Over at his inestimable Whatever, John Scalzi has been reposting some of his old posts from up to a decade ago.
One of them, from December 2, 2005: How to Tell SF from F. That’s the “reprint” version in 2008; for a comparison of comment threads, here’s the original 2005 edition.
My contribution to the 2008 thread was this:
It’s actually a bit amusing to read the later Pratchett books, which actually seem to fall under medieval science fiction, just with trolls and dwarves as, essentially, alien races that live alongside the humans. Their cultures are real and don’t come from magic stuff apart from what appears in science fiction (i.e., trolls as creatures made from rocks. SF has silicon critters. Whatever).
There is magic, but nowadays it’s treated more or less as different physics, in a scientific way. And there are things like dimension bending and time travel, and usually they just happen—but there’s SF where such things just happen too. I don’t really see where waving hands about tachyons makes much of a difference versus a world where the same phenomenon is understood as magic.
In other words, Discworld is science fiction.
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And because this is a blog about Kindle ebooks, here’s a list of Discworld books that underline this point. (All Discworld books are available on Kindle, by the way.)
Some of these themes are repeated in other books to smaller extent; those books are not included here.
The Science Fiction of Discworld
Note: Not in chronological order.
Pyramids by Terry Pratchett
Buy: 6.39
Mathematics rip into space/time producing an alternate dimension.
Yeah. That’s totally never been a science fiction plot at all.
Soul Music by Terry Pratchett
Buy: 6.39
The Wizards at Unseen University manage to capture sound in a string. While a meeting of magic and science, the string isn’t as important as much of the other magic floating around. Any kind of science isn’t a strong feature of the Death books.
Feet of Clay by Terry Pratchett
Buy: 6.39
This features golems, which are created through magic—but it really is about the nature of artificial intelligence versus human beings. Without the spastic hand-waving.
Night Watch by Terry Pratchett
Buy: 6.39
Space/time travel through sheer amounts of energy. And also what would be classified as an alternate history novel.
Going Postal by Terry, Pratchett
Buy: 6.39
In Discworld, the “clacks” are communication over long distances via chains of towers that produce light in patterns. It’s the internet, with “c-mail”, encryption, the tech bubble bursting, the “Trunk” aka backbone, and more. Most of that appears here.
The Truth by Terry Pratchett
Buy: 6.39
The printing press shows up—and all of its implications and consequences as well.
Fifth Elephant, The by Terry, Pratchett
Buy: 6.39
More political than science fiction; however, the impact of the clacks/Internet making the world smaller is an important theme.
Jingo by Terry, Pratchett
Buy: 6.39
Not just the invention of terrible war machines (which happen in fantasy quite a bit) but also a submarine plays an important role.
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And also, not to make too a fine point of it: Nation is almost here! Yes it is! You can pre-order the Kindle book too!
Spontaneous ∂erivation 
Thank you! I’ve been trying to put this into words myself for a while and you’ve done it brilliantly! THIS is why I, an SF fiend and NOT a fantasy fan, LOVE LOVE LOVE Discworld. Pratchett is one of today’s greatest practicioners of the Philip K Dick “imagine our world. now change it a little. how might we deal with our problems then?” (I’m paraphrasing, poorly) definition of science fiction. Ankh-Moporkians are us, with a twist, and Pratchett is THE master of self-scrutiny through defamiliarization.
Hi Sam!
Thanks for the kind words. :) And the Philip K. Dick reference is neat! I never thought of that. Pratchett, for me, has always occupied a strange space in the world of fantasy, even with his non-Discworld books. I call science-fiction on him, but at the same time, he also occupies a strange space in the world of science-fiction, which has many people pre-occupied with the hand-waving that he simply skips over.
Pratcett combines both disciplines, I think. Sort of the intellect of science-fiction and the heart of fantasy.