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:VERIFY WP:SOURCE

This page in a nutshell: Any material challenged or likely to be challenged, and all quotations, must be attributed to a reliable, published source using an inline citation. This applies to all articles, lists, and sections of articles, without exception.

The threshold for inclusion in Wikipedia is verifiability, not truth—what counts is whether readers can verify that material added to Wikipedia has already been published by a reliable source (see below), not whether we think it is true.

This policy requires that a reliable source in the form of an inline citation be supplied for any material that is challenged or likely to be challenged, and for all quotations, or the material may be removed. This is strictly applied to all material in the mainspace—articles, lists, and sections of articles—without exception, and in particular to information about living persons: unsourced contentious material about living persons should be removed immediately.

Because this is the English-language Wikipedia, English-language sources are preferred, although non-English sources are allowed.

Wikipedia:Verifiability is one of Wikipedia's core content policies, along with Wikipedia:No original research and Wikipedia:Neutral point of view. Jointly, these determine the type and quality of material that is acceptable in articles. They should not be interpreted in isolation from one another, and editors should therefore familiarize themselves with all three.

Burden of evidence

For how to write citations, see Wikipedia:Citing sources

The burden of evidence lies with the editor who adds or restores material.^[1] All quotations and any material challenged or likely to be challenged must be attributed to a reliable, published source using an inline citation. The source should be cited clearly and precisely, with page numbers where appropriate, and must clearly support the material as presented in the article.^[2] If no reliable, third-party sources can be found on a topic, Wikipedia should not have an article on it.

Any material lacking a reliable source may be removed, but how quickly this should happen depends on the material and the overall state of the article. Editors might object if you remove material without giving them time to provide references. It has always been good practice to make reasonable efforts to find sources oneself that support such material, and cite them.

If you want to request a source for an unsourced statement, consider tagging a sentence by adding the {{citation needed}} template, a section with {{unreferencedsection}}, or the article with {{refimprove}} or {{unreferenced}}. Alternatively, you may leave a note on the talk page requesting a source, or move the material to the talk page. Do not leave unsourced or poorly sourced material in an article if it might damage the reputation of living persons or organizations, and do not move it to the talk page.^[3]

Sources

See also: Wikipedia:Neutral point of view, Wikipedia:Biographies of living persons, and Wikipedia:No original research#Primary, secondary and tertiary sources

Reliable sources

The word "source", as used in Wikipedia, has three meanings: the piece of 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, The New York Times). All three can affect reliability.

Articles should be based on reliable, third-party, published sources with a reputation for fact-checking and accuracy. Reliable sources are needed to substantiate material within articles, and citations are needed to direct the reader to those sources to give credit to the writers and publishers. This avoids plagiarism, copyright violations, and unverifiable claims being added to articles. Sources should directly support the material as it is presented in an article, and should be appropriate to the claims made: exceptional claims require high-quality sources.

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. The most reliable sources are usually peer-reviewed journals; books published by university presses; university-level textbooks; magazines, journals, and books published by respected publishing houses; and mainstream newspapers. Electronic media may also be used, subject to the same criteria. Academic and peer-reviewed publications are highly valued and usually the most reliable sources in areas where they are available, such as history, medicine, and science. Material from reliable non-academic sources may also be used in these areas, particularly if it appears in respected mainstream publications. Where there is disagreement between sources, their views should be clearly attributed in the text: "John Smith argues that X, while Paul Jones maintains that Y," followed by an inline citation.

All articles must adhere to Wikipedia's neutrality policy, fairly representing all majority and significant-minority viewpoints that have been 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.

To discuss the reliability of specific sources, consult the Wikipedia:Reliable sources/Noticeboard. For a guideline discussing the reliability of particular types of sources, see Wikipedia:Reliable sources, but note that policies take precedence over guidelines, so in the case of inconsistency between this page and that one, this page has priority.

Questionable sources

Questionable sources are those with a poor reputation for checking the facts, or with no editorial oversight. Such sources include websites and publications expressing views that are widely acknowledged as extremist, or promotional in nature, or which rely heavily on rumors and personal opinions. Questionable sources should only be used as sources of material on themselves, especially in articles about themselves. (See below.) Questionable sources are generally unsuitable as a basis for citing contentious claims about third parties.

Self-published sources (online and paper)

Anyone can create a website or pay to have a book published, then claim to be an expert in a certain field. For that reason self-published media, whether books, newsletters, personal websites, open wikis, blogs, Internet forum postings, tweets, etc., are largely not acceptable.^[4]

Self-published material may, in some circumstances, be acceptable 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. However, caution should be exercised when using such sources: if the information in question is really worth reporting, someone else is likely to have done so.

Self-published sources should never be used as third-party sources about living persons, even if the author is a well-known professional researcher or writer; see WP:BLP#Reliable sources.

Self-published and questionable sources as sources on themselves

Self-published or questionable sources may be used as sources of information about themselves, especially in articles about themselves, without the requirement that they be published experts in the field, so long as:

1. the material is not unduly self-serving;
2. it does not involve claims about third parties;
3. it does not involve claims about events not directly related to the subject;
4. there is no reasonable doubt as to its authenticity;
5. the article is not based primarily on such sources.

Wikipedia and sources that mirror or source information from Wikipedia

Articles and posts on Wikipedia, or on websites that mirror its content, should not be used as sources, as this would amount to Wikipedia citing itself, a self-reference. As an exception, Wikipedia may be cited as a primary source (with caution) for information about itself, such as in articles about itself.

Editors should be careful not to use sources that present material originating from Wikipedia to support that same material in Wikipedia, as this would create circular sourcing—Wikipedia citing a source that derives its material from Wikipedia.

Non-English sources

Because this is the English Wikipedia, English-language sources should be used in preference to non-English ones, except where no English source of equal quality can be found that contains the relevant material. When quoting a source in a different language, provide both the original-language quotation and an English translation, in the text or in a footnote. Translations published by reliable sources are preferred over translations by Wikipedians. When citing a source in a different language, without quotations, the original and its translation should be provided if requested by other editors: this can be added to a footnote, or to the talk page if too long for a footnote. If posting original source material, editors should be careful not to violate copyright; see the fair-use guideline.

Exceptional claims require exceptional sources

Certain red flags should prompt editors to examine the sources for a given claim:

• surprising or apparently important claims not covered by mainstream sources;
• reports of a statement by someone that seems out of character, embarrassing, controversial, or against an interest they had previously defended;
• claims that are contradicted by the prevailing view within the relevant community, or which would significantly alter mainstream assumptions, especially in science, medicine, history, politics, and biographies of living persons. This is especially true when proponents consider that there is a conspiracy to silence them.

Exceptional claims in Wikipedia require high-quality sources.^[5] If such sources are not available, the material should not be included. Also be sure to adhere to other policies, such as the policy for biographies of living persons and the undue weight provision of Wikipedia:Neutral point of view.

Access to sources

Verifiability, in this context, means that anyone should be able to check the sources to verify that material in a Wikipedia article has already been published by a reliable source, as required by this policy and by No original research. 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 copies/excerpts of sources that are not easily accessible.

See also

Listen to this page (info/dl)

This audio file was created from a revision dated 2006-12-04, and does not reflect subsequent edits to the page. (Audio help)

More spoken pages

• Wikipedia:Core content policies, an essay with a summary of these policies and their brief history
• Wikipedia:List of free online resources
• Wikipedia:Fringe theories, a guideline
• Wikipedia:Template messages/Sources of articles
• WikiProject Fact and Reference Check
• WikiProject Resource Exchange
• Wikipedia:When to cite, an essay

Further reading

Notes