Wikipedia:Must I add a citation?

Editors sometimes wonder what they should do on finding a correct but uncited statement in an article.

If there is unsourced info in an article, but you believe it to be true, you have several options:
 * 1) You could find and add a valid source. This helps the article, probably more than anything else you could do.
 * 2) You could add a cn tag, in effect asking someone else to provide the source. This at least notes that a source is needed. You could include in your edit summary that you think the statement is correct, and why.
 * 3) You could post a message on the article’s talk page, describing why you think the unsourced statement is in fact accurate, but needs a source, and any hints of where to find a source you might have. In such a post you might ping the editor who added the statement, which can be found from the article history. That editor might know of a valid source.
 * 4) If the content was not inserted by you, you could just ignore the issue. No one on Wikipedia is ever required to edit any particular article, or to clean up another editor's errors. However this does not improve the article at all.

Note that not all statements need be cited to a source (see You don't need to cite that the sky is blue). If a statement is not a quotation, is not an extraordinary claim, is not controversial or challenged or likely to be challenged, and is not a negative statement about a living person, a source is not required (see When to cite). Adding a source in such cases may be helpful, but is not essential. In some cases it can even be over-citation.

Things that are general or subject-specific common knowledge often do not need citations. The plot of a work of fiction (particularly in an article about that work) is implicitly cited to the work itself, and does not normally need any other citation. A fact cited in one place in an article but mentioned in other places in the same article need not be re-cited at each mention. This is particularly true of statements in the lead section that properly summarize cited content from the body of the article.

Incorrect citations
When a statement is cited, but the statement is not properly supported by the cited source, it is usually a good idea to add fv after the citation, to indicate that a verification has failed. After that, one may proceed as if the statement was uncited.