Equivalent Exchange: Difference between revisions

{{quote|''"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 [[Trope Namer|Equivalent Exchange]]. In those days, we really believed that to be the world's one, and only truth." ''|'''Alphonse Elric''', in the [[Opening Narration]] to ''[[Fullmetal Alchemist (anime)|Fullmetal Alchemist]]''}}

For magic to be performed, for something to come into existence, for [[Make a Wish|a wish to be granted]], or for a loved one to be [[Empathic Healer|healed]] or [[Back From the Dead|returned to life]], another thing of equal value [[Power Source|must be given up]]. It has a simple dramatic purpose: It avoids the dangers of giving heroes [[Story-Breaker Power|Story Breaker Powers]] while adding conflict and sacrifice to an already hard moral choice.

Are the gifts, [[Love Interest|loves]], and [[Cast From Hit Points|life]] you possess truly worth losing for what you desire? Beware Desire, [[The Sandman|s/he is a fickle thing]].

Much like King Midas's gift of the Golden Touch was a great boon, it ultimately robbed him of [[Thicker Than Water|his greatest treasure, his daughter]]. [[Be Careful What You Wish For|Wishers may not truly understand]] [[Literal Genie|the full effects of what they desire]], and the gift itself can [[Blessed with Suck|become]] [[Came Back Wrong|its own]] [[Who Wants to Live Forever?|cost.]] This is [[Truth in Television]], given the [[wikipedia:First law of thermodynamics|First Law of Thermodynamics]]. Building in the cost to the boon usually results in a [[Fantastic Fragility]].

* Although it's not too much of a regular magic as it's more of a one-use, people at ''[[Hell Girl]]'', when contracting Enma Ai, can send one person they dislike immediately to Hell - with the price of their own souls 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. But then, 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]]? [[Lost Aesop|Who knows?]]

* It is practically the premise of ''[[The Law of Ueki]]''.

* ''[[Code Breaker]]'': It turns out that {{spoiler|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...}}

* The second arc of ''[[Naruto]]'' started off with Gaara dying, but he was an immensely popular and critical character so he needed to be revived. Enter Chiyo, who has a ninjutsu capable of reviving the dead. To avoid this being used to prevent every death in-series, the jutsu was equivalent exchange: the user sacrifices their own life to resurrect another.

** 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 ''[[Puella Magi Madoka Magica]]'', 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 bring.

** To gain the incredible powers of God's Right Seat, a magician must give up his or her ability to use normal spells. {{spoiler|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.}}

== Comic Books ==

* 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 Evil in a Can|sealed it in the same universe where they sent most of the magic]] to ensure that the [[The Golden Age of Comic Books|Golden Age]] [[Green Lantern]] would be around to deal with it.

* Storm's weather-controlling powers in the ''[[X-Men (Comic Book)|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.

* The magic [[Time Travel|time traveling]] scepter of ''[[Teenage Mutant Ninja Turtles (film)|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 [[Fanon Discontinuity|not all that popular]], it did make for [[Hilarity Ensues|some interesting events]] going on while the Turtles were back in Feudal Japan.

* 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 {{spoiler|the day of Shrek's birth, so once the day is over, so is he}}.

* 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.

** 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.

** 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 {{spoiler|producing and selling finely made lacework for ladies garments}}.

* This also comes up a lot with magic in the ''[[Discworld]]'' 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.

** Near the end of the first book, {{spoiler|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 {{spoiler|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 {{spoiler|hatch three dragons from their fossilized eggs}}.

** Melisandre kills {{spoiler|Renly Baratheon with a nigh-unstoppable intangible assassin, [[Fan Nickname|dubbed a "shadowbaby" by fans]]}}. Althouh the details are never quite revealed, it seems to involve [[Deus Sex Machina|getting herself pregnant]] and sacrificing the life of the ({{spoiler|royal-blooded}}) unborn child. There are also hints that the spell was at least partially [[Cast From Hit Points]] {{spoiler|on Stannis' part}}.

* ''The Recluce Saga'' by L. E. Modesitt Jr. are 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.

* [[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). [[Nightmare Fuel]] indeed.

** And as he mentioned in ''How to Write Science Fiction and Fantasy'', [[Orson Scott Card|Card]] actually wrote a novel in such a setting: ''Hart's Hope''.

** 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.”

* In the ''[[Coldfire 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 Bastard|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''.

* 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 ''[[Duel of Sorcery|Changer's Moon]]'', {{spoiler|[[Magic Knight|Serroi]] turns [[Evil Sorcerer|Ser Noris]] [[Taken for Granite|into a tree]].}} The price? {{spoiler|She turns into a tree herself}}. (Although that was less a function of the magic itself—she'd previously {{spoiler|turned [[Mooks]] into trees with no ill effect}}—than of using it on an opponent of such power.)

* Stephen Donaldson's second ''[[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 chronicles has Mhoram realizing {{spoiler|the key to power is despair, which will lead to the destruction of the Land.}}

== Live Action TV ==

* 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, {{spoiler|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]])

* In ''[[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; Buffys 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".

** This reappeared in the season finale, where {{spoiler|Merlin offered [[Balancing Death's Books|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.}}

* In the ''[[Supernatural (TV series)|Supernatural]]'' 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]] [[Evil Is Not a Toy|is not a toy]].

* 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 ''[[Kaizoku Sentai Gokaiger]]'', the [[Series Goal|Greatest Treasure in the Universe]] has the [[Reality Warper|power to change history and reality]], and confirms that it could be used to erase [[The Empire]] from history...but doing so would ''also'' [[Ret-Gone|retroactively erase]] all of the [[Super Sentai]] from existence. The Gokaiger end up deciding not to do this, since the Sentai mean too much to humanity and it isn't their right to make that call for the entire planet.

* The Defilers in the [[Dark Sun]] ''[[Dungeons and Dragons]]'' setting. 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 Dark Sun is a gigantic desert world, it's not hard to deduce the popularity of defiler magic.

* 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.

** 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.

* In ''[[Warhammer Fantasy Battle]] 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. [[The Chessmaster|Tzeentch is kind of a dick like that]].

* The magic system in "The Valdorian Age" (a setting for [[Hero System|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. ''[[Black Magic|Maho]]'' is directly powered by the shedding of blood - but good news! It doesn't have to be ''your'' blood.

== 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...)

* Whenever the Nameless One from ''[[Planescape: Torment]]'' {{spoiler|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}}.

** Subverted, however, with the Nameless One being able to shrug off almost any price that doesn't kill him. Thus, what would be a painful exchange for a [[Squishy Wizard]]--learning secrets of fire magic from an insane pyromaniac--is nothing more than the loss of a few hit points, and you ''regenerate'', so a few hit points won't hurt.

*** Then, double subverted with the {{spoiler|Pillar of Skulls}} and a particular (semisentient and evil) book of magic, which soon begin to ask for things ''aside'' from and greater than, just for an example, a taste of your flesh or you to commit some minor evil act.

* The ritual of Soul Exchange in ''[[Valkyrie Profile]]'' 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.

* In ''[[The Legend of Zelda: Twilight Princess|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.

* In ''Final Fantasy'' games, to use magic, you must sacrifice MP, the amount of which is proportional to the spell's power, most of the time.

* ''[[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. {{spoiler|Then he followed the path as agreed, [[Put on a Bus to Hell|petrification being the result]]}}.

* ''[[Futurama]]'' uses this trope when regarding time travel in ''Bender's Big Score''. Their theory states that two of the same people in different timelines can freely interact with each other. However, to correct the issue of having two of the same person, one will be "doomed" to perish in one way or another. The paradox is gone and the time stream is fixed.

* Eric gets a lecture to this effect from Dungeon Master in the "Day of the Dungeonmaster" episode of ''[[Dungeons and Dragons (animation)|Dungeons and Dragons]]''.

* The ending of ''[[X Men the Animated Series]]''' take on [[The Dark Phoenix Saga]] has Jean Grey [[Heroic Sacrifice|dying to stop the Phoenix threat]] as per source, but since here it was the real Jean posessed by a cosmic force, instead of [[Tomato Surprise|the force itself taking her form]], she really does die. The force itself is okay though, but it [[My God, What Have I Done?|realises that it was wrong]], and [[Must Make Amends|offers to ressurect 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.

* 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"<ref>In scare quotes because the energy still ''exists'', it's just not doing anything useful.</ref> some of the input energy to waste heat.

** There's actually [[wikipedia:Conservation law|quite a few of these]]. Some are played straight, but others are subverted and only hold true under most circumstances.

** 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 & [[I Need a Freaking Drink|those grading their papers]].

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