In the introduction to one of my John Wyndham books, he notes that some chap called Crispin (Best Science Fiction Stories in 1955) has defined Science Fiction as:
'A science fiction story is one which presupposes a technology, or an effect of technology, or a disturbance in the natural order, such as humanity, up to the time of writing, has not in actual fact experienced'.
So according to this chap the vast majority of what is ostensibly Science Fiction television doesn't really qualify - they're mostly stories (usually westerns, occasionally horror and weird tales) from other genres played out with science fiction props.
Don't get me wrong, I'm not complaining, just thinking about what kind of drama we're watching. In searching for this quote Ive found* another one from John W. Campbell, Jr. I don't know who he is either, and he says that:
'The major distinction between fantasy and science fiction is, simply, that science fiction uses one, or a very, very few new postulates, and develops the rigidly consistent logical consequences of these limited postulates. Fantasy makes its rules as it goes along. The basic nature of fantasy is "The only rule is, make up a new rule any time you need one!" The basic rule of science fiction is "Set up a basic proposition--then develop its consistent, logical consequences.'
As far as I can recall, the vast majority of Doctor Who episodes fit into the latter and when handled badly, some of the weaker ones can come across as a bit Deus Ex Machina as a result.
The Moffat episodes on the other hand are (as well as being (i think) the strongest episodes emotionally) the only episodes which have solid science fiction foundations - playing on one of the cornerstones of science fiction that is 'Robots what obey the letter of their programming not the spirit with disastrous consequences for any nearby humans'**.
In The Empty Child, and the Doctor Dances these robots were alien nano medics who misunderstood the nature of the patient, in The Girl in the Fireplace, these beautifully designed clockwork robots. It's kind of a pity the aesthetics of the spacecraft didn't fit with that of their staff, but was instead pretty Red Dwarf / Alien Nostromo in feel. I can envisage huge towering engines of clockwork powered by human muscles and tendons, kind of based on a collage I did for my Art foundation course a decade ago.
Outside the Box...
And at this point I'm beginning to fall into the trap which all fans fall into from time to time: creating our own narratives and stories to make the series fit what we think it should be. There's something both fun and also quite a bit embarrassing about fan fiction (even if it only ever exists at the back of your own mind) designed to explain the gaps and logical inconsistencies of a TV series. At least it means that the series has inspired people to care about it's characters, so that must count for something?
Long running series, particularly Sci-Fi seem to inspire quite a lot of words about what is objective canon and what isn't (I don't really know much about how Who fandom operates, since this is the only Who site I visit, but I'm aware that Star Wars fans have a vast scale of shades of canon gray). With a series like Doctor Who we really don't need to bother: since the raw material of the series is Time Travel, an episode or idea can quite easily have both happened and not.
Which is where Moffat's second pure science fiction element of this episode appears: The Girl in the Fireplace takes us into a canon where the subjectivity of the viewer is as important as the events they observe. Schrödinger's famous thought experiment illustrating the difficulties of understanding quantum physics are perfectly expressed by this episode:
Depending on who's looking, The Doctor simultaneously gets his end away and doesn't.
Now that's real science fiction***
*I found them here: https://www.panix.com/~gokce/sf_defn.html
** The Doctor Who perennial 'Utopia with a Corrupt Heart' plot isn't necessarily a sci-fi story, but then again, you can find the 'Spirit rather than the Letter' plot in age old Genie and Horror stories (and on another note, I wrote this a few hours before Rise of the Cybermen)
*** or, as some prefer: 'Speculative fiction', indeed...