All quotations and any material challenged or likely to be challenged must be attributed to a reliable published source using an inline citation. The citation should fully identify the source, and the location within the source (specifying page, section, or such divisions as may be appropriate) where the material is to be found. See Citing sources for details of how to do this.
Burden of evidence
WP:BURDEN
WP:UNSOURCED
The burden of evidence lies with the editor who adds or restores material. You may remove any material lacking an inline citation to a reliable source. Whether and how quickly removal should happen depends on the material and the overall state of the article; consider adding a citation needed tag as an interim step.[2] Editors might object if you remove material without giving them time to provide references. It has always been good practice to try to find and cite supporting sources yourself. Do not leave unsourced or poorly sourced material in an article if it might damage the reputation of living people; you should also be aware of how the BLP policy applies to groups.[3]
Reliable sources
WP:SOURCES
What counts as a reliable source
The word "source" in Wikipedia has three meanings: the work itself (a document, article, paper, or book), the creator of the work (for example, the writer), and the publisher of the work (for example, Oxford University Press). All three can affect reliability.
Articles should be based on reliable, third-party, published sources with a reputation for fact-checking and accuracy. Source material must have been published (made available to the public in some form); unpublished materials are not considered reliable. Sources should directly support the material presented in an article and should be appropriate to the claims made. The appropriateness of any source depends on the context. In general, the best sources have a professional structure in place for checking or analyzing facts, legal issues, evidence, and arguments; as a rule of thumb, the greater the degree of scrutiny given to these issues, the more reliable the source. Content related to living people or medicine should be sourced especially carefully.
Where available, academic and peer-reviewed publications are usually the most reliable sources, such as in history, medicine, and science. But they are not the only reliable sources in such areas. Material from reliable non-academic sources may also be used, particularly if it appears in respected mainstream publications. Other reliable sources include university-level textbooks, books published by respected publishing houses, magazines, journals, and mainstream newspapers. Electronic media may also be used, subject to the same criteria. See details in Wikipedia:Identifying reliable sources and Wikipedia:Search engine test.
Newspaper and magazine blogs
WP:NEWSBLOG
Several newspapers, magazines, and other news organizations host columns on their web sites that they call blogs. These may be acceptable as sources if the writers are professionals but should be used with caution because the blog may not be subject to the news organization's normal fact checking process.[4] Where 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 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.
Questionable sources are those with a poor reputation for checking the facts, or which lack meaningful editorial oversight, or those with an apparent conflict of interest.[5]Such sources include, but are not limited to, websites and publications expressing views that are widely considered by other sources to be extremist or promotional, or which rely heavily on rumor and personal opinion. Questionable sources should be used only as sources of material on themselves, especially in articles about themselves; see below. They are unsuitable for citing contentious claims about third parties.
Self-published sources
WP:SPS
WP:SELFPUBLISH
WP:BLOGS
Anyone can create a personal web page or pay to have a book published, and then 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, 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 topic of the article whose work in the relevant field has previously been published by reliable third-party publications.[4] Take care when using such sources: if the information in question is really worth reporting, someone else will probably have done so.[6]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
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 requirement in the case of self-published sources that they be published experts in the field, so long as:
the material is not unduly self-serving and exceptional in nature;
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 sites such as Twitter, Tumblr, and Facebook.
Wikipedia and sources that mirror or use it
WP:CIRCULAR
Do not use articles from Wikipedia or from websites that mirror its content as sources, because this would amount to self-reference. Similarly, do not use sources that present material originating from Wikipedia to support that same material in Wikipedia, as this would create circular sourcing. Citing Wikipedia to support a descriptive statement about Wikipedia itself is not a form of circular referencing. Instead it is the use of Wikipedia as a primary source and should follow the relevant policy for the use of primary sources.
Accessibility
Access to sources
WP:PAYWALL
WP:SOURCEACCESS
Verifiability in this context means that other people should be able to check that material in a Wikipedia article has been published by a reliable source. The principle of verifiability implies nothing about ease of access to sources: some online sources may require payment, while some print sources may be available only in university libraries. WikiProject Resource Exchange may be able to assist in obtaining source material.
Because this is the English Wikipedia, English-language sources are preferred over non-English ones, assuming English sources of equal quality and relevance are available.
When quoting a source in a different language, provide the original text and an English translation, either in the body of the article or in a footnote.
When citing a non-English source for information, it is not always necessary to provide a translation. However, if a question should arise as to whether the non-English original actually supports the information, relevant portions of the original and a translation should be given in a footnote, as a courtesy.[7]
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. When posting original source material, be careful not to violate copyright; see the fair-use guideline.
Other issues
Tagging a sentence, section, or article
If you want to request a source for an unsourced statement, consider tagging a sentence with the {{citation needed}} template by writing {{cn}} or {{fact}}. Other templates are available here for tagging sections or entire articles. Alternatively, leave a note on the talk page requesting 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.
Special care should be used in regard to material about living people. Unsourced or poorly sourced contentious material about living people should be removed immediately, not tagged or moved to the talk page.
Exceptional claims require exceptional sources
WP:REDFLAG
WP:EXCEPTIONAL
Any exceptional claim requires multiple high-quality sources.[8]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;[5]
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
Take care to avoid plagiarism and breaches of 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.
Material that violates the copyrights of others per contributors' rights and obligations should not be cited. Linking to websites that display copyrighted works is acceptable 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 believe that a source is in violation of 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
All articles must adhere to the Neutral point of view policy (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. Where 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 present 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.[7]
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.
Wales, Jimmy. "Insist on sources", WikiEN-l, July 19, 2006: "I really want to encourage a much stronger culture which says: it is better to have no information, than to have information like this, with no sources."—referring to a rather unlikely statement about the founders of Google throwing pies at each other.
