The scope of an article is the topic or subject matter, which is defined by reliable sources. The extent of the subject matter identifies the range of material that belongs in the article, and thus also determines what does not belong (i.e., what is "out of scope").
The lead, ideally the introductory sentence or at least introductory paragraph, of an article, should make clear what the scope of the article is.
Aim of scope
- All material that is notable, referenced, and that a reader would be likely to agree matches the specified scope must be covered (at least in a summarised fashion).
- What reliable sources say about material that is out of scope for the decided-upon subject is largely irrelevant to that article and can be removed or moved to another article.
Identifying the scope
- Article scope, in terms of what exactly the subject and its scope is, is defined by reliable sources, and the suitability of Wikipedia having an article on that subject is decided by reference to WP:Inclusion criteria—appropriate topics are those that have gained sufficiently significant attention by the world at large and over a period of time—so they are "notable", and are not disallowed by policy.
- The issue of scope should not be confused with NPOV, which controls how much of the article should be devoted to any given topic; scope limits whether or not a topic is relevant to the subject, and therefore appropriate to be mentioned or summarised.
- Artificially or unnecessarily restricting the scope of an article to select a particular POV on a subject area is frowned upon, even if it is the most popular POV.
- When the name of an article is a term that refers to several related topics in secondary reliable sources, primary topic criteria should be followed to determine if any of the uses of that term is the primary topic, and, if so, then the scope of the article should be limited to, or at least primarily, cover that topic. For example, Cat is limited in scope to the primary topic for cat, the Domestic cat (which is a redirect to Cat), even though lions and tigers are considered to be "cats" in the broad sense of that term.
- Use the most general scope for each article you can. Since Wikipedia is a general encyclopedia, it's supposed to summarise essentially all knowledge. Hence accidental or deliberate choice of a limited scope for an article can make notable information disappear from the encyclopedia entirely, or make it highly inaccessible. Since the primary purpose of the Wikipedia is to be a useful reference work, narrow article scopes are to be avoided.
- Looking at what scopes other encyclopedias have chosen can often be useful.
Editors are advised to stay on topic, and to ensure that articles contain no irrelevant (nor only loosely relevant) information.
When to split
The two main reasons for splitting material out from an article, are size and content relevance. If either the whole article, or the specific material within one section becomes too large, or if the material is seen to be inappropriate for the article due to being out of scope, then a split may be considered or proposed. Consideration must be given to size, notability and potential neutrality issues before proposing or carrying out a split.