Retroactive continuity

Retroactive continuity, or retcon for short, is a literary device in which established diegetic facts in the plot of a fictional work (those established through the narrative itself) are adjusted, ignored, or contradicted by a subsequently published work which breaks continuity with the former.
There are various motivations for applying retroactive continuity, including:
Retcons are used by authors to increase their creative freedom, on the assumption that the changes are unimportant to the audience compared to the new story which can be told. For instance, by retroactively setting a prior story in a parallel universe, departed popular characters can be reintroduced. More subtly, a minor plot point might be retroactively expunged (for instance, the heroine leaving home without any food), removing an obstacle to further storytelling (that she should be getting hungry).
Retcons are common in pulp fiction, and especially in comic books published by long-established publishers such as DC and Marvel. The long history of popular titles and the number of writers who contribute stories can often create situations that demand clarification or revision. Retcons also often appear in manga, soap operas, serial dramas, movie sequels, cartoons, professional wrestling angles, video games, radio series, and other forms of serial fiction.
Etymology.
The first published use of the phrase "retroactive continuity" is found in theologian E. Frank Tupper's 1973 book "The Theology of Wolfhart Pannenberg": "Pannenberg's conception of retroactive continuity ultimately means that history flows fundamentally from the future into the past, that the future is not basically a product of the past."
The first known printed use of "retroactive continuity" referring to the altering of history in a fictional work is in "All-Star Squadron" #18 (February 1983) from DC Comics. The series was set on DC's Earth-Two, an alternate universe in which Golden Age comic characters age in real time. "All-Star Squadron" was set during World War II on Earth-Two; as it was in the past of an alternate universe, all its events had repercussions on the contemporary continuity of the DC multiverse. Each issue changed the history of the fictional world in which it was set. In the letters column, a reader remarked that the comic "must make you [the creators] feel at times as if you're painting yourself into a corner", and, "Your matching of Golden Age comics history with new plotlines has been an artistic (and I hope financial!) success." Writer Roy Thomas responded, "we like to think that an enthusiastic ALL-STAR booster at one of Adam Malin's Creation Conventions in San Diego came up with the best name for it a few months back: 'Retroactive Continuity'. Has kind of a ring to it, don't you think?" The term then took firm root in the consciousness of fans of American superhero comics.
At some point, "retroactive continuity" was shortened to "retcon", reportedly by Damian Cugley in 1988 on Usenet. Hard evidence of Cugley's abbreviation has yet to surface, though in a Usenet posting on August 18, 1990, Cugley posted a reply in which he identified himself as "the originator of the word "retcon"". Cugley used the neologism to describe a development in the comic book "Saga of the Swamp Thing", which reinterprets the events of the title character's origin by revealing facts that previously were not part of the narrative and were not intended by earlier writers.
Types.
Addition.
Retcons sometimes do not contradict previously established facts but instead fill in missing background details, usually to support current plot points. Thomas referred to "retroactive continuity" in this sense, as a purely additive process that did not undo any previous work; such additions were common in "All-Star Squadron". Kurt Busiek took a similar approach with "Untold Tales of Spider-Man", a series which told stories that specifically fit between issues of the original "The Amazing Spider-Man" series, sometimes explaining discontinuities between those earlier stories. John Byrne used a similar structure with "". Possibly the earliest Marvel Comics example of new stories placed between long-established stories was the 1977–1978 magazine "The Rampaging Hulk". In "The Godfather Part II", the character Frank Pentangeli is introduced as an old friend of the family though he is not referenced in the first movie; similarly Don Altobello is one of the "old time" Dons, though he is not mentioned until "The Godfather Part III". Neither addition affects the plot line of the previous films. The addition, in later seasons, of an attic to the family's home in "Full House" stands as a similar additive example.
A similar concept is that of secret history, in which the events of a story occur within the bounds of already-established events (especially real-world ones), revealing different interpretations of the events. Some of Tim Powers' novels use secret history, such as "Last Call", which suggests that Bugsy Siegel's actions were due to his being a modern-day Fisher King.
Alan Moore's additional information about the Swamp Thing's origins – revealing that Swamp Thing was not actually scientist Alec Holland converted into a plant, but actually a plant that had absorbed Holland's body and consciousness so that it merely thought it was Holland – did not contradict or change any of the events depicted in the character's previous appearances, but instead changed the reader's interpretation of them. Such additions and reinterpretations are very common in "Doctor Who".
In the "Star Wars" franchise, one of the most cited plot holes is that of the Galactic Empire's superweapon, the Death Star, having a glaring, poorly defended weak point: an exhaust port. However, the movie "Rogue One: A Star Wars Story", which acts as a direct prequel to "A New Hope", presents the design flaw as deliberate: Galen Erso, the head engineer of the Death Star project, designed the reactors to be unstable, thus needing an exhaust port, and gave the plans to the Rebel Alliance in order to sabotage the Empire and to secretly show the Rebels how to destroy the Death Star.
Alteration.
Retcons sometimes add information that seemingly contradicts previous information. This frequently takes the form of a character who was shown to have died but is later revealed to have somehow survived. This is a common practice in horror films, which may end with the death of a monster that goes on to appear in one or more sequels. The technique is so common in superhero comics that the term "comic book death" has been coined for it. An early example of this type of retcon is the return of Sherlock Holmes, whom writer Arthur Conan Doyle apparently killed off in "The Final Problem" in 1893, only to bring him back, in large part because of readers' responses, with "The Empty House" in 1903. Another example is the character Phil Coulson, who was killed off in the Marvel Studios film "The Avengers" (2012), but is later shown to have survived in the television series "Agents of S.H.I.E.L.D".
In many of his detective novels, Rex Stout implies that his character Nero Wolfe was born in Montenegro, giving some details of his early life in the Balkans around World War I. But in 1939's "Over My Dead Body", Wolfe tells an FBI agent that he was born in the United States. Stout revealed the reason for the change in a letter obtained by his authorized biographer, John McAleer: "In the original draft of "Over My Dead Body" Nero was a Montenegrin by birth, and it all fitted previous hints as to his background; but violent protests from "The American Magazine", supported by Farrar & Rinehart, caused his cradle to be transported five thousand miles."
In the 1940s and 1950s, Isaac Asimov placed the planet Trantor, capital of the Galactic Empire, at the "center of the galaxy", but later astronomical research indicated that the actual Galactic Center might be occupied by a supermassive black hole, making human life there impossible; in later works, Asimov adjusted his galaxy and Trantor's location in it.
When E.E. "Doc" Smith wrote the original "The Skylark of Space", space flight was a completely theoretical proposition. However, the last book of the series, "Skylark DuQuesne", was written in 1963, when the United States and the Soviet Union were involved in the space race. Smith adjusted the past of his series accordingly, mentioning an American base and a Soviet one being established on the Moon prior to the protagonist Seaton discovering faster-than-light flight.
Alan Moore's retcons often involve false memories. He has used this technique in the "Marvelman" series, "Swamp Thing" and "".
Retconning can bring back characters who were initially killed off. An example of this occurs on the CBS comedy "Two and a Half Men". The character Charlie Harper (Charlie Sheen) was killed in a train accident and briefly returns as a ghost (played by Kathy Bates) in the ninth season. Despite numerous instances that confirm his demise, including the fact that a mutilated body was in his coffin, in the season twelve series finale "Of Course He's Dead" it is revealed that Charlie survived the ordeal and has been held captive against his will for over four years. It is mentioned that there was no body, only random body parts. Bringing back dead characters is also common in soap operas. On "The Bold and the Beautiful", Taylor Forrester (Hunter Tylo) was shown to flatline and have a funeral. When Tylo reprised the character in 2005, a retcon explained that Taylor had actually gone into a coma.
The TV series "Dallas" annulled its entire Season 9 as being just the dream of another character, Pam Ewing. Writers did this to offer a supposedly plausible reason for the major character of Bobby Ewing, who had died onscreen at the end of Season 8, to be still alive when actor Patrick Duffy wanted to return to the series. This season is sometimes referred to as the "Dream Season" and was referred to humorously in later TV series such as "Family Guy". Other series such as "St. Elsewhere", "Newhart", and "Roseanne" would notably employ the same technique.
In "", the character of Spock dies in the film. This was done because actor Leonard Nimoy would not agree to appear in the film unless the character was killed off. After the film was finished, Nimoy told producers he enjoyed making the movie and wanted to return if a third "Star Trek" film was made. As a result, an epilogue was added to the film, hinting at the possibility of Spock's resurrection, described as a result of the Genesis Device, a technology designed to reorganize dead matter into habitable worlds.
Also in "Star Trek II", the characters of Khan (Ricardo Montalbán) and Pavel Chekov (Walter Koenig) remember each other from Khan's appearance in the first season "" television series episode "Space Seed", 15 years earlier; The character of Chekov did not appear in "Star Trek" until the second season; It was later explained that Chekov was not a member of the "Enterprise" bridge crew at that time and was assigned elsewhere on the ship. 
Alternatively when a series runs for a number of seasons, an alternative time-line may be used to explain the reappearance of supposedly dead characters. For example in Star Trek: The Next Generation, the character of Lieutenant Tasha Yar was killed off but in a later episode, a change in the timeline (alternative reality) caused by the appearance of the previously destroyed USS Enterprise C brings the character seemingly back to life. Tasha then transfers to the doomed Enterprise C and returns through the time anomaly on board the Enterprise C which apparently restores the correct timeline. The fact that Tasha Yar had previously died and now seemingly was set to die again was ignored. 
In "Beverly Hills 90210", Kelly Taylor starts out in the first season initially not knowing Dylan McKay. Later when Brenda Walsh is sent to Paris with Donna Martin, Kelly Taylor has suddenly known him since kindergarten. This apparent retooling of the storyline contradicted years of prior character development and was apparently done to prepare viewers for Shannen Doherty's exit from the series. 
Marvel Comics' Beyonder was originally stated to be omnipotent and the most powerful being in Marvel Universe, coming from the Beyond Realm. However, after his creator, Jim Shooter, left Marvel, writer-editor Tom DeFalco re-tooled the Beyonder, diminishing his power greatly: he was no longer omnipotent, as certain other cosmic entities were retroactively vastly upgraded to transcend the scale of infinity on which the character worked. Even after this, Beyonder was still one of the most powerful beings in Marvel, with several characters exceeding him.
In 2003, in the title of DC Comics' Teen Titans, Geoff Johns changed the entire genetic code of Kon-El (the modern version of Superboy) from a genetically altered human clone that was designed to be as Kryptonian as possible into a hybrid clone of both Superman and Lex Luthor. This change contradicted years of continuity and various facts that proved that Kon-El was human and in the process mostly ignored his unique ability of tactile telekinesis that made his powers very different from those of Superman.
In "Boy Meets World", both Shawn Hunter and Topanga Lawrence have siblings in the first season but later in the series are retconned to be only children (though Shawn's half-brother Jack is introduced in later seasons). The ages of the characters of "Boy Meets World" are altered notably where Cory is age 11 in 6th grade during season 1 to age 13 and 7th grade in season 2. This happens again in high school skipping another grade. The age gap between Cory and Eric also narrows from 4 years apart in age to 2 years apart in age. Another prominent retcon during that series was that of the character of Morgan Matthews, who was portrayed by two actresses during the show's run; in the series finale of the sequel series "Girl Meets World", the continuity suggests that they were two separate people who both appeared together for the only time during that episode.
Subtraction.
Unpopular or embarrassing stories are sometimes later ignored by publishers, and effectively erased from a series' continuity. Later stories may contradict the previous ones or explicitly establish that they never happened.
A notable example of subtractive retconning is the "X-Men" film series. The 2014 film " features the character Wolverine traveling in time to 1973 to prevent an assassination that, if carried out, would lead to the creation of a new weapons system called the Sentinels that threatens the existence of mutants — and potentially, all of humanity. The events of this film retconned those of two previous films in the series:
The film, a loose adaptation of "The Dark Phoenix Saga" from the "Uncanny X-Men" comic book series, featured the unceremonious deaths of select key characters (including Cyclops), triggering a mixed fan response from those who felt the deaths were sudden and under-explored. "Days of Future Past" erased these deaths and the characters are shown to have survived at the end of the film. "The Dark Phoenix Saga" would subsequently be adapted a second time in "Dark Phoenix" (2019).
The film featured the character Deadpool, who is created by the character Colonel William Stryker as an amalgamation of several other mutants. He is referred to as "the Deadpool" due to having the other mutants' abilities "pooled" together. This version of the character was poorly received by fans due to his appearance and origin, both of which were considered unfaithful to the comics version of the character. The events of "Days of Future Past" allowed a more faithful version of the character to be adapted in "Deadpool" (2016) and its 2018 sequel, both of which were positively received by fans and critics. "Deadpool 2" even includes a scene where Deadpool uses a time machine to kill the "X-Men Origins" version of himself.
An unpopular retcon may itself be retconned away, as happened with John Byrne's "".
Temporal compression.
Film sequels often employ temporal compression to maintain a sense of urgency in each installment, despite more time having elapsed diegetically ("in-universe") between one installment and another than has elapsed in the real world. For example, despite the implied contemporaneity in each of the films of "The Omen" series, the lead character ages some 15 or 20 years across three films released over a period of less than 6 years.
Related concepts.
Retroactive continuity is similar to, but not the same as, plot inconsistencies introduced accidentally or through lack of concern for continuity; retconning, by comparison, is done deliberately. For example, the ongoing continuity contradictions on episodic TV series such as "The Simpsons" (in which the timeline of the family's history must be continually shifted forward to explain why they are not getting any older) reflects intentionally lost continuity, not genuine retcons. However, in series with generally tight continuity, retcons are sometimes created after the fact to explain continuity errors. Such was the case in "The Flintstones", where Wilma Flintstone was mistakenly given two separate maiden names, "Pebble" and "Slaghoople", over the course of the series.
Retconning is also generally distinct from replacing the actor who plays a part in an ongoing series, which is more commonly an example of "loose continuity" rather than retroactively changing past continuity. The different appearance of the character is either ignored (as was done with the characters of Darrin Stephens and Gladys Kravitz on the television series "Bewitched") or explained within the series, such as with "regeneration" in "Doctor Who", or the Oracle in "The Matrix Revolutions". Sometimes, there are referential, inside jokes on actor changes in the show, such as with "My Wife & Kids" and "Roseanne", where there was a change of actresses playing a role (characters Claire Kyle and Becky Conner, respectively). In the latter, another character observes that children can change as they reach adulthood, remarking that when Becky came back from college (played by a new actress), they could not even recognize her. When the actor playing Rory was replaced in "Mrs Brown's Boys", the new actor first appeared on set bandaged up, supposedly following cosmetic surgery on his face. When the bandages were removed, the other characters claimed not to notice any difference. A similar set up gag was used with the character of Herr Flick in the BBC sitcom "Allo Allo".
Retconning also differs from direct revision. For example, when George Lucas re-edited the original "Star Wars" trilogy, he made changes directly to the source material, rather than introducing new source material that contradicted the contents of previous material.
Retconning is not the same as a reboot or reimagining which completely discards the original timeline, such as in "Battlestar Galactica". However, there have been partial reboots of franchises where the core of the franchise is still canonical but the expanded universe is relegated to a secondary continuity which, while not completely invalid, is subject to revision and critical review. "Robotech" is an example of this. With the release of the 2006 sequel film "Robotech The Shadow Chronicles", Harmony Gold established that only the original 1985 animated series and the 2006 sequel film are considered canonical relegating the aborted ', comics, and novels from the 80s and 90s to secondary continuity and, if elements are used from them, they are subject to selective revision and updating as appropriate to mesh with future canonical productions and to prevent conflict with the original animated series. While the Jack McKinney "Robotech" novel "End of the Circle" is evidently no longer canon, the prequel comic ' establishes that the general storyline of The Sentinels still occurred in some fashion, but various elements, including the timeline, specific unfolding of events, and some characterizations are different from what was previously depicted in earlier comics and novels. In such cases, the franchise producer may state that there is no intention to address the changes through remakes or direct retellings of such stories. It is essentially left to the viewer's imagination as to how differently the revised story unfolded.