The setting is the medieval ages, vaguely European. No magic exists except what is explicitly stated in the question. The judicial system is similar to historic examples, with the head-of-state directly overseeing cases of sufficient magnitude to warrant his or her direct attention.

In this world there exists a small kingdom; three large cities and then the towns and communities that support it. One day the king receives a Truth Stone as a present.

Whenever someone holds this Truth Stone and (verbally) speaks the stone will use the holder's own mind to judge any intended deception. If he or she remains silent, the stone will not react at all.

  • If the speaker is intentionally speaking falsehood or is intentionally misleading or misdirecting, the stone will glow red.
  • If the speaker is intentionally speaking the truth, and is not intending to mislead or misdirect, the stone will glow blue.
  • In any situation where the above two condition groups can't be determined from the holder's/speaker's point of view the stone will do nothing at all.

The stone does not account for cases of insanity, misunderstanding, or any other situation in which the speaker/holder believes themselves to be speaking truthfully but is in fact in error.

If he believes the world is flat and says it is round, the stone will glow red. If he believes the world is round and says it is flat, the stone will also grow red. If he believes himself to be a unicorn, and says that he's a unicorn, the stone will glow blue.

Further the stone divides phrases based on the speaker's views on the division of phrases. If somebody says: "I am a man, a carpenter, and have never eaten meat" the stone will probably evaluate each statement separately (going dark momentarily between each statement), but may not if the speaker sees that as a collective idea (such as if he was denying being part of the Guild of Female Carnivorous Stone Masons).

If a person was taught different meanings to terms, such as "guilty" meaning "innocent" the stone will evaluate it based on the speaker's/holder's understanding of the term.

To clarify: every reaction by the stone is based on the speaker's/holder's views on the statements that he or she just spoke, and has no direct dependence on the actual reality.

When there exists effectively a polygraph test that is as-perfect-as-possible (like the polygraph, targeting belief of truth) is injected into the legal system, and where the accused's belief of innocence can absolutely be determined, how would such as stone force the legal system to evolve, and how would it force criminal activity to evolve?

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Tim B Dec 1 '16 at 16:06
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    $\begingroup$ I just want to point out to all of those saying this wouldn't work because the stone could be tricked with half truths or speaking like a politician etc. this could be fixed as the accused must speak an unambiguous sentence (such as "I am completely innocent of all charges") and if the stone glows blue then they are innocent. Otherwise a narrowing down process begins (e.g. accused must speak "I am guilty of the first charge but only on one of the days"). $\endgroup$ – Celeritas Dec 1 '16 at 23:24
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    $\begingroup$ As the ruler of a medieval kingdom, I depend heavily on lies to keep the trains running on time. In light of this, you can bet I would keep this thing a very close secret. I might use it for purposes of interrogation, but only if I was the interrogator and I could use it without risk of revealing its very existence to my subjects. Because then I'd be expected to hold it all the time. $\endgroup$ – Doug Warren Dec 2 '16 at 15:43
  • $\begingroup$ This seems to be a contradiction, "If he believes the world is flat and says it is round, the stone will glow red. If he believes the world is round and says it is flat, the stone will also grow red. If he believes himself to be a unicorn, and says that he's a unicorn, the stone will glow blue." If the person believed it true, why would the stone glow red for the world and blue for a unicorn, shouldn't both be the same color as there is no intent to mislead? $\endgroup$ – xQbert Dec 2 '16 at 20:38
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    $\begingroup$ @xQbert Read it again, there's no contradiction. Case #1 he's telling actual truth he believes to be false: red. Case #2 he's lying: red. Case #2 is false but he believes it true and says so: blue. $\endgroup$ – Loren Pechtel Dec 3 '16 at 6:45

18 Answers 18


Scenario 1:

The King declares: "I have decided to use the Truth Stone to root out any and all corruption in my administration."
Stone vanishes from behind 5 supposedly locked and guarded doors, with nary a trace the very next day.
King Terren reloads.

Scenario 2:

The King declares: "I have decided to use the Truth Stone to root out any and all cheating spouses in my kingdom."
The Kingdom descends into complete chaos the next day, as 1 in 4 spouses know they will be revealed as cheaters.
King Terren reloads.

Scenario 3:

The King declares: "I have decided to use the Truth Stone to root out any and all common crime in my kingdom."
All criminals now decide to never leave any witness behind, since any and all evidence leading to them will now lead to a conviction. Murder rate soars.
King Terren reloads.

Scenario 4:

The King picks up the stone and declares: "The sentence I am saying currently is a lie."
According to a survivor, the stone reportedly turned an impossible bluish-yellow color, grew hotter and hotter over the next few hours, and finally detonated with a light so bright and a thundering noise so loud that it was seen, heard and felt in the neighboring kingdoms. The entire court, the royal palace, the citadel, the city walls, all the city houses, as well as the surrounding countryside were devastated for many miles. A giant mushroom of smoke hung over the ruined city for hours, and winter arrived early that fall, bringing famine and foreign invasion to the battered kingdom.
King Terren reloads.

Scenario 5:

After a minute's thought, the King gracefully thanks the stranger for the gift, then orders all present in the room to be killed by his guards, then has all the guards murdered in turn. The Truth Stone remains the highest guarded state secret for the next century, as the kingdom expands greatly, with the king and the following 3 kings using the truth-detection method for ferreting out spies, double agents and untrustworthy allies and vassals, thus gaining an unmatched strategic advantage over any and all rivals.

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    $\begingroup$ Ahh, if only life came with Quick Save/Reload functionality! Might be a somewhat more useful stone. $\endgroup$ – Nex Terren Nov 28 '16 at 16:06
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    $\begingroup$ +1 for the Fantastic Nuke scenario. Logic. A weapon of mass distraction. $\endgroup$ – Michael Schumacher Nov 28 '16 at 21:56
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    $\begingroup$ As cool as the nuke scenario is, as the King is intending on telling neither lie nor truth, instead just sciencing it, it will probably do nothing. :P $\endgroup$ – AlbeyAmakiir Nov 29 '16 at 1:16
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    $\begingroup$ F9 duh. Haven't you ever played Skyrim? $\endgroup$ – Lu22 Nov 29 '16 at 5:13
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    $\begingroup$ Scenario 4 probably doesn't happen. If the speaker understands the paradox and is using it to mislead the stone, the stone glows red. If they believe it to be both true and false it glows red and blue. If they believe it to be neither, it doesn't glow. If they don't understand it, it glows red, blue, both or neither depending on their belief of the statement. $\endgroup$ – Samthere Nov 30 '16 at 14:46

How about this?

The stone goes into a church/temple/palace. The accused in any trial has the right to demand a Trial by Stone instead of the usual legal process, but only before that process starts.

  • The accused will be transported to the stone. This can be a slow and degrading route at the king's expense (chain gang) or a faster one paid for by the accused.
  • The accused will be asked three questions: "Are you guilty of whatever?" "Did you call for the Trial by Stone in good faith?" "Are you a loyal subject of the king?" If the stone is blue three times, the accused is free. If it is not blue three times, the accused has wasted the king's time and his head will roll for that.

An alternate option would be to have the stone "tour" through the kingdom and check the inmates of local jails, but doing that would mean there has to be a jail to start with. Locking up people as punishment is a rather new invention. Peasants need to work the fields, not sit idle.

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    $\begingroup$ Everyone is guilty of whatever. $\endgroup$ – Davor Nov 28 '16 at 22:44
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    $\begingroup$ Literally what happened during trial by ordeal, if you believe Stephen Dupner. The idea was that more truly innocent (and faithful) people would choose trial by ordeal, and so the religious practitioners apparently had a practice of moderating the ordeal based on this and other self-selecting behaviors of the accused. $\endgroup$ – bright-star Nov 29 '16 at 3:24
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    $\begingroup$ @Davor, with whatever I meant whatever the accused stands accused of. Don't ask if he stole an apple at age 10. $\endgroup$ – o.m. Nov 29 '16 at 6:22
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    $\begingroup$ While locked up as punishment is indeed new, I believe locked up waiting for punishment has been around for quite a long time. $\endgroup$ – Angew Nov 29 '16 at 9:33
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    $\begingroup$ They could answer "Yes. No. No" and as long as the stone was blue, they would walk? $\endgroup$ – jayjay Nov 30 '16 at 11:35

The real problem is that the stone does not actually force you to speak truth. So when you speak a half-truth or a misleading truth it will still identify it as a lie. A clever person could still work their way through this by only saying things intended to mislead or deceive. The listener would still have to interpret which parts are a lie.

For example, I and my accomplice commit a crime. The witness only saw me at the crime scene. I am asked if I committed the crime. The truth is that I and my buddy committed the crime. In order to protect my accomplice, I claim that "I" committed the crime. The stone shows I am misleading them. Everyone now believes that I did not commit the crime. They may wonder why I choose to lie about it but the more guilty I say I am, the more innocent the stone makes me look since I am intentionally misleading them. This is just one example.

Deceive and manipulate with every statement you make. At worst you will muddy the waters and sow confusion. At best, if the questioning is not extremely careful, you can inversely prove your innocence in your attempts to mislead them when admitting the exact nature of your guilt.

A few incidents like this and people will wonder if the stone really works or whether it is really some kind of political tool the king uses to make anyone he wants appear to be guilty of something so he can execute them.

Edit: I just wanted to clear up some things brought up in the comments.

First, the base assumptions are:
1) No one but the accused actually saw the exact moment the crime was committed.
2) The accused was seen at the scene of the crime (perhaps even doing something very suspicious)

If there is other evidence then you really aren't making a conviction based on what the stone indicates. You are just using it to confirm. However, in this case you would probably be found guilty even without a magic stone. So I am not talking about that.

Second, I am not suggesting that lies and deception can always get you off the hook. That is definitely at one end of a scale of different possibilities. If you tell a lot of lies, people might just assume you are guilty even if they aren't sure exactly what you are hiding. However, that won't help them find the loot, identify your accomplices, or force you to incriminate yourself on additional items they don't already know about (unless you are careless in your wording). They still can't actually force you to say specific words. You can keep these secrets all the way to the grave if you really want to.

Third, considering there is only 1 king and 1 stone, how long do you really think he will spend interrogating someone for any single case? Assumptions that the prosecutor is hyper-competent and has all the time in the world are just as unlikely as the king asking a single question and then letting the accused go because that single answer was really slick.

Fourth, there is no such thing as a question that can only be answered by yes or no. Even if a question can be answered with one word, doesn't mean it has to be. Some of the comments about this sort of thing actually reminded me of a scene from one of Steven Brust's novels. I don't have the exact quotes but let me summarize:

The assassin/sorcerer/witch Vlad Taltos is brought before the empress to answer questions about a murder. The empress questions him with the imperial orb (basically just like our truth stone). When asked if he killed the man, he does not answer yes or no. Instead he says something like: I believe he chose to die. When they ask if he is saying that the man committed suicide, he basically says that suicide is an accurate description.

Vlad did in fact assassinate the man. However, the orb shows that all his statements are true. This is because he genuinely believes that anyone who voluntarily chooses to pick a fight with an assassin/sorcerer/witch is definitely committing suicide...and who wouldn't agree with that? :-)

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    $\begingroup$ Clever! I hadn't thought about this, though I think in practice they would punish people for lying about their innocence because it "muddies the waters" so much. $\endgroup$ – David Schwartz Nov 29 '16 at 1:04
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    $\begingroup$ @David Schwartz: Punishment for lies probably leads to silent criminals (unless the punishment is really light and lying is still getting you out of an even worse punishment). Silent criminals basically make the stone useless. $\endgroup$ – David Cram Nov 29 '16 at 1:17
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    $\begingroup$ @DavidCram Only if you use the "innocent until proven guilty" model, which was not the case in medieval times. Being silent could just be taken as "guilty as charged". $\endgroup$ – kat0r Nov 29 '16 at 8:29
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    $\begingroup$ The solution is to ask the respondent questions, and not give them an opportunity to spin. If refusing to answer results in an automatic death sentence, there is little use in lying. Lawyers write contracts the way they do to prevent this type of obfuscation and deceit. $\endgroup$ – Andrew Neely Nov 29 '16 at 17:24
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    $\begingroup$ @DavidCram, as Graham points out, follow-up questions would make such prevarication very close to impossible. Simple yes-no answers prevent carefully worded answers (aka the kind we hear from politicians) designed to skirt the truth while avoiding untruth. Following up with slightly reworded questions could poke around any mental spinning (e.g. I didn't kill the person. I just paid for it to be done. Imagine the questions: "Did you kill him", "Are you involved in his death?", "Did you know he was going to die?", "Are you responsible for his death?" would be false.) $\endgroup$ – Andrew Neely Nov 30 '16 at 15:28

The main thing everyone is overlooking is economy of scale. You've only got one truth stone, but justice needs to happen all over the country. If you are rich and noble you will probably be able to appeal to visit the Final Court (where the truth stone resides). If you are poor and common and guilty you may try to appeal in the hopes that it gives you more time. Regardless only the biggest and most important cases will go to the Final Court, most will still be handled by the local justice system, whatever that is.


There is another legal system where participants face a similar threat, where participants believe that false testimony has dire consequences even if no witness could otherwise prove they're lying. So we can look to that system for guidance on how this one might play out.

I'm talking about rabbinic courts, specifically in the time of the Sanhedrin. The ultimate "stick" that the court had was to require somebody to swear an oath. What's the big deal about swearing an oath? To modern-day Americans, maybe not much -- just words and all that. But in its original context, a false oath was (and to many today still is) a transgression against God. Who, you know, would punish you for that. So you really, really don't want to swear a false oath, and it's safer to avoid swearing an oath at all because of a reluctance to bring out the "big guns", so to speak. The passages in the talmud that talk about how the Sanhedrin operated and what the laws of various cases are show a tendency to avoid oaths at all unless necessary. The truth stone, being not only a big gun but a singleton, will be similarly reserved for special cases. Most trials will be conducted as they were before.

Second, when an oath was required, its text was fixed. I'm not sure if it's fixed by the law itself or by the judges, but either way, the accused (or witness) doesn't get to say "sure I'll swear, and what I swear is (carefully-crafted dodge)". When your truth stone is brought into a case, expect the one presiding over the case to similarly dictate what the speaker must testify to.

Just having the "truth" isn't enough to settle some cases, though. Your truth stone, and an oath, measures the speaker's perspective. It doesn't measure actual truth. You could therefore end up with situations where two litigants both have the "truth" on their side, but their positions are incompatible. One of them is mistaken, but not lying. ("I picked up the lost bag of gold first!" "No, I did!" They both ended up holding onto it; who was really first? You don't know.) You will have cases where the truth stone didn't help you, in other words, and you should expect to fall back on what you would have done without it. (Sometimes rabbinic cases end with no oaths and "they divide the proceeds".)

A final note: the rabbinic system I'm describing didn't rely only on the fear of false oaths, any more than the king here should rely only on the truth stone. Testimony of eye-witnesses and evidence are still big factors, same as with courts today. Using the truth stone is still the exception, as I argued earlier.

  • $\begingroup$ Interesting, but misguided. The problem with this approach was and is that really everything depends on the high regard that oaths are at least hard to overcome. Sociopaths, who occur in every culture and cannot be teached to respect or believe in social customs and beliefs, will learn quickly that lies, even under oaths, go undetected and use them deliberately to absolve themselves or use them as weapon to accuse others because it is hold in such high regard. $\endgroup$ – Thorsten S. Nov 29 '16 at 20:09
  • $\begingroup$ @ThorstenS. it does depend on everyone sharing the premise that (in this case) God will zot you if you swear a false oath. I don't know what the Sanhedrin did about sociopaths. (The system wasn't only oath-based; maybe I didn't make that clear enough? Evidence, witnesses, that sort of thing is still in play.) $\endgroup$ – Monica Cellio Nov 29 '16 at 20:12
  • $\begingroup$ Hm, given that and your explanation as last resort gives me the suspicion as gentile that it was actually the whole time the other way round: The Sanhedrin knew that the oath was crappy, but they wanted a way to have a final option when they were at their wit's end. If they are in danger to lose face, they said that this really, really big stick is in the background and hoped that one of the parties loses the nerve. And even if God zings you, the punishment is in most cases at least for disinterested observers not attributable. There is no message on it "This is for you". $\endgroup$ – Thorsten S. Nov 29 '16 at 20:31
  • $\begingroup$ You say that (in a rabbinic court) "oaths" were taken more seriously because lying afterwards was a transgression against God. I was told by a Jew that in a rabbinic court, someone caught lying after swearing an oath was supposed to be killed. So it wasn't merely the esoteric threat of God's smiting, but the more immediate threat that the judge might stone a "false witness" rather than the accused. You didn't mention that-- is it because it isn't true? Anyway, he said that people avoided swearing oaths, so it often difficult to find two witness willing to swear given the potential punishment. $\endgroup$ – David Schwartz Jan 27 '17 at 18:53
  • $\begingroup$ @DavidSchwartz I was focusing on the case where nobody else can prove you're lying. If the court knew that witnesses swore falsely they could of course punish, but if they didn't know and only suspected, they couldn't do much. (The penalty under rabbinic law for a false witness is whatever penalty you were trying to inflict on the other guy.) $\endgroup$ – Monica Cellio Jan 27 '17 at 19:27

The perfect premeditated crime in this world would have a focus on obscurity: if you don't know who helped you rob a bank, then you can't incriminate them in court, truth stone or no. That type of cloak and dagger crime is infeasible in most cases, however. Most crime, then, would still need to depend on simply not being caught. Same as in our reality, Criminals would just have to make sure there are no witnesses, any witnesses won't turn to the law for help, or the law is in their pockets.

While the initial reaction would be to use the truth stone in every case, it's likelier the justice system would evolve to only use the stone in the most extreme cases. There are many situations where the state would rather not let the infallible truth get out: when it wants to punish an individual regardless of their guilt, when the witness is a wealthy noble who has favor with the court, when a savvy criminal bribes the judge, etc.


The most pressing matter to any sovereign is staying alive and in power, and this stone would solidify his reign. Therefore, the king would use it to ensure the loyalty of those closest to him, such as his spouse, children, attendants, and advisers.

Once the king realizes the great value of the stone(maybe after an assassination plot is foiled by it), he would take steps to secure it against theft. He would create a very secure site, guarded night and day by only the most loyal troops, whose loyalty is checked weekly by the very stone they guard.

He would require all potential commanders of the army must be examined under the stone before taking commission, to ensure their loyalty, thus forestalling rebellion.

The aristocracy would demand access to the stone for serious matters (including potential paternity of children.) They would have to petition the king, travel to the site of the stone and pay the king for the use.

The priestly class would also demand access to the stone for serious matters (such as heresies and conspiracies.) While they would travel to the site, they would give favors instead of gold for use.

Notable criminal cases which inflame the public's passions would also have the stone applied.

Since the above situations would keep the stone pretty busy, common criminals would not have access unless they could get help from a member of the aristocracy.


Oh the mischief this would cause and so many ways the stone could be tricked!

Some liars are so skilled that they actually trick themselves into believing their own lies. Pathological liars do it by nature.

Imagine, if you will, a pathological liar making outlandish claims about witchcraft, or anything else. Someone drugged could believe that they have seen demons. The Salem witch trials were thought to be started by hallucinations brought on by illness or a fungus! Then again, there are faulty or false memories, especially during heated difficulties. How many people have already been sent to jail on false witness identification because the person looked like someone else or the witness remembered incorrectly. I once watched a social experiment (long before the internet) where they had someone walk into a classroom, steal a purse, then have a lineup. The instructor asked someone if the person had a beard (to plant the idea) and then the entire class falsely identified a man with a beard as the person who did it.

Given this, it could cause a legal system to devolve into utter chaos until the stone is discarded.

If you want to go this route, have the "gift" be given by someone who knows it will have this effect. It could either be an active enemy of the king, or a trickster archetype.


How much justice does the king really want?

Commoners might come out a little up (until the civil war comes through) but kings justice was often counted as pretty good. Most crime is pretty simple, and leaders who aren't good judging people are in a lot of trouble anyway. Depending on a stone may support the mystical awe of kingdom, but might sap some of the personal majesty.

And then there's the problem of the stone giving the politically wrong answer. Dubious allies are quite possibly the only allies a small king has, putting them to the question could be very embarrassing.

Even the threat of such a thing would cause elites to become unstable. Plotting is traditionally the sport of choice for many nobilities. The whole truth and nothing but the truth would ruin the court; I'd predict a rash of wealthy people suddenly being too sick to meet the king. Possibly sending younger sons or whatever innocents could be procured at short notice in their place, but quite possibly taking a stand of rebellion rather than submit to what they know will doom them.

  • $\begingroup$ People who plot things would just make sure they are not public people and hence will not be called to questioning. You can not call to court someone whose existence is not proven. Also, stone-questioning would be a very serious deal and used sparingly because all kinds of irrelevant embarassing secrets will come out. $\endgroup$ – Daerdemandt Nov 29 '16 at 9:06
  • $\begingroup$ i like the idea of sending somebody else, as long as you are able to convince that person of your lie, he will tell said lie as truth, and the stone will be blue. $\endgroup$ – Brian H. Nov 29 '16 at 10:28

Brainwashing is not particularly difficult with the right setup, and memory is famously fallible. Organised crime would quickly learn to implant suggestions in their own operatives that they did not do the things they did, and soon after that they'd learn the value, in a world with an external arbiter of truth that is believed to be infallible, of 'convincing' bystanders that they saw something that never happened.

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    $\begingroup$ Not only that, guards during questioning can convince random people that they did commit a crime. This happens sometimes now. Memory is not only fallible, it's malleable. $\endgroup$ – Daerdemandt Nov 29 '16 at 9:17

Its very unlikely to have a significant effect on the world, assuming a stereotypical medieval ruler.

First, in regards to criminal justice, it is likely to restrict the options of those with power - the ruler is going to be able to do what he wants under a medieval system, which is more difficult to do if a stone keeps telling people he's wrong. It's more likely to be kept for use in the ruler's interest (which is unlikely to involve justice beyond that necessary for keeping the kingdom functioning).

Further, on those instances when it is used, it's unlikely to be foolproof: The way to tell a lie to a stone that detects intentional falsehoods is... to believe it's not a lie.

This is something (I've read) politicians do to be able to speak falsehoods convincingly - using mental gymnastics to consciously change their beliefs. You can do it with application of various cognitive bias, repetition and wordplay.

For example, If a noble is plotting to overthrow a King and asked a question: "Are you plotting to overthrow the King?" They can choose to take the question via e.g. separation of individual from office - they can think: 'I'm not plotting to overthrow the King, I love the Monarchy, I'm doing it to 'save' the monarchy from the current monarch and install a better one (me) that safeguards it'

Or lets say that the accusation was a noble mass murdered a bunch of peasants in front of many witnesses: They could say "I have never killed a single person" and mean

  • I have not killed only one person
  • I stabbed them, but blood loss is what killed them
  • I merely ended their miserable existence, they had no lives
  • They were not real people, just peasants. They don't count.
  • The 'me' back then isn't the 'me' now, I've changed, therefore "It wasn't me"(Like shaggy indicated, this works on any accusation)

All you have to do is believe it for as long as it takes to speak a sentence and get away with murder.

How many instances like that before the stone is thrown out as useless junk?


Expanding on most of the up-voted answers, I'd say the main change on the justice system would be that philosophy and logic get a massive development boost and a strong influence on the justice system. There would be a short arms race about tricking the stone vs. asking questions in a good way that doesn't allow trickery.


Never mind the Middle Ages - it would drastically change the legal system even today!

Basically what you've described is a "High Court" or "Supreme Court" whose judgement is not just the best available but actually correct. If everyone has a right to a fair trial (and even today and even in the West this can be a questionable concept), the judicial system has to have the possibility to escalate up to Judgement By Stone. Beyond that, no appeal is possible.

If sentencing is delayed until after appeals up to JBS, every criminal will try to push for that. Since there's only one Stone, this will inevitably lead to a backlog, so clearly this isn't in the public interest. You would want some kind of penalty if you initiate a JBS appeal and are found guilty (or if you back out before the appeal happens because you know it'll find you guilty). Something like parole being unavailable for a failed JBS appeal might do the trick.

Since the Stone is now critical to your judicial process though, it needs to be kept in the local equivalent of Cheyenne Mountain, so that nothing short of a massive invading army can tamper with it.


Sadly, as often happens in real life, people will deny that the stone actually works, no matter how much evidence is presented as to its inerrant nature.

Furthermore, if the King attempts to enforce the stone's results, the narrative will then shift to portray them as favoring the King, and thus paint them as corrupt.

It would probably take many generations and a solid record of veracity for society to start slowly accepting the results as "true", and even then, a single influential person claiming the results are wrong could sway the opinion of significant portions of the populace.

For real life examples of this process, look no further than 9/11 truthers, the moon landing "hoax", the anti-vaccines movement or global warming denial.


The answer can be derived from one of your comments:

@CortAmmon For the case of this stone, it's 100% on the speaker's shoulders. If the speaker is talking to a stuffed bear (believing, incorrectly, that the bear can hear him) and is trying to deceive the stuffed bear, the stone will turn red. The listener (deceived, not deceived, not listening, or nonexistent) doesn't actually matter as far as the stone's reaction

This says that, so long as the speaker does not believe they are deceiving, they can say just about anything.

A natural result of this would be the omnipresence of religion. Religious leaders are constantly trying to enlighten others to the truths of their religions, and we may assume they 100% believe their claims. Accordingly, they could make any statement they please, so long as they feel they are leading the listener towards the greater truth. Any lie would be accepted so long as the lie's apparent purpose is to lead people towards the truth as the speaker perceives it.

Thus, every individual in the world who might be subjected to the stone will soon find a "higher calling" which permits them to say anything without believing that they are speaking deceitfully. Machiavelli will say "The ends justify the means" and the stone will glow bright bright blue.

  • $\begingroup$ Down voted this answer as I believe you are twisting the logic of the stone in question. Believing they are lying to bring someone to a higher truth does not negate the fact that they believe they are lying. The stone will therefore detect the lie, regardless of its purpose. $\endgroup$ – SRM Dec 16 '16 at 4:33
  • $\begingroup$ @SRM I think you underestimate the complexity of language and the conveyance of ideas. For example, if I were to say "objects fall to the ground because of gravity," I would be consciously lying by the standard you claim we should hold to. I know that science has a hypothesis called gravity which is pretty well agreed upon, but it's not "truth" because I know philosophically the ontological limits of science. I also know that, even if I handwaved those issues aside, there is also a minor electrostatic effect which does indeed exist, so some of what you are experiencing is actually $\endgroup$ – Cort Ammon Dec 16 '16 at 4:47
  • $\begingroup$ partially electrostatics, not just gravity (there's some fun rotational motion terms also). As an engineer, I actually get paid to lie, by your definition, because my customers don't want to hear the truth. They pay me, as an engineer, to know the truth and tell them half-truths about what will happen to build their confidence (well, they prefer better than half-truths, maybe nine-tenths truths, but it's still not full truths, to the degree that you suggest). $\endgroup$ – Cort Ammon Dec 16 '16 at 4:48
  • $\begingroup$ By your comments, I might buy an answer that the stone will always glow red, but not blue. $\endgroup$ – SRM Dec 16 '16 at 5:01
  • $\begingroup$ @SRM In either case, the entire system is called into question because the linguistics of lying are more complicated than we think. Interestingly enough, i would be immune under such a system, because as a skeptic, I argue that we can never truly "know" anything, so the only truthful answer I could give to any question would be "I don't know." It'd be an infuriating trial, for sure! $\endgroup$ – Cort Ammon Dec 16 '16 at 5:04

How many of all crimes are actually NOT solved because of a lie?

If you think of a medieval society, most crimes will actually not be solved, because you have no perpetrator. If something was stolen or there was a break-in, the problem was usually not that you had a suspect who is lying. Most of the time you will have no likely suspect. And if you have a likely suspect, the burden of proof was not with the court in most cases - if you catch a lowlife with stolen goods, he will meet his fate.

So the truth stone will most likely change nothing for 95% of common crimes and law enforcement, because investigation to find the suspect is harder than convictim him.

So the only cases where the stone would actually change the system are when you have a likely suspect (or a small set of suspects) and have to find proof. These will mostly be cases involving nobles or rich citizens. - And many cases there will revolve around corruption, conspiracies and a lot of money or power.

Everyone with power as something to hide

Since you will probably find a "guilty" question for everyone if you just know enough about them, the main question will not be how the stone works, but who will be tried and asked what question. So there will be a lot of blackmailing, because almost everybody can likely be sentenced by the truth stone, if you just ask the right questions.

In the end the stone will most likely be used to get to know important truths outside of court, or for big publicity stunts. So the king will train with the stone, what he can say in front of the crowd and will give some important public announcements with the stone in hand for effect. Just as the king will regularly check his advisors, ambassadors, most nobles and other important figures for loyalty. Maybe anyone with power or money has to come to the king once a month and declare their loyalty and love. And a red glow will have to be amended with a high fee, and a promise to work on ones love for the king.


Trails would be shorter if there wouldn't be as much need for Witnesses when accused himself can be his own witness. Less people would be falsely accused since now you can't torture someone into a confession. ( unless he really is guilty). That's not to say that torture wouldn't be used this is still the Middle Ages after all but only for those who were found to be lying. Overall I think would make any medieval Kingdom a slightly better place to live. Wouldn't solve all the problems of the time but it would improve justice system somewhat.

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    $\begingroup$ Why can't I? If I'm a king, can declare that divine power of the stone is not to be wasted and still send someone to torture, right? $\endgroup$ – Mołot Nov 28 '16 at 15:27
  • $\begingroup$ @Mołot true but I'm assuming since the king actually has a stone that the only reason he would want it would be if he cared about the truth if he didn't care about the truth there be no need for the stone he just decided if it would be more convenient if someone was to be found guilty or not. $\endgroup$ – Bryan McClure Nov 28 '16 at 15:41
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    $\begingroup$ King got the stone as a gift. We don't know if he wanted to get it. $\endgroup$ – Mołot Nov 28 '16 at 15:50
  • $\begingroup$ @Mołot since we know nothing about the king except that he has a Stone the question wouldn't have asked how this would change the justice system unless he intended to use it. Otherwise they're obviously you would be no change to the justice system. $\endgroup$ – Bryan McClure Nov 28 '16 at 16:05
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    $\begingroup$ No change except where King cares enough, and wants to. Avoiding torture is probable, I hope, but saying "can't" is a stretch. $\endgroup$ – Mołot Nov 28 '16 at 16:25

There's a book that explores this: https://en.wikipedia.org/wiki/The_Truth_Machine

However, you have only one which opens up the possibility to it disappearing/being destroyed. I would consider one of these outcomes to be almost inevitable--too many people in power are guilty of dirty deeds they won't want exposed.


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