Wikipedia:Verifiability
 | This page documents an English Wikipedia policy. It describes a widely accepted standard that all editors should normally follow. Substantive edits to this page should reflect consensus. |
 | This page in a nutshell: People must be able to check that facts and claims in Wikipedia articles are not just made up. This means each fact or claim must be attributable to reliable, published sources. Additionally, quotations and any facts or claims challenged or likely to be challenged must be supported by inline citations. |
In the English Wikipedia, verifiability means that people can check that facts or claims correspond to reliable sources. Wikipedia's content is determined by published information rather than editors' beliefs, experiences, or previously unpublished ideas or information. Even if you are sure something is true, it must have been published in a reliable source before you can add it.[a] If reliable sources disagree with each other, then maintain a neutral point of view and present what the various sources say, giving each side its due weight.
Each fact or claim in an article must be verifiable. All quotations, and any material whose verifiability has been challenged or is likely to be challenged, must include an inline citation to a reliable source that directly supports[b] the material. Any material that needs an inline citation but does not have one may be removed. Please immediately remove contentious material about living people that is unsourced or poorly sourced.
When material that needs an inline citation appears in two or more articles, an inline citation is needed in each.
For how to write citations, see citing sources. Verifiability, no original research, and neutral point of view are Wikipedia's core content policies. They work together to determine content, so editors should understand the key points of all three. Articles must also comply with the copyright policy.
Responsibility for providing citations
All content must be verifiable. A fact or claim is "verifiable" if a reliable source that supports it could be cited, even if there is no citation for it in the article at the moment. The burden to demonstrate verifiability lies with the editor who adds or restores material, and it is satisfied by providing one inline citation to a reliable source that directly supports[b] the contribution.[c]
The cited source must clearly support the material as presented in the article. Cite the source clearly, ideally giving page number(s)—though sometimes a section, chapter, or other division is appropriate instead; see Wikipedia:Citing sources for details of how to do this.
Facts or claims without an inline citation to a reliable source that directly supports[b] them may be removed. They should not be restored without an inline citation to a reliable source.
Whether or how quickly material should be removed for lacking an inline citation to a reliable source depends on the material and the overall state of the article. Consider adding a citation needed tag as an interim step to removing unsourced material, to allow references to be added.[d] When tagging or removing material for lacking an inline citation, state your concern that it may not be possible to find a published reliable source, and the material therefore may not be verifiable.[e] If you think the material is verifiable, you are encouraged to provide an inline citation yourself before removing or tagging it.
Do not leave unsourced or poorly sourced material in an article if it might damage the reputation of living people or existing groups, and do not move it to the talk page, per Wikipedia's biographies of living persons policy (common shortcut: WP:BLP). The latter policy also applies to some groups.
Reliable sources
What counts as a reliable source
A cited source on Wikipedia is often a specific portion of text (such as a short article or a page in a book). But when editors discuss sources (for example, to debate their appropriateness or reliability) they are usually talking about one or more related characteristics:
- The work itself (the article, book) and works like it ("An obituary can be a useful biographical source", "A recent source is better than an old one")
- The creator of the work (the writer, journalist: "What do we know about that source's reputation?") and people like them ("A medical researcher is a better source than a journalist for medical claims").
- The publication (for example, the newspaper, journal, magazine: "That source covers the arts.") and publications like them ("A newspaper is not a reliable source for medical claims").
- The publisher of the work (for example, Cambridge University Press: "That source publishes reference works.") and publishers like them ("An academic publisher is a good source of reference works").
All four can affect reliability.
Base articles on reliable, independent, published sources with a reputation for fact-checking and accuracy. Source material must be published, on Wikipedia meaning made available to the public in some form.[f] Unpublished material is not considered reliable. Use sources that directly support the material presented in an article and are appropriate to the claims made. The appropriateness of any source depends on the context. Be especially careful when sourcing content related to living people or medicine.
If available, academic and peer-reviewed publications are usually the most reliable sources on topics such as history, medicine, and science.
Editors may also use material from reliable non-academic sources, particularly if it appears in respected mainstream publications. Other reliable sources include:
- University-level textbooks
- Books published by respected publishing houses
- Mainstream (non-fringe) magazines, including specialty ones
- Reputable newspapers
Editors may also use electronic media, subject to the same criteria (see details in Wikipedia:Identifying reliable sources).
Best sources
The best sources have a professional structure for checking or analyzing facts, legal issues, evidence, and arguments. The greater the degree of scrutiny given to these issues, the more reliable the source.
Newspaper and magazine blogs
Some newspapers, magazines, and other news organizations host online pages or columns they call blogs. These may be acceptable sources if the writers are professionals, but use them with caution because blogs may not be subject to the news organization's normal fact-checking process.[g] If a news organization publishes an opinion piece in a blog, attribute the statement to the writer, e.g. "Jane Smith wrote ..." Never use the blog comments that are left by the readers as sources. For personal or group blogs that are not reliable sources, see § Self-published sources below.
Reliable sources noticeboard and guideline
To discuss the reliability of a specific source for a particular statement, consult Wikipedia: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:Reliable sources. In case of conflict between this policy and the Wikipedia:Reliable sources guideline, or any other guideline related to sourcing, this policy has priority.
Sources that are usually not reliable
Questionable sources
Questionable sources are those that have a poor reputation for checking the facts, lack meaningful editorial oversight, or have an apparent conflict of interest.
Such sources include websites and publications expressing views widely considered by other sources to be promotional, extremist, or that rely heavily on unsubstantiated gossip, rumor, or personal opinion. Questionable sources should be used only as sources for material on themselves, such as in articles about themselves; see below. They are not suitable sources for contentious claims.
Predatory open access journals are questionable due to the absence of quality control in the peer-review process.
Self-published sources
Anyone can create a personal web page, self-publish a book, or claim to be an expert. Self-published material, such as books, newsletters, personal websites, open wikis, personal or group blogs (as distinguished from newsblogs), content farms, podcasts, Internet forum posts, and social media posts, are largely not acceptable as sources. Patents, despite undergoing a patent review process, are treated as self-published.
Self-published sources may be considered reliable if published by an established subject-matter expert, whose work in the relevant field has previously been published by reliable, independent publications.