Defining truth.

[Belial666]

In one of my campaigns (not a DF game but still) one of the major NPCs is one of those Powers who are bound by their word, cannot lie, the whole nine yards. Unfortunately (for the PCs) she is also one of those annoyingly manipulative mentor figures. So the subject of Truth has come up a lot.

The question is then, is there some limit to how creative one can be when speaking the truth? Some of the things that have come up;

1) Saying "My name is X", while having a lot more than one name specifically so you can be truthful with that phrase without revealing your true name.

2) Telling someone that very dangerous action X won't kill him. It does. When questioned about that, she claims that it was said person's stupidity and blind belief in his own invulnerability that harmed him because due to them he took no precautions, not the action itself. Besides, he's just sleeping for the time being.

3) Saying "the sky is red" just to make fun of people expecting her to speak true. (It is, at dusk. Or in Venus.)

4) Speaking in code. As in, spending subjective years to create another language that sounds like english but isn't english and in which the meaning of some words/phrases is often reversed or altered. I.e. "blue" referring to the color red, "yes" meaning no and so on - specifically so she can speak in code and not english and thus technically telling the truth while speaking utter falsehood.

[Ophidimancer]

1) The standard way around this one is, "You can call me ..."
2) "I don't find that dangerous at all."
3) Ok that one is kinda douchey of you to pull.  Ronald McDonald is President ... in my dreams!
4) Also douchey and I wouldn't d it if I were you.

[Tsunami]

1) that's really a basic tool for "truth speakers"... leave stuff out.
You can only speak the truth, that doesn't mean you have to answer every question, or are unable to conceal parts of said truth. You just cannot speak a direct lie.
You can always say "I'm not gonna tell ya... nanana"
And as long as people don't suspect you to have more info than you are sharing, you don't even have to do that.
Also you can say stuff like. "I'm not going to hurt you." and then have some lackey do it anyways.

2) Doable, to a certain degree. But it's really only a variation of 1).
"Will I die if I go to the fortress of darkness?" asked the righteous knight... "No, you won't." said the truthspeaker, quietly thinking "Not if you only go there... trying to get in and free the prisoners... oh yes, thats going to kill you... but I'm not telling you that"

3) this one could basically justify anything... not much fun, and not much of a restriction if it would work... so I wouldn't do that.

4) Speaking a language that sound like english but isn't, is a lie in itself in my opinion. Now obviously cryptic language, or Riddles that contain the truth would be allright. But a Code that sounds like one thing, but means the exact opposite... thats a lie, so no that wouldn't be possible IMO.

[toturi]

"... you're going to find that many of the truths we cling to depend greatly on our own point of view."

[smoore]

Watch politicians. The good ones never lie. They make vague statements that were true once, but may not be now and speak in the past tense, they avoid answering the question, they put qualifiers around everything.

1. "I have been called X" works. Making a truthful statement about the past is always acceptable. Of course its really douchy to look at a follower and say "Call me Ceaser". He does. Then tell the players "I have been called Ceaser". If you can't answer then say something like "My name isn't important", "I have many names", "You may call me what you wish", "We are in a Church so lets go with Mr. Church". There are so many variations there is no reason for this to be a problem.

2. Is your truthsayer an oracle? They shouldn't be answering questions about the future directly  unless they know the future because if they make any statement about the future that doesn't come to pass they lied. Their answer should be something like "death is always an option", "it is possible you could survive", "it would be safe for me".  Your truthsayer simply can't say that the action will or won't kill the person unless they have knowledge of the future. They can suspect and be pretty sure it will, but something in the universe could make it so that they would be wrong and hence lie.

3. Gramatically the person is lying. Without additional qualifiers when saying the "sky is red" it applies to the present location and time, not some unstated far off place or time. You cant say "the sky in red" and then think in your head "on Venus" and make it count. The person spoke a lie, they spoke and thought the truth.

4. If you directly pulled this crap as described after I punched you in the face I'd leave and never game with you again.  You can speak in code, but you must first notify the listeners you are doing so, and they need a copy of the code or a basis to translate it. They don't have to have read it just had it made available. Now if they miss the line or misunderstand "Admiral, if we go "by the book". like Lieutenant Saavik, hours could seem like days. " that's their fault. But they were told you were speaking in code, and what the code was. Spock is a great example, he does not lie (usually). He might exaggerate the truth, speak in an open code or leave out info but he doesn't just lie which is what you are suggesting.

If you have to resort to #3 or #4 (as you described it, not with the additions I described) its time for you to get rid of the character your not a good manipulator and shouldn't by trying this sort of thing. It will a better game if you play to your strengths as a GM and not try things that end up making the players mad.

[Lanir]

I'd have to agree with Tsunami, Ophidimancer, and Smoore on this. 3 & 4 as you've listed them just don't give anything to work with. You wouldn't directly use #3. You would allow people to think things that weren't true and just not correct them. Like if you're a witness to something and they ask you about it you can tell them part of what you saw. It might point at the wrong conclusion but you're not outright lying. Just deliberately misleading. As far as #4 goes, I think the closest you could reasonably get to this is if someone else told you that the person was incapable of any true deception. But didn't tell you that they always spoke in opposites. This is an uncommon but known style so you probably won't get blank stares from all of your players, and it's a speech oddity that's always in effect. You can summarize the known rules easily and apply them to everything that person says. It could (and should) pop up in the initial conversation with them in a way that might be a tip-off.

The problem you'll likely run into if you run it the way you've mentioned (assuming I've read it correctly) is you've effectively got someone who can say literally anything. So no matter what you say about them not lying, it would end up seeming obvious that you were lying. From outside it sounds like it would be impossible to distinguish between the speech mannerisms you've described and willful falsehood. Even after it's all over and you're looking back with the full knowledge of hindsight. By contrast, if you set the characters up to hear only part of a truth and they go haring off in the wrong direction, later on they can look at what they were told and see that the NPC was just being very clever. In the future they may be wary. Which is alright, it means they're getting into the world you're presenting more. "The NPC isn't lying even though he's lying" ala #4 just hurts the suspension of disbelief.

[Steed]

I think 3 is okay for the utterly stupid, nonsensical questions.  Let's say you're dealing with Mab.  Technically, she can't lie.  However, if someone decides to mock that by asking her some inane, pointless question?  I think 3 is fine.  Although Mab would probably come up with something more vicious than a simple half-truth.

4 could work, if done correctly, but if someone sprang it on me without warning that would be the point where I quietly got up from the table and left.  No need to make a scene or be a dick about it, but it's not cool to deliberately screw your players like that and it's not something I could see working in a game about cooperative storytelling.