Logic is the necessary base of any philosophical thought. Or, as Sir Terry might have said, it is the deep toffee bedrock that supports the flowing treacle seams of philosophical speculation.

It may come as a surprise for some that Terry Pratchett, not unjustly known for his absurd comedy and nonsensical satire, has quite a lot to say on the subject of Logic, its importance, and its limits, throughout his work.

This is the second instalment in the “Tao of Sir Terry” series (please feel free to pause here to read the previous article if you have not yet done so), in which we will dive more deeply into a single philosophical theme from the works of Terry Pratchett. And there could be no better subject to delve into, nothing more fundamental for philosophy and more fundamentally Pratchettian, than Logic.

Logic in an Illogical World

“On the way to the tavern Xeno had explained to him, for example, why it was logically impossible to fall out of a tree.” –Pyramids (1989)

The Discworld itself is, from an astrozoological point of view, founded on the exploration of a logical fallacy. Specifically, the infinite regress fallacy illustrated by the “turtles all the way down” cosmological myth, popularised in the West by the late philosopher and logician Bertrand Russell, but dating back centuries, with the earliest known references found in 16th century Hindu mythology.

And yet, most interestingly, Pratchett cuts straight to the core, does away with the infinite regress, and shows that fallacy is only false through lack of imagination. This is how we end up with the four Elephants, Jubul, Jerakeen, Berilia and Great T’Phon, standing on the back of Great A’Tuin the World Turtle (sex unknown), who is not standing in turn upon an infinite tower of “turtles all the way down”, but is far more sensibly swimming through space, towards an unfathomable destination all its own.

Take that, logical fallacy! And is a giant turtle swimming through space fundamentally less logical, or any more ridiculous, than a ball of mostly molten rock spinning around a natural fusion reactor wobbling up and down as it spins around a supermassive black hole?

The answer probably depends on how you define what logic is. In Philosophy, Logic is first and foremost a language. Typically, a logic consists of a formal or informal language, along with a deductive system and a way for things to mean something (semantics).

Without going too deeply into the various schools of thought when it comes to Logic, it’s interesting to see that both major historical branches of Logic are duly represented and lampooned in Pratchett’s works.

Traditional Logic is largely identified today with Aristotle’s works on the subject, transmitted to us by later scholars such as Avicenna and Averoes, in a body of work collected in what is known as the Organon—not to be confused with the Necrotelicomnicon.

Traditional Logic is based not only on formal propositions but also thought experiments designed to highlight fallacies and paradoxes, often reducing them to absurd arguments. And if there’s anything Pratchett readers love, it’s a good dose of the absurd.

This is how we end up with a hilarious satire of formal Logic in works like Pyramids and Small Gods (1992), where real-life philosopher Zeno of Elea becomes Xeno of Ephebe who makes a living coining axioms and paradoxes, alongside his fellow philosophers Ibid and Didactylos. Likewise, on a larger scale, Strata (1981) is in essence a study of how cocksure Logic and Reason can conquer death, build worlds, and can even be used to fool rational thinking, but are themselves nothing more than a delusion.

Beyond the realm of traditional Logic, modern mathematical logic, which rose to defy the assertion that Aristotle had said everything there would ever be to say on the subject of Logic, is duly represented in Pratchett’s works as well. Little surprise, since one of its founders is none other than Bertrand Russell himself—he of the world on the back of infinitely regressive turtles.

On the Disc, mathematical Logic is well represented. The brilliant mathematician You Bastard, camel humps and all, provides the immediate foil to the Ephebian philosopher’s traditional Logic in Pyramids. And, as superior as his own brand of Logic is, his powers pale in comparison with those of Evil-Smelling-Bugger, who famously “invented a math of eight-dimensional space while lying down with his nostrils closed in a violent sandstorm.”

Back in Ankh-Morpork, Ponder Stibbons and Hex develop their own brand of mathematical, computational Logic in a largely failed and always hilarious attempt to impose some Reason onto a deeply unreasonable Discworld. Or, as Pratchett puts it himself: “Logic is a wonderful thing but doesn’t always beat actual thought.” — The Last Continent (1998)

Stands to Reason: The Limits of Logic

“He was determined to discover the underlying logic behind the universe. Which was going to be hard, because there wasn’t one.” —Mort (1987)

On the Discworld, as on our Roundworld, the first and greatest enemy of Logic is often its far more pervasive cousin, common sense. And on the Disc, nobody’s sense is more common than Sergent Colon’s and Nobby Nobbs’. As Pratchett writes in Jingo (1997), “Sergeant Colon had a broad education. He’d been to the school of My Dad Always Said, the College of it Stands to Reason, and was now a post graduate student of the University of What Some Bloke in the Pub Told Me.”

Jingo is an excellent example of the absurdity of common sense in motion, especially when set next to the other two bastions of Logic, each in their own way, in Ankh Morpork: the cold, calculating Logic of Lord Havelock Vetinari, who embraces and exploits the absurdity of life on the Disc in order to maintain a modicum of sanity and stability, and the dangerous, impractical genius Leonard Da Quirm, who devises flying machines and weapons of mass destruction as intellectual exercises no person could ever, logically, seek to abuse or employ.

The entire Colon/Nobbs/Vetinari/Leonard subplot of Jingo is an in-depth exploration of the dynamics of these different and conflicting types of Logic, each bringing its own excesses and its own strengths into play, under the bemused direction of Lord Vetinari, to stop a war, save lives, and land Colon and Nobbs a position in their own, cushy new division of the Watch, perfect for their particular skill sets and grifting proclivities.

Logic Finds a Way: A Logic Greater Than Logic

“It was all very well going on about pure logic and how the universe was ruled by logic and the harmony of numbers, but the plain fact of the matter was that the Disc was manifestly traversing space on the back of a giant turtle and the gods had a habit of going round to atheists’ houses and smashing their windows.” —The Colour of Magic (1983)

If one had to sum up the role of Logic in Pratchett’s work in a single sentence, it would be that his worlds always find their own consistency, their own necessary Logic, in spite of whatever absurdities Sir Terry finds to toss in their way to prevent it. And therein lies a large part of their amazing charm.

On the Disc, that new, homegrown Logic is labelled narrativium, a fundamental causal force that explains why million-to-one chances must always happen nine times out of ten, and why any collision between speeding carts must always end with a single wheel rolling away dramatically from the site of impact.

Narrativium is a known factor, a force of nature that the most powerful of Pratchett’s characters are fully aware of, and which they know how to exploit rationally. The entire plot of Witches Abroad (1991) is based on a character exploiting narrativium for personal gain, and the touring Witch protagonists using those same weapons against her to restore balance.

Instead of turtles all the way down, the Disc is in reality supported by Logic, all the way down. Right down to the most fundamental forces in the Disc Universe, in fact: the grey-cloaked and faceless Auditors of Reality.

Indeed, while the Auditors represent cold, calculating Logic taken to its most terrifying (and ultimately ridiculous) extremes, their own weakness, and the key to their defeat time and time again, particularly in Thief of Time (2001), is their strict adherence to those same Logical principles—the ones that state that they cannot ever think, act, or experience existence as an individual, only as a faceless expression of their whole.

Which leads to lovely comedic use of Logic, such as this interlude in Thief of Time:

One said, It is the Discworld. It rides through space on the back of a giant turtle. One said, Oh, one of that sort. I hate them. One said, You’re doing it again. You said “I.” One said, No! No! I didn’t! I never said “I!”… oh, bugger… It burst into flame and burned in the same way that a small cloud of vapor burns, quickly and with no residual mess. Almost immediately, another one appeared. It was identical in appearance to its vanished sibling. One said, Let that be a lesson. To become a personality is to end. And now… let us go.

Both from a narrative and a philosophical point of view, everything in Pratchett’s work has, and must necessarily have, its own intrinsic Logic that it either sticks to, or strives against and pays the cost.

Logic is, ultimately, what saves the characters. It’s even Logic and Reason which—with the unlikely assistance of time-travelling Wizards from the Disc—save our own Roundworld from destruction at the hands of the “terrific” forces of illogic and obscurantism, in The Science of Disworld II: The Globe (2002).





Sir Terry is known and celebrated as a brilliant satirist, and rightfully so. Since he is best known for his magnificent silliness, his comedy, and his unique take on the absurd, then it can truly be said that the single theme he has made the greatest, and the most complete, satire of is Logic itself.

And like any proper satire, Terry Pratchett’s funhouse mirror take on Logic, in all its various guises, serves to tell us more about what Logic is—and how important it is for meaning and understanding in our everyday lives, even in the most extreme circumstances imaginable—than any direct examination of the thing itself ever could. So, despite appearances, maybe there is a Logic behind the madness of the Discworld after all…

J.R.H. Lawless is a multiple award-winning Canadian SF author who blends comedy with political themes—drawing heavily, in both cases, on his experience as a lawyer and as Secretary General of a Parliamentary group at the French National Assembly. A member of SFWA and Codex Writers, his short fiction has been published in professional venues, and most recently in the Third Flatiron Press Terra! Tara! Terror! anthology, to great reviews, placement as 2018 Recommended Reading, and an award for Best Positive Future Story 2018. He is also a craft article contributor to the SFWA blog, the SFWA Bulletin, and Tor.com. His next story will be released on April 15th in the Third Flatiron Hidden Histories anthology. He would love to hear from you on Twitter, over at @SpaceLawyerSF!