What is Canon?
The term "canon" is occasionally referred to by the people who make Star Trek, and much more frequently by the fans and here at EAS. The usefulness of the canon is under permanent debate, as are the interpretations what has to be regarded as canonical and what not. This write-up attempts to clarify what canon actually is, why it exists, how we can handle moot cases and how the canon policy at EAS works.
Although the concepts are different (which becomes evident as soon as we're looking at more than one timeline), "canon" and "continuity" are often used interchangeably. Read also the separate article on The Continuities of Star Trek.
General definition of canon
The word "canon" has more than one meaning in the English language. Several definitions can be found on the disambiguation page at Wikipedia (see the latest version of "Canon" at Wikipedia). The following two are relevant for the assessment of the Star Trek canon:
- "A list of books accepted by an ecclesiastic communion as authoritative or divinely inspired. The term was originally Christian, referring to books declared divinely inspired by the canons of Church councils..."
- "In fiction, the officially authorized interpretation of characters and events. In fandom, the term is often used to distinguish between 'canonical' accounts (i.e. those authorized by the copyright holder) and those of fan fiction, sometimes called fanon..."
As we can easily recognize, the word originally used for the "divinely inspired" literature of Christian churches has been adopted to denote the valid parts of a fiction. In this sense, canon stands for what we could find in the history books or other records of the fictional universe. Certainly the canonical fictional universe is not supposed to be as authoritative as the teachings of a church. Still, there are various similarities.
Side note "Canon" is a noun, the correct adjective would be "canonical". Yet, it has become quite common to use "canon" in the way of an adjective, such as in "It is canon that all Vulcans can meld their minds." This is how the word is often used here at EAS too, although "canonical" would be correct in this example.
Star Trek's canon
This is the practical explanation of canon as it could be found at the official Star Trek website until 2006:
"As a rule of thumb, the events that take place within the real action series and movies are canon, or official Star Trek facts. Story lines, characters, events, stardates, etc. that take place within the fictional novels, the Animated Series and the various comic lines are not canon.
There are only a couple of exceptions of this rule: the Jeri Taylor penned novels 'Mosaic' and 'Pathways'. Many of the events in these two novels feature background details of the main Star Trek: Voyager characters. (Note: There are a few details from an episode of the Animated Adventures that have entered into the Star Trek canon. The episode 'Yesteryear', written by D.C. Fontana, features some biographical background of Spock.)"
Many of these positions, especially those concerning TAS and Jeri Taylor's novels, sound like they were arbitrarily made up and are debatable, as will be pointed out later. But the key statement is that only "events within the real action series" are canon. At least that much is generally accepted. Irrespective of any concerns of how they could possibly fit together, this definition of canon encompasses the live action TV shows (TOS, TNG, DS9, Voyager, Enterprise, Discovery, Picard) and the feature films (classic and Abramsverse), all in the versions in which they were shown on TV or in the theaters, respectively.
Side note The notion that any books could be canonical is contested by professional writers posting at the TrekBBS. Paramount's policy that Jeri Taylor's novels should be canon is said to be non-existent and may have been made up just for the fans.
From 2006 to 2010, the following more elaborate explanation could be found at startrek.com:
"As a rule of thumb, the events that take place within the live-action episodes and movies are canon, or official Star Trek facts. Story lines, characters, events, stardates, etc. that take place within the fictional novels, video games, the Animated Series, and the various comic lines have traditionally not been considered part of the canon. But canon is not something set in stone; even events in some of the movies have been called into question as to whether they should be considered canon! Ultimately, the fans, the writers and the producers may all differ on what is considered canon and the very idea of what is canon has become more fluid, especially as there isn't a single voice or arbiter to decide. Star Trek creator Gene Roddenberry was accustomed to making statements about canon, but even he was known to change his mind.
In the publishing world, there used to be two exceptions to the novel rule: the Jeri Taylor-penned books 'Mosaic' and 'Pathways.' Many of the events in these two novels feature background details of the main Star Trek: Voyager characters and were to be considered as references by writers on the show. Now that the show is over, some of those events may never be incorporated into a live action format, so the question of whether details from these novels remain canon is open to interpretation.
With regard to the Animated Series, there are a few details from the episode 'Yesteryear,' written by D.C. Fontana, that reveal biographical background on Spock and planet Vulcan. Details from this episode have been successfully incorporated into the canon of Star Trek (such as in 'The Forge') and now that the Animated Series is out on DVD, we hope that even more can make its way in!"
Note that the revised definition is overall watered down. While the canonicity of some facts from the movies (obviously because of fan reactions to "Star Trek V") is suddenly questioned, TAS is slated to become canon (following a fan vote at startrek.com). Another former article on the site confirms this intention, and the TAS DVD special features even assure the viewers of the full canonicity of the series. Something of further interest is that at startrek.com canon is now stated to be a question of if and when something from the previously non-canon realm is incorporated into a canon series. This practice may work out well for the people who make Star Trek. In its ultimate consequence it would remove the need to care about canon at all. But it makes the decision if and where to draw a line increasingly complicated for the archivists and hence essentially for the fans.
Canon vs. official
In a simple approach it may seem that anything about the fictional Star Trek Universe that is officially released by Paramount/CBS should be automatically canonical. But as the word "official" is rather used as an administrative or legal term as opposed to "canon" as a purely fictional quality, the two are different. While Paramount Pictures or CBS may *officially* endorse books or games of their licensees, this does not imply that these products are *canon* too. On the contrary, as will be explained further down, Paramount/CBS keeps licensed products strictly non-canon.
This is merely the negation of "canon". If only live action is to be taken into account, then Star Trek novels, no matter if written by licensed authors or by fans, are never canon. In order to avoid misunderstandings: The designation "non-canonical" does not imply that they are badly written or that loyal fans should not read them. It just says that they are not a part of the canonical Star Trek Universe and are therefore irrelevant in its assessment. All novels, comics, reference books, calendars, role playing games, computer games, fanfic websites, merchandising items and everything else dealing in any way with Star Trek is non-canon, regardless of its origin or authorship.
Fans occasionally refer to material whose canonicity is debatable as "apocryphal". Wikipedia (see the latest version of "Apocrypha" on their server) defines the term like this:
- "In Judeo-Christian theologies, apocrypha refers to religious Sacred text that have questionable authenticity or are otherwise disputed. When most in the Western world refer to the Apocrypha, they are typically referring to the 14 books excluded from Protestant Bibles..."
In Star Trek fandom, the term "apocryphal" represents any information that is not canon in a narrow sense, but is by some treated like, or accepted as, canon. This may include The Animated Series, the books by Jeri Taylor, selected information from any other novels, reference books, deleted scenes or behind-the-scenes information. However, accounts from the live series, which are canon by their very definition, shouldn't be declared "apocryphal" just because some doubt its canonicity - even if there was an according allusion in the former FAQ at startrek.com.
In fandom, licensed Star Trek literature and games are sometimes referred to as "beta canon", most often in conjunction with TAS being fully canon. While "apocryphal" may become obsolete, the classification as beta canon establishes a new and somewhat more authoritative additional level between "canon" and "non-canon". In more recent years, writers working for the additional production have begun to include facts from beta canon into canon (or official) Trek, such as the species of Rok-Tahk, the Brikar.
This word is obviously a portmanteau of "fandom" and "canon". Wikipedia (see the latest version of "Fanon" on their server) says about "fanon":
- "Fanon is a fact or ongoing situation in fan fiction stories related to a television program, book, movie, or video game that has been used so much by fan writers that it has been more or less established as having happened in the fictional world, but it has not actually been established as having happened on the show, book or movie itself. Fanon is a portmanteau word of fan and canon..."
So "fanon" denotes views and opinions that are non-canon but widespread in fan fiction. Examples include minutiae like Uhura's first name Nyota, which was never mentioned on screen until 2009 when it finally became canon, or the notion that Romulans did not have warp drive in 2266, which is just a perpetuated misconception, as can be seen in the article about Warp Drive and Romulan History. More examples along these lines are listed on the page about False Canon.
These words are often used to denote material, which is either not canon in its entirety or whose canonicity remains debatable. The latter could be described as "apocryphal" too.
Parts of the fandom or of licensed literature that are in irreconcilable contradiction to canon facts may be called "anti-canon". In a discussion dealing just with canon facts it is irrelevant whether non-canon evidence may help or obstruct the assessment. But when reading (fan) fiction it is obvious that a knowledgeable fan may accept non-canon facts but will not appreciate it as soon as it becomes anti-canon.
Personal canon or "headcanon"
These terms can be found in discussion forums or on personal websites. Many fans have decided to include additional works (such as TAS, novels or even fan fiction) to their so-called "personal canon", or they deny parts of the franchise their otherwise definite status as canonical (like some purists disregard Enterprise or even everything that came after TOS and the first six movies). A "personal canon" may and is supposed to be more consistent than the official canon and may contribute to a "fanon". Yet, owing to its arbitrary nature and limited validity a "personal canon" usually obstructs the assessment of canon material.
The expansions of the Star Trek canon in the form of novels and of Star Trek Online are sometimes referred to as "Expanded Universe", rather than as beta canon. However, unlike in the case of Star Wars, this is not an officially endorsed and coordinated concept in Star Trek. Overall, there have been increasing efforts to align licensed works with each other and with canon in more recent years, but they don't form a unified science fiction universe. So the term beta canon describes better how the the novels and games relate to canon Trek.
The reasons for the existence of an ecclesial canon are diverse. It is debatable whether it was created in the first place to defy heretics who might take away power and prosperity from the official church, or whether it was first of all a honest matter of faith. Regarding the Star Trek Universe, the canon has a relatively harmless impact on the lives of most fans and it certainly is not intended by TPTB to control the fans. Still, there are reasons for a canon of the Star Trek Universe.
Canon and continuity
As outlined in the article on the Realism of (Science) Fiction, Star Trek is (or at least, used to be) a franchise with internal consistency, as opposed to shows that are rebooted or that even take pleasure in creating deliberate continuity errors. Yet, during the three seasons of The Original Series from 1966 to 1969, there was no obvious canon policy, just as there was no particular attention to inter-episode continuity either. But as the fictional universe kept growing, it was necessary to come up with rules what has to be taken into account by future writers (the canon), as well as with a collection of such canon data for reference (The Star Trek Encyclopedia and its forerunners that must have existed behind the scenes).
Keeping looks and events in new episodes compliant with canon was a quality mark of the show, at least until the end of Star Trek Enterprise in 2005.
Canon and creativity
Canon may be seen as an obstacle to creativity, simply because not all real-world possibilities are allowed to be exploited in-universe. On the other hand, in a creative process canon boils down to a simple list of what has been shown or told before and what not. This is not really a creative limitation. On the contrary, knowledge of canon can help avoid rehashes of a previous story. There is always a risk that writers consciously recycle plots just because they think it is a good idea to show familiar situations already established in the canon. Still, they better closely base their stories on canon events than just on stereotypes.
The knowledge about canon may have a quite beneficial impact on storylines. A prominent example is DS9: "Trials and Tribble-ations" with its slavish adherence to the canon events of TOS: "The Trouble with Tribbles". Another one is the Vulcan arc of ENT: "The Forge", "The Awakening" and "Kir'Shara" that successfully removes a previous continuity error concerning Vulcan Mind Melds from canon. These episodes are commonly said to be among the most creative and most enticing installments of all Star Trek.
Canon and commerce
Star Trek takes place in many different forms, among which the TV series and movies are (or at least, should be) in the center of interest. In addition, Trek-themed novels, comics and computer games are available as well as typical merchandising items such as action figures, t-shirts and coffee mugs. Any company with the intention to sell anything with "Star Trek" printed on it needs a license from the brand owners Paramount Pictures and CBS Television. This franchise makes up a major part of the business.
Paramount and CBS give away the valuable name of Star Trek to various third-party products, and they have an interest that these products adhere to certain standards. But irrespective of their quality, these products are not supposed to tell stories that have an impact on the TV series or movies. The copyright owners want to maintain full control of their own creative base.
There is actually an even more important reason why Paramount and CBS do not want any licensed products, especially those of literary relevance (novels and games), to be canon. If Paramount or CBS decided to adopt anything that was not originally created by an employee but by a contractor, they might have to pay royalties for each and every mention of this character or concept! So the Kzinti species from The Animated Series (TAS: "The Slaver Weapon") never found its way into any of the live series. The episode involving the Kzinti was written by Larry Niven, based on one of his novels (The Soft Weapon). Niven was irritated when Dean Foster wrote the novelization of the episode instead of himself, although he contradicts the common rumor that he threatened legal actions against Paramount (interview at Trekplace). Nevertheless it seems that Paramount preemptively banned the Kzinti from canon Star Trek, as well they prohibited their use in licensed works in at least three cases (Kzinti at Memory Alpha). Still, it was planned to finally include them in the fifth season of Enterprise. Another prominent example is the character of T'Pol, who was named T'Pau in the draft of the series. But TPTB cautiously changed it to T'Pol in order to avoid the due credit to the author of TOS: "Amok Time", Theodore Sturgeon, in every episode. T'Pau was eventually included in the Vulcan arc on Star Trek Enterprise, though.
Canon and practicability
Star Trek writers are expected to be creative and not perfect librarians (something that is largely left to the fans and particularly Memory Alpha today after Richard Arnold and later the Okudas used to fill that role). With 600 hours of TV it is already extremely hard to come up with stories that are original and still not in contradiction to previous installments. Without the help of the Star Trek Encyclopedia and other reference works as well as of their colleagues and editors, a writer would find himself lost in a confusing maze of facts that must be taken into account. This would become many times as complicated if they additionally had to take into account all novels. All of them because where could a line be drawn? And what about the games? They establish many facts as well. At some point it wouldn't be possibly any longer to insert new data because the adventures would fill many lifetimes of characters or ships, with incalculable inconsistencies.
Canon and the fans
As already mentioned, the term "canon" shows up in fan circles a lot more frequently than on startrek.com or in official reference works. Even casual viewers, who may not be aware of the word "canon", care more about it than the studio could hope for. They notice goofs like the epitaph "James R. Kirk" because everyone knows that his true name is "James T. Kirk". They wonder if the contents of novels or comics may have any bearing on the TV series. They compare Star Trek with other franchises like Marvel or DC Comics where the establishment of a credible (non-multiverse) canon is practically impossible because of lacking continuity. In this regard the canon policy gives the fans something to chew on. It allows to limit discussions among fans to a reasonable common ground, and it ultimately enables the setup of websites like Memory Alpha, which would be a bottomless pit without the canon foundation, and of EAS, which would become utterly pointless. In this sense, the canon allows Star Trek to earn a "meta quality" when fans take care of episodes that the production staff has long finished and almost forgotten.
As already mentioned in the introductory note, the criteria for what type of evidence is canonical under which preconditions are under permanent discussion. Moreover, Gene Roddenberry and his successors are said to have included additional material to the canon, as well as they purportedly removed some of the live action from the canon. It will be discussed in the following whether the material in question should be acknowledged as canon, and whether the said exceptions are useful. But most notably, new rules are required for the alternate universe movies produced by J.J. Abrams (since 2009), for the e re-imagined universe of Star Trek Discovery (since 2017), as well as for old and newly produced animated Star Trek.
The views in this section reflect the canon policy at EAS; other fan-made websites may arrive at slightly different conclusions, considering that the Star Trek Universe has become very complicated, contradictory and controversial in more recent years.
Novels and games
Only televised Star Trek is canon. This explicitly excludes books, and above all the myriad of novels based on Star Trek. None of them are canon in the view of Paramount/CBS, although many of them would fit into the timeline and would be largely free of anti-canon notions. The above mentioned royalty issue forbids (or makes it very unlikely) that characters established in the books ever find their way into canon Trek. The same applies to all Trek-themed games and other merchandise.
Novels based on movies
The circumstances seem to be different if a novel is directly based on a feature film, written by the same author and usually more comprehensive than the movie. One prime example is the novelization of "Star Trek: The Motion Picture" by Gene Roddenberry that adds many facts and aspects that can't be found in the movie. If much of the book's content is canon because it describes the events on the screen, shouldn't the rest be canon too?
Novels by Jeri Taylor
The two novels Mosaic and Pathways were explicitly mentioned on the official Star Trek website to be theoretically canon, the reason being that Jeri Taylor, at that time co-producer of the series, added essential background information on the Voyager main characters. But can this statement be maintained, considering that Voyager writers have been ignoring the novels all along? If they should have looked up facts there when writing episodes but actually didn't do it, the canonicity of her two books is at most theoretical, and some smaller parts may be even anti-canonical.
Star Trek: The Animated Series
Gene Roddenberry is said to have decanonized TAS, but this is uncertain. The official website previously stated that it is non-canon, but without giving reasons. The Star Trek Encyclopedia and all other official manuals written since the late 1980s (since the canon officially exists) are without references from The Animated Series. Nonetheless TAS may be treated as canon according to the TAS DVD and the official site (until 2010), at least partly because of a fan vote at startrek.com. Yet, the official website also used to state that the canonicity of TAS, even if it is earned effortlessly, must be gradually confirmed by referring to events from TAS in future incarnations of Star Trek.
This particular TAS episode (review) is commonly regarded as the best of the whole series. But its quality alone should not be the reason to include it to the canon, especially considering the problems of partially canonical material. The actual reason cited for TAS: "Yesteryear" to be canonical is that it adds to the background of Spock's character. While this is true and is quite useful, it is still no reason why these facts should be made canonical and other events from TAS not. Moreover, if canonicity were just a matter of quality or of usefulness, disappointed fans could turn the tables and demand that trainwrecks like "Star Trek V" or VOY: "Threshold" be declared non-canon.
Here at EAS, I would have no problem accepting this one TAS episode as canon. But I have no particular motivation to create a precedent and treat it differently than the rest of the series.
Star Trek: Lower Decks
According to creator Mike McMahan, his animated comedy series Lower Decks is canon. McMahan as well as other sources repeatedly cite that the series fits well into the year 2380 and respects the visuals and other facts of previous Trek series of the era. Yet, the classification of Lower Decks being fully canon is in contrast to the status of TAS, which is commonly debated and still not fully recognized until today.
Star Trek: Prodigy
Just like Lower Decks, Star Trek: Prodigy has been declared canon by its producers, with much the same rationale.
Star Trek V & VI
It may be just a rumor that Gene Roddenberry wanted these two movies removed from canon, allegedly because they don't reflect the true spirit of Star Trek. We may have to wonder anyway why Roddenberry was so opposed to the alleged racism in "Star Trek VI" (according to director Nicholas Meyer), a movie that came into the theaters after his death, that he condemned it before it was even completed.
The first two seasons of Star Trek Discovery are officially set in the 2250s of the Prime Universe. There is no doubt that the producers of the series consider Discovery an integral, fully canon part of Star Trek. Yet, the series does not adhere to the existing canon at all on the visual side. Established looks were completely redesigned far beyond what could qualify as a visual update, most obviously everything related to the Klingons. The changes are much more than only cosmetic. They are not rooted in real-life progress of visual effects and make-up techniques but unquestionably in the desire to create something very different looking than the Star Trek as we knew it. Furthermore, the series establishes events that couldn't realistically have occurred in the 2150's and lots of technology that should not yet exist or should not exist at all. The latter is explained in "Such Sweet Sorrow II", but more like in an "out of sight, out of mind" fashion. After the setting of Discovery has been changed to the far future, where the damage to the continuity can be kept in check, the spin-off Strange New Worlds continues to take place in an era whose facts and looks it does not actually respect.
EAS acknowledges the official stance that Discovery and Strange New Worlds are canon Star Trek series. But there are colossal obstacles to their integration because practically all visuals as well as numerous other facts of the series vehemently clash with what has been established before. The continuity issues are even worse than those with the Abrams movies (see below), considering that Discovery and Strange New Worlds are supposedly set in the Prime Universe, just a few years before Kirk takes command of the Enterprise. In cases of conflicts, I will give the existing Star Trek precedence, and I will never try to blend in the Discoverse with far-fetched explanations, unless these are hinted at in the stories themselves. Discovery tried to reconcile a few visuals and other facts with canon in its second season, but couldn't bridge the wide rift that had previously opened. Strange New Worlds may continue to make a few things look a little bit like they did in TOS. But DIS and SNW will stay in confinement at EAS.
It was the intention of producer and director J.J. Abrams and his staff to reboot the franchise while respecting Star Trek's continuity. "Star Trek (2009)" takes place a few years before The Original Series, but establishes an entirely new timeline (officially called the Kelvin Timeline). It would be possible for the "Abramsverse" to be fully canon. At least, this is the official position.
Star Trek: Countdown and Nero
These two comic series are tied into the the story "Star Trek (2009)". In an interview with Trekmovie.com, dated 9 December 2008, "Star Trek (2009)" writer Bob Orci said that he personally considered some novels canon, but that it is not up to him to declare Countdown canon. In a later Q&A session, dated May 22, 2009, he explained the inconsistencies between the movie "Star Trek (2009)" and Countdown with the comic being non-canon. The same applies to the Star Trek: Nero comics and the whole story about Nero's imprisonment on Rura Penthe.
Official reference books
Books are non-canon because of their printed nature, even those officially released by Paramount/CBS via Pocket Books and with people working on the show as authors (reviews). The TNG Technical Manual and the DS9 Technical Manual can be regarded as apocryphal because a good deal of them consists of facts that supplement the scarce technical information given in the series itself and that were expected to be an official guideline for the writing staff too. The same applies to the Official Starships Collection and other ship-related publications by Eaglemoss in more recent years with their information on names and registries that were supposedly on the actual CG models. The Star Trek Encyclopedia extracts data from the canon episodes. Where it is correct, it is a reproduction of canon facts, but not canon by itself. Even a few occurrences of False Canon can be found in the Encyclopedia.
Star Trek Technical Manual
Prior to TNG, the STTM (review) was commonly regarded as authoritative, yet no one called it "canon" when it was released in 1975. It was a time when no Star Trek was on air and when fans were hungry for any kind of information. So the author, Franz Joseph Schnaubelt, got the blessing from Gene Roddenberry to write a technical manual of Star Trek. Franz Joseph went ahead and created a manual that included schematics of canon devices, rooms, uniforms. He supplemented this with what we would call fan fiction today, namely the Federation Charter, emblems of alien civilizations and the ship schematics.
Even if we attempt to establish an exception, the STTM as a whole fails to fulfill the requirements for canon data in several regards. First of all, a definition of canon didn't technically exist when the STTM was written. And as unfair as it may seem, just when Roddenberry set up the canon policy for TNG, the STTM was not included.
Side note Some time prior to TNG, they didn't get along with each other any longer, and it is said that Roddenberry intentionally laid out technical specs of TNG so as to disparage Franz Joseph's work - but this doesn't really belong here. If you would like to know more about Franz Joseph's background, please visit Trekplace.
Secondly, no printed publication, not even the official technical manuals by Sternbach or Okuda, are regarded as canon themselves, but at most as apocryphal. Thirdly, certain major parts of the manual are of a debatable nature or are anti-canon, like the alien emblems, the map of the galaxy, the Federation Charter (actually a mostly literal rip-off of the UN Charter) and the circuit schematics of the tricorder etc. I simply wouldn't want to include these just to have a couple of more ships on the list.
Fandom reference books
Unlike the at least apocryphal TNG Technical Manual, the DS9 Technical Manual and the Star Trek Encyclopedia, publications like those of FASA, Jackill or Todd Guenther are unquestionably non-canon, as is the Spaceflight Chronology too. The same applies to some more recent books like Star Trek Star Charts (review) or The Starship Spotter. From Paramount/CBS's viewpoint they fall into the same category as novels, even if some depictions from FASA manual made it into TNG episodes. But this must be seen rather as an accident because the Art Department is usually quite careful not to include copyrighted material.
Star Trek Online
Ships designs from the MMORPG Star Trek Online appear in the second season of Star Trek Picard. This has prompted some fans to declare that "all STO ships are canon now" or "all of STO is canon now". This is a misconception. Single ships from the Star Trek Technical Manual or even from other sci-fi universes have appeared in Trek shows and movies before, without making them canon within the Star Trek Universe.
The Klingon language devised by James Doohan for the first feature film consisted of just a few words and was later developed to a fully-fledged language by linguist Mark Okrand. Applying the same criteria to the language as to anything else in Star Trek, only the Klingon spoken on screen is canon (regardless of its consistency and of Okrand's involvement), not the complete grammar and vocabulary created by Okrand.
This is an interesting point to be considered because some of the behind-the-scenes information is widely accepted without actually being canonical. For instance, the Miranda class was never called by that name in any episode, not even in a screenplay. Still, it has become the commonly accepted name of the ship class thanks to the Star Trek Encyclopedias (well, until the 1990s rivaled by the fandom name "Avenger class"). Fundamentally, behind-the-scenes information as it can be found in official reference manuals is just as apocryphal as these books are in their entirety.
Like with information from behind the scenes, most screenplays (or preliminary version thereof) include additional lines or annotations that find their way into fandom but not into the final episode or movie. We certainly need to disregard them as soon as they are contradicted by canon facts. This happens with the so far common notion that the Klingon BoP in "Star Trek: The Search for Spock" was actually a Romulan vessel. The Klingon retro-BoPs in ENT: "Expanse" is the ultimate proof that there is no Romulan link. In some other cases there were little facts, especially names in scripts that were not mentioned on screen.
Cut scenes/additional scenes
Did Picard and Data drink wine in "Nemesis" or not? The DVD has an additional scene, which is not in the theatrical version. Moreover, this scene is not embedded into the very movie track, but separate. The same question, with a more definite impact, crops up in "Star Trek: The Undiscovered Country". The scenes with Colonel West were cut from the movie, but inserted into later releases. So does he exist at all? And what about Kirk's orbital skydiving in "Generations", which was only available in the internet so far, not on DVD?
Without forgetting about the original versions, EAS generally takes into account additional or changed scenes if they were included in a way to form a new and improved version of the movie, most obviously in the case of "Star Trek: The Motion Picture" (new Vulcan landscape and V'ger's revised diameter in the Director's Cut). On the other hand, anyone who can rip a movie could easily insert unused scenes that were kept separately to where they belong, but we are obviously not supposed to view the movies like that. The decision what to take into account is the same as with the already mentioned script contents and remains somewhat arbitrary.
TOS and TNG Remastered
Whilst the producers have reassured that nothing is changed in the storylines, the remastering (TOS-R) of The Original Series still stirs up continuity issues. The remastered version comes with improved effects such as of phaser shots, with new planetscapes and with new vessels too. TOS-R is designed to be more internally consistent. But which is correct: the old phaser beams that were occasionally red, or the new consistently blue ones? The old blurry planets, or the new highly detailed ones? Note that, once again, the question what is canon should not be primarily about quality or taste. The same question arises with the remastered version of TNG (TNG-R), although here the changes are less extensive.
Many fans tend to disregard silly or otherwise disagreeable events like the DS9 version of the Mirror Universe because it is not "our" universe after all. Some extend this practice to whole incarnations of Star Trek, such as Star Trek Enterprise, the Abrams movies or Star Trek Discovery. They assert that these take place in alternate universes and hence should be discarded as non-canon. The official canon policy, however, makes no difference between such "unreal" and "real" events. Even the content of dreams or hallucinations is canonical in the sense that it is visible on screen.
Their canon nature doesn't prevent information from the live action series from sometimes being contradictory. This may happen because of negligent writing but also in case of a conscious reboot. In some cases the contradictions may be explained away rather easily. But by no means such speculation should itself be declared canon, although fans are tempted to believe into the validity of their favorite hypothesis. Actually much of the fanon came to life as such conjectural explanations. A prominent pre-Discovery example of contradictory canon is the Trill Problem, a fundamental revision of the nature of this race that defies a complete explanation. Star Trek Discovery takes this one step further, by redesigning the Klingons, the arguably best-known race of Star Trek, without providing an in-universe rationale.
Ex Astris Scientia
No, I don't suffer from megalomania. The reason why I'm listing EAS as a candidate for a canon source is that some fans refer to my website as canon. But actually EAS does not create any canon content. It can only convey canon data and, in debatable cases, suggest reasonable solutions with a minimum of speculation.
The real world
Is the real world canonical in Star Trek? The question wouldn't occur in a galaxy far, far away. But since Star Trek aims to depict the very future of humanity, its past has to be taken into account. The real world influences Star Trek by providing historical side notes, character and ship names and locations on Earth. In this sense the real world is definitely canonical, although Star Trek sometimes alters the course of human history or even the laws of physics. As long as the fictional events are set far enough in the future, there is no danger of our real world becoming "non-canon". The article on 21st Century Earth History demonstrates what happens if this precondition is not given.
Canon Policy @ Memory Alpha
There are good reasons for a canon policy - at the CBS/Paramount as well as here at EAS. But fans shouldn't go as far as refusing everything non-canon from the outset; Star Trek can be more than the collected facts in the Okudas' Encyclopedia. On the other hand, there is the kind of fans who stir up canon and fandom at will, be it because of their limited knowledge about the Star Trek Universe or because they don't want their creativity be limited by the canon. In my many years in the fandom I have encountered lots of either type of fans, and any shade in between.
One typical situation is that some people in a message board explicitly talk about the number of nacelles on canon starships and someone throws in that the Federation class and Saladin class (from Franz Joseph's Star Fleet Technical Manual) are odd-nacelled. The result is a fruitless discussion about the definition of "canon", about the authority of Roddenberry, Okuda, Paramount or Pocket Books, about books which should be considered canon because they are written by Jeri Taylor, about Colonel West and the Starfleet Marines, and so on. Very often ideas of False Canon or "headcanon" are involved too. This is one more reason why a well-established canon is a useful reference.
As a universal reference, the idea of a canon in an uninterrupted continuity worked well in the years between 1994 (release of the first Star Trek Encyclopedia) and 2005 (end of Star Trek Enterprise). The Abramsverse and ultimately Discovery call the principle of canonicity into question. While the new Star Trek is canon by its very nature, it establishes numerous facts that cannot be reconciled with the pre-existing continuity. It is an ongoing process, at EAS just like in the whole fandom, to handle the extreme discrepancies, and (as far as EAS is concerned, I can't speak for other fan projects) to still apply the same well-established criteria as they were valid until 2009. In particular, EAS will neither resort to lackadaisical apologist statements like "there are many races of Klingons, hence the differences" (unless this shows up in a canon story), nor will I declare Discovery non-canon (because it's not up to me to make such a decision).
The canon policy at EAS accepts the definition of canon given by TPTB as a way to avoid unnecessary discussions. Actually, I would go as far as saying that EAS couldn't exist without the canon because if there were not one supposedly true and authentic version of the fictional universe, it would become utterly pointless to file and analyze anything about it beyond a mere list what happened in which episode or book. In contrast to websites that are based on a "headcanon", EAS neither ignores canon accounts at the outset nor adds non-canon information. EAS includes some apocryphal reference works (but no beta canon) only if these fill in necessary details that would never be mentioned in an episode. This doesn't mean that EAS slavishly follows the interpretations put forth in reference works.
But canon is not everything. Every fan should feel encouraged to include whatever he likes to his personal view (not "personal canon") of the Star Trek Universe. That's what I'm doing with my ship designs, the ASDB and the Starfleet Museum too. I would never want to miss the fan-made stuff all around the planet because they really enrich the universe, no matter if I "believe" in their existence. I probably can't help those who don't even want to see anything that has not the seal of Paramount/CBS on it or the other extreme group, those who don't care about the idea of Star Trek and turn Starfleet into a military organization with big-gunned warships. For anyone in between, canon is a common ground. Everything else is left to our imagination and tolerance or better, mutual understanding. There are always possibilities!
Some screen caps from TrekCore. Some ideas, especially concerning cut scenes, script information and other moot cases, were inspired by an article at Green Mole. Thanks also to the people at the SCN for discussing issues of canon. Thanks to Andrew Briggs for pointing me to the reason for Gene Roddenberry to condemn "Star Trek VI", to Kobi for correcting some facts about the Kzinti and to Spike for the revision of the alleged official canon policy.