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Wikipedia:Citing sources

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For information on referencing citations in Wikipedia articles, see Help:Footnotes, Wikipedia:Inline citation, and Help:Referencing for beginners.
For information about citing Wikipedia articles for use in work outside of Wikipedia, see Wikipedia:Citing Wikipedia.
"WP:CS" redirects here. For the essay about using common sense, see WP:UCS.
"WP:REF" redirects here. For the Wikipedia Reference desk, see WP:RD.

A citation, also called a reference,[1] uniquely identifies a source of information:

Ritter, Ron (2002). The Oxford Style Manual. Oxford University Press. p. 1.

Wikipedia's Verifiability policy requires inline citations for any material challenged or likely to be challenged, and for all quotations, anywhere in article space.

A citation or reference in an article usually has two parts. In the first part, each section of text that is either based on, or quoted from, an outside source is marked as such with an inline citation. The inline citation may be a superscript footnote number, or an abbreviated version of the citation called a short citation. The second necessary part of the citation or reference is the list of full references, which provides complete, formatted detail about the source, so that anyone reading the article can find it and verify it.

This page explains how to place and format both parts of the citation. Each article should use one citation method or style throughout. If an article already has citations, preserve consistency by using that method or seek consensus on the talk page before changing it (the principle is reviewed at § Variation in citation methods). While you should try to write citations correctly, what matters most is that you provide enough information to identify the source. Others will improve the formatting if needed. Help:Referencing for beginners provides a brief introduction on how to reference Wikipedia articles.

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Contents

Types of citation

  • A full citation fully identifies a reliable source and, where applicable, the place in that source (such as a page number) where the information in question can be found. For example: Rawls, John. A Theory of Justice. Harvard University Press, 1971, p. 1. This type of citation is usually given as a footnote, and is the most commonly used citation method in Wikipedia articles.
  • An inline citation means any citation added close to the material it supports, for example after the sentence or paragraph, normally in the form of a footnote.
  • A short citation is an inline citation that identifies the place in a source where specific information can be found, but without giving full details of the source – these will have been provided in a full bibliographic citation either in an earlier footnote, or in a separate section. For example: Rawls 1971, p. 1. This system is used in some articles; the short citations may be given either as footnotes, or as parenthetical references within the text.
  • In-text attribution involves adding the source of a statement to the article text, such as Rawls argues that X.[5] This is done whenever a writer or speaker should be credited, such as with quotations, close paraphrasing, or statements of opinion or uncertain fact. The in-text attribution does not give full details of the source – this is done in a footnote in the normal way. See In-text attribution below.
  • A general reference is a citation that supports content, but is not linked to any particular piece of material in the article through an inline citation. General references are usually listed at the end of the article in a References section. They are usually found in underdeveloped articles, especially when all article content is supported by a single source. They may also be listed in more developed articles as a supplement to inline citations.

When and why to cite sources

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By citing sources for Wikipedia content, you enable users to verify that the information given is supported by reliable sources, thus improving the credibility of Wikipedia while showing that the content is not original research. You also help users find additional information on the subject; and you avoid plagiarising the source of your words or ideas by giving attribution.

In particular, sources are required for material that is challenged or likely to be challenged – if reliable sources cannot be found for challenged material, it is likely to be removed from the article. Sources are also required when quoting someone, with or without quotation marks, or closely paraphrasing a source. However, the citing of sources is not limited to those situations – editors are always encouraged to add or improve citations for any information contained in an article.

Citations are especially desirable for statements about living persons, particularly when the statements are contentious or potentially defamatory. In accordance with the biography of living persons policy, unsourced information of this type is likely to be removed on sight.

Multimedia

For an image or other media file, details of its origin and copyright status should appear on its file page. Image captions should be referenced as appropriate just like any other part of the article. A citation is not needed for descriptions such as alt text that are verifiable directly from the image itself, or for text that merely identifies a source (e.g., the caption "Belshazzar's Feast (1635)" for File:Rembrandt-Belsazar.jpg).

When not to cite

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Citations are not used on disambiguation pages (sourcing for the information given there should be done in the target articles). Citations are often omitted from the lead section of an article, insofar as the lead summarizes information for which sources are given later in the article, although quotations and controversial statements, particularly if about living persons, should be supported by citations even in the lead. See WP:LEADCITE for more information.

Inline citations

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Further information: Wikipedia:Inline citation

Inline citations allow the reader to associate a given bit of material in an article with the specific reliable source(s) that support it. Inline citations are added using either footnotes (long or short) or parenthetical references. This section describes how to add either type, and also describes how to create a list of full bibliography citations to support shortened footnotes or parenthetical references.

If long or short inline citations placed in footnotes are used, the first editor to add footnotes to an article must create a section where the list of those citations is to appear. This is not necessary for inline parenthetical references, as these appear directly inline in the article prose.

Footnotes

See also: Help:Footnotes

How to create the list of citations

This section, if needed, is usually titled "Notes" or "References", and is placed at or near the bottom of the article. For more about the order and titles of sections at the end of an article (which may also include "Further reading" and "External links" sections), see Wikipedia:Footers.

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With some exceptions discussed below, citations appear in a single section containing only the <references /> tag or the {{reflist}} template. For example:

==References==
{{reflist}}

The footnotes will then automatically be listed under that section heading. Each numbered footnote marker in the text is a clickable link to the corresponding footnote, and each footnote contains a caret which links back to the corresponding point in the text. Scrolling lists, or lists of citations appearing within a scroll box, should never be used. This is because of issues with readability, browser compatibility, accessibility, printing, and site mirroring.[2]

If an article contains a list of general references, this is usually placed in a separate section, titled (for example) "References". This usually comes immediately after the section(s) listing footnotes, if any. (If the general references section is called "References", then the citations section is usually called "Notes".)

How to place an inline citation using ref tags

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Further information: Footnotes: the basics

To create a footnote, use the <ref>...</ref> syntax at the appropriate place in the article text, for example:

  • Justice is a human invention.<ref>Rawls, John. ''A Theory of Justice''. Harvard University Press, 1971, p. 1.</ref> It...

which will be displayed as something like:

  • Justice is a human invention.[1] It...

It will also be necessary to generate the list of footnotes (where the citation text is actually displayed); for this, see the previous section.

As in the above example, citation markers are normally placed after adjacent punctuation such as periods and commas. For exceptions, see the Punctuation and footnotes section of the Manual of Style. Note also that no space is added before the citation marker.

The citation should be added close to the material it supports, offering text–source integrity. If a word or phrase is particularly contentious, an inline citation may be added next to that word or phrase within the sentence, but it is usually sufficient to add the citation to the end of the clause, sentence, or paragraph, so long as it's clear which source supports which part of the text.

Repeated citations

Further information: Footnotes: using a source more than once

For multiple use of the same inline citation or footnote, you can use the named references feature, choosing a name to identify the inline citation, and typing <ref name="name">text of the citation</ref>. Thereafter, the same named reference may be reused any number of times by typing just <ref name="name" />. The use of the slash before the > means that the tag is self-closing, and the </ref> used to close other references must not be used in addition.

The text of the name can be almost anything‍—‌apart from being totally numeric. If spaces are used in the text of the name, the text must be placed within double quotes. Placing all named references within double quotes may be helpful to future editors who do not know that rule. To help with page maintenance it is recommended that the text of the name have a connection to the inline citation or footnote, for example "author year page": <ref name="Smith 2005 p94">text of the citation</ref>.

Separating citations from explanatory footnotes

If an article contains both footnoted citations and other (explanatory) footnotes, then it is possible (but not necessary) to divide them into two separate lists, using the grouping feature described in the Grouping footnotes section of the footnotes help page. The explanatory footnotes and the citations are then placed in separate sections, called (for example) "Notes" and "References" respectively.

Avoiding clutter

Inline references can significantly bloat the wikitext in the edit window and can become difficult and confusing. There are two main methods to avoid clutter in the edit window:

As with other citation formats, articles should not undergo large-scale conversion between formats without consensus to do so.

Citing multiple pages of the same source

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Further information: Help:References and page numbers

When an article cites many different pages from the same source, to avoid the redundancy of many big, nearly identical full citations, most Wikipedia editors use one of three options:

The use of ibid. or Id. (or similar abbreviations) is discouraged, as these may become broken as new references are added (op. cit. is less problematic in that it should refer explicitly to a citation contained in the article; however, not all readers are familiar with the meaning of the terms). If the use of ibid is extensive, use the {{ibid}} template.

Duplicate citations

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Please combine precisely duplicated full citations, in keeping with the existing citation style (if any). Do not discourage editors, particularly inexperienced ones, from adding duplicate citations when the use of the source is appropriate, because a duplicate is usually better than no citation. But any editor should feel free to combine them, and doing so is the best practice on Wikipedia.

Citations to different pages or parts of the same source can also be combined (preserving the distinct parts of the citations), as described in the previous section. Any method that is consistent with the existing citation style (if any) may be used, or consensus can be sought to change the existing style.

Short citations

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Main page: Help:Shortened footnotes

Some Wikipedia articles use short citations, giving summary information about the source together with a page number, as in <ref>Smith 2010, p. 1.</ref>. These are used together with full citations, which give full details of the sources, but without page numbers, and are listed in a separate "References" section. Short citations are used in articles which apply parenthetical referencing (see below), but they can also be used as footnote citations, as described here.

Forms of short citations used include author-date referencing (APA style, Harvard style, or Chicago style), and author-title or author-page referencing (MLA style or Chicago style). As before, the list of footnotes is automatically generated in a "Notes" or "Footnotes" section, which immediately precedes the "References" section containing the full citations to the source. Short citations can be written manually, or by using the {{sfn}} or {{harvnb}} templates. (Note that templates should not be added without consensus to an article that already uses a consistent referencing style.) The short citations and full citations may be linked so that the reader can click on the short note to find full information about the source. See the template documentation for details and solutions to common problems. For variations with and without templates, see wikilinks to full references. For a set of realistic examples, see these.

This is how short citations look in the edit box:

The Sun is pretty big,<ref>Miller 2005, p. 23.</ref> but the Moon is not so big.<ref>Brown 2006, p. 46.</ref> The Sun is also quite hot.<ref>Miller 2005, p. 34.</ref>

== Notes ==
{{Reflist}}

== References ==
*Brown, Rebecca (2006). "Size of the Moon", ''Scientific American'', 51(78).
*Miller, Edward (2005). ''The Sun''. Academic Press.

This is how they look in the article:

The Sun is pretty big,[1] but the Moon is not so big.[2] The Sun is also quite hot.[3]

Notes

  1. ^ Miller 2005, p. 23.
  2. ^ Brown 2006, p. 46.
  3. ^ Miller 2005, p. 34.

References

  • Brown, Rebecca (2006). "Size of the Moon", Scientific American, 51(78).
  • Miller, Edward (2005). The Sun. Academic Press.

Shortened notes using titles rather than publication dates would look like this in the article:

Notes

  1. ^ Miller, The Sun, p. 23.
  2. ^ Brown, "Size of the Moon", p. 46.
  3. ^ Miller, The Sun, p. 34.

When using manual links it is easy to introduce errors such as duplicate anchors and unused references. The script User:Ucucha/HarvErrors will show many related errors. Duplicate anchors may be found by using the W3C Markup Validation Service.

Parenthetical referencing

Further information: Wikipedia:Parenthetical referencing

While most articles use footnote citations as described in the above sections, some articles use a parenthetical referencing style. Here, short citations in parentheses, such as (Smith 2010, p. 1), are placed within the article text itself. Full details of each source used are given in a full citation, e.g., Smith, John. Name of Book. Cambridge University Press, 2010. The full citations are listed in alphabetical order, according to the authors' surnames, at the end of the article in a "References" section.

Several forms of short citation are used in Wikipedia; see Short citations above. The inline citation and full citation may be linked using a template (see linking inline and full citations); as with other citation templates, these should not be added to articles without consensus.

This is how it looks in the edit box:

The Sun is pretty big (Miller 2005, p. 1), but the Moon is not so big (Brown 2006, p. 2). The Sun is also quite hot (Miller 2005, p. 3).
== References ==
*Brown, R (2006). "Size of the Moon", ''Scientific American'', 51(78).
*Miller, E (2005). ''The Sun'', Academic Press.

This is how it looks in the article:

The Sun is pretty big (Miller 2005, p. 1), but the Moon is not so big (Brown 2006, p. 2). The Sun is also quite hot (Miller 2005, p. 3).

References

  • Brown, R (2006). "Size of the Moon", Scientific American, 51(78).
  • Miller, E (2005). The Sun, Academic Press.

Notice that, unlike footnotes, parenthetical references are placed before adjacent punctuation such as commas and periods.

General references

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A general reference is a citation to a reliable source that supports content, but is not linked to any particular piece of material in the article through an inline citation. General references are usually listed at the end of the article in a "References" section, and are usually sorted by the last name of the author or the editor.

The appearance of a general references section is the same as those given above in the sections on short citations and parenthetical references. If both cited and uncited references exist, their distinction can be highlighted with separate section named, e.g., "References" and "General references".

A general references section may also be included in an article that will eventually use inline citations throughout if such citations have not yet been given for all the information in the article. In underdeveloped articles, a general references section may exist even though no inline citations at all have yet been added, especially when all article content is supported by a single source. The disadvantage of using general references alone is that text–source integrity is lost, unless the article is very short.

General references are frequently reworked by later editors into inline citations.

What information to include

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Listed below is the information which a typical inline citation or general reference will provide, though other details may be added as necessary. This information is included in order to identify the source, assist readers in finding it, and (in the case of inline citations) indicate the place in the source where the information is to be found. (If an article uses parenthetical referencing or short citations, then the inline citations will refer to this information in abbreviated form, as described in the relevant sections above.)

Examples

Books

See also the template {{cite book}}.

Since around 1970, a unique ISBN has been assigned to each English language edition and variation (except reprintings) of a book. It is acknowledged that there are (at least potentially) variations between editions as distinct from reprints that occur between editions. In effect, different editions of the same work can be considered different sources. A reprint in this context is distinctly different from a contemporary reprint of an historical publication (see Reprints of older publications). Reference details should include the edition (if not the first edition) and the date/year published reported is the year that the particular edition became available (see On the Origin of Species for an example that references multiple editions of the same work). Where publishers list multiple locations/offices on the title page, the location used is the first of these.

Citations for books typically include:

  • name of the author(s)
  • title of the book in italics
  • translated title of the book in square brackets after the title if not in English
  • volume when appropriate
  • name of the publisher
  • city of publication is optional
  • edition number if not the first edition
  • year of publication of the particular edition being referenced
  • chapter or page number(s) if appropriate
  • ISBN is optional
Citations for individually authored chapters in books typically include:
  • name of author
  • the title of the chapter
  • translated title of the chapter book if not in English
  • name of the book's editor
  • name of book and other details as above
  • the chapter number or page numbers for the chapter (optional)

In some instances, the verso of a book may record, "Reprinted with corrections XXXX" or similar, where 'XXXX' is a year. This is a different version of a book in the same way that different editions are different versions. In such a case, record: the year of the particular reprint, the edition immediately prior to this particular reprint (if not the first edition) and a note to say "Reprint with corrections". If {{cite}} (or similar) is being used, the notation, "Reprint with corrections", can be added immediately following the template. Reprints of older publications gives an example of appending a similar textual note.

Journal articles

See also the template {{cite journal}}.

Citations for journal articles typically include:

  • name of the author(s)
  • year and sometimes month of publication
  • title of the article within quotation marks
  • translated title of the article in square brackets after the title if not in English
  • name of the journal in italics
  • volume number, issue number, and page numbers (article numbers in some electronic journals)
  • DOI and/or other identifiers are optional

Newspaper articles

See also the template {{cite news}}.

Citations for newspaper articles typically include:

  • byline (author's name), if any
  • title of the article within quotation marks
  • translated title of the article in square brackets after the title if not in English
  • name of the newspaper in italics
  • city of publication (if not included in name of newspaper), in parentheses
  • date of publication (the "{{Cite news}}" template places the date after the byline if there is one)
  • page number(s) are optional

Web pages

See also the template {{cite web}}.

Citations for World Wide Web pages typically include:

  • URL of the webpage – that is the URL of the webpage where the referenced content can be found, not, e.g., the main page of a website when the content is on a subpage of that website (see Wikipedia:Shallow references)
  • name of the author(s)
  • title of the article within quotation marks
  • translated title of the article in square brackets after the title if not in English
  • title or domain name of the website
  • publisher, if known
  • date of publication
  • page number(s) (if applicable)
  • the date you retrieved (or accessed) the webpage (required if the publication date is unknown)

Sound recordings

For more details on this topic, see Help:References and page numbers § Other in-source locations.

Citations for sound recordings typically include:

  • name of the composer(s), songwriter(s), script writer(s) or the like
  • name of the performer(s)
  • title of the song or individual track in quotation marks
  • title of the album in italics (if applicable)
  • name of the record label
  • year of release
  • medium (for example: LP, audio cassette, CD, MP3 file)
  • approximate time at which event or point of interest occurs, where appropriate

Do not cite an entire body of work by one performer. Instead, make one citation for each work your text relies on.

Film, television, or video recordings

See also the template {{cite AV media}}.

Citations for films, TV episodes, or video recordings typically include:

  • name of the director
  • name of the producer, if relevant
  • names of major performers
  • for a TV episode, the title of the episode in quotation marks
  • title of the film or TV series in italics
  • name of the studio
  • year of release
  • medium (for example: film, videocassette, DVD)
  • approximate time at which event or point of interest occurs, where appropriate

Other

See also the template {{cite album notes}}.
See also the template {{cite comic}}.
See also the template {{comic strip reference}}.
See also the template {{cite conference}} for conference reports or papers.
See also the template {{cite court}} for court cases or legal decisions.
See also the template {{cite encyclopedia}}.
See also the template {{cite episode}} for TV or radio series.
See also the template {{cite mailing list}}.
See also the template {{cite map}}.
See also the template {{cite newsgroup}}.
See also the template {{citation}} for patents.
See also the template {{cite press release}}.
See also the template {{cite thesis}}.
See also the template {{cite video game}}.

Identifying parts of a source

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Further information: Help:References and page numbers

When citing lengthy sources, you should identify which part of a source is being cited.

Books and print articles

Specify the page number or range of page numbers. Page numbers are not required for a reference to the book or article as a whole. When you specify a page number, it is helpful to specify the version (date and edition for books) of the source because the layout, pagination, length, etc. can change between editions.

If there are no page numbers, whether in ebooks or print materials, then you can use other means of identifying the relevant section of a lengthy work, such as the chapter number or the section title.

In some works, such as plays and ancient works, there are standard methods of referring to sections, such as "Act 1, scene 2" for plays and Bekker numbers for Aristotle's works. Use these methods whenever appropriate.

Audio and video sources

Specify the time at which the event or other point of interest occurs. Be as precise as possible about the version of the source that you are citing; for example, movies are often released in different editions or "cuts". Due to variations between formats and playback equipment, precision may not be accurate in some cases. However, many government agencies do not publish minutes and transcripts but do post video of official meetings online; generally the subcontractors who handle audio-visual are quite precise.

Links and ID numbers

A citation ideally includes a link or ID number to help editors locate the source. If you have a URL (webpage) link, you can add it to the title part of the citation, so that when you add the citation to Wikipedia the URL becomes hidden and the title becomes clickable. To do this, enclose the URL and the title in square brackets—the URL first, then a space, then the title. For example:

Carr A, Ory D (2006). [http://dx.doi.org/10.1371/journal.pmed.0030496 "Does HIV cause cardiovascular disease?"] ''PLoS Medicine'', 3(11):e496.

For web-only sources with no publication date, the "Retrieved" date (or the date you accessed the webpage) should be included, in case the webpage changes in the future. For example: Retrieved 15 July 2011 or you can use the accessdate parameter in the automatic Wikipedia:refToolbar 2.0 editing window feature.

You can also add an ID number to the end of a citation. The ID number might be an ISBN for a book, a DOI (Digital Object Identifier) for an article, or any of several ID numbers that are specific to particular article databases, such as a PMID number for articles on PubMed. It may be possible to format these so that they are automatically activated and become clickable when added to Wikipedia, for example by typing ISBN (or PMID) followed by a space and the ID number.

If your source is not available online, it should be available in reputable libraries, archives, or collections. If a citation without an external link is challenged as unavailable, any of the following is sufficient to show the material to be reasonably available (though not necessarily reliable): providing an ISBN or OCLC number; linking to an established Wikipedia article about the source (the work, its author, or its publisher); or directly quoting the material on the talk page, briefly and in context.

Linking to Google Books pages

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Further information: Wikipedia talk:Citing sources/Archive 29 § Linking to Google Books pages

Google Books allows book pages to be linked to directly if both the book and the individual pages have been made available for preview. These can be written in a number of ways, with or without citation templates:

In edit mode, the URL for p. 18 of A Theory of Justice is entered like this using the {{Cite book}} template:

{{cite book |last=Rawls |first=John |title=A Theory of Justice |publisher=Harvard University Press |date=1971 |page=18 |url= https://books.google.com/books?id=kvpby7HtAe0C&pg=PA18}}

or like this, in the second of the above examples, formatted manually:

Rawls, John. [https://books.google.com/books?id=kvpby7HtAe0C&pg=PA18 ''A Theory of Justice'']. Harvard University Press, 1971, p. 18.

When the page number is a Roman numeral, commonly seen at the beginning of books, the URL looks like this for page xvii (Roman numeral 17) of the same book:
     https://books.google.com/books?id=kvpby7HtAe0C&pg=PR17
The &pg=PR17 indicates "page, Roman, 17", in contrast to the &pg=PA18, "page, Arabic, 18" the URL given earlier.

You can also link to a tipped-in page, such as an unnumbered page of images between two regular pages. (If the page contains an image that is protected by copyright, it will be replaced by a tiny notice saying "copyrighted image".) The URL for eleventh tipped-in page inserted after page 304 of The Selected Papers of Elizabeth Cady Stanton and Susan B. Anthony, looks like this:
     https://books.google.com/books?id=dBs4CO1DsF4C&pg=PA304-IA11
The &pg=PA304-IA11 can be interpreted as "page, Arabic, 304; inserted after: 11".

Page links should only be added when the book is available for preview; they will not work with snippet view. Keep in mind that availability varies by location. No editor is required to add page links, but if another editor adds them, they should not be removed without cause; see the October 2010 RfC for further information.

Note that the Citation Style 1, Citation Style 2 and Citation Style Vancouver templates properly support links only in the |url= and |archive-url= parameters. Placing links in the |page= or |pages= parameters may not link properly and will cause mangled COinS metadata output.

There is a Wikipedia citation tool for Google Books that may be helpful.

Linking to PDF files

Links to long PDF documents can be made more convenient by taking readers to a specific page with the addition of #page=n to the document URL, where n is the page number. For example, using http://www.domain.com/document.pdf#page=5 as the citation URL displays page five of the document in any PDF viewer that supports this feature; otherwise, it goes to the first page.

Note that this functionality depends on support from the web browser's PDF viewer. In some cases, the browser may ignore the PDF page specification and display the first page instead.

Convenience links

Further information: Wikipedia:Copyrights § Linking to copyrighted works

A convenience link is a link to a copy of your source on a webpage provided by someone other than the original publisher or author. For example, a copy of a newspaper article no longer available on the newspaper's website may be hosted elsewhere. When offering convenience links, it is important to be reasonably certain that the convenience copy is a true copy of the original, without any changes or inappropriate commentary, and that it does not infringe the original publisher's copyright. Accuracy can be assumed when the hosting website appears reliable. Where several sites host a copy of the material, the site selected as the convenience link should be the one whose general content appears most in line with Wikipedia:Neutral point of view and Wikipedia:Verifiability.

Say where you read it

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Don't cite a source unless you've seen it for yourself. If you want to cite John Smith, but you've only read Paul Jones who cites Smith, then it should be written in a manner that makes it clear which source you consulted (this formatting is just an example):

John Smith, Name of Book I Haven't Seen, Cambridge University Press, 2009, p. 99, cited in Paul Jones, Name of Encyclopedia I Have Seen, Oxford University Press, 2010, p. 29.

However, if you have read Smith's book yourself, you may cite it directly; there is no need to give credit to any sources, search engines, websites, library catalogs, etc., that led you to that book. You also do not need to specify how you obtained and read Smith's book; so long as you are confident that you read a true and accurate copy, it does not matter whether you read the book using an online service like Google Books, using preview options at a bookseller's website like Amazon, on an e-reader (except to the extent that this affects page numbering), through your library, with online paid databases of scanned publications, using reading machines, or any other method.

Dates and reprints of older publications

Editors should be aware that older sources (especially those in the public domain) are sometimes reprinted with modern publication dates. When this occurs and the citation style being used requires it, cite both the original publication date, as well as the date of the re-publication. E.g.:

  • Darwin, Charles (1964) [1859]. On the Origin of Species (facsimile of 1st ed.). Harvard University Press. 

This is done automatically in the {{citation}} and {{cite book}} templates when you use the |orig-year= parameter.

Alternately, information about the reprint can be appended as a textual note:

  • Boole, George (1854). An Investigation of the Laws of Thought on Which are Founded the Mathematical Theories of Logic and Probabilities. Macmillan.  Reprinted with corrections, Dover Publications, New York, NY, 1958.

Seasonal publication dates and differing calendar systems

Publication dates, for both older and recent sources, should be written with the goal of helping the reader find the publication and, once found, confirm that the correct publication has been located. For example, if the publication date bears a date in the Julian calendar, it should not be converted to the Gregorian calendar.

If the publication date was given as a season or holiday, such as "Winter" or "Christmas" of a particular year or two-year span, it should not be converted to a month or date, such as July–August or December 25. If a publication provided both seasonal and specific dates, prefer the specific one.

Additional annotation

In most cases it is sufficient for a citation footnote simply to identify the source (as described in the sections above); readers can then consult the source to see how it supports the information in the article. Sometimes, however, it is useful to include additional annotation in the footnote, for example to indicate precisely which information the source is supporting (particularly when a single footnote lists more than one source – see § Bundling citations and § Text–source integrity, below).

A footnote may also contain a relevant exact quotation from the source. This is especially helpful when the cited text is long or dense. A quotation allows readers to immediately identify the applicable portion of the reference. Quotes are also useful if the source is not easily accessible.

In the case of non-English sources, it may be helpful to quote from the original text and then give an English translation. If the article itself contains a translation of a quote from such a source (without the original), then the original should be included in the footnote. {See the WP:Verifiability § Non-English sources policy for more information.)

Citation style

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While citations should aim to provide the information listed above, Wikipedia does not have a single house style, though citations within any given article should follow a consistent style. A number of citation styles exist including those described in the Wikipedia articles for Citation, APA style, ASA style, MLA style, The Chicago Manual of Style, Author-date referencing, Vancouver system and Bluebook.

Although nearly any consistent style may be used, avoid all-numeric date formats other than YYYY-MM-DD, because of the ambiguity concerning which number is the month and which the day. For example, 2002-06-11 may be used, but not 11/06/2002. The YYYY-MM-DD format should in any case be limited to Gregorian calendar dates where the year is after 1582.

Variation in citation methods

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Editors should not attempt to change an article's established citation style merely on the grounds of personal preference, to make it match other articles, or without first seeking consensus for the change. The arbitration committee ruled in 2006:

Wikipedia does not mandate styles in many different areas; these include (but are not limited to) American vs. British spelling, date formats, and citation style. Where Wikipedia does not mandate a specific style, editors should not attempt to convert Wikipedia to their own preferred style, nor should they edit articles for the sole purpose of converting them to their preferred style, or removing examples of, or references to, styles which they dislike.

As with spelling differences, it is normal practice to defer to the style used by the first major contributor or adopted by the consensus of editors already working on the page, unless a change in consensus has been achieved. If the article you are editing is already using a particular citation style, you should follow it; if you believe it is inappropriate for the needs of the article, seek consensus for a change on the talk page. If you are the first contributor to add citations to an article, you may choose whichever style you think best for the article.

If all or most of the citations in an article consist of bare URLs, or otherwise fail to provide needed bibliographic data – such as the name of the source, the title of the article or web page consulted, the author (if known), the publication date (if known), and the page numbers (where relevant) – then that would not count as a "consistent citation style" and can be changed freely to insert such data. The data provided should be sufficient to uniquely identify the source, allow readers to find it, and allow readers to initially evaluate it without retrieving it.

To be avoided

When an article is already consistent, avoid:

  • switching between major citation styles, e.g. parenthetical and <ref> tags, or replacing the preferred style of one academic discipline with another's;
  • adding citation templates to an article that already uses a consistent system without templates, or removing citation templates from an article that uses them consistently;
  • changing where the references are defined, e.g. moving reference definitions in the reflist to the prose, or moving reference definitions from the prose into the reflist.

Generally considered helpful

The following are standard practice:

  • improving existing citations by adding missing information, such as by replacing bare URLs with full bibliographic citations: an improvement because it aids verifiability, and fights linkrot;
  • replacing some or all general references with inline citations: an improvement because it provides more verifiable information to the reader, and helps maintain text–source integrity;
  • imposing one style on an article with inconsistent citation styles (e.g., some of the citations in footnotes and others as parenthetical references): an improvement because it makes the citations easier to understand and edit;
  • fixing errors in citation coding, including incorrectly used template parameters, and <ref> markup problems: an improvement because it helps the citations to be parsed correctly;
  • combining duplicate citations (see § Duplicate citations, above).

Handling links in citations

As noted above under What information to include, it is helpful to include hyperlinks to source material, when available. Here we note some issues concerning these links.

Avoid embedded links

Further information: Wikipedia:Embedded citations

Embedded links to external websites should not be used as a form of inline citation, because they are highly susceptible to linkrot. Wikipedia allowed this in its early years—for example by adding a link after a sentence, like this [http://media.guardian.co.uk/site/story/0,14173,1601858,00.html], which looks like this. [1] This is no longer recommended. Raw links are not recommended in lieu of properly written out citations, even if placed between ref tags, like this <ref>[http://media.guardian.co.uk/site/story/0,14173,1601858,00.html]</ref>. Since any citation that accurately identifies the source is better than none, do not revert the good-faith addition of partial citations. They should be considered temporary, and replaced with more complete, properly formatted citations as soon as possible.

Embedded links should never be used to place external links in the content of an article, like this: "Apple, Inc. announced their latest product...".

Convenience links

Further information: Wikipedia:Copyrights § Linking to copyrighted works

A convenience link is a link to a copy of your source on a webpage provided by someone other than the original publisher or author. For example, a copy of a newspaper article no longer available on the newspaper's website may be hosted elsewhere. When offering convenience links, it is important to be reasonably certain that the convenience copy is a true copy of the original, without any changes or inappropriate commentary, and that it does not infringe the original publisher's copyright. Accuracy can be assumed when the hosting website appears reliable. Where several sites host a copy of the material, the site selected as the convenience link should be the one whose general content appears most in line with Wikipedia:Neutral point of view and Wikipedia:Verifiability.

Indicating availability

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If your source is not available online, it should be available in reputable libraries, archives, or collections. If a citation without an external link is challenged as unavailable, any of the following is sufficient to show the material to be reasonably available (though not necessarily reliable): providing an ISBN or OCLC number; linking to an established Wikipedia article about the source (the work, its author, or its publisher); or directly quoting the material on the talk page, briefly and in context.

Links to sources

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For a source available in hardcopy, microform, and/or online, omit, in most cases, which one you read. While it is useful to cite author, title, edition (1st, 2nd, etc.), and similar information, it generally is not important to cite a database such as ProQuest, EbscoHost, or JStor (see the list of academic databases and search engines) or to link to such a database requiring a subscription or a third party's login. The basic bibliographic information you provide should be enough to search for the source in any of these databases that have the source. Don't add a URL that has a part of a password embedded in the URL. However, you may provide the DOI, ISBN, or another uniform identifier, if available. If the publisher offers a link to the source or its abstract that does not require a payment or a third party's login for access, you may provide the URL for that link. If the source only exists online, give the link even if access is restricted (see WP:PAYWALL).

Preventing and repairing dead links

See also: Wikipedia:Link rot
Shortcut:

To help prevent dead links, persistent identifiers are available for some sources. Some journal articles have a digital object identifier (DOI); some online newspapers and blogs, and also Wikipedia, have permalinks that are stable. When permanent links aren't available, consider archiving the referenced document when writing the article; on-demand web archiving services such as WebCite (http://www.webcitation.org) or the Wayback Machine (http://www.archive.org/web) are fairly easy to use (see pre-emptive archiving).

Dead links should be repaired or replaced if possible. Do not delete a citation merely because the URL is not working. Follow these steps when you encounter a dead URL being used as a reliable source to support article content:

  1. Confirm status: First, check the link to confirm that it is dead and not temporarily down. Search the website to see whether it has been rearranged. The online service "Is it down right now?" can help to determine if a site is down, and any information known.
  2. Check for a changed URL on the same Web site: Pages are frequently moved to different location on the same site as they become archive content rather than news. The site's error page may have a "Search" box; alternatively, in the popular Google search engine the keyterm "site:" is used, as in ⟨site:en.wikipedia.org "New Zealand police vehicle markings and livery"⟩.
  3. Check for web archives: Many Web archiving services exist; link to their archive of the URL's content, if available. Examples:
If multiple archive dates are available, try to use one that is most likely to be the contents of the page seen by the editor who entered the reference on the |access-date=. If that parameter is not specified, a search of the article's revision history can be performed to determine when the link was added to the article.
For most citation templates, archive locations are entered using the |archive-url=, |archive-date= and |dead-url= parameters. The primary link is automatically switched to the archive when |dead-url=yes. This retains the original link location for reference.
If the webpage now leads to a completely different website, set |dead-url=usurped to hide the original website link in the citation.
Note: Some archives currently operate with a delay of ~18 months before a link is made public. As a result, editors should wait ~24 months after the link is first tagged as dead before declaring that no web archive exists. Dead URLs to reliable sources should normally be tagged with {{dead link|date=January 2017}}, so that you can estimate how long the link has been dead.
Bookmarklets to check common archive sites for archives of the current page:
Archive.org
javascript:void(window.open('https://web.archive.org/web/*/'+location.href))
WebCite
javascript:void(window.open('http://www.webcitation.org/query.php?url='+location.href))
Archive.is
javascript:void(window.open('http://archive.is/?run=1&url='+location.href))
Mementos interface
javascript:void(window.open('http://www.webarchive.org.uk/mementos/search/'+encodeURIComponent(location.href)+'?referrer='+encodeURIComponent(document.referrer)))
  1. Remove convenience links: If the material was published on paper (e.g., academic journal, newspaper article, magazine, book), then the dead URL is not necessary. Simply remove the dead URL, leaving the remainder of the reference intact.
  2. Find a replacement source: Search the web for quoted text, the article title, and parts of the URL. Consider contacting the website/person that originally published the reference and asking them to republish it. Ask other editors for help finding the reference somewhere else, including the user who added the reference. Find a different source that says essentially the same thing as the reference in question.
  3. Remove hopelessly lost web-only sources: If the source material does not exist offline, and if there is no archived version of the webpage (be sure to wait ~24 months), and if you cannot find another copy of the material, then the dead citation should be removed and the material it supports should be regarded as unverified if there is no other supporting citation. If it is material that is specifically required by policy to have an inline citation, then please consider tagging it with {{citation needed}}. It may be appropriate for you to move the citation to the talk page with an explanation, and notify the editor who added the now-dead link.

Text–source integrity

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For WikiProject Integrity (which is not related to text–source integrity), go here.

When using inline citations, it is important to maintain text–source integrity. The point of an inline citation is to allow readers and other editors to check that the material is sourced; that point is lost if the citation is not clearly placed. The distance between material and its source is a matter of editorial judgment, but adding text without clearly placing its source may lead to allegations of original research, of violations of the sourcing policy, and even of plagiarism.

Both of the following are acceptable:

YesY Mary likes cake, but John doesn't.<ref name=Mary/><ref name=John/>

YesY Mary likes cake,<ref name=Mary/> but John doesn't.<ref name=John/>

Editors should exercise caution when rearranging or inserting material to ensure that text–source relationships are maintained. References need not be moved solely to maintain the chronological order of footnotes as they appear in the article, and should not be moved if doing so might break the text-source relationship.

If a sentence or paragraph is footnoted with a source, adding new material to that sentence without a new source—or without making sure it is supported by the existing source—is highly misleading. When new text is inserted into a paragraph, make sure it is supported. For example, when editing text originally reading

The sun is pretty big.[1]

Notes

  1. ^ Miller, Edward. The Sun. Academic Press, 2005, p. 1.

an edit that does not imply that the new material is sourced by the same reference is

The sun is pretty big.[1] The sun is also quite hot.[2]

Notes

  1. ^ Miller, Edward. The Sun. Academic Press, 2005, p. 1.
  2. ^ Smith, John. The Sun's Heat. Academic Press, 2005, p. 2.

Do not add other facts or assertions into a fully cited paragraph or sentence:

N

The sun is pretty big, but the moon is not so big.[1] The sun is also quite hot.[2]

Notes

  1. ^ Miller, Edward. The Sun. Academic Press, 2005, p. 1.
  2. ^ Smith, John. The Sun's Heat. Academic Press, 2005, p. 2.

Include a source to support the new information. There are several ways to write this, including:

YesY

The sun is pretty big,[1] but the moon is not so big.[2] The sun is also quite hot.[3]

Notes

  1. ^ Miller, Edward. The Sun. Academic Press, 2005, p. 1.
  2. ^ Brown, Rebecca. "Size of the Moon", Scientific American, 51(78):46.
  3. ^ Smith, John. The Sun's Heat. Academic Press, 2005, p. 2.

Bundling citations

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Further information: Wikipedia:Citation overkill

Sometimes the article is more readable if multiple citations are bundled into a single footnote. For example, when there are multiple sources for a given sentence, and each source applies to the entire sentence, the sources can be placed at the end of the sentence, like this.[4][5][6][7] Or they can be bundled into one footnote at the end of the sentence or paragraph, like this.[4]

Bundling is also useful if the sources each support a different portion of the preceding text, or if the sources all support the same text. Bundling has several advantages:

  • It helps readers and other editors see at a glance which source supports which point, maintaining text–source integrity;
  • It avoids the visual clutter of multiple clickable footnotes inside a sentence or paragraph;
  • It avoids the confusion of having multiple sources listed separately after sentences, with no indication of which source to check for each part of the text, such as this.[1][2][3][4]
  • It makes it less likely that inline citations will be moved inadvertently when text is re-arranged, because the footnote states clearly which source supports which point.

When formatting multiple citations in a footnote, there are several layouts available, as illustrated below. Within a given article, only a single layout should be used.

The sun is pretty big, but the moon is not so big. The sun is also quite hot.[1]

Notes

  1. Bullets
  2. ^ For the sun's size, see Miller, Edward. The Sun. Academic Press, 2005, p. 1.
    • For the moon's size, see Brown, Rebecca. "Size of the Moon", Scientific American, 51(78):46.
    • For the sun's heat, see Smith, John. The Sun's Heat. Academic Press, 2005, p. 2.
    Line breaks
  3. ^ For the sun's size, see Miller, Edward. The Sun. Academic Press, 2005, p. 1.
    For the moon's size, see Brown, Rebecca. "Size of the Moon", Scientific American, 51(78):46.
    For the sun's heat, see Smith, John. The Sun's Heat. Academic Press, 2005, p. 2.

    Paragraph

  4. ^ For the sun's size, see Miller, Edward. The Sun. Academic Press, 2005, p. 1. For the moon's size, see Brown, Rebecca. "Size of the Moon", Scientific American, 51(78):46. For the sun's heat, see Smith, John. The Sun's Heat. Academic Press, 2005, p. 2.

In-text attribution

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Further information: Wikipedia:Neutral point of view § Attributing and specifying biased statements

In-text attribution is the attribution inside a sentence of material to its source, in addition to an inline citation after the sentence. In-text attribution should be used with direct speech (a source's words between quotation marks or as a block quotation); indirect speech (a source's words modified without quotation marks); and close paraphrasing. It can also be used when loosely summarizing a source's position in your own words. It avoids inadvertent plagiarism and helps the reader see where a position is coming from. An inline citation should follow the attribution, usually at the end of the sentence or paragraph in question.

For example:

YesY John Rawls says that, to reach fair decisions, parties must consider matters as if behind a veil of ignorance.[2]

When using in-text attribution, make sure it doesn't lead to an inadvertent neutrality violation. For example, the following implies parity between the sources, without making clear that the position of Darwin is the majority view:

N Charles Darwin says that human beings evolved through natural selection, but John Smith writes that we arrived here in pods from Mars.

Neutrality issues apart, there are other ways in-text attribution can mislead. The sentence below suggests The New York Times has alone made this important discovery:

N According to The New York Times, the sun will set in the west this evening.

It is preferable not to clutter articles with information best left to the references. Interested readers can click on the ref to find out the publishing journal:

N In an article published in The Lancet in 2012, researchers announced the discovery of the new tissue type.[3]

Simple facts such as this can have inline citations to reliable sources as an aid to the reader, but normally the text itself is best left as a plain statement without in-text attribution:

YesYBy mass, oxygen is the third most abundant element in the universe after hydrogen and helium.[4]

Dealing with unsourced material

Shortcuts:

If an article has no references at all, then:

  • If the entire article is "Patent Nonsense", tag it for speedy deletion using criterion G1.
  • If the article is a biography of a living person, it can be tagged with {{subst:prod blp}} to propose deletion. If it's a biography of a living person and is an attack page, then it should be tagged for speedy deletion using criterion G10, which will blank the page.
  • If the article doesn't fit into the above two categories, then consider finding references yourself, or commenting on the article talk page or the talk page of the article creator. You may also tag the article with the {{unreferenced}} template and consider nominating it for deletion.

For individual unreferenced claims in an article:

  • If the article is a biography of a living person, then any contentious material must be removed immediately: see Biographies of living persons. If the unreferenced material is seriously inappropriate, it may need to be hidden from general view, in which case request admin assistance.
  • If the material added appears to be false or an expression of opinion, remove it and inform the editor who added the unsourced material. The {{uw-unsourced1}} template may be placed on their talk page.
  • In any other case consider finding references yourself, or commenting on the article talk page or the talk page of the editor who added the unsourced material. You may place a {{citation needed}} or {{dubious}} tag against the added text.

Citation templates and tools

Shortcut:
Further information: Wikipedia:Citation templates and Help:Citation tools
For a comparison of citations using templates with citations written freehand, see Wikipedia:Citing sources/Example edits for different methods § Footnotes.

Citation templates can be used to format citations in a consistent way. The use of citation templates is neither encouraged nor discouraged: an article should not be switched between templated and non-templated citations without good reason and consensus – see Variation in citation methods above.

If citation templates are used in an article, the parameters should be accurate. It is inappropriate to set parameters to false values to cause the template to render as if it were written in some style other than the style normally produced by the template (e.g., MLA style).

Metadata

Citations may be accompanied by metadata, though it is not mandatory. Most citation templates on Wikipedia use the COinS standard. Metadata such as this allow browser plugins and other automated software to make citation data accessible to the user, for instance by providing links to their library's online copies of the cited works. In articles that format citations manually, metadata may be added manually in a span, according to the COinS specification.

Citation processing tools

Programming tools

See also: Help:Citation tools § Tools
  • Wikicite is a free program that helps editors to create citations for their Wikipedia contributions using citation templates. 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 page for further details.
    • Wikicite+ is a program based on the original Wikicite source code. It features extra validation, bug fixes, additional cite templates (such as cite episode) as well as tools for stub sorting and more. It is also available for free under the Apache License 2.0 and is open source.
  • User:Richiez has tools to automatically handle citations for a whole article at a time. Converts occurrences of {{pmid XXXX}} or {{isbn XXXX}} to properly formatted footnote or Harvard-style references. Written in Ruby and requires a working installation with basic libraries.
  • pubmed2wiki.xsl an XSL stylesheet transforming the XML output of PubMed to Wikipedia refs.
  • RefTag by Apoc2400 creates a prefilled {{cite book}} template with various options from a Google Books URL. The page provides a bookmarklet for single-click transfer.
  • wikiciter web interface, does Google Books, pdf files, beta.

Citation export tools

You can insert a link beside each citation in Wikipedia, allowing you to export the citation to a reference manager such as EndNote. To install the script just add the following line to Special:MyPage/skin.js (applies to the currently selected skin) or Special:MyPage/common.js (applies to all skins)"

importScript("User:Smith609/endnote.js");

Then save the page and follow the instructions at the top of that page to bypass your browser's cache.

Reference management software

Reference management software can output formatted citations in several styles, including BibTeX, RIS, or Wikipedia citation template styles.

Comparison of reference management software – side-by-side comparison of various reference management software
Wikipedia:Citing sources with Zotero – essay on using Zotero to quickly add citations to articles. Zotero (by Roy Rosenzweig Center for History and New Media; license: Affero GPL) is open-source software with local reference database which can be synchronized between several computers over the online database (up to 300 MB without payment).
EndNote (by Thomson Reuters; license: proprietary)
Mendeley (by Elsevier; license: proprietary)
Paperpile (by Paperpile, LLC; license: proprietary)
Papers (by Springer; license: proprietary)

See also

How to cite

Citation problems

Changing citation style formats

Notes

  1. ^ Words like citation and reference are used interchangeably on the English Wikipedia. On talk pages where the language can be more informal or in edit summaries or templates where space is a consideration, reference is often abbreviated ref with the plural refs. Footnote may refer specifically to citations using ref tag formatting or to explanatory text; endnotes specifically refers to citations placed at the end of the page. See also: Wikipedia:Glossary.
  2. ^ See this July 2007 discussion for more detail on why scrolling reference lists should not be used.

Further reading

External links

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