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I had a very interesting discussion with my players on the effects of the Zone of Truth in D&D 5e. They have committed a murder / killing in self defense and will be tried for it and we talked about whether the Zone of Truth is balanced.

We were discussing the use of Zone of Truth as part of a court process.

As a DM, I think this spell is either always OP or always useless according to its interpretation: All cases take into account that the caster knows if the target of the spell resisted the spell, therefore it will not be used in court unless the affected person didn't resist. Furthermore, if such resistance could be willingly forgone, any court would condemn immediately any resisting person. So we are talking about when the spell is not resisted.

  1. In the case that it only prevents one from speaking false statements (as far as they know) but doesn't compel one to answer the question presented to them, they can always detach themselves from it and answer a different question that they ask themselves within their mind (the same technique used against a lie detector machine). This will make the spell useless.
  2. In the other case in which one is compelled to answer the question that's presented to them in its exact formulation, there is no way of not telling the truth as long as the interrogator follows a simple algorithm:
  • Ask a question as specific as possible. (The affected can withhold parts of the truth.)
  • Ask "Did you hide any information that you think is relevant while answering the last question?" (The question is a subjective yes or no question and refers to the information the affected tried to hide, therefore they have to not answer, or confess hiding information. The affected can only hide information if they subjectively think it's relevant).
  • Ask "Will you tell us now the information you kept from us before without withholding any relevant information?" (Another yes or no question that by answering either condemns or compels the affected to keep to the truth, because if they know they're going to withhold information they are unable to say yes because that would require them to believe they will tell the truth. During a timeframe so short it's not possible change their belief about telling the truth without a reason.)
  • Repeat step 2 until the answer is no and no more information that the affected knows is relevant is left unsaid.
  • End with "Do you know any more relevant information that was not discussed here that would prove your guilt?" (ending the interrogation only if the answer is no) This question is to reveal the existence of information the affected thinks is relevant but was not asked about.

The philosophical discussion is very interesting:

  • Is it possible under the effect of Zone of Truth to answer half of a question? Q: "Do you like red and blue?" A: "I like red."

Here the question was referring to both red and blue and answering only to one part of it would also allow for the following:

Q: "Did you kill the king?" A: "I did not" (kill a chicken)

Or must the answer regard the full question?

Q: "Do you like red and blue?" A: "I do like red but don't like blue."

My players were saying that Zone of Truth is balanced because it's the intelligence of the affected that prevents them from splitting a question "Did you kill the king?" into "Did you kill?" or even "Did you?" while not binding the affected to answer the question presented, because the affected knows the question was about the king and can't deliberately answer "no" when they know they did.

To that my answer was that the same intelligence would prevent the affected from using technically truthful statements when they know they are falsifying the truth.

So it all comes down to the basic question:

Does Zone of Truth only deal with technically true/false statements, or does it screen the mind of the affected for any subjective truth/lies?

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  • \$\begingroup\$ While some fascinating things where raised in comments, they were straying a fair bit from how comments are best used. Further discussion can be taken to chat, and I'll leave a gentle reminder that solutions to the problem should go in answers (in full form and with sufficient support). Thank you :) \$\endgroup\$ – Someone_Evil May 5 at 11:09
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Zone of Truth is still useful even if it works according to your first interpretation

To be honest, if the king's murderer is asked the direct question "did you kill the king?", and they respond "no", then most people are going to rule that as a lie, even if murderer is cunningly ignoring the question they were asked and "actually" saying something completely unrelated. However - even if you allow this kind of shenanigan to get around the zone of truth and don't consider it a lie - a skilled interrogator can still effectively use the zone of truth to compel truthful statements from their subject, and thus arrive at the truth (if only by implication or omission). The trick is not to allow the subject to respond with ambiguous or unqualified sentences, but require them to make a full statement which does not depend on context.

Say our murderer, Alice, has killed King Bob, and knows full well she did it. Under the effect of a zone of truth, Alice cannot say "I did not kill King Bob", because she did, and that would be a lie. Our interrogator, Eve, knows exactly how the spell works, and so she decides that the only statement Alice can make which will prove she did not kill King Bob is "I did not kill King Bob." Rather than ask "Did you kill King Bob?", knowing that Alice is tricky and can weasel her way out of a direct answer to the question, Eve instead gives Alice a simple instruction - "Say the words 'I did not kill King Bob'."

Now Alice is trapped. She cannot say such a thing, because it would be a lie. But of course, someone who did not kill King Bob would be able to say that immediately, and so prove that they didn't do it. But Alice cannot - and so she cannot satisfy Eve's demand. She might say a lot of other things, attempting to distract or confuse Eve, but so long as Eve sticks to her guns and requires that Alice simply and definitively say that she did not kill King Bob, Alice's inability to say so is strong evidence that she did kill Bob.

The zone of truth still has a hole in it, though. A subject under the spell cannot lie out loud, but they can lie by omission, in the sense that they could refuse to say things that are true with the intent to mislead their interrogator into believing those things are false. For instance, if Alice did not in fact kill Bob - but she knows who did, and is willing to go down to protect them - she could implicate herself by refusing to say she didn't do it, and thus divert suspicion from the real killer.

Ultimately, the zone of truth will guarantee that any independent statement the subject makes is one they believe to be true. If a subject cannot - or will not - say a certain thing, it is strong, but not incontrovertible, evidence that they don't believe that thing to be true. A skilled investigator who keeps these things in mind will still find the zone of truth to be a very useful tool in their arsenal.

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$ – linksassin May 5 at 8:00
  • \$\begingroup\$ Totally nailed it. Great Answer. \$\endgroup\$ – KilrathiSly May 5 at 19:36
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A creature is free not to answer at all

A creature in the Zone of Truth

can't speak a deliberate lie while in the radius

The spell description says nothing about answering questions. Therefore, Zone of Truth does not force anyone to answer questions at all.

Moreover, the spell description explicitly says that a creature which is aware of the effect can (and will) "be evasive" in its answers:

An affected creature is aware of the spell and can thus avoid answering questions to which it would normally respond with a lie. Such a creature can be evasive in its answers as long as it remains within the boundaries of the truth.

So, if a creature is asked "Do you like red and blue?" it can answer "I like red", or it can say "I like cooking", or "I don't want to answer" — all these answers are permitted providing they are true.

However, when you say "I did not" having different question in mind (like, talking about chickens when being asked about the king's death) this would be a deliberate lie, hence forbidden.

As with other things in 5e, all the corner cases are up to the DM. I suggest not to play "Gotcha!" with players and avoid situations when an obvious answer within the Zone of Truth is actually a well-hidden lie, because this leads to absurd and frustrating situations very fast (like "I didn't say 'no', I just say the letter 'n' and then 'o', so technically that wasn't a lie"). I suggest using a simple rule instead — Zone of Truth forbids speaking any words which the speaker itself would identify as a lie.

If you want answers, Zone of Truth is probably a bad choice

Zone of Truth is a 2nd level spell, it isn't meant to be an ultimate solution. There are another low-level magic means like Suggestions or Detect Thoughts, but they all aren't so great. If you want an unwilling creature to answer all of your questions completely and honestly to the best of its ability, you provably need something stronger like Dominate Person.

@Sumyrda made a fair suggestion in comments below — you could combine Zone of Truth with the Command spell to get around the no need to answer problem. Did you kill the King, yes or no? Command: Answer!

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    \$\begingroup\$ Could you combine zone of truth and command to get around the no need to answer problem? Zone of Truth + Did you kill king Bob, yes or no? Command: Answer! \$\endgroup\$ – Sumyrda - remember Monica May 3 at 7:59
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    \$\begingroup\$ In the fantasy court setting, this doesn't really matter. The court is at liberty to treat the failure to answer as a confession of wrong-doing, so whether the subject answers is of limited importance. \$\endgroup\$ – Jack Aidley May 3 at 14:18
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Zone of Truth is not necessarily an area truth serum

Per the description:

An affected creature is aware of the spell and can thus avoid answering questions to which it would normally respond with a lie. Such a creature can be evasive in its answers as long as it remains within the boundaries of the truth.

In theory, avoiding this is as easy as refusing to answer questions. And that is okay, this is just a 2nd level spell. Many campaigns/stories rely on characters being deceptive, and just casting this would throw a wrench into the whole thing.

However, it can be a very interesting utility spell; you could cast it to prove you are not lying when speaking to an authority figure. You could cast it while all parties involved in a conversation give consent to ensure they are not being intentionally deceptive. The fact that someone would not consent the use of a zone of truth is also very indicative, or if someone answers half truths and gives non-answers. The fact that they are hiding something itself might be valuable information.

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  • \$\begingroup\$ Only the caster knows whether other parties have failed the ZoT save. If an authority figure doesn't trust the caster, but knows exactly how the spell works, they're unlikely to just take the caster's word for it. Also, there's no visible effect, and unless they or someone they trust have significant Arcana training, they won't be able to know that you actually cast ZoT, rather than Prestidigitation or Detect Thoughts for example. (And their guards may not let you cast while they're in the room, if they really don't trust you.) TL:DR: "I cast ZoT" is not much better than "I promise". \$\endgroup\$ – Peter Cordes May 3 at 7:39
  • \$\begingroup\$ Now, if you can get someone the authority figure already trusts to cast ZoT and relay saving-throw failure to them, then yes ZoT can extend their trust from that caster to you. Of course, some people may know that there are ways to beat ZoT, like being a lvl17 Rogue (Mastermind) - Soul of Deceit feature: Additionally, no matter what you say, magic that would determine if you are telling the truth indicates you are being truthful if you so choose, and you can't be compelled to tell the truth by magic. \$\endgroup\$ – Peter Cordes May 3 at 7:41
  • \$\begingroup\$ @PeterCordes the existence of "Soul of Deceit" actually makes for a strong case that ZoT shouldn't be easily defeated except by resisting the effect - if a rogue needs to be lvl 17 to get around it, then why would we expect a common criminal to be able to? \$\endgroup\$ – Rob Watts May 3 at 17:59
  • \$\begingroup\$ @RobWatts: Agreed, but only to some degree. I haven't looked into magic items that can potentially defeat ZoT (potentially accessible to much lower-level creatures). But mechanically in 5e, there aren't a lot of ways to definitely know if another creature has class levels. Depending on the situation, a paranoid authority figure wouldn't want to assume that someone truly is what they appear to be without some confirmation they're not magically truth-defeating or a high-level mastermind. \$\endgroup\$ – Peter Cordes May 3 at 18:08
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Zone of truth relies on deception, so no.

You create a magical zone that guards against deception in a 15-foot-radius sphere centered on a point of your choice within range. Until the spell ends, a creature that enters the spell's area for the first time on a turn or starts its turn there must make a Charisma saving throw. On a failed save, a creature can't speak a deliberate lie while in the radius. You know whether each creature succeeds or fails on its saving throw.

Deception is defined as such.

Your Charisma (Deception) check determines whether you can convincingly hide the truth, either verbally or through your actions. This deception can encompass everything from misleading others through ambiguity to telling outright lies. Typical situations include trying to fast-talk a guard, con a merchant, earn money through gambling, pass yourself off in a disguise, dull someone's suspicions with false assurances, or maintain a straight face while telling a blatant lie.

So, ambiguous answers like noting that you didn't kill (a chicken) wouldn't fly, but half truths like saying you like red (but not blue) would fly. As such, it's not easily defeated unless you can state a truth which is true unambiguously.

Even then, as others have noted, they can just force you to say something clear and unambiguous. Without higher level spells like modify memory, you can't defeat those issues.

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    \$\begingroup\$ If it prevents deception (with that definition) it "prevents hiding the truth either verbally or through an action". So there's no way to hide the truth verbally under it. If asked "did you kill the king?" you can't answer dodgingly because that's a verbal way to hide the truth. I think you contradicted yourself here. \$\endgroup\$ – Toma May 3 at 0:57
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    \$\begingroup\$ @Toma Lying is not the same as saying things that are not true. Lying is saying something with the intent of deceiving the person yo are talking to. In that context, if you ask yourself "Did I kill a chicken?" in order to not answer the question asked to you, you are knowingly trying to (verbally) deceive. It won't work under a Zone of Truth unless you convince yourself the interrogator will interpret the question with the same interpretation as you. \$\endgroup\$ – Martin Epsz May 3 at 9:59
  • \$\begingroup\$ It says you can't hide the truth, not that you can't omit the truth. If they ask you "Did you kill the king" and you say "I didn't stab the king." (you bludgeoned him) that's fine, but you can't hide the truth with a statement that is ambiguous. \$\endgroup\$ – Nepene Nep May 3 at 15:18
  • \$\begingroup\$ But it's obvious that the statement about bludgeoning the king was only said because of the attempt to hide the truth. A true statement, yes, but still as an attempt to hide the truth. According to this you can try to verbally hide the truth by giving other true statements So why would a true statement about not killing a chicken, while not complete, is not allowed but a true statement about not stabbing is? Where does it say that a statement must be complete? \$\endgroup\$ – Toma May 3 at 18:18
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    \$\begingroup\$ @Toma "I did not stab him" is not a lie because the spoken statement itself makes no claim that you did not kill him - only that you did not stab him. If you are asked "did you kill the king" and you answer "no" and then mentally add "I did not kill a chicken", then your spoken statement does make a claim that you did or did not kill him. The check is for a deliberate lie, not a deliberate untruth. Lying requires that the statement be both false and deliberately deceptive. \$\endgroup\$ – Pilchard123 May 4 at 13:27
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Zone of Truth prevents the affected creature from speaking a "deliberate lie". It does not prevent accidental lies and presumably does not allow accidental truths that were intended to be lies (otherwise it could be used to divine information that we would otherwise have no way of knowing).

Therefore, it depends on what the affected creature considers to be "a lie". If I believe that I have not spoken a lie, yet my statement would be a lie according to the definitions provided by every philosopher, lawyer, and commoner on the street, then it was still only an accidental lie.

So the first interpretation only works if the creature honestly believes that ignoring the question asked and responding to a question that they silently asked themselves in their own head is not "lying". I would argue that the vast majority of creatures do not believe that, and you cannot simply choose to not believe it because it would be convenient for you. (Also allowing this, except in extreme cases of insanity or mind-modification, would largely make this spell useless, I'd advise against it.)

As for the second interpretation - you aren't compelled to answer at all. The court may assume your guilt in such cases, but there are still any number of reasons why an innocent creature might refuse to answer, especially in a world where magical compulsions exist. There are also reasons that a creature might believe themselves to be guilty even if there aren't. A good court system probably shouldn't rely too heavily on Zone of Truth for these exact reasons. Throw in even one famous precedent of a creature using Glibness or otherwise finding a way to bypass this spell, and you easily justify why people wouldn't entirely trust this spell in a court setting.

But yeah, if the interrogator is persistent enough, you would be stuck with either telling the truth or making it obvious that you are hiding something. I would argue that this isn't OP since it's a highly specific situation that this spell happens to be precisely suited for, but really there isn't any "balance" that we could compare it to, so it's more a question of "how do I make the story work, if this spell exists?"

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Adding a mental "noooooot" at the end of sentence you speak does not magically make the loud-spoken sentence not a lie.

This is some toddler-grade logic bending. Now it becomes debatable if you trail off and then very low-key mumble the "not" at the end, but IMHO, the point where that becomes valid is where a decent investigator has a good chance at spotting it, and will ask you to repeat what you said out loud without mumbling at the end.

And doing so [adding a "not lol" mentally] would definitely require a Deception roll, which is exactly what the zone guards against

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  • \$\begingroup\$ The question deals with context, to which only a true statement can be spoken. Your answer takes the serious debate around that context as not serious and therefore is not helpful. I believe you misunderstood the importance of that debate. \$\endgroup\$ – Toma May 5 at 13:28
  • \$\begingroup\$ @Toma no, I understood the debate but just thought OPs option 1 to be wholly ridiculous and therefore phrased my answer in that manner \$\endgroup\$ – Hobbamok May 5 at 13:31

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