It is not surprising that during the course of Doctor Whos (almost) 46 years, some of the writers involved in the show have been unfamiliar with the details of some of the previous episodes. This has inevitably lead to contradictions in the shows mythos.
This article will attempt to list some of the most obvious...
Doctor Who is one of the longest-running TV series in history. Over the course of 26 seasons of the original series and (at the time of writing) four of the revamped version, plus assorted specials, it has clocked up more screen time than any sci-fi series other than Star Trek.
It is not surprising that during the course of those years, some of the writers involved in the show have been unfamiliar with the details of some of the previous episodes. This has inevitably lead to contradictions in the show's mythos1. This Entry will attempt to list some of the most obvious.
Anything To Do With the Sixth Doctor
Major disruption to the timelines was caused by the BBC's decision to unceremoniously dump Colin Baker from the role of Doctor in 1986.
Actress Bonnie Langford joined the show during the season 23 story Trial of a Time Lord. Her character, Mel Bush, initially appeared only in 'flash-forward' scenes from the Doctor's future as the Doctor used the mega-computer called 'The Matrix' to show future events as part of his defence. Later on, she appears in person as a witness at the trial. This is where it gets complicated. The version of Mel called as a witness has already met, travelled with and left the Doctor - she remembers the flash-forward events (known to Who aficionados as Terror of the Vervoids2) we have just seen. The Doctor, on the other hand, has never met Mel before - those events are in his future. Presumably the intention was that after the trial, the Doctor would drop future-Mel home, then resume his travels and eventually meet her again for the first (for her) or second (for him) time, going on to live through the Terror of the Vervoids events.
However, Colin Baker was acrimoniously dropped as Doctor before any further stories could be made. In the subsequent story, Mel is travelling with the Doctor as he regenerates into Sylvester McCoy. So we never see Mel's first meeting with the Doctor, and the viewer is now confused as to why she was not surprised to see the Colin Baker Doctor in Trial of a Time Lord. This would best be explained if Mel's appearance as a witness took place prior to her seeing the regeneration. Therefore when Langford left the series in the story Dragonfire, we are left to wonder whether this was the first time she had left the Doctor, or the third (after some unseen adventure(s) where she left the Sixth Doctor and her witness appearance at Trial of a Time Lord, followed by another unseen adventure when she rejoined the Sixth Doctor), which would explain why she's not surprised to see the Sixth Doctor in Trial of a Time Lord.
Mostly, however, we were just glad to get rid of her. And let's not even get into how many of his 'future' adventures the Doctor saw while researching his evidence in The Matrix...
Then there are the problems with the script of Trial of a Time Lord. Apparently the Valeyard3 is 'an amalgam of the Doctor's darker side, somewhere between his twelfth and thirteenth regenerations', whatever that means. How he came to exist, why he's working with the Time Lords... a bit of a plot gap. In the first section of Trial of a Time Lord - The Mysterious Planet - much is made of 'the Sleepers', a mysterious reference which the Time Lords attempt (with only partial success) to edit out of the evidence given at the Doctor's trial. We never find out who or what the Sleepers are.
The novels only make things more complicated. In Killing Ground, a Past Doctor Adventure (PDA), the Sixth Doctor meets Grant Markham, who becomes his companion, and the two travel off together in the Tardis. Unfortunately, Steve Lyons never got around to writing a sequel where Grant leaves, so the Sixth Doctor's already convoluted continuity gets even worse.
All of which just goes to prove the old Time Lord adage: 'You can't mess with the Sixth Doctor's continuity enough'.
The Brigadier and UNIT Dating
This is what you get when you don't bother to actually watch the programme you're writing for. When the Third Doctor was exiled to Earth in Season Seven, he joined up with a military organisation called UNIT, headed by Brigadier Lethbridge-Stewart. It was always the production team's intent that these stories were set a few years in the future - in about the 1980s. Lethbridge-Stewart first appears in The Invasion, which is said to be set four years after Web of Fear, which is in turn stated on-screen to be at least 40 years after 1935 - therefore meaning the Doctor first meets UNIT in 1979 at the earliest. Sarah Jane Smith claims to be from 1980 in Pyramids of Mars, where Lethbridge-Stewart is still with UNIT, supporting this 'late dating'.
However, not all of the production team worked to this assumption. Some assumed that the UNIT adventures were set around the time they were broadcast in the 1970s. Therefore when the Brigadier returned to the series in Mawdryn Undead, we see that he retired from UNIT in 1976, after all his adventures with the Doctor.
So it appears that the Brigadier retired from UNIT before he started working for them.
The paperback novels add even more complexity to Lethbridge-Stewart's life, with promotion to General, retirement, youthing and whatnot. Fortunately for us, many fans have written long, complex treatises explaining how all this is possible without contradiction. Even more fortunately, none of them will be repeated here.
The Eighth Regeneration and the Time War
Another casualty of TV realities was Paul McGann's run as the Eighth Doctor. Although a pilot was made, aired and entered the canon, the mooted series failed to materialise with a wheezing, groaning sound on our screens.
When the BBC revived the series, they began in media res with the Ninth Doctor in a deliberate attempt to add some mystery to the Doctor's history. Vague allusions to a Time War are all we have to explain what may have happened to him. To date, that mystery has not been resolved. Long-time readers of the Eighth Doctor Adventures (EDA) paperbacks are none the wiser, but possibly slightly more confused since the Time War contained in them is clearly not the same as the Time War off the telly, despite Gallifrey being destroyed in both Time Wars. Instead, the series ended with an amnesiac Doctor and his companions jumping into a nest of aliens.
Continuity is something that happens to other people when you are an evil, galaxy-destroying genius.
Sadly, the original incumbent to the role, Roger Delgado, died in a car crash. However, the character was simply too good to drop, so a new actor was cast in The Deadly Assassin as a rotten, decayed living corpse. Quite how he got himself into this state is only hinted at4, but for a while things pick up and we see the decayed Master steal himself a new body to become the Anthony Ainley version. There are, of course, the usual unexplained escapes from certain doom - notably somewhere between Planet of Fire and Mark of the Rani - but these fall into the usual inverse relationship between continuity gaps and heroism.
However, from then on, the writers seem to have simply given up on the whole idea of continuity in the Master's life. He turns up in Survival infected with some weird Cheetah Virus; then is suddenly executed by the Daleks in the pre-credit sequence of the TV Movie before equally suddenly revealing a previously-unnoticed ability to survive as a giant ghostly snake. He's then swallowed by the Eye of Harmony in the Tardis5. Finally, we are told that he survived the Time War and ended up disguised as a human with no memory of his past and living at the end of the Universe.
With that amount of continuity trauma, it's amazing he hasn't become some kind of psychotic megalomaniac.
The Cybermen's History
The final foes the First Doctor faced were to become fan favourites, second only to the Daleks. The Cybermen were introduced as an alternate version of humanity from Earth's twin planet, Mondas. Later, in Tomb of the Cybermen, it is stated that Telos is their home planet, though later episodes still (such as Attack of the Cybermen) revert to the Mondas theory, and Telos is relegated to just another conquest.
In the revised series, the Cybermen were created by John Lumic in an alternate dimension.
The Doctor destroys Atlantis during the 20th Century in The Underwater Menace. He can therefore only be irked to hear Azal boasting during The Daemons that he has destroyed it. Just to make sure, the Doctor travels back in time to ensure that the Chronovore Kronos destroys Atlantis in The Time Monster6.
Who can blame him? There's nothing more frustrating than someone else trying to take the credit for your efforts.
The Daleks appeared in the second ever Doctor Who story, and rocketed the series to immortality. Those early Daleks were crude, though. Powered by static electricity, they were unable to leave the metal floors of their city and could be disabled by being pushed onto a carpet (or a conveniently-placed cloak).
When they returned, they had been improved, with little radar dishes on their back to receive power being beamed to them so that they could Invade Earth. From then on, they seem to have developed the Generic Monster Robot Infinite Internal Power Source and there was no stopping them (except, of course, when the Doctor stopped them, which was every time). Yet when the Doctor travels to the original creation of the Daleks in Genesis of the Daleks, there is no sign of this earlier form.
Oh, and you can add to that the Dalek's age-long war with their enemies, the Thals. In The Daleks, we are told that prior to the war the Daleks were peaceful humanoid farmers called Dals. When we see them in Genesis, they are called Kaleds and their peaceful nature seems to include poison gas and Iron Crosses.
But not to worry. PDA War of the Daleks tells us that the whole of Dalek history is a fraud to trick Davros into... erm, something. By season four of the new series, this seems to have been forgotten. This can also be combined with the Daleks' on-again off-again time travel technology (in The Chase they have a fully working Tardis-like time machine, by Evil of the Daleks they are resorting to using mirrors for time travel, and by Planet of the Daleks they are apparently without time travel).
This raises the interesting possibility that the main reason for the Dalek's bad attitude is that they are trying to remove all witnesses to their history. After all, who wants their continuity errors widely known?
The Daleks were finally destroyed in The Evil of the Daleks. And Remembrance of the Daleks. And The Parting of the Ways. And Doomsday. And Journey's End. So they're quite definitely dead, and we certainly won't be seeing them in the series again.
Who is the Ultimate Evil?
The Black Guardian. Fenric. The Eternals. The Daemons. The Great Old Ones. Ken Dodd. The Beast. The Gods of Ragnarok. The Great Intelligence. The Enemy7.
There's a poem in there somewhere. Russell T Davies was clearly thinking small when he decided to have the Daleks fight the Cybermen.
A major plot point in the TV Movie revolves around the sudden revelation that the Doctor is a Spock-like half human. To which fandom replies: 'Nyah nyah nyah, I can't hear you'.
One possible explanation was that this was an after-effect of the Seventh Doctor becoming human in the New Adventure: Human Nature by Paul Cornell. Unfortunately, the Tenth Doctor did exactly the same thing in, erm, the episode Human Nature by Paul Cornell, with no such after-effects.
How Many Regenerations?
It has been categorically stated several times on-screen that the First Doctor we saw (William Hartnell) was the first Doctor there was - for instance in The Five Doctors, where Peter Davison introduces himself by number.
Unfortunately, in The Brain of Morbius, the Doctor is forced back through his regenerations in a mental duel, and we see a further eight faces. In flat contradiction of the evidence - Morbius is gloating, Tom Baker is gurning and a cliff is hanging - fans are forced to assume that these faces are in fact Morbius' past lives and he is losing at this point.
To complicate things further, the script for the TV Movie states that the Doctor can regenerate twelve times, thus giving him twelve bodies. It was not until after filming that someone who could count without using their fingers insisted that the word 'thirteen' be crudely dubbed in over the second number.
This is certainly not a definitive list of all contradictions and continuity gaps within the series. Indeed, in a universe in flux, it is not certain that such a list could exist without the Blinovitch Limitation Effect causing a dimensional rift. So here are a few more oddities from the Doctor's personal timeline.
More companion mayhem. The Tenth Doctor meets time-travelling companion River Song for the first time in Silence in the Library - but she's met him before. Worse, with David Tennant opting to leave the role, it seems we may never get to see them together again. It's Melanie Bush all over again, only without the ginger hair and carrot juice.
How Many Hearts?
It is well established that the Doctor has two hearts. Unfortunately, this was established only after the First Doctor had been shown to have just one. The solution? Couldn't be simpler. Time Lords only gain their second heart during their first regeneration.
The Doctor's Name
In The War Machines, evil super-computer WOTAN refers to the Doctor as Doctor Who. In every other programme, he is only ever called The Doctor. Some people see this as a foolish error caused by a production team who didn't watch their own show. Others say that WOTAN is mistaken.
Clearly, in truth he's called Doctor Who8 but just likes people to be informal. There is not contradiction here, none at all. Besides, if WOTAN can deduce what 'TARDIS' stands for apparently from first principles, shouldn't we trust its word on the Doctor's name?
What is it? Who knows? Who cares? Certainly not the Doctor or the Time Lords, who have variously described it as generated by Time Lord minds (The Deadly Assassin), something to do with the link between a Time Lord and his Tardis (Four to Doomsday) or something caused by time travel (Torchwood episode Reset, Sarah Jane Adventure: Invasion of the Bane).
1 An alternative theory, held by many muscular and socially able Who fans, is that these errors are deliberately introduced by the script-writers to frustrate them.
2 Rumours that this title is a reference to Mel are unfounded.
3 A character from Trial of a Time Lord.
4 Legacy of the Daleks tries to fill in some of the gaps here.
5 Let's not go there.
6 Also featuring the soon-to-be-continuity-plagued Master. Perhaps continuity is contagious?
7 From the EDAs.
8 Try reading the title credits from any 1960s or 1970s episode.