This is an essay on the Wikipedia:Core content policies. It contains the advice or opinions of one or more Wikipedia contributors. This page is not an encyclopedia article, nor is it one of Wikipedia's policies or guidelines, as it has not been thoroughly vetted by the community. Some essays represent widespread norms; others only represent minority viewpoints.

Multiple policies require editors to base articles upon certain types of sources. This page explains what it means for a page to be based upon a source.

As applied to content, based upon means that the essence of an article – its topic, its sections, its themes and items of knowledge – must have some supporting basis as prescribed.

Incidental details and uncontroversial information filling-in around these does not constitute the basis of content.

An article that is based upon a particular type of source will have, at bare minimum, more than 50% of its content taken from that type of source. This can be measured through methods such as the amount of readable prose that is cited to that source type, or the number of facts taken from that source type. For example, if 70% of the sentences in an article about Alice Expert come from Alice's own writing, or Alice's employer's website, then the article is based upon non-independent sources. On the other hand, if 70% of the content in that article comes from magazine articles written by journalists, then the article is based upon independent sources.

Additionally, an article that is based upon a source may draw structural and stylistic elements from that source. For example, if a source divides Alice's life with her education, family, career, and research, and an editor copies that structure to create sections on ==Education==, ==Family==, ==Career==, and ==Research==, then the structure of the page is based upon that source. If, instead, the order of suggestions is taken from a Wikipedia article on a similar subject, then the structure is "based upon" that other Wikipedia article.

All Wikipedia articles should be based upon sources that are secondary and upon sources that are independent. (Remember that Wikipedia:Secondary does not mean independent, so these are separate requirements.) There are no exceptions to this rule, even though we know that we haven't achieved the goal yet in every article.

• WP:NOT says that "All article topics must be verifiable with independent, third-party sources".
• WP:V says that "Articles must be based on reliable, independent, published sources with a reputation for fact-checking and accuracy".
• WP:NOR says that "Wikipedia articles should be based on reliable, published secondary sources and, to a lesser extent, on tertiary sources and primary sources".

Additionally, certain types of content require particular attention to what sources they're based upon. For example, all biomedical information must be based on reliable, third-party published secondary sources. Controversial "red flag" content should be more carefully sourced than routine, uncontroversial information. Some content benefits from having a higher proportion of secondary sources than usual, or near-exclusive use of independent sources, and an even higher quality of sources than usual.

If it is not possible to write an encyclopedia article about the subject, without basing it upon non-independent and primary sources, then Wikipedia should not have a separate article on that subject. Not qualifying for a separate article does not mean that Wikipedia does not want information about that subject. See WP:FAILN for advice on what to do when you can't write an entire article without over-reliance on non-independent and primary sources.

• Wikipedia:Identifying and using primary sources – especially useful for identifying primary sources in news media
• Wikipedia:Permastub – what we don't want
• ((One source)) – the tag for articles based almost entirely upon a single source
• ((Third-party)) – the tag for articles based upon non-independent sources
• ((Self-published)) – the tag for articles based upon self-published sources
• ((Primary sources)) – the tag for articles based upon primary sources