several editions, and sometimes a book may be published by several different publishers. This can raise serious problems for citations, because different editions may be paginated differently. Ideally, all citations in a given article should refer to the same edition by the same publisher, and this edition information should be included in the reference at the end of the article and/or the ISBN (see there) should be given. That way, there would be no confusion over the correct page number for cited quotes or material.

If the "References" section contains two or more works by the same author but published the same year, use a letter after the year to distinguish the different sources (for example 2005a and 2005b).
If you do not know the date of publication, try to find it (you could try your local library, the web-page of a national library such as the Library of Congress, or Amazon.com)
If the date of publication is unavailable, use "n.d." (meaning, no date)
Many times editors use an edition of a book that was published long after the original publication. In such cases, they must provide the date of the edition they are using or else the ISBN, and preferably both. This is important because different editions may be paginated differently.

As Wikipedia grows it is likely that different editors may rely on different editions of the same book.

Usually, different editions of the same book are published in different years. In such cases knowing the year is enough information to distinguish the different editions.
Sometimes, different editions of the same book are published in the same year. This often happens after a copyright has expired, and different publishing companies publish different editions. In such cases, one must know the publisher to distinguish the different editions, or else the ISBN.

It is crucial that complete references be provided for each distinct edition referred to (or cited) in the article, and that each such in-line citation provide enough information to distinguish between editions.

Footnotes

Issues

Editors should not switch from one citation system to another without checking on the talk page that there are no reasonable objections. For example, editors should not switch from footnotes to Harvard referencing for citations, or vice versa. If no agreement can be reached, the system used by the first major contributor to use one should remain in place. Switching from one footnote style to another may constitute a simple technical improvement, but insisting on one style against objections can be inflammatory.

Another issue is that footnotes cost the reader time and effort: switching back and forth between footnotes and text can confuse or distract a reader; and they may find a combination of footnotes and Harvard referencing intimidating or unattractive.

Footnotes come after punctuation

Footnotes at the end of a sentence or phrase are placed immediately after the punctuation. For example: President Bush called for a halt to the violence,^[1] and opposed a timetable for withdrawal.^[2]

What footnotes are normally used for

Some publications use footnotes for both the full citation of a source, and for additional comments or information of interest to the reader.
Some publications use Harvard style notation for sources, and use footnotes exclusively for tangential comments or more detailed information. In this case, in other words, footnotes are notes with relevant text that would distract from the main point if embedded in the main text, yet are helpful in explaining a point in greater detail. Such footnotes can be especially helpful for later fact-checkers, to ensure that the article text is well-supported. Thus, using footnotes to provide useful clarifying information outside the main point is fine where this is needed.

"Notes" section

Technically, footnotes appear at the bottom of a page; endnotes appear at the end of a chapter or book. Since Wikipedia articles may be considered to consist of one long page, or of no pages at all, Wikipedia footnotes appear at the end of an article, but are nevertheless called footnotes.

Recommended section names to use for footnotes in Wikipedia:

==Notes== or ==Footnotes==
==Notes and references== section: Used if there is no separate section with general references, and if all sources of the general content of the article are covered by the footnotes, but see the note about this below.

Maintaining a separate "References" section in addition to "Notes"

It is helpful when footnotes are used that a References section also be maintained, in which the sources that were used are listed in alphabetical order. With articles that have lots of footnotes, it can become hard to see after a while exactly which sources have been used, particularly when the footnotes also contain explanatory text. A References section, which contains only citations, helps readers to see at a glance the quality of the references used.

Page numbers

When citing books and articles, provide page numbers where appropriate. Page numbers must be included in a citation that accompanies a specific quotation from, or a paraphrase or reference to, a specific passage of a book or article.

According to Jessica Benjamin, one weakness of radical politics has been "to idealize the oppressed, as if their politics and culture were untouched by the system of domination, as if people did not participate in their own submission" (Benjamin 1988:9).
Jessica Benjamin has argued that radical politics has been weakened by its inattention to the ways oppressed people participate in their own oppression (Benjamin 1988:9).

Page numbers are especially important in case of lengthy unindexed books. As different editions of a book may be paginated in different ways, it is useful to include, either with the citation, or in the reference section, the edition of the book which is being cited (see the section above "Complete citations in a "References" section" for more details on this issue). In books, articles, and web pages, if there are chapters or section headings, these may be included in the citation, if it makes it easier for readers to find the cited information.

Page numbers are not required when a citation accompanies a general description of a book or article, or when a book or article, as a whole, is being used to exemplify a particular point of view.

In the 1980s several feminists explored feminist readings of psychoanalytical thought (e.g. Gallop 1985, Hamilton 1982, Rose 1986, Benjamin 1988).
Jessica Benjamin, for example, has drawn on Freudian and feminist theory to argue that in modern Western society, the relationship between males and females is paradigmatic for a variety of relations of domination and submission" (Benjamin 1988).

What to do when a reference link "goes dead"

When a link in the Reference section (a link to a source for information in the article) "goes dead", it should be repaired or replaced if possible. External links/Further reading sections are not as important, but should also be fixed. Often, a live substitute link can be found. In most cases, one of the following approaches will preserve an acceptable citation.

A very large proportion of pages can be recovered from the Internet Archive. Just go to http://www.archive.org/ and search for the old link by URL. Make sure that your new citation mentions the date the page was archived by the Internet Archive.
If this was a non-blind citation of web-only material, it may be worth the effort to search the target site for an equivalent page at a new location, an indication that the whole site has moved, etc.
If the link was merely a "convenience link" to an online copy of material that originally appeared in print, and an appropriate substitute cannot be found, it is acceptable to drop the link but keep the citation.
If you cannot find the page on the Internet Archive, remember that you can often find recently deleted pages in Google's cache. They won't be there long, and it is no use linking to them, but this may let you find the content, which can be useful in finding an equivalent page elsewhere on the Internet and linking to that.

If none of those strategies succeed, do not remove the inactive reference, but rather record the date that the original link was found to be inactive — even inactive, it still records the sources that were used, and it is possible hard copies of such references may exist, or alternatively that the page will turn up in the near future in the Internet Archive, which deliberately lags by six months or more. When printed sources become outdated, scholars still routinely cite those works when referenced.

Tagging unsourced material

If an article needs references but you are unable to find them yourself, you can tag the article with the templates {{Unreferenced}}, {{Not verified}}, or {{Primarysources}}. It's often useful to indicate specific statements that need references by placing {{fact}} ("citation needed") after the sentence, but be careful not to overuse these tags. Don't be inappropriately cautious about removing unsourced material.

To summarize the use of in line tags for unsourced or poorly sourced material:

If it is doubtful but not harmful to the whole article, use the {{fact}} tag to ask for source verification, but remember to go back and remove the claim if no source is produced within a reasonable time.
If it is doubtful and harmful, you should remove it from the article; you may want to move it to the talk page and ask for a source, unless you regard it is as very harmful or absurd, in which case it shouldn't be posted to a talk page either. Use your common sense.

All unsourced and poorly sourced contentious material about living persons should be removed from articles and talk pages immediately. It should not be tagged. See Wikipedia:Biographies of living persons and Wikipedia:Libel.

Templates

The use of citation templates is not required by Wikipedia:Citing sources, and is neither encouraged nor discouraged by any other Wikipedia citation guideline. Templates may be used at the discretion of individual editors, subject to agreement with the other editors on the article. Some editors find them helpful, while other editors find them annoying, particularly when used inline in the text. Because they are optional, editors should not add templates without consensus.

Landmark Citation Machine is regularly updated and runs on three separate servers.
Wikicite is a free program that helps people to properly reference their Wikipedia contributions. It is written in Visual Basic .NET, making it suitable only for users with the .NET Framework installed on Windows, or, for other platforms, the Mono alternative framework. Wikicite and its source code is freely available, see the developer's user page for further details.
The arbiters of the criteria for being a "Good Article" have declared the use of inline citations mandatory, and articles relying on other forms of citation are being delisted as Good Articles.

References

Concordia Libraries (Concordia University). Citation and Style Guides. Retrieved December 28, 2004. (This provides a list of common citation styles.)
Citation Styles Handbook: APA
Citation Styles Handbook: MLA
APA Style.org
Using American Psychological Association (APA) Format (Updated to 5th Edition)
Citing Electronic Documentation (APA, Chicago, MLA)
The Columbia Guide to Online Style
Ritter, R. (2002). The Oxford Style Manual. Oxford University Press. ISBN 0-19-860564-1
University of Chicago Press Staff. (2003). The Chicago Manual of Style, 15th edition. University Of Chicago Press. ISBN 0-226-10403-6