Also spelled alternately as geis[[note]]Geas is a Scottish Gaelic word pronounced as "gas" in English, and its plural is Geasa. Geis is the Irish equivalent, is pronounced "gesh", and its plural is geisi.[[/note]], a '''''geas''''' is a form of magical compulsion or curse that originates in {{Celtic mythology}}. Those under a geas are required to fulfill certain conditions or risk suffering a penalty bestowed by fate. If you have more than one such geas placed upon you, and they come into conflict, you're screwed. One of the most famous cases is that of Cuchulainn, who was under numerous geasi, including that he must never eat the meat of a dog, nor refuse food offered by a woman. When an old hag offered him dog meat, he was forced to break one geas or the other, which eventually led to his death.

A geas usually takes the form of either a command or a prohibition: "You shall do this," or "You shall not do this." In practical terms, the geas may be prophetic, bringing about its own fulfillment either through manipulation of cosmic events or by simply instilling into the subject a compulsion which he cannot resist. If the geas can be broken, and is, doing so typically brings about the death of the subject, either directly or by cosmic retribution.

Compare: MagicallyBindingContract (which can have similar effects but is more of a deal rather than a spell or curse), RestrainingBolt (where an object produces similar effects).

NotToBeConfusedWith a ''[[Anime/CodeGeass Geass]]''[[note]]which actually combines a {{Magical Eye|s}} with a CompellingVoice for a CharmPerson effect[[/note]].

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!!Examples:

[[foldercontrol]]

[[folder:Anime]]
* A very interesting case in ''Manga/{{Bleach}}'' is Giriko and his Time Tells No Lies ability. Essentially, it's a contract he invokes on himself or on others, with the spirit of his watch. It can take multiple forms; increased strength, the power to kill by line of sight, and so on. The catch is that no party involved can violate this contract, or they'll be incinerated--the part that makes it a Geas. Wonder what ever happened to [[spoiler:Giriko's eye?]] Sadly, Giriko doesn't see much action.
** In more of a direct mind control example, Zommari the 7th Espada can hit you with a spell from any one of his 50-something eyes, controlling whatever he hits. If he hits your head, he gets your whole body.
* In ''Anime/CodeGeass'' (the title of which this trope inspired), Lelouch has the ability to place a person he makes eye contact with under a geas, as they have to do whatever he tells them to do once Lelouch's "Geass" power kicks in (though it only works once per person). The "Geass" powers in this series often work more like a psychic power or ability (such as making people fall in love or mind reading), which makes the majority of those powers unrelated to this trope. Only Lelouch appears to have the ability to lay a proper geas on people.
** The ExpandedUniverse introduces more characters with the same type of power as Lelouch. Rai, protagonist of the VisualNovel ''Lost Colors'', has a version based off of hearing rather than eye contact, while the NintendoDS RPG's {{Big Bad}}s [[TerminatorTwosome Castor and Pollux]] have "The Bless", which works on the same person more than once.
* In HunterXHunter, it's eventually revealed that Nen can be used this way to provide a power boost, or to become proficient in a Nen style the user isn't normally able to master. For example, Kurapika eventually gains the ability to conjure unbreakable Nen chains, under the condition that if he ever uses them on anyone other than a Phantom Troupe member, it will kill him. He can also imbed nen spikes in people's hearts, which will kill them if they don't follow a command he gives while doing it. [[spoiler: He manages to effectively de-power Chrollo this way, making the nen spike activate if he uses his powers.]]
* In ''Film/HowlsMovingCastle'', the Witch of the Waste puts a spell on Sophie that ages her into an elderly woman; one of the provisions of the curse is that she can't tell anyone about what's happened. When Sophie attempts to do so at one point, her mouth quite literally seals itself shut.
* This also appears in ''SpiritedAway'', another Miyazaki film. The witch Yubaba uses [[MagicallyBindingContract enchanted contracts]] to keep her workers in eternal servitude, but is herself under a geas: if someone demands a job, she must grant their request. Yubaba complains about it--"I can't believe I took that oath, to give a job to anyone who asks..."--but is still bound to the rules. There's nothing stopping her from attempting to distract the person requesting employment, or even outright threatening them, but so long as they keep asking, they'll be hired.
[[/folder]]

[[folder:Comic Books]]
* Dunstan in ''ComicBook/ADistantSoil'' is a FairFolk, and he says he is under a Geas that he can't tell a mortal soul who he really is while he's on mortal soil. However, it applies only to soil, that is to say, the ground - which means when he's on a cruise ship or a spaceship, he can actually mention this without violating it.
[[/folder]]

[[folder:Literature]]
* The otherworld beings from the ''[[TheBartimaeusTrilogy Bartimaeus]]'' books are automatically compelled to obey their orders from magicians by something perhaps like an obsessive compulsive disorder.
** Bartimaeus explains that obeying the orders is necessary, since there was one djinni that refused to kill another djinni it loved. The djinni's repeated refusal to obey the order tore apart his essence and caused him to explode, destroying the prince commanding him and the prince's entire palace. Since then, magicians tend to be more careful about which djinni they summon.
** It's also in the djinn's best interest to just do what the magician commands and get it over with, lest the magician cast the [[AndIMustScream Curse of Indefinite Confinement]] or the [[KillItWithFire Curse of the Shriveling Fire]], which is exactly as unpleasant, painful, and deadly as it sounds.
* Features into the backstory of Diarmuid in ''FateZero''. He was bound to serve Fionn mac Cumhaill, but also had a curse on him that caused women to fall instantly in love with him, which is worse than it sounds: his lord's fiancee, Grainne, succumbed to it and placed him under a geas to make him run away with her. They eventually got married with Fionn's consent, but when Diarmuid was mortally injured and needed Fionn's HealingHands to save his life, Fionn delayed long enough that Diarmuid died. As a Heroic Spirit summoned into the fourth Grail War, Diarmuid's only wish is to be able to make up for the whole mess by serving his Master faithfully. [[spoiler:History repeats for poor Diarmuid. His master Kayneth's wife Sola falls in love with him and tries to use the Command Seals to make him reciprocate. Then he is betrayed by Kayneth and forced to kill himself. Diarmuid [[DyingCurse dies cursing]] everyone involved.]]
** Kiritsugu Emiya convinces Kayneth to bow out of the Grail War by, as part of the terms of their deal, offering to bind himself with a geas that will prevent him from harming Kayneth or Kayneth's fiancee Sola-Ui on penalty of losing his magecraft. When Kayneth takes the deal, Kiritsugu does indeed geas himself... [[spoiler:but the geas [[ExactWords doesn't say anything]] about letting someone ''else'' harm Kayneth and Sola-Ui, who are promptly gunned down by Kiritsugu's associate.]]
* Not stated to be such, but this is more or less the case with the Witch King of Angmar in ''Literature/TheLordOfTheRings''. It was prophesied that he shall not fall by the hand of Man, and in the end he is taken down by a hobbit and a woman.
* ''Franchise/{{Halo}}'':
** The novel ''[[Literature/HaloCryptum Cryptum]]'' has a technological variant that can be imposed by Forerunners on other species (the term ''geas'' being the closest word in human vocabulary to describe the condition). The Librarian imposed one on the ''entire human race'' to make sure her husband was found and awakened at the proper time, the compulsion being that the humans present at his location would unknowingly sing a song that contained the codes needed to allow his reviver passage. Some Forerunners believe that ''their'' forerunners, the Precursors, had imposed a geas on Forerunners as well.
** ''Literature/HaloPrimordium'' takes it farther. One character has to deal with rejecting a geas that forces her to go to the dreaded Palace of Pain, which would ensure her and her companions' deaths. Turns out, gei are subject to change via nearby beacons, and the ones on that particular Halo have been hijacked by the less favorable side in the EnemyCivilWar.
** Another aspect of the human geas is that the memories, and eventually entire personalities, of ancient humans are carried by many humans, "germinating and blossoming" as they do/see/hear/etc. something that triggers it. It gets to the point where the "old spirits" can [[GrandTheftMe hijack their host's body to communicate.]] None of this is considered a pleasant experience, to say the least.
* Used in ''Literature/TheLaundrySeries'' by Charles Stross, which is essentially MI6 meets Creator/HPLovecraft. Figures prominently into the second book, ''The Jennifer Morgue'' where the protagonist is put under a reality-warping geas that essentially transforms him into a [[Film/JamesBond James Bond-esque]] hero (Turns out [[spoiler:this is exactly what the BigBad wants, as he plans on dismissing the geas right before the protagonist is about to win, at which point RealityEnsues and he can kill the protagonist easily. Fortunately, it turns out the protagonist was actually playing the role of ''Bond girl'']]).
* Creator/JoWalton's ''Tanagiri'' novels feature several geases, courtesy of the Irish FantasyCounterpartCulture.
* In the ''TheWitchesOfEileanan'' series several people are put under Geasa. Most of them are, or given them by, Khan'cobans (Like Inuit elves with ram's horns), though there isn't a spell involved, it's mostly just a task or obligation that is given social significance if one were to break it or accomplish it. It's less a spell and more a binding of honor.
* In the ''[[Literature/CassandraPalmer Cassandra Palmer]]'' series, the Geis is like a love spell, a magical claim that warns off any would-be suitors and compels the the two people to be attracted to each other.
* In ''Literature/DeepSecret'', Rupert defeats one of the villains by laying a geas on him such that if he tries to use magic again he'll die.
* ''Literature/{{Discworld}}'':
** Parodied in ''Discworld/{{Sourcery}}'', where everyone else thinks the guy under the geas is talking about geese, leading to much confusion. [[spoiler:And then it turns out a geas really is a kind of bird.]]
** Parodied again in ''Discworld/AHatFullOfSky'' and ''Discworld/{{Wintersmith}}'', where Rob Anybody is put under a geas by his wife, Jeannie, to protect Tiffany Aching. It becomes a RunningGag that Daft Wullie keeps thinking Rob means an actual goose.
--> Rob: 'Tis a heavy thing, tae be under a geas.\\
Daft Wullie: Well, they're big birds.
* In Creator/ClarkAshtonSmith's "The Seven Geases", the protagonist is put under of a sequence of, well, seven geases. Which comes off as mind control.
* In the ''Literature/LordDarcy'' story "A Case of Identity", Lord Seiger is by nature a conscienceless psychopath; a very extensive geas has been laid upon him never to hurt anyone save at the direct order of his superior in the King's Service. He shows no signs of resenting this, but he clearly enjoys those moments when he's let off the leash.
* Fairies in ''Literature/ArtemisFowl'' are under a geas set by their first king, Frond, to never enter a human's dwelling without permission. The idea was that fairies were mischievous and would abuse the humans. Over time, the magic has faded a little, but is still binding. [[spoiler:At least until a certain imp warlock tears it down singlehanded for them between the fifth and sixth books, anyway.]]
* In the ''[[HeraldsOfValdemar Vows & Honor]]'' stories, the sorceress Kethry's magical sword, Need, compels her to aid women in trouble, beginning with an insistent mental tugging that escalates to excruciating pain if Kethry fails to respond promptly. As noble as the intent of the geas is, in practice Kethry and her partner Tarma mostly find it enormously inconvenient given that it makes no distinctions regarding context and has almost no sense of proportion, forcing the pair to stick their noses into everything from cases of basic domestic violence all the way up to demon-worshipping cults - whether their interference is appreciated by the victims or not. It also gives them a reputation as heroes crusading selflessly on behalf of women everywhere, greatly complicating their efforts to actually make a living as freelance mercenaries since people assume they're more interested in just causes than in getting paid.
** Need's geas also prevents its bearer from ever using it to harm a woman - again with no sense of context or proportion. Kethry's granddaughter Kerowyn, who mostly manages to avoid being yanked around by the sword the way her grandmother was, nearly gets killed when she runs up against an enemy priestess in the midst of a battle and Need abruptly paralyzes her in place rather than allow her to defend herself.
* In the ''InheritanceCycle'', a character who swears an oath in the Ancient Language is incapable of breaking it. (Though they only have to obey the letter, [[LoopholeAbuse not the spirit]].) What is more, a person can be compelled to swear such an oath by someone who knows their true name. There is an out however-if who they are changes so much that their True Name in the Ancient Language changes all oaths they've sworn up to that point are null-and-void.
* The Faerie Queens are known to put these on people in ''Literature/TheDresdenFiles''. Titania in particular put a geas on the Summer Lady, Lily, and Summer Knight, Fix, both friends of Harry's, such that they could not offer information or help to him, despite them ''also'' owing Harry a favor for past deeds. They manage to get around it, either by Harry transferring the favor (they can't help him, but they can help the person with him), or by the Lady and Knight getting creative (while Fix can't ''warn'' Harry about Summer's forces, he can make a show of ''threatening'' Harry, which still lets him know they're on the prowl).
* These are called "Unbreakable Vows" in ''Literature/HarryPotterAndTheHalfBloodPrince'', wherein [[TheMole Severus]] [[ReverseMole Snape]] agrees to let Narcissa Malfoy place this spell on him as an act of good faith. It's explained that breaking the vow is fatal, but this never actually happens in the story so details are vague.
* In ForgottenRealms during and before the Time of Troubles, Kelemvor and his family were under such a curse. Originally the curse condemned Kelemvor's family to never accept payment for helpful deeds. In Kelemvor's case, the curse flipped so that he can never do anything for anybody without accepting a fair compensation for it.
* In ''[[Literature/ZeusIsDead Zeus Is Dead: A Monstrously Inconvenient Adventure]]'', any oath sworn by the River Styx (figuratively or literally) is binding, even for a god. Hermes even wiretaps the Styx so he can spy on anyone who utters such an oath in secret or in unthinking rage, and uses this to [[spoiler: blackmail Zeus]].
[[/folder]]

[[folder:Mythology and Religion]]
* This is all over the place in IrishMythology:
** Diarmuid O'Duibhne was "under geis" not to hunt the Boar of Ben Bulben. But Finn [=MacCool=] tricked him into participating in a hunt that tracked the very same boar, and the boar killed Diarmuid.
** Cuchulainn was under geasa never to refuse an offer of food, and never to eat dog meat. Of course, eventually his enemies [[MortonsFork offered him dog meat]]. He ate, and was killed soon afterwards.
** High King Conaire Mór was under a whole host of geasa. Eventually events conspired to make him break all his geasa in a single day. The same night, he was killed by sea-raiders.
** ''Literature/TheChildrenOfTuireann'': Lugh of the Long Hand was under geis never to refuse a second request. The sons of Tuireann exploit this by asking him to lend them the horse of Manannan, which he refuses, then ask him for the boat of Manannan, which is what they actually want.
* Samson in the Literature/BookOfJudges of the [[Literature/TheBible Old Testament]] was bound to the terms of the [[http://en.wikipedia.org/wiki/Nazirite Nazirite vow]] (he was not allowed to partake of wine or anything else made from grapes, nor cut his hair) due to a promise made by his mother; breaking the vow would result in the loss of the super strength God had blessed him with. Sure enough, when Delilah, who had been hired by the Philistines to trick him into revealing his secret weakness, shaved him bald, he was left defenseless and promptly taken captive. [[spoiler:It turned out the effect was as temporary as his baldness.]] By that point Samson had already broken the other terms of the Nazirite vow. The hair-cutting was just the last straw.
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[[folder:Tabletop Games]]
* As befits the genre, the 3rd Edition {{GURPS}} sourcebook Celtic Myth has rules for imposing geasa on characters.
* There is a spell called geas in ''DungeonsAndDragons'' that forces the character to fulfill the terms. Clerics call the same spell "Quest", and also have a "Mark of Justice" that places a curse on a character who breaks the conditions of the Mark.
** The powers of Wu Jen and characters under the various Vows of the Book of Exalted Deeds have specific behaviors or tasks they must perform to maintain their powers.
* Geasa were used in 3rd edition ''TabletopGame/{{Shadowrun}}'' to recover points of magic that had been lost by shaman/magicians/adepts. Your character had to accept some sort of condition to recover a point of magic. Usually anything the GM wanted/was willing to allow but classic ones were some sort of talisman that you had to keep on your person, having to fast on a regular basis, spend time in meditation, or only use magic in certain circumstances. Breaking the geas reduced your magic back to it's normal level.
* In ''TabletopGame/MageTheAwakening'', geasa can be inflicted by mages who have gained Mastery of the Fate Arcanum. Working against the terms of a geas (or even failing to actively do something required by the geas) inflicts a very debilitating curse. A geas (and the curse for breaking it) can be made hereditary, affecting the subject's descendants as well.
* SeventhSea has the geas, a special ability that can be purchased at character creation. As long as you have the geas, it gives you an extra experience point each session, but if you fail it's condition you lose the geas forever.
* This is the power the demonic lilim have in ''TabletopGame/InNomine''. They can look into a person's eyes and discover their true desires (ranging in intensity from 'needs a light for their cigarette' to 'needs to get a million dollars'). If they then fulfill one of them (or more) for the person, they can (attempt to) attach a geas to the person to do something in return. They're limited only by the scale of the desire (an easy-to-fulfill desire would grant a geas that only lasts an hour or so) and the target's ability to resist the compulsion. The dangerous part is the target is usually ''not aware'' the lilim is doing this, and doesn't have to agree to a DealWithTheDevil for the lilim to get the geas. The only real defense is a combination of never looking a lilim in the eyes, and never accepting anything they offer, ever.
* In ''{{Exalted}}'', [[AbusivePrecursors the Primiodals]] placed one on their creations, [[ServantRace the gods]]. It forbad them from directly attacking any Primoldial (except in self defence or on the order of [[KingOfAllCosmos Theion]]). The gods got around this by giving power to mortals whose free will means that their actions are seen as sperate from the gods. They were then free to help these humans as long as they themselves didn't attack a Primoldial; anything else was fair game.
[[/folder]]

[[folder:Video Games]]
* Lancer in ''VisualNovel/FateStayNight'', whose true identity is Cuchulainn himself, has a geas that if a man from Ulster uses Caladbolg against him, he must lose the fight, [[spoiler:but it never happens]]. The sequel, ''VisualNovel/FateHollowAtaraxia'' has Shirou play a trick on him involving his original two geas, though they are never stated outright: Three female friends of his from school offer Lancer a hot dog, an offer he can't refuse and (were it actually dog meat) something that could potentially kill him. This is actually related to how he originally died.
** At one point in Unlimited Blade Works Rin threatens to use Geas on Shirou.
** In ''LightNovel/FateZero'', Kiritsugu uses one to eliminate Lord El-Melloi as a Master: he kidnaps El-Melloi's wife, and threatens to kill her, unless El-Melloi orders his Servant to commit suicide, removing himself from the Holy Grail War, in which case Kiritsugu will geas himself into never harming El-Melloi or his wife. El-Melloi accepts (as a magus himself, he can see that the self-geas scroll Kiritsugu is holding is genuine), and [[spoiler:Kiritsugu's partner immediately kills both El-Melloi and his wife... after all, ''she'' wasn't under a geas to do them no harm.]]
* In ''VideoGame/NeverwinterNights: Hordes of the Underdark'', as a way of avoiding the ButThouMust faux-choice, the player character gets a geas to kill the evil sorceress Valsharess.
* [[spoiler:Yoshimo]] in ''BaldursGateII'' is under a geas to betray you at a certain point of the plot.
* Referenced in ''VideoGame/WildARMs3'' - Janus, [[spoiler:after acquiring his demon form]] is bound to follow the Prophets' instructions, under pain of being blown apart by the remote bomb called ''Geas''.
* In ''QuestForGloryIV'', the Hero is placed under a geas by [[spoiler: Katrina]], giving him three days to recover the rituals needed to free the [[SealedEvilInACan the Dark One]]. The geas is removed once he returns successfully with them.
%%* The entire plot of FinalFantasyXIII.
* Continuing from the ''Franchise/{{Halo}}'' plot thread mentioned in the "Literature" section, ''VideoGame/{{Halo 4}}'' has [[spoiler:the Librarian imprint mentioning to the Chief that a good part of the UNSC's advancement, including Cortana's design and the Chief himself, has to do with the geas she implanted into humanity over 100,000 years ago]].
[[/folder]]

[[folder:Web Comics]]
* In ''Webcomic/TheOrderOfTheStick'', Belkar is put under a spell which prevents him from dealing lethal damage (a D&D rules term, basically meaning any damage that isn't the kind you'd use in a sport fight -- and Belkar never bothers with sublethal damage when he can get away with lethal) to any living thing within the bounds of a settlement. He also cannot travel more than a mile from Roy, on pain of suffering from a sickening curse. The curse is eventually [[spoiler:invoked when Belkar stabs the Oracle, [[CrazyPrepared who had established a village around his tower for exactly that purpose]], and then removed by a cleric who needed Belkar to protect him from an invading horde of goons]].
* One of the powers that Acanthus Mages such as Amical or Tyler have in ''Webcomic/{{Morphe}}''.
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[[folder:Web Original]]
* In ''Roleplay/TheGamersAlliance'', the archdemon [[FourStarBadass Malphas]] ends up under a geas when he kisses fellow archdemon [[TheVamp Nina Heeate's]] enchanted ring, and the geas forces him to serve Nina's every whim. It turns out that Nina was using magic and her female physique to mess with Malphas's mind, which confused Malphas enough to make the geas take effect. Nina doesn't keep Malphas on a tight leash, however, and instead lets him do what he wishes as long as he doesn't stand in her [[TheLegionsOfHell horde's]] way. The geas also requires Malphas to keep his mouth shut about the whole endeavour, further ensuring that Nina's part in the whole mess stays out of the limelight.
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[[folder:Western Animation]]
* An unusual example in ''WesternAnimation/{{Gargoyles}}''; Demona once placed Goliath under a spell compelling him to obey the spoken orders of "whoever held the spell." Brooklyn seized the book from her, found the page with the compulsion spell, and tore it out before Demona could reclaim it, so that Goliath would follow Brooklyn's orders rather than Demona's. After Brooklyn and Goliath defeated Demona, Eliza found a way around the spell: holding the page, she commanded Goliath to act as he would if he were ''not'' under a spell from then onward. So essentially, for the rest of the show's run, Goliath was under a geas--to be himself.
* CandleJack has the power to kidnap children--but only if they say his name out loud. At one point in his [[{{Freakazoid}} debut episode]], he's in a bunk at a camp filled with kids, but is only able to speak to and interact with the ones who have spoken his name.
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