Wikipedia:Verifiability
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 | This page in a nutshell: Material challenged or likely to be challenged, and all quotations, must be attributed to a reliable, published source. |
The threshold for inclusion in Wikipedia is verifiability, not truth—that is, whether readers are able to check that material added to Wikipedia has already been published by a reliable source, not whether we think it is true. Editors should provide a reliable source for quotations and for any material that is challenged or likely to be challenged, otherwise the material may be removed.
Wikipedia:Verifiability is one of Wikipedia's core content policies. The others 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 familiarize themselves with all three policies. To discuss the reliability of particular sources, see the reliable sources noticeboard.
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. All quotations and any material challenged or likely to be challenged must be attributed to a reliable, published source using an inline citation.[1] The source cited must unambiguously support the information as it is presented in the article.[2] The source should be cited clearly and precisely to enable readers to find the text that supports the article content in question. Editors should cite sources fully, providing as much publication information as possible, including page numbers when citing books.
If no reliable, third-party sources can be found for an article 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 in question and the overall state of the article. Editors might object if you remove material without giving them enough time to provide references, especially in an underdeveloped article. 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 {{fact}} 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. However, 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; see Wikipedia:Biographies of living persons.[3]
Sources
Reliable sources
Articles should be based upon reliable, third-party published sources with a reputation for fact-checking and accuracy.[4] Reliable sources are needed to substantiate material within articles, and citations directing the reader to those sources are needed to give credit to authors and publishers, in order to avoid plagiarism and copyright violations. Sources should directly support the information as it is presented in an article and should be appropriate to the claims made: exceptional claims require high-quality sources.
In general, the most reliable sources are peer-reviewed journals and books published in university presses; university-level textbooks; magazines, journals, and books published by respected publishing houses; and mainstream newspapers. Electronic media may also be used. As a rule of thumb, the greater the degree of scrutiny involved in checking facts, analyzing legal issues, and scrutinizing the evidence and arguments of a particular work, the more reliable the source is.
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 they are respected mainstream publications. The appropriateness of any source always depends on the context. Where there is disagreement between sources, their views should be clearly attributed in the text.
For a guideline discussing the reliability of particular types of sources, see Wikipedia:Reliable sources (WP:RS). Because policies take precedence over guidelines, in the case of an inconsistency between this page and that one, this page has priority, and WP:RS should be updated accordingly. To discuss the reliability of specific sources, consult the Wikipedia:Reliable sources/Noticeboard.
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 and fringe theories need not be included, except in articles devoted to them.
Questionable sources
Questionable sources are those with a poor reputation for fact-checking, 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.[5]
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:
- the material is not unduly self-serving;
- it does not involve claims about third parties;
- it does not involve claims about events not directly related to the subject;
- there is no reasonable doubt as to its authenticity;
- 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 result in a self-reference (Wikipedia citing itself). An exception may be made in articles about Wikipedia. In addition, sources that present material known to originate from Wikipedia should not subsequently be used to support that same material in Wikipedia, as this would create circular sourcing (Wikipedia citing a source which already cited Wikipedia for the same material).
Non-English sources
English-language sources are preferable to sources in other languages so that readers can easily verify the content of the article. However, sources in other languages are acceptable where an English equivalent is not available. Where editors translate a direct quotation, they should quote the relevant portion of the original text in a footnote or in the article. Translations published by reliable sources are preferred over translations made by Wikipedia editors.
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.[6] 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.
See also
- Wikipedia:Accuracy dispute
- Wikipedia:Core content policies
- Wikipedia:Free online resources
- Wikipedia:Fringe theories
- Wikipedia:List of sources
- Wikipedia:Template messages/Sources of articles
- WikiProject Fact and Reference Check
- WikiProject Resource Exchange
Notes
- ^ When content in Wikipedia requires direct substantiation, the established convention is to provide an inline citation to the supporting references. The rationale is that this provides the most direct means to verify whether the content is consistent with the references. Alternative conventions exist, and are acceptable if they provide clear and precise attribution for the article's assertions, but inline citations are considered 'best practice' under this rationale. For more details, please consult Wikipedia:Citing sources#How to cite sources.
- ^ When there is dispute about whether the article text is fully supported by the given source, direct quotes from the source and any other details requested should be provided as a courtesy to substantiate the reference.
- ^ As Wikipedia co-founder Jimmy Wales has put it: "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" (Jimmy Wales Zero information is preferred to misleading or false information, WikiEN-l, May 16, 2006, accessed June 11, 2006).
- ^ The word "source", as used in Wikipedia, has three related meanings: the piece of work itself (an article, book, paper, document), the creator of the work (for example, the writer), and the publisher of the work (for example, The New York Times or Cambridge University Press). All three can affect reliability.
- ^ "Blogs" in this context refers to personal and group blogs. Some newspapers host interactive columns that they call blogs, and these may be acceptable as sources so long as the writers are professionals and the blog is subject to the newspaper's full editorial control. Where a news organization publishes the opinions of a professional but claims no responsibility for the opinions, the writer of the cited piece should be attributed (e.g. "Jane Smith has suggested..."). Posts left by readers may never be used as sources.
- ^ This idea—that exceptional claims require exceptional sources—has an intellectual history which traces back through the Enlightenment. In 1758, David Hume wrote in An Enquiry Concerning Human Understanding: "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 endeavors to establish." (available here at Project Gutenberg)
Further reading
- Jimmy Wales. "WikiEN-l insist on sources", WikiEN-l mailing list, July 19, 2006.
