Characteristics
The modern definition of copyright, especially under United States copyright law, considers the expansion of a previous work's setting or characters to be a derivative work. Especially for material being considered for publication, this often necessitates licensing agreements. For this reason, some fan fiction and other amateur works written in established settings without permission, are sometimes distinguished from shared universe writings or even described as a "stolen universe". However, fair use claims have been raised, and not all authors believe that fan fiction should be distinguished from other literature in this manner at all. In a process similar to brand licensing, the intellectual property owners of established fictional settings at times allow others to author new material, creating an expanded universe. Such franchises, generally based on television programs or film, allow for series of novels, video games, original sound recordings and other media. Not all shared universe settings are simply the expansion or combination of pre-existing material by new authors. At times, an author or group of authors has created a setting specifically for development by multiple authors, often through collaboration.
Especially when a shared universe grows to include a large number of works, it becomes difficult for writers to maintain an internally consistent continuity and to avoid contradicting details in earlier works. The version that is deemed official by the author or company controlling the setting is known as canon. Not all shared universes have a controlling entity capable of or willing to determine canonicity, and not all fans agree with these determinations when they occur. A fanon may instead find some degree of consensus within the setting's fandom. Some writers, in an effort to ensure that a canon can be established and to keep details of the setting believable, employ tools to correct contradictions and errors that result from multiple contributors working over a long period of time. One such tool is retconning, short for "retroactive continuity", where later adjustments result in the invalidation of previously-written material. The most severe form of retcon involves a wholesale rewrite of the groundwork for the entire setting. These reboots, most closely associated with DC Comics, are not always effective at resolving underlying problems and may meet with a negative reaction from fans. Contributors to expanded universes, also known as tie-in writers, have sometimes been stereotyped as "hacks" because such writing is perceived as less creative or of consistently poor quality. These stereotypes have been disputed by authors who consider contributing to a larger setting "intellectually demanding."
Readers may also object when a story or series is integrated into a shared universe, feeling it "requir one hero's fans to buy other heroes' titles" or leads to mischaracterizations and inappropriate comparisons.
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