The Parable of the Dagger

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Animation director: Evan Streb
Writer: Eliezer Yudkowsky
Producer: :3

Production Managers:
Grey Colson
Jay McMichen

Line Producer:
Kristy Steffens

Quality Assurance Lead:
Lara Robinowitz

Animation:
Grey Colson
Gabriel Diaz
Jay McMichen
Skylar O'Brien
Patrick O'Callaghan
Vaughn Oeth
Lara Robinowitz

Background Art:
Olivia Wang

Compositing:
Patrick O' Callaghan

Voices:
Robert Miles - Narrator
Krystle Futrell - The Jester
Lucas Schuneman - King

VO Editing:
Tony Di Piazza

Sound Design and Music:
Epic Mountain

[dragons]

The moral of this story is twofold: Moral number one is always check your priors and don't assume just because something is reasonable and elegant that its true. And the second moral is be careful who you piss off.

[YoungGandalf]

The king probably already has plenty of gold. An angry frog might be pretty entertaining though. It's a win-win for him.

[__-cxlg]

Note something crucial about the story: the jester said (truthfully) that one inscription was true and the other was false. The king never made any such promise. As the author said, "One of the morals of the parable is that the king didn't lie."
EDIT: Elaborating:

The point is that the king never made _any promise at all_ as to the truth-value of the inscriptions (unlike the jester did in the first puzzle). The first inscription is like the Liar's Paradox, in that it can't be either true or false — with the dagger in the second box, it's meaningless. The jester assumed that the sentence bore *some* relationship to reality (either true or false); this assumption was so automatic that he believed it without thinking, without even the word of the king as evidence. Because of that mistake (assuming that the sentence was meaningful), he concluded that a physically-possible situation was logically-impossible!

[maxwell]

The first one is actually very easy. You pick the box that is heavy, and not the one angrily croaking at you.

[sirnikkel]

The guard punching the jester caught me...


*off guard*

[JH-cpwf]

To join the "what's the moral here", I took away "you can't tell what's a good play until you know what game you're playing".

[AlekVoropova]

I like presenting my students with the following two statements:

1) Both statements are wrong.
2) You must give me a cookie.

And then demanding cookies.

[elidoz]

the jester's fatal error was assuming that there was correlation between the inscriptions and what was in the boxes.
it's very subtle by the king to make a trick like that

[Blate]

So the moral of the story is to beware of meta games?

To not forget that when you’re playing chess, your opponent can win by shooting you in the face?

[anoninunen]

"Both boxes have daggers. I lied and I hate you" - Spy

[PanzerschrekCN]

Plot twist: both boxes from the second set contain a dagger. Nothing prevents the king to do this.

[andrewphilos]

Spoilers for a 5-minute video:


Aww, the dagger was a trick retracting dagger. That's cute! Also in keeping with the theme of the story of statements being misleading.

[Ancientmarella]

This animation is suprisingly just cute. Not cosmic horror, not mind shattering problem. I love you

[raymond-rj]

Jester: Source? What's your evidence?
King: None, I made it up.

[Saulegraza_Solarpunk]

Instead of "a dagger for your heart" I was really hoping for "20 angry frogs". Would've been one cool way to go.

[thiiink]

What I really love about this parable is its layers. On the surface, the king is just being a meanie. He is placing the dagger in the box where the key should be, as considered with classical logic. But under this facade of a tale of logic vs wisdom, there is some insightful discussion about non-classical logic.

The jester presented a liar cycle to the king, a pair of sentences that behaves just like the liar sentence, "this sentence is false". To justify his prank to the king, the jester would resolve the apparent inconsistency in his riddle by resorting to some form of non-classical logic. The leading systems on this in philosophy would be something like paracomplete logic that reject the Law of Excluded middle (A proposition is either True or not True) with some gap (e.g "uhh maybe perhaps yes"), or paraconsistent logic that reject the principle of explosion (If a proposition is True and not True then anything goes) with a glut: let that proposition be both True and not True. What is striking about the king's response is that in the riddle of the key and dagger, the jester can draw the logical conclusion that one of the boxes must contain the key only in classical logic, but not in the non-classical logics used to resolve the problem of liar sentences.

Notice how the jester starts his chain of reasoning by invoking the Law of Excluded Middle and supposing in turn that the inscriptions are true. This would not be a valid line of reasoning in paracomplete logics, where the inscriptions may be some gap value as well. With the first inscription being a gap value, the jester is wrong to conclude that the second inscription is true. If we instead suppose the jester is using a paraconsistent logic that preserves the Law of Excluded Middle but rejects the principle of explosion, then both inscriptions may have a glut value: they can be both true and not true. As the second box’s inscription that “This box contains the key” can be not true (due to being both true and not true), the king thus acted in a way consistent with the inscriptions on the boxes when he placed the dagger into the second box.

The jester’s riddle was unreasonable unless interpreted in non-classical logic. Beautifully, the king beat the jester at his own game with a riddle with a reasonable solution in classical logic as the bait, punishing the jester with a “logically impossible” reality that is nonetheless reasonable in the very same non-classical logic.

[alexpotts]

Moral of the story: don't be a smartass. And especially don't be a smartass to a tyrannical absolute monarch with a taste for ironic punishments.

[michaeltullis]

On a shelf in my house is a book called "The Princess Bride", in which it's written that there's a country called Florin, wherein dwells or dwelt giants, wisemen, and fantastic characters of all stripes.

Not a word of it is true, the book's a work of fiction.

You can hear or read or make an extremely convincing argument (for instance: "therefore the second box has the key", or "the Dread Pirate Roberts is Westley"), but if one of the assumptions that the logic rests on is wrong ("words on the boxes will tell you where the key is", "there's such a historical figure as the Dread Pirate Roberts, or as Westley"), it doesn't matter how ironclad your logic is, you live in the "logically impossible" world.

[saebelorn]

Realising that the channel is some kind of clandestine initiative by LessWrong actually increases my appreciation for it honestly

[larrywitcher]

This is the cutest thing I've ever seen.

And the fact that no true cruelty befell the jester gave me a sigh of relief as well.