Wikipedia:Verifiability

The canonical description of this policy is at the unified WP:ATT page. This page is policy, but should track that page in terms of details. This page exists to give a rich explanation of the policy.

The threshold for inclusion in Wikipedia is verifiability, not truth. "Verifiable" in this context means that any reader should be able to check that material added to Wikipedia has already been published by a reliable source. Editors should provide a reliable source for quotations and for any material that is challenged or is likely to be challenged, or it may be removed.

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

Burden of evidence

For how to write citations, see Wikipedia:Citing sources

For how to dispute statements, see Wikipedia:Disputed statement

The burden of evidence lies with the editor who adds or restores material. Any material that is challenged or likely to be challenged needs a reliable source, which should be cited in the article. If an article topic has no reliable, third-party sources, Wikipedia should not have an article on it.

Any edit lacking a source may be removed, but editors may object if you remove material without giving them a chance to provide references. If you want to request a source for an unsourced statement, consider moving it to the talk page. Alternatively, you may tag the sentence by adding the {{fact}} template, or tag the article by adding {{not verified}} or {{unsourced}}. Leave a note on the talk page or edit summary explaining what you have done.

Be careful not to go too far on the side of not upsetting editors by leaving unsourced information in articles for too long, or at all in the case of information about living people. Jimmy Wales has said of this: "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."

Sources

See also: Wikipedia:Reliable sources and Wikipedia:Biographies of living persons

Articles should rely on reliable, third-party published sources with a reputation for fact-checking and accuracy. Sources should be appropriate to the claims made: exceptional claims require stronger sources.

Sources of dubious reliability

In general, sources of dubious reliability are sources with a poor reputation for fact-checking or with no fact-checking facilities or editorial oversight. Sources of dubious reliability should only be used in articles about the author(s). (See below.) Articles about such sources should not repeat any potentially libelous claims the source has made about third parties, unless those claims have also been published by reliable sources.

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 books, personal websites, and blogs are largely not acceptable as sources.

Self-published material may be acceptable when produced by a well-known, professional researcher in a relevant field or a well-known professional journalist. These may be acceptable so long as their work has been previously published by reliable third-party publications. However, exercise caution: if the information in question is really worth reporting, someone else is likely to have done so.

Self-published sources, such as blogs, 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.

Self-published and dubious sources in articles about themselves

Material from self-published sources, and published sources of dubious reliability, may be used as sources in articles about the author(s) of the material, so long as:

• it is relevant to their notability;
• it is not contentious;
• it is not unduly self-serving;
• it does not involve claims about third parties, or about events not directly related to the subject;
• there is no reasonable doubt as to who wrote it.

Sources in languages other than English

Because this is the English Wikipedia, for the convenience of our readers, English-language sources should be used in preference to foreign-language sources, assuming equal quality, so that readers can easily verify that the source material has been used correctly.

Keep in mind that translations are subject to error, whether performed by a Wikipedia editor or a professional, published translator. In principle, readers should have the opportunity to verify for themselves what the original material actually said, that it was published by a credible source, and that it was translated correctly.

Therefore, when the original material is in a language other than English:

• Where sources are directly quoted, published translations are generally preferred over editors performing their own translations directly.
• Where editors use their own English translation of a non-English source as a quote in an article, there should be clear citation of the foreign-language original, so that readers can check what the original source said and the accuracy of the translation.

See also

• WikiProject Fact and Reference Check
• Forum for Encyclopedic Standards
• WikiProject Resource Exchange

Further reading

• Jimmy Wales. "WikiEN-l insist on sources", WikiEN-l mailing list, July 19, 2006.