Wikipedia:Verifiability

This page documents an English Wikipedia policy, a widely accepted standard that all editors should normally follow. Changes made to it should reflect consensus.

Shortcuts: WP:V WP:VER WP:VERIFY

This page in a nutshell: Readers must be able to check that Wikipedia articles are not just made up. This means that all quotations and any material challenged or likely to be challenged must be attributed to a reliable, published source using an inline citation.

In Wikipedia, verifiability means that anyone using the encyclopedia can check the information comes from a reliable source. Wikipedia does not publish original research. Its content is determined by previously published information rather than the beliefs or experiences of its editors. Even if you're sure something is true, it must be verifiable before you can add it.^[1] When reliable sources disagree, present what the various sources say, give each side its due weight, and maintain a neutral point of view.

All material in Wikipedia mainspace, including everything in articles, lists and captions, must be verifiable. All quotations, and any material whose verifiability has been challenged or is likely to be challenged, must include an inline citation that directly supports the material. Any material that needs a source but does not have one may be removed. Please remove contentious material about living people that is unsourced or poorly sourced immediately.

For how to write citations, see citing sources. Verifiability, no original research and neutral point of view are Wikipedia's core content policies. They work together to determine content, so editors should understand the key points of all three. Articles must also comply with the copyright policy.

1 Responsibility for providing citations
2 Reliable sources
3 Sources that are usually not reliable
4 Accessibility
- 4.1 Access to sources
- 4.2 Non-English sources
  - 4.2.1 Citing non-English sources
  - 4.2.2 Quoting non-English sources
5 Other issues
6 Verifiability and other principles
7 See also
8 Notes
9 Further reading

Responsibility for providing citations

Policy shortcuts: WP:UNSOURCED WP:CHALLENGE WP:BURDEN WP:PROVEIT

All content must be verifiable. The burden to demonstrate verifiability lies with the editor who adds or restores material, and is satisfied by providing a citation to a reliable source that directly supports the contribution.^[2]

Attribute all quotations and any material challenged or likely to be challenged to a reliable, published source using an inline citation. Cite the source clearly and precisely (specifying page, section, or such divisions as may be appropriate). The citation must clearly support the material as presented in the article. See Citing sources for details of how to do this.

Any material lacking a reliable source directly supporting it may be removed and should not be restored without an inline citation to a reliable source. Whether and how quickly this should happen depends on the material and the overall state of the article. In some cases, editors may object if you remove material without giving them time to provide references; consider adding a citation needed tag as an interim step.^[3] When tagging or removing material for lacking an inline citation, please state your concern that there may not be a published reliable source for the content, and therefore it may not be verifiable.^[4] If you think the material is verifiable, you are encouraged to provide an inline citation yourself before considering whether to remove or tag it.

Do not leave unsourced or poorly sourced material in an article if it might damage the reputation of living people or existing groups, and do not move it to the talk page. You should also be aware of how the BLP policy applies to groups.^[5]

Reliable sources

Policy shortcuts: WP:SOURCE WP:SOURCES

What counts as a reliable source

The word "source" in Wikipedia has three meanings:

The type of the work (some examples include a document, an article, or a book)
The creator of the work (for example, the writer)
The publisher of the work (for example, Oxford University Press)

All three can affect reliability.

Base articles on reliable, third-party, published sources with a reputation for fact-checking and accuracy. Source material must have been published, the definition of which for our purposes is "made available to the public in some form".^[6] Unpublished materials are not considered reliable. Use sources that directly support the material presented in an article and are appropriate to the claims made. The appropriateness of any source depends on the context. The best sources have a professional structure in place for checking or analyzing facts, legal issues, evidence, and arguments. The greater the degree of scrutiny given to these issues, the more reliable the source. Be especially careful when sourcing content related to living people or medicine.

If available, academic and peer-reviewed publications are usually the most reliable sources, such as in history, medicine, and science.

Editors may also use material from reliable non-academic sources, particularly if it appears in respected mainstream publications. Other reliable sources include:

University-level textbooks
Books published by respected publishing houses
Magazines
Journals
Mainstream newspapers

Editors may also use electronic media, subject to the same criteria. See details in Wikipedia:Identifying reliable sources and Wikipedia:Search engine test.

Newspaper and magazine blogs

Policy shortcut: WP:NEWSBLOG

Several newspapers, magazines, and other news organizations host columns on their web sites that they call blogs. These may be acceptable sources if the writers are professionals, but use them with caution because the blog may not be subject to the news organization's normal fact-checking process.^[7] If a news organization publishes an opinion piece in a blog, attribute the statement to the writer (e.g. "Jane Smith wrote..."). Never use blog posts that are left by readers as sources. For personal or group blogs that are not reliable sources, see Self-published sources below.

Reliable sources noticeboard and WP:IRS

To discuss the reliability of a specific source for a particular statement, consult the reliable sources noticeboard, which seeks to apply this policy to particular cases. For a guideline discussing the reliability of particular types of sources, see Wikipedia:Identifying reliable sources (WP:IRS). In the case of inconsistency between this policy and the WP:IRS guideline, or any other guideline related to sourcing, this policy has priority.

Sources that are usually not reliable

Policy shortcuts: WP:NOTRELIABLE WP:NOTRS WP:QS

Questionable sources

Questionable sources are those that have a poor reputation for checking the facts, lack meaningful editorial oversight, or have an apparent conflict of interest.^[8] Such sources include websites and publications expressing views that are widely considered by other sources to be extremist or promotional, or that rely heavily on unsubstantiated gossip, rumor or personal opinion. Questionable sources should only be used as sources of material on themselves, especially in articles about themselves; see below. They are not suitable sources for contentious claims about others.

Self-published sources

Policy shortcuts: WP:SPS WP:SELFPUBLISH WP:BLOGS

Anyone can create a personal web page or publish their own book, and also claim to be an expert in a certain field. For that reason, self-published media, such as books, patents, newsletters, personal websites, open wikis, personal or group blogs (as distinguished from newsblogs, above), Internet forum postings, and tweets, are largely not acceptable as sources. Self-published expert sources may be considered reliable when produced by an established expert on the subject matter, whose work in the relevant field has previously been published by reliable third-party publications.^[7] Exercise caution when using such sources: if the information in question is really worth reporting, someone else will probably have done so.^[9] Never use self-published sources as third-party sources about living people, even if the author is an expert, well-known professional researcher, or writer.

Self-published or questionable sources as sources on themselves

Policy shortcuts: WP:ABOUTSELF WP:SELFPUB WP:TWITTER WP:SOCIALMEDIA

Self-published and questionable sources may be used as sources of information about themselves, usually in articles about themselves or their activities, without the self-published source requirement that they be published experts in the field, so long as:

the material is neither unduly self-serving nor an exceptional claim;
it does not involve claims about third parties;
it does not involve claims about events not directly related to the source;
there is no reasonable doubt as to its authenticity;
the article is not based primarily on such sources.

This policy also applies to pages on social networking websites such as Twitter, Tumblr, and Facebook.

Wikipedia and sources that mirror or use it

Policy shortcuts: WP:CIRC WP:CIRCULAR

Circular citations in real life, featuring a real life Wikipedian

Do not use articles from Wikipedia as sources. Also, do not use websites that mirror Wikipedia content or publications that rely on material from Wikipedia as sources. Content from a Wikipedia article is not considered reliable unless it is backed up by citing reliable sources. Confirm that these sources support the content, then use them directly. (There is also a risk of circular reference when using a Wikipedia article or derivative work as a source.)

An exception is allowed when Wikipedia is being discussed in the article, which may cite an article, guideline, discussion, statistic or other content from Wikipedia or a sister project to support a statement about Wikipedia. Wikipedia or the sister project is a primary source in this case, and may be used following the policy for primary sources. Any such use should avoid original research, undue emphasis on Wikipedia's role or views, and inappropriate self-reference. The article text should make it clear that the material is sourced from Wikipedia so the reader is made aware of the potential bias.

Accessibility

Access to sources

Policy shortcuts: WP:PAYWALL WP:SOURCEACCESS

Some reliable sources may not be easily accessible. For example, an online source may require payment, and a print source may be available only in university libraries or other offline places. Do not reject sources just because they are hard or costly to access. If you have trouble accessing a source, others may be able to do so on your behalf (see WikiProject Resource Exchange).

Non-English sources

Policy shortcuts: WP:RSUE WP:NOENG WP:NONENG

Citing non-English sources

Citations to non-English sources are allowed. However, because this is the English-language Wikipedia, English-language sources are preferred over non-English ones whenever English sources of equal quality and relevance are available. As with sources in English, if a dispute arises involving a citation to a non-English source, editors may request that a quotation of relevant portions of the original source be provided, either in text, in a footnote, or on the article talk page.^[10] (See Template:Request quotation.)

Quoting non-English sources

When quoting a non-English source (whether in the main text, in a footnote, or on the talk page), a translation into English should always accompany the quote. Translations published by reliable sources are preferred over translations by Wikipedians, but translations by Wikipedians are preferred over machine translations. When using a machine translation of source material, editors should be reasonably certain that the translation is accurate and the source is appropriate. Editors should not use machine translations of non-English sources in contentious articles or biographies of living people. If needed, ask an editor who can translate it for you.

In articles, the original text is usually included with the translated text when translated by Wikipedians, and the translating editor is usually not cited. When quoting any material, whether in English or in some other language, be careful not to violate copyright; see the fair-use guideline.

Other issues

Verifiability does not guarantee inclusion

Shortcut: WP:ONUS

While information must be verifiable in order to be included in an article, this does not mean that all verifiable information must be included in an article. Consensus may determine that certain information does not improve an article, and that it should be omitted or presented instead in a different article. The onus to achieve consensus for inclusion is on those seeking to include disputed content.

Tagging a sentence, section, or article

If you want to request a source for an unsourced statement, you can tag a sentence with the {{citation needed}} template by writing {{cn}} or {{fact}}. There are other templates here for tagging sections or entire articles. You can also leave a note on the talk page asking for a source, or move the material to the talk page and ask for a source there. To request verification that a reference supports the text, tag it with {{verification needed}}. Material that fails verification may be tagged with {{failed verification}} or removed. When using templates to tag material, it is helpful to other editors if you explain your rationale in the template, edit summary, or on the talk page.

Take special care with material about living people. Contentious material about living people that is unsourced or poorly sourced should be removed immediately, not tagged or moved to the talk page.

Exceptional claims require exceptional sources

Policy shortcuts: WP:REDFLAG WP:EXCEPTIONAL

Any exceptional claim requires multiple high-quality sources.^[11] Red flags that should prompt extra caution include:

surprising or apparently important claims not covered by multiple mainstream sources;
challenged claims that are supported purely by primary or self-published sources or those with an apparent conflict of interest;^[8]
reports of a statement by someone that seems out of character, or against an interest they had previously defended;
claims that are contradicted by the prevailing view within the relevant community, or that would significantly alter mainstream assumptions, especially in science, medicine, history, politics, and biographies of living people. This is especially true when proponents say there is a conspiracy to silence them.

Verifiability and other principles

Copyright and plagiarism

Do not plagiarize or breach copyright when using sources. Summarize source material in your own words as much as possible; when quoting or closely paraphrasing a source use an inline citation, and in-text attribution where appropriate.

Do not link to any source that violates the copyrights of others per contributors' rights and obligations. You can link to websites that display copyrighted works as long as the website has licensed the work, or uses the work in a way compliant with fair use. Knowingly directing others to material that violates copyright may be considered contributory copyright infringement. If there is reason to think a source violates copyright, do not cite it. This is particularly relevant when linking to sites such as YouTube, where due care should be taken to avoid linking to material that violates copyright.

Neutrality

Even when information is cited to reliable sources, you must present it with a neutral point of view (NPOV). All articles must adhere to NPOV, fairly representing all majority and significant-minority viewpoints published by reliable sources, in rough proportion to the prominence of each view. Tiny-minority views need not be included, except in articles devoted to them. If there is disagreement between sources, use in-text attribution: "John Smith argues that X, while Paul Jones maintains that Y," followed by an inline citation. Sources themselves do not need to maintain a neutral point of view. Indeed, many reliable sources are not neutral. Our job as editors is simply to summarize what the reliable sources say.

Notability

If no reliable third-party sources can be found on a topic, Wikipedia should not have an article on it.

Original research

The "No original research" policy (NOR) is closely related to the Verifiability policy. Among its requirements are:

All material in Wikipedia articles must be attributable to a reliable published source. This means that a source must exist for it, whether or not it is cited in the article.
Sources must support the material clearly and directly: drawing inferences from multiple sources to advance a novel position is prohibited by the NOR policy.^[10]
Base articles largely on reliable secondary sources. While primary sources are appropriate in some cases, relying on them can be problematic. For more information, see the Primary, secondary, and tertiary sources section of the NOR policy, and the Misuse of primary sources section of the BLP policy.

Notes

^ This principle was previously expressed on this policy page as "the threshold for inclusion is verifiability, not truth." See the essay, WP:Verifiability, not truth.
^ Once an editor has provided any source that he or she believes, in good faith, to be sufficient, then any editor who later removes the material has an obligation to articulate specific problems that would justify its exclusion from Wikipedia (e.g., undue emphasis on a minor point, unencyclopedic content, etc.). All editors are then expected to help achieve consensus, and any problems with the text or sourcing should be fixed before the material is added back.
^ It may be that the article contains so few citations that it is impractical to add specific citation needed tags, in which case consider tagging a section with {{unreferencedsection}}, or the article with {{refimprove}} or {{unreferenced}}. In the case of a disputed category or on a disambiguation page, consider asking for a citation on the talk page.
^ When tagging or removing such material, please keep in mind that such edits can be easily misunderstood. Some editors object to others making chronic, frequent, and large-scale deletions of unsourced information, especially if unaccompanied by other efforts to improve the material. Do not concentrate only on material of a particular POV, as that may result in accusations that you are in violation of WP:NPOV. Also check to see whether the material is sourced to a citation elsewhere on the page. For all of these reasons, it is advisable to communicate clearly that you have a considered reason to believe that the material in question cannot be verified.
^ Wales, Jimmy. "Zero information is preferred to misleading or false information", WikiEN-l, May 16, 2006: "I can NOT emphasize this enough. There seems to be a terrible bias among some editors that some sort of random speculative 'I heard it somewhere' pseudo information is to be tagged with a 'needs a cite' tag. Wrong. It should be removed, aggressively, unless it can be sourced. This is true of all information, but it is particularly true of negative information about living persons."
^ This includes material such as documents in publicly-accessible archives, inscriptions on monuments, gravestones, etc., that are available for anyone to see.
^ ^a ^b Please do note that any exceptional claim would require exceptional sources
^ ^a ^b Sources that may have interests other than professional considerations in the matter being reported are considered to be conflicted sources. Further examples of sources with conflicts of interest include but are not limited to articles by any media group that promote the holding company of the media group or discredit its competitors; news reports by journalists having financial interests in the companies being reported or in their competitors; material (including but not limited to news reports, books, articles and other publications) involved in or struck down by litigation in any country, or released by parties involved in litigation against other involved parties, during, before or after the litigation; and promotional material released through media in the form of paid news reports. For definitions of sources with conflict of interest:
- The Columbia Center for New Media Teaching and Learning, Columbia University mentions: "A conflict of interest involves the abuse – actual, apparent, or potential – of the trust that people have in professionals. The simplest working definition states: A conflict of interest is a situation in which financial or other personal considerations have the potential to compromise or bias professional judgment and objectivity. An apparent conflict of interest is one in which a reasonable person would think that the professional's judgment is likely to be compromised. A potential conflict of interest involves a situation that may develop into an actual conflict of interest. It is important to note that a conflict of interest exists whether or not decisions are affected by a personal interest; a conflict of interest implies only the potential for bias, not a likelihood. It is also important to note that a conflict of interest is not considered misconduct in research, since the definition for misconduct is currently limited to fabrication, falsification, and plagiarism."
- The New York Times Company forwards this understanding: "Conflicts of interest, real or apparent, may come up in many areas. They may involve the relationships of staff members with readers, news sources, advocacy groups, advertisers, or competitors; with one another, or with the newspaper or its parent company. And at a time when two-career families are the norm, the civic and professional activities of spouses, family and companions can create conflicts or the appearance of conflicts."
^ Self-published material is characterized by the lack of independent reviewers (those without a conflict of interest) validating the reliability of contents. Further examples of self-published sources include press releases, material contained within company websites, advertising campaigns, material published in media by the owner(s)/publisher(s) of the media group, self-released music albums and electoral manifestos:
- The University of California, Berkeley library states: "Most pages found in general search engines for the web are self-published or published by businesses small and large with motives to get you to buy something or believe a point of view. Even within university and library web sites, there can be many pages that the institution does not try to oversee."
- Princeton University offers this understanding in its publication, Academic Integrity at Princeton (2011): "Unlike most books and journal articles, which undergo strict editorial review before publication, much of the information on the Web is self-published. To be sure, there are many websites in which you can have confidence: mainstream newspapers, refereed electronic journals, and university, library, and government collections of data. But for vast amounts of Web-based information, no impartial reviewers have evaluated the accuracy or fairness of such material before it's made instantly available across the globe."
- The Chicago Manual of Style, 16th Edition states, "any Internet site that does not have a specific publisher or sponsoring body should be treated as unpublished or self-published work."
^ ^a ^b When there is dispute about whether a piece of text is fully supported by a given source, direct quotes and other relevant details from the source should be provided to other editors as a courtesy. Do not violate the source's copyright when doing so.
^ Hume, David. An Enquiry concerning Human Understanding, Forgotten Books, 1984; first published 1748, pp. 82, 86: "A wise man ... proportions his belief to the evidence. ... That no testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavours to establish; and even in that case there is a mutual destruction of arguments, and the superior only gives us an assurance suitable to that degree of force, which remains, after deducting the inferior." In the 18th century, Pierre-Simon Laplace reformulated the idea as "The weight of evidence for an extraordinary claim must be proportioned to its strangeness." Marcello Truzzi recast it again, in 1978, as "An extraordinary claim requires extraordinary proof." Carl Sagan, finally, popularized the concept broadly as "Extraordinary claims require extraordinary evidence" in 1980 on Cosmos; this was the formulation originally used on Wikipedia.