{{nutshell|A [[WP:good article|good article]] should not contain any claims that a competent editor could, reasonably and in [[WP:AGF|good faith]], tag with {{tl|citation needed}}.}}
[[Wikipedia:Good article criteria]] refersand [[Wikipedia:Did you know/Guidelines]] refer to "'''content that could reasonably be challenged'''". This concept is in some ways similar to [[Wikipedia:Verifiability]]'s concept of "[[WP:likely to be challenged|likely to be challenged]]", but is a fair bit broader. That is to say, some things that are not "likely to be challenged" may still "reasonably be challenged". "Likely to be challenged" means a greater-than-50-percent chance of an editor requesting a citation in [[WP:good faith|good faith]], and is a rough proxy for whether a given claim is at all controversial.{{efn|Note that "controversial" in the context of citations does not necessarily refer to ideology or scandals. Unsourced assertions of specific details—people's full names, dates of events, population statistics, etc.—are controversial from an article-writing perspective and will usually be tagged with {{tl|citation needed}}, except in very short articles that use [[WP:general references|general references]] (which are ineligible to be good articles regardless).}} "Could reasonably be challenged" means that, were an editor to request a citation, this would be a reasonable exercise of editorial discretion, rather than pedantry or [[WP:NOTBURO|bureaucracy]]. This is more a definition of exclusion: It applies to all but the most obvious claims.
The "could reasonably be challenged" rule only ever supplements other citation rules. The [[WP:MINREF|minimum referencing requirements]] must always be met, as must specialty requirements such as [[WP:BLPSOURCE|those regarding living people]] and [[WP:MEDRS|those regarding biomedical topics]].
