In Doctor Who S9E2, The Witch's Familiar,

the Doctor saves the young Davros by pointing a Dalek gun at the hand mines and exterminating them, and then he teaches Davros about "mercy" to ensure the Daleks will know the word and Clara can prove her identity.

However, during that scene, the Doctor also

shouts "Exterminate!" to preface his hand mine killing spree.

I get that non-canonically, the point was to make an epic cliffhanger (and it succeeded!), but if the Doctor knew that the aforementioned character and his creations would remember everything that was said on that day, then why did the Doctor teach him the word that would become his creations' catchphrase?

  • I never quite understood that scene.. In 'The Big Bang', a Dalek indicates that records show the Doctor's associates would 'show mercy', until River has the Dalek look her up, specifically. The Dalek then asks for 'Mercy!' three times before she kills it. So... Is the Doctor just missing a Timey-Wimey detail or something?
    – K-H-W
    Commented Oct 7, 2015 at 16:01
  • @K-H-W This question attempts to offer some explanation for that.
    – user24601
    Commented Oct 7, 2015 at 16:03
  • 3
    Yet another stable time loop, like those Moffat seems to love. The "catchphrase" has been shouted for 50+ years, so it makes sense (at least in Doctor Who) that the Doctor himself caused it. Just my .02, that's why I don't post this as an answer.
    – tilley31
    Commented Oct 7, 2015 at 16:06
  • 2
    He used a Dalek weapon, perhaps that was needed to prime / fire it?
    – Politank-Z
    Commented Oct 7, 2015 at 16:22
  • 1
    Hmmm, it just occured to me this is the second... Uh... "time"... that Clara has found herself transformed into a Dalek. Kind of. She's at least mentally linked to one. This could have been made into an interesting little "insiders" sub-plot; I always throught that the whole Clara-throughout-the-Doctor's-life deal should be subtly hinted at throughout her adventures as a full companion, instead of been shelved away completely. Commented Oct 10, 2015 at 3:57

3 Answers 3


It's all timey-wimey (as usual) but I'll try my best to EXPLAIN!!! EXPLAIN!!!

Remember that Christmas special when the Doctor met Michael Gambon (sorry, can't remember the name of his character) and rewrote his whole life while projecting what was happening to him in his past? I think it's a similar concept. The Doctor has been fighting Davros and his Daleks for most of his life (or lives). He went back in time and -perhaps by accident- rewrote Davros' childhood just enough to give the Daleks a little bit of mercy, and while at it, their world-famous catchphrase. The Daleks shout EXTERMINATE because the Doctor told that to a young Davros in the past, because the Doctor has been hearing them for centuries. The cause becomes the effect, the effect becomes the cause. Like I said, timey-wimey. Another stable time loop by Moffat.

We don't know how much time Davros was left standing in the "hand mine". Maybe it was just enough to make him become what he became. "Davros knows. Davros remembers"...he created the Daleks, and remembered that old scot who saved him in his childhood, and gives them their catchphrase, and just a little bit of "mercy" to mantain the time loop stable.

  • 1
    The old scot? Oh wait, you mean the old frey...
    – Mr Lister
    Commented Oct 7, 2015 at 21:29
  • He should've dropped Davros off at a daycare in 20th-century England. Problem solved.
    – Liesmith
    Commented Oct 8, 2015 at 7:22
  • 1
    Pretty much, he had to keep the Daleks close to what they were originally and since a tiny bit of Mercy was placed in the Daleks' vocabulary so that he could save his friends. Commented Oct 8, 2015 at 12:50

He wasn't teaching Davros a word: he was reloading his weapon.

Go back to the scene where Clara was in the dalek, and Missy had her attempt all sort of words that the dalek's shell simply could not say. Clara even managed a misfire, leading the evil Time Lady to quip

"That's why they're always shouting 'exterminate', my dear; its how they reload."


Because he heard the Daleks say it for centuries and probably realised Davros must have heard it himself once in his lifetime. It is actually pretty well explained with the paradox the doctor describes in before the flood. he said something in these lines:

"If i were to go to the past to let Beethoven sign all my records and find out that Beethoven never existed, I would publish all his works so they will still exist in the future but the question remains, Who wrote the Beethoven the 5th?"

It is basically a paradox without a clear answer, i think the same applies to this situation. The doctor heard the daleks say Exterminate thousands of times (and mercy only a few times) and he realised that someone have told Davros those words.

  • But why did he ever believe in the first place that the word "shouldn't" be in their vocabulary?
    – Random832
    Commented Oct 14, 2015 at 15:23

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