The Question of Canon: What Is It and How Is It Decided?

Originally written as an answer to a question on Quora.

Writings or other works that are generally agreed to be good, important, and worth studying.

https://dictionary.cambridge.org/dictionary/english/canon

A word to describe something that is true to the original story.

https://www.urbandictionary.com/define.php?term=Canon

When a writer produces a novel, film, television series or video game he or she creates a fictional story, and a fictional universe within which that story is set. If that creation is successful, it may expand into sequels, spin-offs and other mediums. Some of those spin-offs may be created by individuals unconnected to the original. An expanded universe will have been created. As this expanded universe continues to grow and new stories are written, some of the details of those stories may clash with what has already been established. This is where canon comes in.

Within a fictional universe, canon is simply the term used to refer to what 'actually happened' when details clash across two or more mediums. An example might be that in a television series a character died without ever having children, while in a video game spin-off of that series the same character has a grown up son. Only one of these details can be accepted within the continuity of the expanded universe, and the one that is will be canon. In order to decide what is accepted as canon and what is not, it is necessary to have a series of standardised rules recognised across the creative industries. To simply have a panel of individuals deciding what is and is not canon within a particular fictional universe would be unacceptable. Not everyone who enjoys a series of films, television programmes or video games is an arrant fan who follows the entire continuity. Someone who only watches a series of films, for example, might have no idea that the events in a prequel have been completely re-written by a novel published years later.

The standard rules for canon are simple. Firstly, anything and everything that has been published within a fictional universe is part of that fictional universe, until it is contradicted by something else. Whether produced by the original series creator, or a creative fan, it is all part of the same universe and it is all just as fictional. Secondly, whatever takes place in the primary medium of a particular fictional universe overrides all others. In the case of Star Wars, for example, the primary medium is a series of thirteen films followed by a number of television series. Therefore, anything in books, comics or video games that contradicts points raised in these on-screen dramas will be non-canon. In the case of fictional universes such as Halo, where the primary medium is a video game, the games override any films or television series.

Although the creators, or other main writers, of a fictional universe cannot unilaterally decide what is and is not canon, they are free to make any changes they wish to these standard rules. An example of this is the Star Wars universe, prior to it's acquisition by Disney. In 2000 Leland Chee, LucasArts' Lead Tester, developed the Holocron, a continuity database and guide for establishing the level of canon. This placed G-canon, which was anything produced by George Lucas, at the top, followed by T-canon, which was any other television series. All other contributions, from whatever medium, were placed at different levels on the Holocron, right down to fan fiction at the bottom.

To summarize, canon is a literary device in the creation of fictional work. It's purpose is to enable the fictional universe to make sense, as it is constantly adapted and expanded. In order for this to work it is necessary to follow, at the very least, the basic standard rules of canon. Those that do not defeat the object for which this literary device exists.

https://en.wikipedia.org/wiki/Star_Wars_in_other_media#Holocron_database_and_canonicity