Language of Truth

Beatrice: From now on, everything I speak in red is the truth. There is no need to doubt or question it.
Battler: And I should believe you when you say that?

— The introduction of the Red Truth in Umineko: When They Cry.

A Language of Truth is a particular language or form of communication in which lies are inherently impossible or inexpressible. This is a frequent feature of Telepathy,^note because, as scholastics said, lying is saying one thing and thinking another, so you can't lie if you think and speak in the same act but it can also appear for more overt languages. A Language of Magic may be this or, slightly differently, it may cause anything said in it to become true — this is known in Real Life as "magical notion of truth" . Beware, of course, the Consummate Liar who is either outright immune or uses Exact Words and other forms of deception to get around this inconvenience.

A Real Life Language of Truth can't possibly exist — not if you want it to be able to express every true statement. Consider:

This statement cannot be translated into a Language of Truth.

Is this statement true, or is it false?

Compare Cannot Tell a Lie, in which the inability to lie is inherent in individual characters. Works using this trope will often discuss The Power of Language itself. It is common for Telepathy to be depicted like this, or at least to transfer knowledge, thoughts, and emotions directly and without any masks or varnishing.

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Examples

Comic Books

• The Chronicles of Wormwood: It is impossible to say anything untrue in the presence of Jay, who happens to be the Second Coming of Jesus Christ. It doesn't matter if you're actually trying to deceive him (if, for example, you're testing the effect with a ridiculous lie like "My parents were secretly elephants"), you just can't finish the sentence. People who are trying to deceive him, even for polite reasons, have a tendency to say what they really mean instead.
• ElfQuest: Telepathy functions this way. Unfortunately for them, the Big Bad's mind is so malicious that it's literally painful to receive her thoughts. So most elves use vocal speech with her instead, and she can lie just fine with words.

Fan Works

• Harry Potter and the Methods of Rationality: Parseltongue, the language of snakes, is revealed to have this effect as neither Harry, Professor Quirrell or Voldemort were able to express direct deception through that language. It becomes an often demanded method of communication between the parties capable of understanding it to avoid such deception. This does not, however, prevent them from telling misleading truths.

Literature

• Belgariad and Malloreon, by David Eddings: It is impossible to tell a lie in the language of wolves. At one point a wolf wants Ce'nedra to stop talking. Garion tells her the wolf wants to sleep. When he tells the wolf to close her eyes to pretend to sleep, the wolf is amazed that is possible to say things that aren't true in the human language. (Interestingly, while the wolf's dialogue wasn't false, it ultimately turns out to been an expression of deception regardless.)
• Between Planets, by Robert A. Heinlein: The language of the Venerian "dragons" is called "true speech" and as one (human) character points out, doesn't even have a word for the concept of deliberate falsehood, meaning that Venerians (at least when they're speaking their own language) are unable to lie.
• The Baroque Cycle: In Quicksilver, philosophers are attempting to make a truly logical language which, when used correctly, makes it impossible to say things which are false. The idea is that it would work like algebra: valid algebraic transformations on correct equations always lead to other correct equations. This is a little bit different from some of the other examples, since it protects not only against the speaker lying, but also against the speaker mistakenly saying something wrong.
• Book of the New Sun: The Ascians are a people whose language is composed of a bunch of Mao-esque revolutionary slogans. However, the book explicitly shows that Ascians are capable of uttering subversive statements even when bound by this language.
• Earth's Children: The language of the Clan is like this. It's a sign language which supposedly involved so much careful observation of body language and expressions that any signs of lying would be obvious. Clan members can in fact lie, but can't get away with it, so nobody ever bothers — to the point where the main character Ayla is confused by lying the first time she encounters it.
• Embassytown, by China Miéville: The Ariekei speak a very unusual language — in fact, the oddness of the language is a central part of the whole book—but one of its features is that they can't really lie. Some of them are trying to learn, however, by starting a statement, and then saying the second half too quietly to be heard.
• Ghattis Tale: Before they became Living Lie Detectors for law enforcement, the ghatti first had to learn what lying was, as like the Clan, their language is a gestural one in which successful lying is impossible.
• Hellspark by Janet Kagan: It is technically possible to lie in Jenji, but the language is structured to provide as much accuracy and detail as possible, and is backed up by cultural and religious penalties for lying. Several times characters refer to speaking in Jenji as synonymous to telling the whole truth and nothing but the truth.
• Heralds of Valdemar: In Mercedes Lackey's Velgarth novels, only the dyheli, an artificial race of deer-like sapients with truly phenomenal telepathic abilities, can lie with Mindspeech.
• Inheritance Cycle: The Language of Magic cannot be used to lie. If someone speaks a statement in it, then they are bound afterwards to stick to its letter. Despite stating that elves are fond of half-truths and misdirection in the ancient language, it's never much of an issue. Although it is impossible to lie directly, lies can be told by thinking to yourself that you mean something else to what you are saying. The language also doesn't contain any measures to stop a speaker from being mistaken. Which partially explains how, in Eldest, Eragon is able to compose a completely fictional story in verse that tells of a battlefield romance — because he was thinking of Arya and it felt true. It's similar to what happens when Eragon tries to demonstrate a spell to take a sort of magic photograph by using it on Arya. It was supposed to be a perfect photo, and it's supposed to be really hard to fool the spell, but it... came out different, because of the way Eragon felt about Arya.
• Lensman, by E. E. "Doc" Smith: It is absolutely impossible to make an untrue state telepathically, and the recipient knows this, with absolute certainty. It is possible, however, to make a correct but uninformative statement, such as "I cannot divulge that."
• Marion Zimmer Bradley: In several works, being under the effect of a truthspell makes any language work like this. However, while you can't lie, you certainly can say things that are not true provided that you believe them to be true. It's also specifically noted that in situations where an objective "truth" is ambiguous or nonexistent (for example, most political disputes), truthspells are next to useless.
• Nineteen Eighty-Four: Newspeak was a decidedly dark take on this, in that the goal was to make anything not deemed "truth" by the Party/Big Brother "unsayable". (It's not particularly effective, and the people who developed it had to be disappeared.)
• Probability Space, by Nancy Kress: One species experiences a consensual, shared reality, and can't say things that disagree with the consensus. It's not so much that they can't lie — but they can't lie unless they all believe the lie.
• Sector General: The Kelgian speech and telepathic communication technically qualify. Kelgian languages are perfectly ordinary: the fun part is that their vocal speech is inextricably linked with the involuntary expression of emotions in the movements of their fur. The species developed no concept of lies. Or tact. They're not so hot on bedside manner, either. Telepathic contact is full awareness of the partner's psyche, making lies exceptionally pointless.
• Transpecial: Downplayed. It's possible for a good actor to lie in the ky'iin languages, but it's much harder than it is in any human language because ky'iin communication is so dependent on body language.
• Ursula K. Le Guin:
  • Earthsea: The Old Speech, except to some extent for dragons. The implication of the Earthsea Old Speech is that what is said in it, if it is not already true, becomes true, even if the world has to bend to make it so. The dragons are simply old enough and crafty enough to say false things in ways that won't change reality.
    While the Old Speech binds a man to truth, this is not so with dragons. It is their own language, and they can lie in it, twisting the true words to false ends, catching the unwary hearer in a maze of mirrorwords each of which reflects the truth and none of which leads anywhere.
  • Hainish: Telepathy works this way. The only exception is an alien race named Shing (the aliens in City of Illusions). Apparently, they used that ability to overthrow The Federation and take over... until a thousand or so years later, they were defeated by a race which was capable of detecting their lies.
• West of Eden, by Harry Harrison: The Yilanè. Learning to speak is what makes a Yilanè yilanè (capable of speech), and the thought is what causes the body motions that make up their language unless they are completely still. Humans who learn the language, however, are capable of lying in it.
• Young Wizards: The Speech is the language that defines the fabric of the universe. Even the Lone Power can't lie in it. Although as the Speech can express every concept, it includes both words and grammar which are inaudible, incomprehensible, or guaranteed to be predictably misunderstood by any non-omniscient listener. Beings on the order of the Lone Power have a lot of potential wiggle room, though the book series only exploits this to the extent of allowing the Lone Power conversational freedom in the Speech. When used in spells as the Language of Magic, saying or writing something in the Speech is what makes something true, which makes truthful descriptions of things especially important.

Live-Action TV

• Star Trek: This is played with and ultimately subverted in Star Trek: Deep Space Nine. For a long time, Odo insists that linking with other Changelings "isn't about information exchange." Then they accidentally reveal the identity of a Changeling infiltrator to him, and the entire cast assumes this trope is in effect. It isn't. The Changelings deliberately misled Odo.
• The Twilight Zone (1959) features an example in the episode "Hocus-Pocus and Frisby." The eponymous Frisby constantly tells Blatant Lies about his accomplishments. Such lies range from the acquisition of degrees, attending prominent schools and being able to solve all sorts of mathematical equations. The town is privy to the fact that Frisby is a liar and chide him often about it. Others just marvel that he doesn't strive for any sort of consistency and point out that thus far he'd have to have been alive during three different eras for his tales to be true. An exception comes in the form of a pair of aliens. They believe every one of Frisby's lies. Realizing that he is about to be abducted, he confesses that he's little more than a big mouthed liar. The aliens explain to him that they don't understand the word "lie" and that there isn't a single equivalent in their native language that comes close to describing what that is.

Tabletop Games

• In Nomine: Celestial, the language of Heaven, is impossible to lie in. The demons don't like that, so after the initial fall they create a butchered version, called Dark Celestial, that can be used to lie, mislead, and deceive.
• Numenera has Truth, a scholarly language which the Church says cannot be used to lie. Played with, however, in that not everyone buys this.

Visual Novels

• Umineko: When They Cry:
  • Its most famous example is the red truth. If anything is said in red text, it must be true. If it's not true, it cannot be said in red text. An infallible language of truth sounds like an incredible power in a Mystery Fiction — but it's mostly used by supernatural beings to torment the protagonist with information that doesn't need to be evidenced or explained. In particular, while red truth can't be used to outright lie, it can (and will) be definitely used to mislead and deceive. One major reveal comes when a character tries to say something in red text and fails, much to his own surprise.
  • Less famous is the gold truth. It seems to work exactly the same as the red truth, except with the additional requirement that the speaker "understand the rules".
  • Zigzagged by the purple truth: While most people cannot lie in purple, those who have committed murder can.

Webcomics

• Gene Catlow: The "Sight of the Soul" telepathic communication works like this — since it's direct communication between souls, it doesn't allow for lies, falsehood, or even withholding the truth. However, at least at one point, there existed a type of etherical being with a mind so insane and fractured that it was capable of lying through the Sight of the Soul...
• Outsider: Communication done through sanzai, the telepathy of the Loroi, is immediate, clear, and absolutely honest. Some Loroi prefer to use it exclusively, feeling that spoken and written language are inherently dishonest and untrustworthy. The issue is that sanzai is so absolutely truthful that it will not mask any nuance or feeling, meaning that tact is also impossible. Loroi diplomacy thus relies on specialized diplomats, who speak to one another verbally, while everyone else holds their tongues and keeps their thoughts to themselves... literally. This becomes the main problem with Alex being among the Loroi — since he can only communicate via verbal speech, there are those who do not trust him since he is incapable of doing the perfectly honest telepathic communication.
  Tempo: Captain Jardin, you will find that tact is a foreign concept to many Loroi. Our sanzai communication is direct and truthful... a Loroi conveys what is on her mind without varnishment or consideration... indeed, she feels it is dishonest to do otherwise. It therefore may not surprise you to learn that Loroi history has been one of endless bloodshed. That is why we have developed rules that leave negotiations to those specially trained for the task... and require others to hold their tongues during the process.
• Roommates: Things said in double lined letters (the Voice of Truth & Magic) are true and not even subjectively true as it even makes mistakes and the like impossible. The only one who ever uses it is Jareth the fae roommate, mostly to magically bind himself to his given word. Considering that nobody tends to trust him and he has a Superpowered Evil Side this is a wise precaution. The one time when he was trying but not able to promise something in it that was actually a plot point.
• Tales of the Questor recommends that if you're going to cut a deal with a fae lord, Latin is the language to do it in. Being a dead language, meanings are fixed and specific. There's also a brief mention of floriography, or the Language of the Flowers, which allegedly carries similar weight.

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