Wikipedia:When to cite

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While this essay is not a policy or guideline itself, it is intended to supplement Wikipedia:Verifiability. Please defer to the relevant policy or guideline in case of inconsistency between that page and this one.

The list of featured-article criteria calls for citations where appropriate. The English Wikipedia's Verifiability policy says that inline citations are required for direct quotations and for material that is challenged or likely to be challenged. This page clarifies that requirement.

1 Examples
- 1.1 When a source is needed
- 1.2 When a source may not be needed
2 Challenging another user's edits
3 Citations in leads
4 Text-source relationship
5 See also
- 5.1 Policies
- 5.2 Guidelines

Examples

This list is not exhaustive, and the examples are purely illustrative. Each case must be dealt with on its merits.

When a source is needed

Material that is actually challenged by another editor requires a source or it may be removed; and anything likely to incur a reasonable challenge should be sourced to avoid disputes and to aid readers (See policy WP:BURDEN). In practice, this means most such statements are backed by a citation. In case of multiple possible references for a statement, the "best reliable sources" should be used.

Quotations – Always add a citation when quoting published material; the citation should be placed directly after (or just before) the quotation (See policy WP:BURDEN).
Exceptional claims – Exceptional claims in Wikipedia require high-quality reliable sources (See policy WP:REDFLAG):

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, and especially when proponents consider that there is a conspiracy to silence them.

Contentious statements about living people – Editors must take particular care adding biographical material about a living person to any Wikipedia page. Such material requires a high degree of sensitivity; do not leave unsourced information that may damage the reputation of living persons or organizations in articles.
Other – Opinions, data and statistics, and statements based on someone's scientific work should be cited and attributed to their authors in the text.

In practice, a citation is used to support any important point that is being made in the text, and it is not unusual for Wikipedia's best articles to have at least one citation per paragraph.

When a source may not be needed

General common knowledge – Statements that the average adult recognizes as true. Example: "Paris is the capital of France."
Subject-specific common knowledge – Material that someone familiar with a topic, including laypersons, recognizes as true. Example (from Processor): "In a computer, the processor is the component that executes instructions."
Plot of the subject of the article – If the subject of the article is a book or film or other artistic work, it is unnecessary to cite a source in describing events or other details. It should be obvious to potential readers that the subject of the article is the source of the information. Where the subject of the article is a work that has been published or broadcast in a serial manner, citing the episode, issue or book can aid comprehension for readers not familiar with the whole of the serial work. It also aids verification where issues of interpretation occur.
When a paragraph derives from a single source – It can be silly to repetitively name the same reference in a single paragraph, especially when the paragraph uses multiple sentences to explain a single idea or describe a single fact. In other instances, such as a paragraph containing several independent statistics, repeating the reference may be desirable. Repeat references in a paragraph when the repetition provides value to the reader, not to mindlessly produce an official reference for each sentence.

Challenging another user's edits

The right to challenge – Any editor has the right to challenge unsourced material by opening a discussion on the talk page or by tagging it. Material that should be removed without discussion includes contentious material about a living person, clear examples of original research, and anything that is ludicrous or damaging to the project.
Challenges should not be frivolous – Challenges should not be made frivolously or casually, and should never be made to be disruptive or to make a point. Editors making a challenge should have reason to believe the material is contentious, false, or otherwise inappropriate.
Responses must be forthcoming – Editors who wish to respond to the challenge should do so in a timely manner. If no response is forthcoming, the challenger may tag or remove the statement in question. Unless the material falls into the class that should be removed without discussion, the challenger should await a timely response prior to removing material.

Citations in leads

Main page: WP:LEAD

Because the lead will usually repeat information also in the body, editors should balance the desire to avoid redundant citations in the lead with the desire to aid readers in locating sources. Leads are usually written at a greater level of generality than the body, and information in the lead section of non-controversial subjects is less likely to be challenged and less likely to require a source. There is not, however, an exception to citation requirements specific to leads. Complex, current, or controversial subjects may require many citations; others, few or none. Contentious material about living persons must be cited every time, regardless of the level of generality.

Text-source relationship

The distance between material and its source is a matter of editorial judgment. The source of the material should always be clear. If you write a multi-sentence paragraph that draws on material from one source, the source need not be cited after every single sentence unless the material is particularly contentious. Editors should exercise caution when rearranging cited material to ensure that the text-source relationship isn't broken.

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