Main Knights And Knaves Discussion

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12:29:45 PM Aug 10th 2016
Someone just found a new possible answer today:

Ask to each one "What does two plus two make?" For obvious reasons, this will tell you who is the lying guard and who is the truthful guard. You are then morally justified in punching the liar through the door. When you do, watch what happens/watch through the door.
01:31:22 PM Nov 6th 2011
I've just added the Orqwith/Doom Patrol one to Puff of Logic, and it looks correct to me:
Rebis: I've come to ask the question. One of you must have the answer. Why is there something instead of nothing?
Priest in Black: I am a liar and I do not know why there is something instead of nothing.
Priest in White: I am an honest man and I do not know why there is something instead of nothing.
Rebis: Tell me then, the Priest in Black, why is there something instead of nothing?
Priest in Black: There is something instead of nothing.
Rebis: Then you can't possibly exist.
Why is it "completely wrong"?

04:19:07 PM Feb 19th 2011
Shouldn't this have an alt title added? I never would have thought to search for Knights and Knaves
02:43:29 AM Apr 28th 2010
Is it certain that Raymond Smullyan invented this type of puzzle? I first came across it in the early sixties, and it was old then.

It's known that Smullyan invented the "knights and knaves" scenario, in order to avoid the Unfortunate Implications of the original "two primitive tribes" scenario, along with the variations involving insanity and vampirism (but not the "me no speak English" variant), but the puzzle itself probably goes back to Lewis Carroll's time.
08:16:24 AM May 10th 2010
Robin Adams: I don't think it is known for certain who invented them.

The earliest mention I've been able to find is a letter by the computer scientist John Mc Carthy in Scientific American in 1957. Mc Carthy gives the "da" and "bal" variant (he uses "pish" and "tush"), but he writes as if the original problem was well-known by then.

Smullyan was born in 1919, so it's possible that he invented the puzzle in time for it to be well-known by 1957, but not very likely.

Lewis Carroll wrote at least one fairly similar puzzle in 1895: the Five Liars. Five people - A,B,C,D,E - each make two statements, of the form "Either B or D tells a Truth and a Lie; either C or E tells two Lies". A few years later, he wrote to his friend Professor Wilson "I hope you will be pleased to know I have decided to abandon my 'Liar' Problems; the metaphysical difficulties are too appaling!", which suggests that sort of puzzle was not common, and maybe was invented by him.
04:55:03 PM May 13th 2010
Yes, I'm going to remove the ridiculous claim that Smullyan invented this type of puzzle from the page. As well as the above facts, Martin Gardner was a friend of Smullyan and would certainly have credited him if he had invented it.
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