Wikipedia:Verifiability
- To discuss particular sources, see the reliable sources noticeboard. For vandalism, see WP:VAND.
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 | This page in a nutshell: All quotations and any material challenged or likely to be challenged must be attributed to a reliable, published source using an inline citation. |
The threshold for inclusion in Wikipedia is verifiability, not truth—whether readers can check that material in Wikipedia has already been published by a reliable source, not whether editors think it is true.
All material in Wikipedia articles must be attributable to a reliable published source to show that it is not original research, but in practice not everything need actually be attributed. This policy requires that anything challenged or likely to be challenged, including all quotations, be attributed to a reliable source in the form of an inline citation, and that the source directly supports the material in question. See the discussion on sources in WP:NOR that describes summarizing matters fully and clearly in your own words, leaving nothing implied that goes beyond the sources. For how to write citations, see Citing sources.
Verifiability is one of Wikipedia's core content policies, along with No original research and 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.
Reliable sources and other principles
Reliable sources and notability
If no reliable third-party sources can be found on a topic, Wikipedia should not have an article on it.
Reliable sources and neutrality
All articles must adhere to the Neutral point of view policy (NPOV) 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. 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.
Reliable sources and original research
The No original research policy (NOR) has three requirements relevant to the Verifiability policy:
- 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. Wikipedia must never be a first publisher.
- Sources must support the material clearly and directly: drawing inferences from multiple sources to advance a novel position—called original synthesis, or original SYN—is prohibited by the NOR policy.[1]
- Articles should be based largely on reliable secondary sources. While primary sources are normally welcome, there are dangers in relying on them. See the Primary, secondary, and tertiary sources section of the NOR policy for more information.
When a reliable source is required
Anything challenged or likely to be challenged
This policy requires that all quotations and any material challenged or likely to be challenged be attributed to a reliable published source using an inline citation. The source should be cited clearly and precisely, with page numbers where appropriate.
Burden of evidence
The burden of evidence lies with the editor who adds or restores material. Any material lacking a reliable source directly supporting it may be removed. 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 yourself that support such material, and cite them. 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.[2]
Reliable sources
What counts as a reliable source
The word "source" 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. Sources should directly support the material as it is 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.
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.
Newspaper and magazine blogs
Several newspapers host columns that they call blogs. These are acceptable as sources so long as the writers are professionals and the blog is subject to the newspaper's full editorial control. In March 2010, the Press Complaints Commission in the UK ruled that journalists' blogs hosted on the websites of newspapers or magazines are subject to the same standards expected of comment pieces in that organization's print editions.[3] Where a news organization publishes an opinion piece, the writer should be attributed (e.g. "Jane Smith has suggested..."). Posts left by readers may never be used as sources.
Sources that are usually not reliable
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, 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 generally unsuitable for citing contentious claims about third parties.
Self-published sources
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, such as books, 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. 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 an expert, or well-known professional researcher or writer.
Self-published or questionable sources as sources on themselves
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;
- 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.
Accessibility
Access to sources
Verifiability in this context means that anyone should be able to check that material in a Wikipedia article has already 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.
Non-English sources
Because this is the English Wikipedia, English-language sources are preferred over non-English ones, unless no English sources of equal quality and relevance are available. When quoting a source in a different language, provide both the original-language text and an English translation in the text or a footnote. Translations published by reliable sources are preferred over translations by Wikipedians. When citing such a source without quoting it, the original and its translation should be provided if requested by other editors: this can be added to a footnote or the talk page. When posting original source material, editors should 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 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. Unsourced or poorly sourced contentious material about living persons should be removed immediately and not tagged or moved to the talk page.
Exceptional claims require exceptional sources
Exceptional claims require high-quality sources.[4] Red flags that should prompt extra caution include:
- surprising or apparently important claims not covered by mainstream sources;
- 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 persons. This is especially true when proponents say there is a conspiracy to silence them.
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, the policy has priority.
Wikipedia and sources that mirror or use it
Articles on Wikipedia or on websites that mirror its content should not be used as sources, because this would amount to self-reference. Similarly, editors should not 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. Wikipedia may be cited with caution as a primary source of information on itself, such as in articles about itself.
See also
- Wikipedia:Core content policies, an essay
- Wikipedia:Identifying reliable sources (medicine), a guideline
- Wikipedia:When to cite, an essay
- Wikipedia:Citation clutter, an essay
- Wikipedia:List of free online resources
- Wikipedia:Template messages/Sources of articles
- WikiProject Fact and Reference Check
- WikiProject Resource Exchange
Notes
- ^ 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.
- ^ 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." See Wales, Jimmy. "Zero information is preferred to misleading or false information", WikiEN-l, May 16, 2006, accessed June 11, 2006.
- ^ Plunkett, John. "Rod Liddle censured by the PCC", The Guardian, March 30, 2010.
- ^ The 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." See Hume, David. An Enquiry Concerning Human Understanding, 1758; this edition Forgotten Books, 1984, p. 86.
Further reading
- Wales, Jimmy. "WikiEN-l 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."