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I've seen a lot of posts about how "Zone of Truth" might be defeated by the target. But my character has the opposite problem: he's extremely truthful but people don't always believe him. Is there any mechanism for using Zone of Truth to make verifiably True statements?

If I cast ZoT, I know (to first order) who in the zone succeeds or fails. I would also have to make a save, which I could fail voluntarily. Is there any way I could reliably convince my interlocutors that I did indeed fail (note: this isn't "convince them I'm telling the truth when I'm lying" but "convince them I'm telling the truth when I am."

The benefit of this is illustrated by a binding oath taken some of the magic users of the Wheel of Time fantasy series:

One of the great powers of the Aes Sedai First Oath was that if an Aes Sedai made a statement without evasion, then all knew it to be true and reliable. And if the Aes Sedai said "I am not trying to mislead you, you understand my point correctly" it was more powerful. Zone of Truth has precisely the opposite power.

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  • \$\begingroup\$ I'm confused by the inclusion of the 'Aes Sedai First Oath' component of the question. Could that be removed and still preserve what I think is your initial question, "How can a character use Zone of Truth to demonstrate they are being truthful?" \$\endgroup\$ – Pyrotechnical Feb 24 '20 at 19:15
  • \$\begingroup\$ Are you certain that you can fail the saving throw voluntarily? That portion is the only one which makes me think the game might not be D&D 5e. The Wheel of Time reference seems only to be an analogy illustrating what the OP hopes to achieve with the proposed usage of Zone of Truth. \$\endgroup\$ – Upper_Case Feb 24 '20 at 19:26
  • \$\begingroup\$ So essentially the problem is the reverse of what ZoT provides: instead of you knowing whether everyone else is lying, you want everyone else to know whether you are lying? \$\endgroup\$ – Ryan C. Thompson Feb 24 '20 at 19:27
  • \$\begingroup\$ @Upper_Case 5e doesn't have rules allowing for deliberately failing saving throws, but IME it's a common house rule (either because it makes sense that you could choose not to resist an effect or just because there were rules for this in previous editions). You probably shouldn't put too much importance on that bit. \$\endgroup\$ – Carcer Feb 24 '20 at 19:29
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    \$\begingroup\$ I think your best bet is finding someone else who can cast ZoT and have them vouch for you. \$\endgroup\$ – RevenantBacon Feb 24 '20 at 20:23
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No.

This is pretty straightforward. The only person who necessarily gains knowledge on whether or not a creature within the radius of Zone of Truth has been affected by the spell, and therefore is or is not capable of lying, is the caster.

Since the character in question is not considered reliably honest by the others (that's why there's a question of honesty in the first place), the character's own word about whether or not they are affected by the spell is similarly unreliable. If that would work, they might as well not bother with Zone of Truth at all.

This is particularly true if you are hoping for others' views of this character to include a reputation similar to inability to lie. Aes Sedai cannot lie, with magical effects physically preventing them from directly expressing, verbally or in writing, something that they believe is untrue. Trying to use Zone of Truth in that way may even backfire-- without the spell being in effect, people may assume that the character is lying simply because they are eliding the situation in which lying would be impossible to get away with.

The correct solution involving RAW Zone of Truth would be for the character to submit to another character casting the spell, perhaps repeatedly until the character fails the saving throw (voluntarily or otherwise). If your character is really focused on this, building them to be able to produce spell scrolls for Zone of Truth and then giving those scrolls to others so that the spell is as available as possible to other people might be the closest RAW solution involving this spell.

Other options in this area will certainly exist as well, but lie outside of the scope of this question. As quick examples, someone could cast Wish on a character to produce this effect, homebrew spells/curses/feats/magic items can impose it, and so on.


Experience Note:

I've run NPCs with inability to lie as a trait, and found mechanics surrounding that to be unimportant (players don't trust them, much like Aes Sedai are not much trusted because they can be misleading without lying). The hard part is actually making sure they never lie, because the players/DM at the table have no constraints on lying whether a character does or not.

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    \$\begingroup\$ It probably isn't necessary to cast zone of truth repeatedly - by the RAW, a creature in the zone must save repeatedly until it eventually fails. You'd have to be extremely lucky to resist the spell for the entire ten-minute duration. \$\endgroup\$ – Carcer Feb 24 '20 at 19:50
  • \$\begingroup\$ Yeah, the reputational problems are ones I'm worried about. That's part of why I'm looking for a method in which I could say "the information written on this piece of paper is 100% correct to the best of my knowledge, without an attempt to evade or mislead" and have that one particular statement be believed. Obviously they will still suspect ulterior motives, but it could potentially be useful in situations such as "my party has done something kind of bonkers and nobody believes us or our warnings". \$\endgroup\$ – Necarion Feb 24 '20 at 21:53
  • \$\begingroup\$ The Glibness spell prevents lie detection via spell. \$\endgroup\$ – Tiger Guy Feb 24 '20 at 22:03
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    \$\begingroup\$ @ScottDunnington as explored a bit in this question, glibness and similar effects which confound "magic that would determine if you are telling the truth" don't necessarily interact with a zone of truth at all. (Zone of truth doesn't detect whether you are lying, it just enchants you so that it is impossible for you to lie; truth is inferred from the knowledge that you have been successfully enchanted.) \$\endgroup\$ – Carcer Feb 24 '20 at 22:18
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    \$\begingroup\$ @scubbo I guess you could bootstrap it? Make the scrolls, then get some trustworthy NPC to cast Zone of Truth, then say "these scrolls are uncursed Zone of Truth scrolls" from inside it. From then on, you can always use your last verified scroll to verify a bunch of new scrolls, so you don't need to keep going back to the NPC. \$\endgroup\$ – user3482749 Feb 24 '20 at 23:11
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Statistically, Yes

There is no game mechanic or loophole in the spell that would allow your interrogator to determine that you have failed your save. However, the spell lasts for 10 minutes and requires you to repeat the save every turn you enter or stay in the spell's radius. Therefore, the following strategy is perfectly viable:

  1. Cast the spell
  2. Enter the spell's area
  3. Repeat the same (true) statement every round, 100 times, until the spell expires

100 repetitions of the saving throw gives you about a 99.5% chance to fail at least once even if you have a 95% chance of success each time. This should be enough to persuade a skeptical interrogator. If not, simply repeat the process.

Of course, this technique requires your interrogator to understand how the spell works and to have a decent understanding of probability. Depending on the type of world your game takes place in and the type of person interrogating you, this may or may not be reasonable to hope for. As a DM, I might allow this trick to work against an intelligent NPC wizard who has studied this particular spell, but probably not anyone else. In the fiction, I would rule that such an NPC has a general understanding of the near-impossible difficulty of resisting the spell for the entire duration, rather than having them calculate the precise probability based on meta-concepts like your saving throw bonus.

As pointed out in a comment by @carcer, if your interrogator doubts that you have actually cast the spell at all, they can simply step into the area with you and experience its effects for themselves. Again, this may only be persuasive to someone who has studied this particular spell themselves.

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    \$\begingroup\$ @NautArch You do, in fact, repeat the save each turn: rpg.stackexchange.com/questions/99740/… \$\endgroup\$ – Joe Feb 24 '20 at 19:58
  • \$\begingroup\$ I totally didn't read it that way! Learned something new :) \$\endgroup\$ – NautArch Feb 24 '20 at 19:59
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    \$\begingroup\$ @Joe you also need a way to convince the interrogator that you have, in fact, cast the spell and are maintaining the spell... which should be doable if they're also in the area with you, since they'll also most likely fail a save quickly and thereafter know the spell is up for as long as they can't lie. \$\endgroup\$ – Carcer Feb 24 '20 at 20:01
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    \$\begingroup\$ @Upper_Case I don't think the NPC needs to understand the mechanics of saving throws, necessarily. If a player tried this in my game, I would rule that a sufficiently learned or experienced caster would understand that anyone under the influence of this spell is constantly fighting the compulsion to tell the truth, and to resist this compulsion for the entire duration would require a nearly impossible reserve of willpower. I do agree it requires fairly niche circumstances to work, as I say in my last paragraph. \$\endgroup\$ – Joe Feb 24 '20 at 20:44
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    \$\begingroup\$ @Joe Sorry, bad timing! I wanted to reword my comment. The core piece of it is that the knowledge of dice rolling mechanics for saving throws is necessary for the statistical precision described here, which seems to me to be the core of this strategy. A line or two about that in the answer will improve it, as the abstracted game mechanics are unevenly assumed to be known by in-universe characters. Repeating this strategy ad infinitum can address the uncertainty from not knowing the mechanics, but is maybe not so practical. \$\endgroup\$ – Upper_Case Feb 24 '20 at 20:46
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By itself, zone of truth can't prove your own honesty

The spell only does what it says it does, and though you could affect yourself with your own zone of truth and therefore be forced to be truthful, there is no mechanism in the spell which grants the knowledge you have about whether or not any subject is affected by the spell to anyone else.

However, if you have a way to give your interlocutor the ability to cast zone of truth, then you have reversed the situation and can invite them to subject you to the effect to prove your honesty. The easiest way I can think of to do this off the top of my head would be to lend your interlocutor a ring of spell storing into which you have cast zone of truth already, so they can attune to it and then cast it on you. Any creature can use the ring of spell storing (unlike a scroll of the same) so it doesn't require the interlocutor to be a capable caster themselves, but it does require you to have an hour available so they can attune to the item (and, ideally, another hour so you can attune to it again after they give it back).

If you're in the specific case of dealing with an individual who is a spellcaster with the spell identify prepared, you could subject yourself to a zone of truth and then invite them to cast identify on you, because:

If you instead touch a creature throughout the casting, you learn what spells, if any, are currently affecting it.

Thus, they can verify with their own magic that you are in fact affected by a zone of truth. If they're also inside the zone of truth, it would be obvious to them if you drop concentration on the spell afterwards, as they will suddenly be able to lie.

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  • \$\begingroup\$ I like this solution, even if it's still difficult. It's still pretty difficult, and requires a trusted interlocutor capable of casting Identify (which is itself an expensive spell, with the 100 GP pearl). However, it does provide a method of verifying the truthfulness of two separate parties. \$\endgroup\$ – Necarion Feb 24 '20 at 22:00
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    \$\begingroup\$ One other option could be to have overlapping Zone of Truth spells, with one caster on each side of the discussion. Then each side would be able to strongly accept that (a) both casters are bound by truth spell, and (b) which other parties are bound by it, since you already have (a). \$\endgroup\$ – Necarion Feb 24 '20 at 22:03
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    \$\begingroup\$ @Necarion I feel like we're getting dangerously close to accidentally inventing high fantasy magical key exchange algorithms... \$\endgroup\$ – Carcer Feb 24 '20 at 22:04
  • \$\begingroup\$ What would a Private Key look like? I'm also amused that someone named @Carcer is giving me advice on how to be honest in a fantasy setting. \$\endgroup\$ – Necarion Feb 24 '20 at 23:21
  • \$\begingroup\$ @Carcer You say that like it's a bad thing. \$\endgroup\$ – John Montgomery Feb 24 '20 at 23:33

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