Equivalent Exchange

You can't make a metal weapon without a little metal floor.

"Humankind cannot gain anything without first giving something in return. To obtain, something of equal value must be lost. That is alchemy's first law of Equivalent Exchange. In those days, we really believed that to be the world's one, and only truth."

Power has consistency.

Power serves a function.

Power always comes with a price.

To acquire the ability to perform something, induce motion, bring change — to bring something into existence, grant a wish, heal a loved one, or even bring someone back to life — someone must give up another thing of equal value. This trope has a simple dramatic purpose: it prevents the pitfalls of a typical Story-Breaker Power by adding laws and the elements of choice and sacrifice.

Would you give up the gifts, loves, and life you possess to get what you desire? Beware the allure of Desire, however, because it doesn't always work in your favorpeople may not truly understand the full effects of what they desire, and the gift itself can end up becoming its own cost. King Midas thought of the Golden Touch as a great boon, but it ultimately robbed him of his greatest treasure: his daughter.

This trope has a layer of truth to it, given the First Law of Thermodynamics. Building in the cost to the boon usually results in a Fantastic Fragility.

The principle of Equivalent Exchange typically says the object or goal a person will trade for must have equal value to what the person trades with. Who and what determines this "equivalency" varies from story to story:
  • Does the Exchange measure emotional value, monetary value, or both? (Someone might find a penny handed down from father to son as worthless as if he found it on the ground, even though the father and son would consider it emotionally valuable.)
  • If a wizard ritually sacrifices a cat to get some magical mojo, what determines how much power the wizard receives: the value of the cat's life to the wizard, the value of the cat's life to the cat, or the value of the cat's life to a deity?
  • In Real Life, the First Law of Thermodynamics follows this dilemma, since it only measures mass and quantitative scale. An action only produces an equal and opposite reaction; a sacrificed cat will only release the energy of a cat, burning a human will work nearly the same as burning a human-sized carbon statue, and deconstructing an atomic nucleus to perform alchemical transmutation requires a nuclear reactor. In fiction, we can assume that souls become necessary to harness cosmic-scale energy or contain magical properties that don't follow the laws of thermodynamics (hence the necessity for Human Sacrifice as a viable form of unobtainium).

Compare this trope to Balancing Death's Books and Mutual Disadvantage. The tropes known as Call It Karma and The Golden Rule attempt to apply this law of physics into ethics and morality.

Examples of this trope include:

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    Anime and Manga 
  • Fullmetal Alchemist:
    • This franchise serves as the Trope Namer for anime and manga, as it makes a big deal out of the principle in its plot. In regards to alchemical transmutation, the law basically works like the Newtonian law of conservation of matter: matter and energy cannot be created or destroyed in a reaction. (It also helps that Isaac Newton, one of the Trope Codifiers in Real Life physics, considered himself an alchemist and formulated the basic principles of this trope.) The energy used to perform Amestrian alchemy comes from either tectonic shifts (the manga and Brotherhood anime) or the souls of our world's deceased (the 2003 anime version). Xingese alkahestry relies on reading and directing the Earth's natural energy through its mantle.
    • Ed gets a wonderful chance to explain the principle at the start of the story. While talking with a religious zealot who believes her leader can resurrect her late boyfriend, Ed lists all the raw materials that exist in the human body — noting that anyone could buy a "body" with pocket change — before he explains that even with the materials gathered together, someone still can't make a human life because the exchange still doesn't have equivalency. He comes to a simple conclusion: you need a soul to complete the transmutation, and the right one at that. First, one can ask just how he figured this out. We soon learn the gory details. Second, if you don't care about what soul you want, you can make a massive army of homunculi...
    • The legend of the Philosopher's Stone says it enables an alchemist to perform any type of alchemy without cost (including human transmutation). The Elrics learn that even the Stone has its own form of Equivalent Exchange: to make one, someone has to sacrifice a hell of a lot of people first. A massive human transmutation collects the souls of those sacrificed to make it and turns the stone into a massive portable power supply — one which lets its user create matter from the massive energy stored inside it, even if the energy seems to come from nothing.
    • One of the central tenets of the series — and a sign of the development of Alphonse and Edward as people — shows that no matter how much they try and apply the rule of Equivalent Exchange to their lives, they always find something missing. At the end of the manga and Brotherhood, they vow to give eleven back to every person or thing they take ten from, thus making the world richer.
    • Alphonse makes a crucial logical conclusion about the principle near the very end of the series. If A equals the cost of B, then the reverse should hold true: you can exchange B back for A. Once he figures it out, Al gives his soul back to Truth so Ed can have his right arm again and defeat Father once and for all. Ed does not take this development well. After it happens, however, Edward is able to top Alphonse by offering up the very truth of alchemy he received when they tried to bring their mother back as payment for Al's return. It's not quite an even equation, however as Ed ends up loosing not only his circle-free alchemy but his entire ability to perform alchemy, though it's later revealed he gave up his alchemy for his brother's soul, either way it's such a clever exchange that even Truth itself is floored.
    • Hoenheim likewise believes the theory has a flaw only in the opposite direction: "Even if I lived forever, I'd never give enough to have earned my sons/family."
    • The 2003 anime demonstrates why one should not use this trope as a philosophy. Real Life is too complicated for such a neat transaction. There are numerous factors involved, and randomness (i.e. Chaos Theory) can drive the result to positive or negative reactions. Dante uses this in a Breaking Speech to Ed.
    • The adherence to this trope makes filler episodes more obvious as they tend to avert it, such as an alchemist turning a small woodcarving tool into a full sized sword.
  • Ah! My Goddess has the Law of Conservation of Happiness.
    • Eventually, granting too many wishes within a short period of time means that someone ends up suffering some form of bad luck.
    • This is also how wishes granted by demons run. They usually come with a myriad of attached strings that cause grief and misfortune to the person making the wish.
  • In Bleach, a Hollow can give up his or her Healing Factor in exchange for extra strength.
  • A Certain Magical Index:
    • Once one becomes an esper, they can never use magic, and vice-versa, without suffering extreme damage to their bodies.
    • To gain the incredible powers of God's Right Seat, a magician must give up his or her ability to use normal spells. Acqua of the Back gets around this because his Divine Mother's Mercy removes limitations and secondary conditions. Fiamma of the Right gets around this by brainwashing Index to do the spells for him.
  • C.M.B. has the rather interesting case in which Shinya requires a price for solving a mystery; luckily he's very easily bought off so long as it is interesting.
  • Code:Breaker: It turns out that Ogami's powers come from a Deal with the Devil: for every upgrade he gets, he loses one of his senses. He's already lost his sense of taste, but "fortunately" Code: Emperor has chosen to take his newly acquired sound powers rather than his hearing... although there's still five upgrades to go...
  • This trope gets applied vaguely in Death Note: though no tangible price or punishment exists for a human who uses the Death Note (according to Ryuk), those who use it always end up miserable. Light vows at the beginning of the story to break this pattern; by the end, he loses everybody who ever cared about him in any way, then dies in a bloody heap as he begs Ryuk to spare his life. Everyone else who writes in the Death Note also ends up either miserable or dead.
  • Dragon Ball GT reveals that the Dragon Balls accumulate energy based off of the wishes made; well-intentioned wishes cause the balls to accumulate negative energy while selfish ones build up positive energy, and over time the energy levels normalize. However, because of all the wishes made over the course of the franchise, the balls built up too much negative energy and cracked, releasing seven evil Dragons. On the other hand, the Four-Star Dragon was more of a Noble Demon because the wish that spawned himnote  was selfish, meaning there was still some positive energy within the four-star ball.
  • Fate/stay night:
    • As with the rest of its multiverse, the series contains this — energy must be taken from somewhere before it runs through the Magic Circuit, though in most cases, Prana is either generated by the magus (Od) or taken from the environment (Mana). Rin can launch A-rank attacks in seconds because she taps directly into her jewels (where she has been saving Prana for ten years) instead of gathering it slowly for a minute or three.
    • This is a plot point for all three scenarios in the game, as protagonist Emiya Shiro has to fight, but the only magecraft he is skilled at is far beyond his capabilities. Whenever he uses it excessively, blood loss (and death) is inevitable.
    • One exception is Rin's Jewel Sword Zelretch, which lets her use strong attacks indefinitely by absorbing mana from alternate realities. The sword is explicitly made with "True Magic", which breaks the usual rules of Equivalent Exchange, and which only about five people in the world are capable of using.
  • Although it's not too much of a regular magic as it's more of a one-use, people at Hell Girl can send one person they dislike immediately to Hell by contracting Enma Ai. The price is their own soul going to Hell when they die. That's the reason why many people hesitate in first place: going to Hell is a really high price. Out of spite, they send their victims into Hell anyways. The lesson is to learn to control your emotions and hatred? or You Can't Fight Fate? Who knows?
  • Hibiki no Mahou. If you want to use magic properly, you need to sacrifice an aspect of your being, like ability to dream, age, or memory; no wonder why magic practitioners are declining.
  • Hunter × Hunter:
    • Nen abilities. It's a special ability invented by a user by using Nen, and it can range from simple super strength to shrinking cloths to memory reading to vacuum cleaners and books and bank accounts. Each of these abilities have unique powers that the user make up in his mind during conception. The more powerful you are, the more powerful ability you can create. The thing is, the more powerful the ability is, the more restrictions the user must needs impose on it as well. Examples are:
    • Kuroro's Skill Hunter ability allows him to steal the Nen abilities of others and record them into his book, thus robbing them of that ability forever. It's an awesome move, but there are many rules. First, he must see the ability in action personally. Second, he has to ask the target about the ability and be answered. Third, the victim's hand must touch the palm print of the cover of the book. Lastly, all of the above must be done within only one hour. Otherwise, it's back to step one. Now, if you get the ability into the book, it's all well and good. But another rule is that if the original user dies, the ability vanishes from the book forever, and he can't use it anymore.
      • There is an exception to said rule though. Since Nen itself isn't a well known subject matter, there are literally hundreds of unknown variables that can improve or decrease Nen effectiveness. One variable in particular is that a person's Nen can actually grow even more STRONGER in death. The best example of this is when Neferpitou's Self Manipulation Puppet Nen activated on its own and allowed her to attack at an even faster and unpredictable rate then ever before, even though by that point she was already dead from being punched to death by Gon. If this post-death phenomenon happens to someone that Kuroro has stolen their Nen from then not only does the skill stay in the book, but it even becomes more effective and powerful then ever!
    • Kurapika's Chain Jail is a long chain used to wrap around the opponent's body. Not only that, it shuts down their aura, and prevents them from using Nen abilities. However, because it is an overpowered ability, he had to impose the condition that he could only use it on a member of the Genei Ryodan. If he uses it on a person who is not a member of the group, he dies. This causes problems because there are only at most thirteen members of the Genei Ryodan at any given time.
    • Alluka Zaoldyk's wish-granting powers are an especially sadistic take on this since the price of the wish is passed on to someone else instead of the person making the wish. If that person can't fulfill Alluka's requests (and the requests can be as severe as ripping out your own brain if the preceding wish was significant enough), then that person and that person's loved one die. Depending on the severity of the wish, everyone that person has ever met is also at risk of dying instantly. It is later revealed that this only applies to wholly selfish wishes. A wish to heal someone for example can be granted for free.
    • Kaito deliberately made his Nen ability annoying and inconvenient (the slot machine clown won't shut up, the weapon it summons is random, the scythe form can only be used for one technique, and the weapon can't be dismissed until it's used, etc.) to increase its power. He still complains about it.
    • Franklin of the Genei Ryodan can fire very powerful Nen bullets from his fingertips. He made them that powerful by mutilating his own fingers.
    • Shizuku, also a member of the Genei Ryodan, summons a vacuum cleaner that can suck up anything as long as it's not something Shizuku considers to be alive, and only the last object sucked up can be recovered.
    • In chapter 305-307, Gon gives in to his rage and despair and "uses everything" to defeat an incredibly powerful enemy. He basically sacrifices his future to rapidly age himself into an adult. This gave him the power to crush his foe, but it left him on the brink of death. The Nen curse he placed on himself to obtain that brief surge of power was too strong for the Hunter Organization's Nen Exorcist to even consider removing. It took the aforementioned Alluka's power to remove it.
  • The spiky rokakaka fruits that appears in JoJo's Bizarre Adventure Part 8 are basically an Healing Potion. However...for whatever ailment the fruits cure, they require the subject to "trade" something in return. An elderly man regrows one of his legs at the cost of his eyesight.
  • Naruto: For the most part, if you want to bring someone back from the dead, someone else is going to have to die.
    • The Edo Tensei jutsu requires a Human Sacrifice, and only brings the dead back as zombies.
    • Suna's puppeteer clan have a technique that can revive the recently dead (they developed it to breathe true life into their puppets), but doing so costs the caster their life. Gaara is brought back in this way.
    • This is also how Nagato/Pein dies, a man with the bloodline trait giving him magic eyes equal to the strongest ninja ever to exist, it goes to show how powerful he was that he killed thousands and was able to revive them all to the last one before succumbing to the jutsu.
  • While most of the magic on Ojamajo Doremi doesn't have this in place (at least for full-fledged witches and wizards), the forbidden types of magic (Healing, Mind Control, Raising the Dead) all have this as part of why they are forbidden.
  • One of the more awesome aspects of the Op-Op Fruit, Trafalgar Law's Devil Fruit in One Piece, is that the user can grant someone eternal youth. The catch is that the user must sacrifice their own life to do it.
  • Puella Magi Madoka Magica:
    • It is an in-universe theory that the wishes that get fulfilled in exchange for the girls becoming magical girls are guaranteed to cause an amount of despair equal to the hope they generate. A Selfless Wish for the sake of others would eventually lead to the wisher suffering in turn, unable to enjoy the very wish she herself generated, especially when the Magical Girl persona is forcing the wisher into isolation. "Hope and despair balance out to zero." Although this is never treated as anything but a hypothesis, and more likely to be based on one of the themes of Goethe's Faust: As part of the Deal with the Devil, should the Faust ever reach the highest state of happiness possible for humanity, he will immediately die and be consigned to hell.
    • Defying this trope is the true goal of the Incubators. Magic generated through emotion breaks Newtonian Equivalent Exchange, and the Incubators are using the additional energy to offset the death of the universe. However, for the Magical Girls themselves, the Equivalent Exchange of hope and despair still remains to screw them over.
  • The multiverse of Tsubasa Reservoir Chronicle and xxxHOLiC:
    • The price for wishes granted by Yuuko works this way. Some characters are much more wary of the possible implications of this than others. In particular, Kurogane and Doumeki will only ask for Yuuko's help if it is flat-out impossible for them to solve the problem under their own power. This is prudent, as false-hearted or impulsive wishes usually result in nasty karmic payback. Yuuko also has rules about not dealing in wishes of value equal to a human life, as that would implicate the wish-granter in murder.
    • For the record, Yuuko accepts items or intangibilities that have both real and emotional power, which include both living and non-living: Kurogane's sword is both a precious reminder of his family and a powerful weapon; Fai's tattoo is imbued with powerful magic for his own safety; and Syaoran and Sakura pay by giving up a portion of Sakura's memories - those which contain Syaoran. This means their previous relationship is sacrificed forever. Syaoran has been edited out of the memories the feathers contain. For example, Sakura can remember the events of her last birthday party, but one seat is mysteriously empty, and there's an odd pause in the dialogue whenever someone would have otherwise said Syaoran's name. One time Sakura almost manages to put two and two together, but passes out and loses all memory of her deduction due to this price. It's not flat-out impossible for Sakura and Syaoran to have a relationship after paying the price, but it has to be rebuilt from the ground up.
    • Interestingly, you apparently don't need someone to trade with, just need to have a payment to be given in exchange for a desired end. Clow and Yuko gained entry into the cycle of reincarnation for the clones by giving their lives up to... nothing in particular. Watanuki and Syaoran Jr. escape from a pocket dimension in exchange for the inability to leave The Shop and the inability to remain in one world for very long, respectively, again not actually selling it to anyone in particular.
    • It eventually is revealed that whoever is the owner of the Wish Shop is essentially contractually bound to live by this principle at all times, lest they risk getting magically induced injuries from the shop itself as compensation. It's sobering when you realize that this is the primary reason for why Yuuko has made payment requests for the slightest things, even to friends, because no matter how much power she has, she can't give anyone anything without needing something from them in return... Except for feelings, which are explained to be the only things people can give without a price.
  • Witch Hunter Robin had a doctor whose special witch power allowed him to transfer Life Energy from one person to another; he used his power to heal patients — and took the necessary energy from mob bosses. He ultimately decides to save his human partner by sacrificing his own life. Since the witch hunters kill most of the witches they go up against—and those captured alive end up taken into custody for experimentation—he made the right decision. (And the STN-J hunts all witches regardless of whether the witches can morally justify the use of their powers, so this less-defensible hunt pokes some critical holes in Robin's philosophies.)
  • YuYu Hakusho had a Magic Mirror that could grant it's user one wish in exchange for their life. Kurama intended to use it to save his human mother's life at the cost of his own, but Yusuke stepped in and offered his life instead so Kurama's mother wouldn't have to mourn him. Subverted at the end when the mirror spares both due to Yusuke's selflessness.

    Comic Books 
  • In the British The Transformers comic, if someone travels back in time, someone from the destination period vanishes into Limbo while the traveler is there. Attempts to avoid this will eventually get you eaten by a time warp.
  • In the Pre-Crisis DCU, the Guardians of the Universe purged themselves of evil, only to find that the evil had to go somewhere. They sealed it in the same universe where they sent most of the magic to ensure that the Golden Age Green Lantern would be around to deal with it.
  • Storm's weather-controlling powers in the X-Men comics are given a similar limit to explain why she can't turn the world into a paradise, or at least bring relief to disaster-stricken areas. The first time she tried that, she successfully ended the drought in her village - only to discover that, since the moisture she'd drawn upon had to come from somewhere, she'd caused even worse droughts to strike the rest of the world.
  • In PS238 there's Toby Marlocke, who has Reality Warper powers with a catch. Every time he tries to do something more complicated than self-levitation, there is an equivalent unintended result. This can range from funny (absorbing the kinetic energy of a super-powered soccer kick caused tulips to sprout at the goal line) to rather disturbing (creating a superhero persona for himself caused the creation of a new supervillain). Part of the reason for this is that he got his powers in the first place as part of a deal between the cosmic forces of Order and Chaos, and both sides insisted that the balance should be preserved...

    Fan Works 
  • In Harry Potter and the Methods of Rationality, Professor Quirrel claims all magic works like this. "Normal" magic works by sacrificing the constantly-regenerating pool of magical energy all wizards and witches have. To contrast, the price of any Dark magic is permanent, and dearer than the price of "normal" magic.
  • From Comic 41 of Kill la Kill AU, we have Ryuuko's wish to be the sick one instead of her then ill sister Satsuki, which, as explained here, traded her health in exchange for Satsuki's poor health, making her the sick one instead. As Rei did point out, said wish would make her suffer and could probably take her life through illness, something that circumstances otherwise would do with Satsuki.
  • Harry in The Next Great Adventure admits to one of his companions that the reason only he can use a ritual that brings the Forsaken back to life is because "all the years [they] now have to live have to come from somewhere."
  • Xanna and Naruto are willing to give a follower who's proven themselves eternal youth in The (Questionable) Burdens of Leadership of a Troll Emperor. However, they will also become incapable of having children (to avoid overly taxing the Empire's resources with a growing immortal population). As a result, very few accept it unless, like Setsuna, they've committed themselves to a cause and aren't interested in having a family.
  • Likewise in Eroninja, the eternal youth granted to Naruto's lovers only lasts until they have a child. As Naruto can't have children, they'd have to break off their relationship with him and have a child with someone else, losing their immortality in the process. Naruto on the other hand will live forever as the Kyuubi doesn't want her beloved dying and leaving her alone. The Kyuubi is willing to offer eternal youth to the immediate family of Naruto's lovers at the same cost of never having children. Like the above example, this is to prevent overly taxing the world's resources and to prevent resentment among the mortals towards immortals.
  • In the Pony POV Series:
    • Most ponies need to use their mana for spells, regardless of species. Changelings have this to a bigger extreme: they will die if they run out of love energy, but need it for their abilities.
    • The Alicorns are unique in that they have The Power of Creation and while they still require mana for spells, can literally create new matter, which is how they regenerate. Draconequi, in contrast, require matter to transmute into new things (this includes Discord), but can violate the other side by being able to destroy matter and energy completely.
  • In Memento Vivere, a Final Fantasy X fanfiction, Rikku’s dilemma is deciding whether to pursue a romance with Auron at the risk of bringing Sin back.
  • A ritual used by Sirius's daughter in Dodging Prison and Stealing Witches gives a witch the physical strength she would have had as a man and the same potential strength as a man. The drawback is being unable to taste sweetness. She notes that ever since she used the ritual, cake tastes like eating a sponge.
    • A ritual spoken of only as the Unforgivable Ritualnote  gives a massive power boost but has two distinct costs. First, it requires completely dedicating yourself to a cause of your choosing and you become somewhat obsessed with it. Second, and more dire, the ritual kills your true love, even if you haven't met them yet. Both Dumbledore and Voldemort are revealed to have used said ritual.

    Films — Animated 
  • Rumplestiltskin's "Ogre for a Day" contract in Shrek Forever After works by taking a day from the signer's past (in this case, Shrek). The day Rumple chose was the day of Shrek's birth, so once the day is over, so is he.
  • In Barbie in a Mermaid Tale 2, in order to exit one of Eris's inescapable whirlpools, someone else has to enter it.

    Films — Live-Action 
  • In Conan the Barbarian (1982), Conan is mortally wounded by his crucifixion on the Tree of Woe, so his lover Valeria convinces the Old Wizard to work a healing spell to save him from the brink of death. The Wizard warns that the gods demand a price for this sort of thing, and she says she'll pay it. When she's later shot with a snake arrow by Thulsa Doom, she decides that her death is her payment. Whether that's true is not revealed, but it seems logical given the bleak universe of the film.
  • The fountain in Pirates of the Caribbean: On Stranger Tides takes life from one to extend another's. However, the rate of exchange isn't exactly equal. The one on the receiving end gets the person's entire natural lifespan, regardless of their age or actual life expectancy, meaning that the recipient is going to get around 100 years from the deal no matter the sacrifice.
  • The magic time traveling scepter of Teenage Mutant Ninja Turtles III required an equal number of people (of roughly the same weight, which didn’t come up) to travel in each direction. While the movie is not all that popular, it did make for some interesting events going on while the Turtles were back in Feudal Japan.
  • In The Covenant, every time a gifted teenager uses his/her Reality Warper powers (which are highly addictive), the person gives up some youth, as we see later in the movie.
  • In the first part of Merlin's Shop of Mystical Wonders, the main character (a jerkass Straw Critic) gains magical powers at the expense of his life force.
  • A relatively benign example of this trope occurs in The Secret of the Magic Gourd. Rather than a life for a life, the Magic Gourd uses magic to swap Wang Bao's blank failure of a test paper with the high-scoring test of a fellow classmate. Being his typically dumb self, Bao Hulu doesn't even bother to change the name at the top of the test, which gets Wang Bao in trouble for cheating.
  • In Men in Black 3, J goes back in time to prevent K's death. He is told that the event he is trying to avoid is destined to happen, and that "Where there is death, there must always be death." Due to J's meddling, K is saved, with J's dad Taking the Bullet.
  • Since the precise details of time travel in the Terminator series are left vague and we never see the aftermath of departure, one possibility is that the Time Sphere doesn't destroy everything around the traveller, but merely transposes the future and past in their location.

  • Christopher Paolini's Inheritance Cycle:
    • The entire magic system of the series is wrapped up in this. Doing something with magic takes the same amount of energy as doing it without magic would have done. And if you try casting a spell that takes up more energy than you have, you die.
    • This is what he says, but at one point, Eragon breaks the calves of dozens (maybe hundreds) of soldiers and doesn't die.
    • And certain spells are just flat-out impossible, presumably because they take far too much energy, or simply cannot be done. For example: Eragon is warned to never try to bring people back from the dead; beyond death, there's just something that magic has no effect on; an attempt would drain the mage of all his life in one go and accomplish nothing. Trying to see the future or the past is a bad idea as well. It's actually explained in the books that if you're trying to see the future, it's a lot like scrying, in that you need to know exactly what's going to happen, down to the last detail. But if you already know what's going to happen, then scrying the future is functionally pointless.
    • Although in the second book, the young woman running the Varden finds some wiggle room in the rules: doing something with magic takes less time than it would otherwise, therefore magic-users can outperform in tasks which are complicated but low-energy. And that's the story of how the Varden climbs out of a financial hole by producing and selling finely made lacework for ladies garments.
  • Discworld:
    • This comes up a lot with magic in the books, where it is referred to as the Law of Conservation of Reality. For example, to teleport someone from one side of the disc to another, you may need to have an equivalent weight to teleport back to where they came from. This is mainly to deal with conservation of momentum; because the Disc rotates, different points on its surface move at different velocities relative to the Hub. Teleporting without such a counterweight means that if you move very far, your velocity relative to your immediate surroundings tends to kill you. But you can do it!
    • This is still an imperfect science, and when the wizards of Unseen University try it to retrieve Rincewind in Interesting Times, he's hit on the head by all the crap they piled up to equal his weight, going the other way.
    • It comes up more often with conjuration than with transportation. If you wanted to make, for example, a loaf of bread appear, the casting thereof would have to expend all the energy that went into making the bread—so, growing the grain, grinding it into flour, mixing the dough, all the heat it took to bake it—or else you'd have a loaf of bread for about half a second and then it would vanish again. It is also described that the magical act of creating that loaf of bread as a permanent thing takes so much effort that it might cause the wizard's brain to forcibly evacuate his skull through his ears. So mostly they just don't bother.
    • Another anecdote describes how using magic to levitate a book from a high shelf to lay it down in front of you will fatigue you as much as actually climbing a ladder to take the book directly.
    • Esk mentions it outright.
      Esk: I don't think magic works like that. You can't just make things happen, there's sort of- like a seesaw thing, if you push one end up, the other goes down.
      Gulta: I can't see Granny on a seesaw.
    • In a non-magical example from Snuff, the only item Vimes can offer Tears of the Mushroom for the loan of her precious unggue pot is the equally-precious iconograph of his son which he keeps in his wallet.
  • In the non-Dragonlance book The Death Gate Cycle by Margaret Weis and Tracy Hickman, the same problem came up. When you brought someone back to life, be it a full resurrection or just as a zombie, somebody else, somewhere, died. One of the two competing races nearly wiped themselves out this way.
  • Vurt. Things are swapped between the real world and the vurt world on the basis of their value. The characters are keeping a weird tentacled creature because it was somehow switched with the protagonist's sister, and they're trying to figure out how to get her back. At one point, he wants to bring a object back to reality, so he leaves something of sentimental value behind.
  • Blood-magic in George Martin's A Song of Ice and Fire works this way:
    • Near the end of the first book, Danaerys sacrifices her husband's prize stallion and her unborn child to save her husband's life — and gets badly screwed by the exchange, since the mage had played upon her desperation to save Drogo's life, and convinced her that the only life required to restore him was the horse's. Later, she uses the same principle to hatch three dragons from their fossilized eggs.
    • Melisandre kills Renly Baratheon with a nigh-unstoppable intangible assassin, dubbed a "shadowbaby" by fans. Although the details are never quite revealed, it seems to involve getting herself pregnant and sacrificing the life of the (royal-blooded) unborn child. There are also hints that the spell was at least partially Cast from Hit Points on Stannis' part.
    • After Arya has saved the lives of Jaqen H'ghar and two other guys, Jaqen explains to her that he is now owing her three assassinations - one for each life Arya has by her actions denied the Red God to claim.
  • The magic system in Eric Nylund's Pawn's Dream works through a variation of Equivalent Exchange, where opposite elementals must be present, but it varies whether users need to trade them or simply summon or banish both. Either way, most of the skill in magic is based on letting both elements flow freely.
  • The Saga Of Recluce series by L. E. Modesitt Jr. is set in a world of Chaos and Order Magic, both of which must be carefully balanced—at times, overuse of either, or just too much Order or Chaos concentrated in one area, has shifted the entire planet's weather patterns, caused volcanic eruptions, and other disasters. Despite that the balance is well-known in-universe, it didn't stop people from trying to cheat. Recluce itself, for example, was protected by a navy of Order-infused ships...and every time they replaced one, it was with a larger, more powerful ship that required more Order.
  • The novels in the Star Wars Expanded Universe emphasize that the Sith path is one of sacrifice, i.e., demolishing attachments instead of the Jedi path of avoiding attachments. Since the Sith draw power from pain and rage, easy or pleasant trade-offs aren't in the picture. Which makes the Emperor's plan of either 'Luke kills his father' or 'Anakin kills his son' at the end of Return of the Jedi make a lot more sense.
  • Orson Scott Card is very fond of this trope and said that it is a practical necessity for a fantasy story driven by magic, writing in How to Write Science Fiction and Fantasy that without it, the "characters become gods...and there is no story". In that book, he proposes some grotesque systems of magical exchange, including killing (a human grants you more power than an animal; a child grants more power than an adult) or losing body parts for power (your own body parts fall off; or someone else's fall off, but they must be given willingly; or body parts of the one you truly love the most fall off; or a random person's fall off, but they tend to have a connection to the spellcaster). And as he mentioned in How to Write Science Fiction and Fantasy, Card actually wrote a novel in such a setting: Hart's Hope.
  • In the Deryni series, magic is physically taxing, with more powerful workings (say, Calling to another Deryni over a great distance, particularly when the other Deryni doesn't expect it and isn’t helping to bridge the gap from the other end) causing more fatigue. Fatigue-banishing spells exist, but they cannot be re-used indefinitely, and the rejuvenation they provide can be quickly lost if the person experiences more stress. Training also seems to extend endurance within limits, much as people who physically train increase athletic endurance to a point. Tiercel makes this analogy: “...you're flexing abilities you've never used before. You have to build up your endurance. I'll bet you've got a headache just from this afternoon's work.”
  • Cold Fire Trilogy:
    • Magical energy is released by sacrifice. The amount of energy gained is directly proportional to how much the sacrificed object was worth to the sorcerer. This is one of the facts used to show the Magnificent Bastardness of Gerald Tarrent, who sacrificed his entire family to gain immortality. The spell wouldn't have worked if he hadn't loved his wife and children very, very much - and he killed them anyway.
    • It's later explained that the sacrifice which made him immortal wasn't actually his wife and children. It was his own humanity, which he lost through the expedient of killing his wife and children. And if he ever tried to act like a compassionate human being again by engaging in an act of life or Healing, his immortality would be forfeit.
    • Another huge example in the backstory explains why humanity is stuck on Erna without any of the technology that got them there in the first place. One of the expedition leaders, Ian Casca, sacrificed the colony ship and most of its advanced technology to make the fae into something humans could harness and control. In exchange for immediate survival, Casca gave up any chance for the colonists to escape the damn planet. The colonists killed him when they discovered this.
  • In the early Anita Blake stories, one must kill a living thing to create undead. Anita routinely uses goats for that purpose. Of course, most magic is swallowed up by Deus Sex Machina as the series moves forward. (She has kept the goats out of that part.)
  • This is a rule of magic in the Tortall Universe by Tamora Pierce, demonstrated in several ways.
    • In Wolf Speaker, a man is turned into a tree and we are told that, somewhere in the world, a tree is now a man. (Pierce later wrote about him in a short story which is collected in Tortall and Other Lands.)
    • Words of Power differ from regular use of The Gift in needing equivalent exchange. You can do more minor stuff rather easily. However, for example, destroying a powerful magical barrier with Words would have caused a major natural disaster elsewhere.
    • Additionally, we find out in Protector of the Small that the use of the Dominion Jewel to prevent an earthquake (at the end of Song of the Lioness) cost the fertility of all the grain in the kingdom. They had to import all their bread and seed wheat the next year, and the kingdom was in debt for years paying it off.
  • In the Young Wizards series, "spells" are essentially equations written in a magical language and equations always have to balance, one way or another. In one book, a character holds off the Big Bad with a shielding spell which is later explained to have been fueled by a year of the character's life per strike. (The Devil hits hard.) In another, that same Big Bad is sealed away by a ritual that requires a willing sacrifice; one character attempts to take the place of the intended victim and a third actually does. It's implied that this event might have come to pass because of events in the prior book: to cast a spell they couldn't have powered alone to seal away an Artifact of Doom they used a "blank check" spell in which they essentially promise that the power they use will be repaid at some unknown date in the future.
  • The "death magic" in Lois McMaster Bujold's The Curse of Chalion is like this: it's a way to murder someone at a distance, but as part of the spell's workings, the person casting the spell will die, too. In addition to this little drawback, it's believed to be very difficult, and requires animal sacrifice as well. Plus, the God of Executioners has to be invoked and he only lets the magic work when the victim deserves to die.
  • The Barry Trotter parody of the Harry Potter series mentions this in the sequel, where everyone has graduated and started families (despite being effectively proven wrong by the final book). It's only then that Barry learns that to summon something with magic is actually just teleportation, thus "created" items always come from somewhere else. This coincidentally results in a poor sap whose possessions always go missing on Barry's birthday.
  • Broken Sky:
    • This series has "spirit stones", which grant people special abilities but drain their energy when used, placed into the spines of characters. Ryushi, for example, can emit a powerful blast of energy, but it drains him to the point of collapsing to do so.
    • We're later introduced to people with healing spirit stones. They can heal the wounds of others by taking them on themselves, although the healers have a slightly improved healing rate.
  • In The Neverending Story, AURYN grants humans the ability to make their wishes come true, by rewriting reality in Fantastia so that it always was so. In exchange, AURYN takes away a memory of the Outer World from the human with each wish. They start off reasonable enough (trading the memory of being fat and scared for a more heroic figure), but eventually descends into taking more and more precious memories, no matter how selfish the wish is (the memory of being from the outer world, the memory of one's parents, the memory of one's own name). In the book, the wishes don't even have to be spoken, either. If you want something badly enough, AURYN will sense it, grant that wish and take a memory with no effort on your part.
  • A system of Equivalent Exchange is enforced in the Night Watch books. Basically, the forces of good and evil have a treaty regulating and limiting their actions. When one side uses their power to interfere with humanity, the treaty demands that the other side receive an equal intervention. Hence a Light mage can heal someone, but that gives a Dark witch the right to curse someone. The system works overall, with most "Others" (the series term for supernatural beings) willing to go through the proper channels to get licensing for using their powers. (For example, vampires annually receive a license to feed on a living human, though not all use them.) If an Other breaks the rules, the Watches (the police of the Others) will locate and punish them (with most crimes being sentenced to death). If a member of the Watches breaks the rules to a relatively small extent, they can offer the other Watch an equal intervention as a compromise.
  • In Robert Silverberg's early novel The Time Hoppers, time travel is done by exchanging matter between the present and the past; when a human is sent back, an equivalent mass of air has to be brought forward.
  • In Cornelia Funke's The Ink World Trilogy, characters can be read out of books into the real world, but not without someone or something from the real world taking their place
  • The three magic systems from Mistborn work this way.
    • Allomancy requires the wielder to consume fragments of metal and "burn" them in their stomachs to power certain effects; some of these metals are considerably rarer than others, and the metal duralumin acts as a catalyst for burning whatever other metals are in the user's stomach very, very fast.
    • Feruchemy allows the wielder to temporarily drain him or herself of a certain quality or ability - memory, skill, age, health, senses - store it in a piece of metal, and retrieve it later as needed (for example, a Feruchemist could temporarily become very weak, and then later "tap" the stored energy to acquire superhuman strength). It's not always much of a cost though. While there are few benefits to making oneself weak, there's mention of feruchemists draining their youth to disguise themselves as old men, and Sazed drains his weight so he can jump down a great height without damage.
    • Hemalurgy does not require fuel, but it does require leeching abilities from Allomancers and Feruchemists by stabbing them with particular metals and then permanently implanting them in oneself in particular places, and often leads to great insanity. Also, it's inherently wasteful: the powers you steal with it are always somewhat weaker than the original.
    • Compounders are a quirk of the system. If someone has matching Allomantic and Ferchemical metals, then they can store an attribute in a metalmind then burn the metalmind, creating a much larger burst of power, which they can then store, and then burn, creating an infinite loop of power. The Lord Ruler managed to gain immortality by Compounding youth in an atiummind (though after a thousand years his age was still catching up with him), and in The Alloy of Law a double-gold Twinborn has a Healing Factor that makes Wolverine look like a wimp. He shoots himself in the face with a shotgun to prove to his men he's invincible, hasn't felt pain in decades, carries around dynamite to blow himself up if someone tries catching him with a net, and doesn't even need to breathe if he flares his power enough. He still ages, but that's his only weakness. As long as he has gold, he can't be killed.
  • The Stormlight Archive: There are at least two types of magic falling under this law:
    • Surgebinding produces various effects (from flight to trasmutation to healing), consuming the stormlight infused in gems in exchange.
    • The Old Magic is granted by a spirit called the Nightwatcher. Everyone who deals with the Nightwatcher can ask for a blessing, but in exchange must also receive a curse, chosen by the spirit. One minor character mentions trying to word his wish in such a way to avoid a curse, but is informed it doesn't work like that. You tell the Nightwatcher what you want, she considers it, and gives you a curse she finds to be of equal value. It might be related, but it could just as easily not.
  • The entire basis of Devon Monk's Allie Beckstrom novels. Magic always exacts a price, usually in pain. The user can choose between an hour-long migraine or a week-long head cold, but the price will be paid. For the protagonist, magic also takes her memories. For small spells, she'll forget what her stepmother's name is. For large spells, she'll wake up with a three week hole in her life. She carries a journal with her everywhere, with her name, address, etc. written on the first page, just in case.
  • In the Bras and Broomsticks series by Sarah Mlynowski, if someone uses magic to get something, that thing will be taken from wherever it comes from. For example, the main character's sister makes oranges to give to the homeless, but there is an orange shortage in stores in the area.
  • At the end of Changer's Moon, Serroi turns Ser Noris into a tree. The price? She turns into a tree herself. (Although that was less a function of the magic itself—she'd previously turned mooks into trees with no ill effect—than of using it on an opponent of such power.)
  • Roger Zelazny's Changeling follows this logic for moving items between universes.
  • Stephen Donaldson's second The Chronicles of Thomas Covenant has the mere mortals of the land required to shed blood (both their own and the blood of others is used) in order to manipulate the Sunbane. The first chronicle has Mhoram realizing the key to power is despair, which will lead to the destruction of the Land.
  • In China Miéville's Iron Council, a character is beholden to an interesting version of this. They are a monk of the God of Secrets; part of this means that they can ask the god for knowledge about a secret: a secret path, what the enemy is planning, and so on. But they have to give up some of their own knowledge to do so. The character in question lost knowledge of her gender as a result of this.
  • Sympathy in The Kingkiller Chronicle follows the actual First and Second Laws of Thermodynamics, so that heat and work applied to a target have to be taken from somewhere and transfer of energy can be rather inefficient. In practice, this means that people have killed themselves trying to raise winds with their diaphragms and light candles with their body heat.
  • In the Stephen King novella Fair Extension, George Elvid offers to cure Dave Streeter's cancer at the cost of inflicting it on someone else. Since that someone else happens to be his ex-girlfriend who cheated on him with his ex-best friend, Streeter isn't exactly bothered.
  • In Ian Irvine's The Three Worlds Cycle, use of magic (or "the Secret Art") is balanced by "aftersickness": debilitating headaches and nausea. Unskilled "mancers" may even get the aftersickness without the magical effect they were going for. This, however, is nothing compared to the risks of trying to draw too much power from the field: you get "anthracised", where the sheer power you're trying to channel burns you alive from the inside out. Of course, it's lovingly described in detail in one of the books.
  • A Civil Campaign: Cordelia Naismith-Vorkosigan points out that her home planet of Beta Colony is extremely sexually liberal, yes, but at the cost of being reproductively conservative. All women, by law, have a contraceptive implant, and people wanting to become parents are subject to a battery of tests before being licensed. Very few families are allowed more than two kids. This is not something the writer just made up, mind you; both the sexual liberality and the implants had been mentioned throughout the series, but it is the first time the connection was explicitly explained.
  • The Wheel of Time: While use of saidar is more or less free, the Aelfinn and Eelfinn operate on this basis, and from most non-main characters important things like valuable knowledge, cooperation and items must be bargained for, often with extensive negotiations over the price the heroes must pay.
  • In Rudy Rucker's Master of Space and Time, time travel supposedly requires sending something forward in time if you send something backward. The twist is that the author ascribed to the shrinking universe theory, which mean that sending his pet lizard forward in time resulted in Godzilla: Jersey Shore.
  • In Coda, one year powering the city takes a year off your lifespan. This is what killed Haven's parents.
  • In the sequel to Those That Wake, healing someone via the neuropleth can bring them back from the brink of death, but it erases you from existence.
  • The cost for Resurrective Immortality in The Night Angel Trilogy. For each resurrection of black ka'kari holder, someone the holder cares about soon dies.
  • In Horus Heresy, it seems that Deathfire's resurrective magic works on "life for life" rule, as Vulkan doesn't come back from the dead until Numeon sacrifices himself.

    Live Action TV 
  • Ben's healing talent in Carnivŕle worked by drawing Life Energy out of the surrounding area. Cure a little girl of polio, the crops wither as she skips away through the cornfield. Heal a broken arm, a bunch of fish go belly-up in a nearby pond.
  • Game of Thrones:
    • Mirri Maz Duur tells Daenerys that only death can pay for life.
    • Jaqen H'ghar also mentions this as his reason for assisting Arya.
  • Chloe Sullivan on Smallville got a similar power in the sixth season finale (in this case, she died and came back to life). In the seventh season, it is explained that she can heal non-fatal wounds so long as she herself takes on that wound (i.e. to heal a paper cut on Jimmy Olsen's finger, her body compensates by receiving a wound of similar size on the same spot on her body).
  • One episode of Forever Knight featured a mystic healer that could take darkness out of people. However, said mystic happened to be a novice at her craft, and didn't know that this darkness had to be put somewhere, (usually into an inanimate object of some sort), and wound up absorbing it herself and being overwhelmed by it. The episode had a really sad end to it, Nick was quite close to becoming human again, with most of his vampiric urges gone. But she herself was absorbing his darkness and becoming a vampire. She died from "OD'ing" on his evil, which he re-absorbed into himself. Her grandfather alluded that she might have been capable of fully healing Nick (or at least making his gains permanent) if she had been more skilled.
  • Ned's talent on Pushing Daisies works the same way, by killing one thing of equal magnitude to whatever was brought back from the dead if the dead thing's alive for longer than 60 seconds. So, if a person's brought back from the dead, then another person is going to die to keep them alive. (See also: Balancing Death's Books)
  • Quantum Leap: Every time Sam leaps, the person he's replaced ends up in 1999.
  • Buffy the Vampire Slayer:
    • When Willow sends Buffy back in time to meet the sages who created the first Slayer, a demon is brought forwards to take her place. Willow says that this is to avoid violating the First Law of Thermodynamics.
    • Similarly, though perhaps a more accurate example of this trope, when Buffy is brought back to life at the start of Season 6, the spell creates a brand new demon through a process Willow calls "Thaumogenesis". As she explains, the universe doesn't like you getting things for free, there has to be a cost and they asked for a huge gift; Buffy's life back, so the universe said "Ok, but you have to have this evil demon too". This fits the trope as its a Good Thing/Bad Thing equal parts deal but as Anya rightfully points out "That's not a cost, that's a gift with purchase".
    • One of the ingredients of the spell to resurrect Buffy is the "blood of an innocent", so Willow cuts the throat of a fawn. However at the end of the season the blood of an Innocent Bystander is indeed shed, Willow's lover Tara, making one wonder if this trope wasn't in play.
  • Torchwood:
    • The Resurrection Gauntlet in the first series could bring someone back from the dead, but usually only for about one or two minutes. However, with enough empathy from the gauntlet's user, a person could be brought back completely from the dead - but the person who used the glove would slowly give up their life (including any fatal wounds the formerly deceased had) while the previously dead person would get healthier and healthier.
    • Of course, since Jack has unlimited life force, the whole thing gets turned on its head when he resurrects Owen - he's immortal, but unable to eat, heal, get drunk, etc.
  • Whenever Frank Parker steps back in time in Seven Days, his self at that time period vanishes from the time stream. It's explained that this is because the same set of molecules cannot exist in two places at the same time. This almost blows the secret once, when Parker steals something the first time through, when he's investigating the problem, and takes it back with him. So it 'magically' vanishes from villain out of air-tight security, out of a locked briefcase, and the villain twigs that that shouldn't be possible, and starts investigating this 'Backstep' project.
  • In Power Rangers there are some examples of the Sixth Ranger being limited due to their awesome power. The most notable were the Green Ranger and the Titanium Ranger. The Green Ranger’s powers were damaged, such that every time he used them, they would weaken, putting physical strain on himself. The Titanium Ranger was branded with a cursed tattoo of a cobra on his back. Every time he morphed, the cobra would move up a little. If it got to his neck, he would die.
  • Merlin (2008):
    • This was also used as a plot point. Arthur was conceived through the use of magic at the cost of his mother's life; she died during childbirth. There was even a reveal in this scene because Nimueh, a recurring villainess in the series, was the one to use the spell that conceived Arthur in order to grant Uther an heir by his barren wife. She herself knew there would be consequences of this spell, but she didn't know how they would appear.
    • This reappeared in the season finale, where Merlin offered his life in exchange for Arthur's, as the prince was being killed by an incurable poison. However, this didn't work as planned, as Nimueh took Merlin's mother's life instead, so his mentor/father figure Gaius offered up his life (confused yet?). The whole saga ended when Merlin killed Nimueh and used her life to save Gaius.
  • Supernatural:
    • In the episode "Faith", a Reaper can restore a dying person's life, but only at the cost of another's. The woman who was holding the Restraining Bolt uses this to set her husband up as a faith healer, while using the exchange to murder various of her faith's bugaboos. When the brothers break the leash, she learns the hard way that True Neutral is not a toy.
    • In the episode "Criss Angel Is a Douchebag", real magic is used to save a magician from lethal escape tricks. The cost of saving his life is that another person dies in the same way the magician would have been.
  • In an episode of Big Wolf on Campus, Merton was given a magical watch that could turn back time. Unfortunately, every time he uses the watch, he loses some of his knowledge.
  • This appears to be how the Phoenix Talisman works in Warehouse 13, though its behavior is not consistent. It will resurrect its user after his or her death, and then the trauma of that death will be transmitted to a random person in proximity. However, it's not always a one-to-one substitution; during Mac Pherson's demonstration of the Talisman, two random mooks die in exchange for the single demonstrator. It may be proportional to the amount of trauma the user suffers.
  • In House of Anubis, the Cup of Ankh will grant immortality to the person who drinks the Elixir of Life out of it, but someone else will die to replace the life that would otherwise have ended eventually.
  • Kaizoku Sentai Gokaiger:
  • Once Upon a Time apparently has it as one of its key tenets. "All Magic comes with a price." While Fairies don't include such a thing normally in their use of magic, it's possible that their conditions for magic use is the price others must pay. (either that or the dwarf mines are the price to make the magic work)
  • In Witches of East End any spell that deals with life or death works on this principle. A novice magic user who does not understand this can cause great harm. Ingrid causes the death of a love interest when she resurrects someone else. Dash, being a doctor, is naturally drawn towards those spells and his first attempt at major magic ends up almost killing his brother. When he tries to use a healing spell on a kid who just died, the kid is brought back to life but Dash's life force is slowly being sucked out to pay for it.

  • The Beatles in "The End" from Abbey Road: "And in the end, the love you take is equal to the love you make."

     Mythology & Religion 

    Tabletop Games 
  • In Battle Spirits, everything has a cost of core, even if it's just a low amount, though it can be reduced through the cards specified reductions and other effects. Some double symbol spirits require the tribute of another spirit to summon them.
  • The Defilers in the Dark Sun setting for Dungeons & Dragons. Both Defilers and Preservers need to drain life forces in order to power arcane magic, but defilers drain it away without worrying about the consequences, while Preservers are careful not to drain enough to kill the plants and animals nearby that are contributing. Considering that Athas is a gigantic desert world, it's not hard to deduce the popularity of defiler magic.
  • In the Ravenloft setting, curses can be invoked by ordinary people, but attempting to do so invites a Powers check. If failed, the curse-layer will suffer karmic retribution from the Dark Powers. In an Equivalent Exchange Of Payback, the curse is actually more likely to work if the curse-layer fails this check.
  • Most magick in Unknown Armies works this way. The "value" of certain actions varies based on what kind of adept you are. Typically an adept gets a "minor charge" for some kind of ritual that's easy enough to be performed every day or so, a "significant charge" for doing something very difficult and painful, and a "major charge" for doing something nigh-impossible. And even the magick that seems to be free usually isn't. In Unknown Armies, ain't nothin' come for free. There's even an in-game term for the concept in UA: The Law of Transaction.
  • The Vampire: The Masquerade version of the Tremere House and Clan is practically built around this trope. Originally mages, the Tremere turned themselves into magical creatures when magic began weakening, out of a supposition that said creatures would last a while longer during magic's decline. However, in doing so, they lost the essence that made them mages in the first place, and got what was, in essence, a surrogate. The price of power, indeed.
  • Present in the TCG Magic: The Gathering to an extent. Every spell has a cost. Most are simply Mana drawn from the land, but others require a life (yours or your creatures), the land itself, or even time (skipping a turn). Several cards will actually kill you if the cost is too much for you to afford. Perhaps the most famous example of this is Necropotence. You don't draw normally near the beginning of your turn; instead, you may pay X life to draw X cards at the end of your turn. However, this particular exchange turned out not too equivalent: both cards with this effect proved to be broken beyond imagination. For the uninitiated: Unless you know exactly what you are doing and have built your deck specifically to respond to various threats, playing Necropotence is pretty much suicide.
    • There are also some cards that are balanced this way: they give you a benefit or harm your opponent, but also do the same thing to every other player. One example is Braids, Conjurer Adept: she lets you play a card for free at the start of every one of your turns, but your opponent(s) get to do the same. There's plenty of cards that follow a similar pattern.
  • In Warhammer Fantasy, the species known as the Dragon Ogres succeeded at making a deal with Tzeentch that rendered their entire species immortal and able to subsist on lightning alone as energy — but the spell also struck them all sterile, so no new Dragon Ogres has been born since. Tzeentch is kind of a dick like that.
  • In Geist: The Sin-Eaters, a Sin-Eater can come back from the dead easily (yes, more than once). Problem is, in addition to the act knocking a chunk off your Karma Meter, your geist is going to draw that life force directly from someone else. And when you wake from your brief dirt nap, your face is covered in an ectoplasmic caul that conveys all the details of that person's death.
  • The magic system in "The Valdorian Age" (a setting for Fantasy Hero) can be summarized as "you convince otherworldly/extraplanar beings to do something for you". However, they're doing it as a favor, and eventually they will require a favor from you in exchange ... which, depending on how big your debt is when it gets called in, could involve things like killing all the inhabitants of a village in one night. No one ever claimed those otherworldly beings were nice.
  • Several of the magic systems in Legend of the Five Rings work this way. Shugenja do not so much manipulate the elements themselves as convince elemental spirits to do them favors, and much of their duties involve making sure said spirits are happy. Maho is directly powered by the shedding of blood - but good news! It doesn't have to be your blood.
  • In Changeling: The Lost, this is the basis of Pledgecraft: Changelings can create magical bargains known as Pledges, each incorporating a task, a boon, a sanction and a duration. Boons and durations count toward the cost of a pledge, while task and sanction count against it, and all Pledges must have a net worth of zero. A clever changeling can still game the system a bit by such expedients as making a pledge that if given a healer's knowledge for a day, they will use it at least once that day, on pain of misfortune. If you make the pledge when a companion is already injured and needs first aid, satisfying the task is laughably easy.
  • Exalted:
    • The Sidereal Exalted have the charm called Of Things Desired and Feared, which uses astrology to provide an infallible way to achieve any objective you can state... for an appropriate price. If what you want to achieve is small, it is likely the price will be something you are willing to pay (a few bruises, the lost of an item, etc.). But if you ask for a Fate-proven way to defeat Big Bad or otherway break the game, the price will be something like "your life, the lives of everyone in your Circle, and the complete destruction of all the thing you value and care for".
    • Some other charms have a drawback to balance out the benefits. This is especially true of a number of Green Sun Prince charms, like the one that allows you to not need sleep, but requires you to run in order to rest, the one that allows you to longer without sleep in exchange for nightmares when you do, and the one that allows you to become telepathic at the cost of turning all noise into white noise for you.
    • In the Third Edition teaser PDF for the Infernals, it's revealed that, to keep the other Primordials from making their own Exalted, Autochthon devised "The Law of Diminishment" and inserted it into She Who Lives in Her Name, which states that any who empowers others is weakened in turn (which is why, even with the divine fire of the Exigence helping them make their own Exalted champions, many weaker gods cannot survive the creation of an Exigent).

    Video Games 
  • The Monkey Island games have this as an element of Voodoo magic. In The Curse of Monkey Island, Guybrush needs to find need a diamond as big as or bigger than the one that turned his fiancé to stone. In Escape from Monkey Island, he needs to make an Ultimate Insult talisman as large as or bigger than the original in order to counter its effects. (No explanation is given on why his enemies can counter Guybrush’s insults even when he has the larger talisman, although it is only the second biggest monkey head Guybrush has ever seen...)
  • Oracle of Tao has a variety of these. Most magic uses MP as its price, but some abilities are Cast from Hit Points. On the other end of the scale, you have a Mana Shield. And then there's Elias's alchemy, which aside from making cool items, has certain alchemy spells. But in order to learn each spell or make a super-rare item (like gold), you sacrifice anywhere from a level to 10 levels (and you can combine spells together, meaning there's a chance you might end up making the same spell more than two times).
  • Whenever the Nameless One from Planescape: Torment dies and comes back, someone else somewhere on the Great Wheel dies as a result, becoming a tormented shadow whose only desire is to hunt down the Nameless One and kill him again.
  • In Valkyrie Profile, the ritual of Soul Exchange allows someone to sacrifice their own life to bring someone else back. However, it won't work on someone who died by using the same ritual, and one character ends up undead for attempting this.
  • This was a main part of The Immortal. Your character starts with a magic amulet that, you eventually discover, has the power to kill a dragon (the creature that awaits you at the end of your adventure). However, it turns out the amulet also kills the person who uses it (you could easily discover this at any point by using the damned thing), and the whole game is an Evil Plan by the Big Bad to get you to kill the dragon (sacrificing your life in the process) because he needed the dragon dead, but obviously couldn't use the amulet himself without dying.
  • In The Legend of Zelda: Twilight Princess, Link can acquire a magical suit of golden armor which will prevent him from taking any damage. However, whenever he wears it, his wallet is slowly drained of money, and he loses extra money every time he takes a hit. Once he runs out of Rupees (the coin of the realm), the armor weighs him down considerably, making his movements slow and awkward.
  • A popular mod for Minecraft by the same name revolves around this trope. This mod gives every item in the game an EMC value (Energy-Matter-Currency). These items can be exchanged for each other using a Minium Stone/Philosopher's Stone if the EMC value is the same.
  • The world Kartia revolves around magical cards, Kartia, that can be used to create basically anything, from living battle-creatures to spells to specific kinds of food and drink. There are a number of Original Kartia (such as "Life" "Death" and "Human"), the use of which is forbidden and will automatically cause the death of the caster. For most of the game, the player and the characters believe that the Kartia creates things from nothingness but as it turns out, it just takes things from Eden, a parallel world inhabited by Elves and rich with natural magic. In fact, it is theoretically possible to "create" the whole Eden with Original Kartia, something that is half-accomplished twice during the story. It also turns out that Original Kartia doesn't kill the user, but rather transports them to Eden.
  • World of Warcraft
    • Warlock magic is said to work like this.
      Grom: With hell's fire, you make a bargain. It costs a little of yourself. The warlock's way was quicker, more effective, or so it seemed. But there comes a time when a price must be paid, and sometimes, it is dear indeed.
    • Don't expect to ever have to pay that price yourself though.
    • Examples include the Life Tap spell (converts health into mana points), Health Funnel (heals your pet demon at a cost of your own health), Hellfire (which burns you as well as your enemies), and Ritual of Doom (summons a powerful demon; originally one party member would die upon completion, now one member is simply badly wounded). Other spells are fuelled with Soul Shards, gained by killing foes with a particular spell.
    • Although now, Warlocks have a low-level spell that lets them restore all their soul shards by apparently breaking off little pieces of their OWN SOUL (at no real cost in gameplay terms, though it is interruptible and thus best used out of combat/between fights).
    • Doomguards don't even require the ritual of summoning or sacrifice of health anymore. Just hit a button, and BOOM he's there fighting on your side for 45 seconds.
    • In the Ashbringer comic, Darion Mograine seeks to free his father Alexandros' soul from the Scourge and the corrupted Ashbringer sword. He is told that an act of love greater than the act of evil that originally stole Alexandros' soul(being betrayed and killed by his oldest son) is needed to free him, but he's also warned that such an act of love is often the greatest test of faith. To free his father's soul, Darion impales himself with Ashbringer, freeing his father but unintentionally became a Death Knight of the Scourge himself.
  • Persona 3
    • Chidori sacrifices herself to revive Junpei under this principle.
    • From the same game, the skill Recarmdra fully heals all your allies' HP in exchange for yours becoming 1. It costs only 1% of your total SP, but it is still terribly risky given how it's game over if the leader is KO'd.
    • Recarmdra is present in many games in the Shin Megami Tensei series, where it often does kill the user to fully heal the rest of the party. Because of how the games are in general, only the recruitable demons and not the main character can get it.
  • The various Dark Powersets from City of Heroes tend to work like this, Dark Miasma in particular. Dark Miasma has some highly potent healing spells (Including the only rezz in the game capable of reviving multiple people.) but in order to use them you have to tap into the life force of your enemies. This is just icing on the cake, really... The only real downside of these powers was that you had to have an enemy to engage to use them. So you couldn't heal or rezz BETWEEN fights.
  • In Guild Wars, many Necromancer spells, mostly under the Blood Magic attribute, require the Necromancer to sacrifice a certain percentage of their maximum health, in addition to a small amount of MP, to cast. In addition, Necromancers also have many spells that require there to be a fresh corpse somewhere nearby for them to "exploit". These spells include raising undead servants, creating a "well" of energy that performs various effects, healing, or simply making the corpse explode.
  • In Dragon Age, Mages can perform magic effortlessly, but more powerful spells and rituals occasionally require the use of Lyrium, distilled into a consumable liquid form for this purpose. Blood Mages however, can use either their Life Energy or another's to perform powerful feats that non-Blood Mages cannot, such as Mind Control, as well as ripping the blood out of their opponents pores. While one can learn the skills safely through books written on the subject, these are usually restricted for obvious reasons, thus forcing more desperate (or foolhardy) mages to make a bargain with a Demon to gain the power. What the bargain requires changes from person to person, but most cases end with the Demon possessing the Mage and turning them into an Abomination.
  • Phantasy Star III allows you to visit a "technique distribution" shop to alter the potency of a magic-wielding character's techniques. With the use of a square-shaped grid, at the expense of one, another can be strengthened. In practice, thanks to Useless Useful Spells, you'll usually end up maxing out Gires and utterly bottoming out Rever or Anti, since those had a high probability of failing anyway.
  • In Quest for Glory I, "Every curse has an equal and opposite countercurse."
  • Equivalent Exchange is one of the major rules of magic in the Nasuverse both in the practical (a spell needs to take its energy from somewhere else) and the social sense (a magus will never do someone a favor without expecting something in return).
  • The "Pandora" feature of Street Fighter X Tekken allows you to sacrifice your partner to give your primary character eight seconds of unlimited super meter and amped-up strength. To make this even more of a desperation move, if those eight seconds elapse before you defeat your opponent, you lose.
  • In Final Fantasy Crystal Chronicles: Ring of Fates the main characters Yuri and Chelinka has access to enough magic power for a Cosmic Retcon, if they need to. However, using that power needs something in return. Chelinka pays by losing her soul for a longer period of time, Yuri, pays with part of his life.
  • In Final Fantasy XII: Revenant Wings summoning Yarhi siphons part of your Anima, the part of you that feels, which is why all the Aegyl who regularly use Yarhi to protect them selves for random monsters appear rather emotionless. Their "god" draining their Anima for himself is a bigger factor in this though.
  • While Calypso from Twisted Metal is either a Literal Genie or a Jerkass Genie, the ending for his daughter winds up universally balancing it out, by wishing that the car crash that killed her mother never happened, the universe balanced things by making the daughter get in the crash herself and put into a coma she probably wouldn't wake up from. Even Calypso is genuinely heartbroken about this outcome.
  • In Juniper's Knot, the rule of the spell binding the fiend is of this type: a life for a life.
  • Touhou has Shinmyoumaru, an inchling that possesses the Miracle Mallet. It is a weapon that is supposedly capable of granting any kind of wishes to it's user, making him or her literally omnipotent. Sounds cool right? Too bad it requieres an equivalent exchange for everything, and may also take its price before the wish is even granted if the wish itself is too great.
  • In the Axis Powers Hetalia fan game Heta Oni, England reveals that he can destroy the Grays all on his own, using his magic. However, it comes at the cost of his eyesight.
  • In An Octave Higher, although mages seem to produce blasts of water and walls of rock from thin air when they cast spells, they are actually summoning these substances from elsewhere in the world and those substances will eventually return to where they came from. Thus, no new matter is actually being created and the conservation of energy is maintained.
  • Valley: When the LEAF suit brings the player character back from the dead, this drains some of the life energy out of the valley, and plants and animals start dying. If you use up all of the life energy, then you have to restart the whole level instead of respawning where you died. You can recharge the valley's life energy by bringing things back to life, but this uses up your suit energy.

    Web Comics 
  • Explicitly averted in Tower of God. Shinsoo is potentially limitless in power and potency, and can be created and destroyed. Killing, shrinking, even creating life are made possible. There's only one catch. To even gain control over one control unit of Shinsoo, one needs to rigorously train for ten years. Every further technique used takes dozens of years to master. Some people aren't even capable of doing so, since Shinsoo would instantly mangle their body. Why does it take so long? Because a single fuck-up with a greater amount of shinsoo is enough to completely obliterate you. It's dangerous stuff, kids. Handle with caution.
  • Fluke of The Young Protectors has the power to redistribute luck. This means that he can give people good luck, but someone else has to suffer bad luck in exchange (i.e. someone escapes a collapsing building, but Fluke totals his car). Nice Guy that he is, he willingly takes on bad luck most of the time so that he has extra luck to give away.

    Web Original 
  • The perfume in Erikas New Perfume seems to function like this, though given she got Fake Memories out of the deal it's debatable if Sarah gave up anything.
  • New York Magician: Michel has to use energy from things like fired bullets and flashbulb capacitors to power his magic. One favorite trick is to fire one bullet, and use the energy from that to do magic to the next one he fires. Then there's the automatic summoning spell running off an old IRT substation.
  • Fey of the Whateley Universe is a massively powerful mage who can, among other things, pull magical energy from ley lines. It turns out there's living things at the other end of those ley lines, and over the course of the first year she unknowingly caused several ecological disasters.
  • SCP Foundation: This is SCP-738's deal. If you sit in the chair across from him, he will make various offers to you. Alternately, you may request something from him. He will grant this request, provided it is a request for you (you cannot request something on someone else's behalf). However, the price is that an equal amount of misery will be introduced into your life as the amount of joy this request brings.

    Western Animation 
  • Eric gets a lecture to this effect from Dungeon Master in the "Day of the Dungeonmaster" episode of Dungeons & Dragons.
  • In Codename: Kids Next Door, in the final episode featuring Heinrich von Marzipan as a major villain, we see said Sweet Tooth's villainous plan of making the world's most unimaginably delicious caramels. The catch? The ritual needed carefully traced lines (which he used to connect all the Treehouses of the central American KND sectors) , Vast quantities of sugar (The KND are known to have ENORMOUS quantities of candy in their bases) and as he put it "You can't get something for nothing", the most prized quality of anyone inside the mystical lines. This turned each of his victim into a Polar Opposite of their past selves, without their distinguishing positive qualities (Leadership for Numbuh 1, Intelligence for Numbuh 2, Sweetness and optimism for Numbuh 3, Ferocity for Numbuh 4, and Numbuh 5's coolness). The reason Heinrich was not affected was because he was already a victim of the ritual, which happened 5 years ago robbing him of his femininity, for you see, Heinrich's real name is Henrietta Von Marzipan. Gender Bender much?
  • Futurama uses this trope when regarding time travel in Bender's Big Score due to the discovery of a paradox-correcting timecode. The timecode ignores all of the problems that normally arise with time travel as long as the end result is close enough to the main timeline. If there are multiple copies of someone created by time travel, then fate will make those copies exceedingly doomed until all but one are dead and the universe considers that perfectly fine. Somewhat justified as the code functions by drawing time bubbles from a creature previously implied to be God, who assumedly would be immune to paradoxes.
  • The fact that all magic has a price is used repeatedly in the DC Animated Universe. In one notable case in Justice League Unlimited, Circe's price for releasing a Baleful Polymorph curse she had on Diana is something from Batman he can never regain once lost... his dignity.
  • Kim Possible has Monkey Fist, who agreed to walk the path of the Yono in exchange for the Yono's power. It was granted to him...until he lost. Then he followed the path as agreed, petrification being the result.
  • The ending of X-Men take on The Dark Phoenix Saga has Jean Grey dying to stop the Phoenix threat as per source, but since here it was the real Jean possessed by a cosmic force, instead of the force itself taking her form, she really does die. The force itself is okay though, but it realises that it was wrong, and offers to resurrect Jean, requiring someone sacrificing their own Life Energy. Cyclops and Wolverine have a More Expendable Than You moment before Phoenix informs them that the necessary amount of life energy can be obtained from several donors, without anybody dying.

    Real Life 
  • As seen in the description, the First Law of Thermodynamics makes this trope not just Older Than Dirt, but Older Than Everything But The Universe Itself. The second law of thermodynamics states that you can't really get even equivalent exchange — you'll always "lose"note  some of the input energy to waste heat.
    • Noether's Theorem shows that there's a one-to-one correspondence between conservation laws and physical symmetries. Conservation of energy is due to time-invariance, so as long as physical constants don't change, it will exist.
    • Technically, increasing entropy is a strict conservation law. If you kept track of all possible outputs for a given set of inputs, the total entropy would remain constant. It's just that it's effectively impossible to keep track of it all, so you have some set of "possible" outputs that includes the real set, and has higher entropy.
  • Most of chemistry is this. It's even been worked out mathematically, much to the annoyance of undergraduate chemistry students and those grading their papers.
    • 6 CO2 + 6 H2O + Energy -> C6-H12-O6 + 6 O2 (6 Carbon Dioxide + 6 Water + Energy -> 1 Sugar + 6 Oxygen)
  • The Golden Rule can be interpreted as an attempt to apply this law of physics to justice and ethics.
  • Also on a physical level, athletes, especially Olympic-level. They can do what seem like superhuman feats of strength, agility, endurance, etc., but the cost is devoting massive amounts of time training for a specific event, and burn out later in life.
    • More generally, while any human is capable of performing similarly superhuman feats, untrained Muggles can only do so under great stress and at the cost of shutting down certain vital functions temporarily, as well as directly damaging their bodies.
  • In a meta example partially related to the above, to achieve anything in life it is necessary for certain things to be used to reach this point. To breathe you must expend the energy needed to inhale oxygen into your lungs, to become successful at something (without relying on luck->chaos->entropy) you must devote a large amount of time to study your chosen field et cetera.
  • The meaning of the proverb "there's no such thing as a free lunch." The proverb itself dates back to the 19th century when bars and saloons lured customers in with the promise of free food. The food was free as long as you bought drinks and the use of salty foods (ham, cheese, oysters, etc) guaranteed the patrons would buy plenty of beers.
  • Few things in this world are free. Money being a key thing to get many of the things we desire. You can't get an HDTV or car without having the cash to give in return for ownership.
  • Privileges at a workplace work the same way. In order to get a special privilege, you must be willing to get the work done to earn it in return.
  • Anything where the costs are hidden or distributive:
    • One example are frequent shopper programs offered by chain stores or supermarkets. These programs offer benefits to those who enroll such as discounts on products. However, any money lost by the business from these discounts is usually passed onto other shoppers not enrolled.
    • This has been a common elite criticism of populist/democratic social policies, such as free policing and schooling: why should the rich pay so that the poor can have them? And that's all there is to say about that.

Alternative Title(s): First Law Of Thermodynamics