The law of equivalent exchange says that for anything to be gained, something of equal value must be lost. This means that if you put in the hard work, you will be rewarded with success. I am a half-metal alchemist who seeks to create a homunculus, an artificial human being without a soul. It possesses unique abilities despite appearing human, and would serve as the perfect slave as they are compelled to obey me. Using a transmutation circle , I was able to communicate with a being called "Truth", who says that I must sacrifice a human being in order to create a homunculus of equal value.

I plan to create an army of homunculi to serve my interests. After sacrificing a human in a ritual, the homunculus was created. However, it is a huge behemoth with mental deformities. Although it has its benefits, such as strength and endurance, it is far from "equal" as it lacks the intelligence to be really useful, similar to a stupid hulk. After experimenting, I eventually find that I need to sacrifice thousands of people to successfully create one single homunculus similar to a regular human.

I am happy that I have created the ideal servant, but it ended up being more expensive in time and resources that I was led to believe. This betrays the law that has governed reality for all time. Either this "Truth" is an idiot who doesn't know what he is talking about, or he is just full of sh*t and a liar. But as he is called Truth, he is supposed to be incapable of the second option.

How can the law of equivalent exchange fail on one of it's basic principles?

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    $\begingroup$ May I ask have you met the little man in the flask? $\endgroup$
    – user6760
    Feb 6 '20 at 3:04
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    $\begingroup$ Who determines what "equal value" is? An equal value for you may be very disproportionate for someone else. $\endgroup$
    – Alexander
    Feb 6 '20 at 3:09
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    $\begingroup$ You seem to be sacrificing souls to create a being without a soul. The math is wrong from the get-go. $\endgroup$
    – Halfthawed
    Feb 6 '20 at 3:52
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    $\begingroup$ @Halfthawed only if the soul is sacrificed. It may not be part of the equation - you just sacrifice the body. It just happens that without a body the soul doesn't survive. So, the deal is correct, you just didn't read the small print. $\endgroup$
    – VLAZ
    Feb 6 '20 at 6:05
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    $\begingroup$ To quote a sea devil: "One Soul is not equal to another." Yes, "All men are created equal" but that is before the law of the ordinary, which makes no attempt to evaluate a metaphysical entity like a soul. Do you think a sinner's soul would be worth the same as a holy man's? You want a good return on investment, bring more dirty souls or sacrifice a man with a pure soul. $\endgroup$
    – hszmv
    Feb 6 '20 at 14:05

10 Answers 10


You're forgetting the key point of "sacrifice"

All alchemy is filtered through the mind of the alchemist.

It's one thing to exchange one form of matter for another or one form of energy for another, but creating life, let alone intelligence, is tricky business. No equation or transmutation circles will provide sufficient information to delineate exactly what's going into the process - there is simply too much data to work with.

This is why the creation of life must involve the sacrifice of life. But it's not just the destruction of living matter - the degree to which the alchemist is aware of the life being sacrificed is critical to the process.

And there's the problem. You sacrificed a stranger - one who you didn't know or care about. The nuance of what their life meant was therefore lost in the transmutation, and you get back exactly what you gave - a piece of meat, no more, and no less.

No, the only way to create a proper homunculus is to sacrifice a person who is important to you. You must have a clear understanding of their mind on a deep spiritual level. Only then can the exchange truly be said to be "equivalent".

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    $\begingroup$ And this is why human transmutation is the most deeply forbidden act of alchemy. $\endgroup$
    – Zeiss Ikon
    Feb 6 '20 at 14:51
  • $\begingroup$ This is a lot like the loved one variant of the trolly problem coursehero.com/file/pg7idda/…. In that it is weighed by how many strangers would have to die for you to choose to save them over someone you care about. Since your alchemist clearly has a low value for stranger's lives (he can bring himself to kill them by the thousands), then it takes a lot of lives for him to hit that point. A person who would sacrifice his own child to save 2 strangers, only needs 2 people. $\endgroup$
    – Nosajimiki
    Feb 6 '20 at 17:48
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    $\begingroup$ "And there's the problem. You sacrificed a stranger - one who you didn't know or care about." Just to add to this - if you sacrifice one stranger and get X but sacrifice 100 strangers to get about 2*X, then it still holds up. You can value the life of a random stranger enough to feel some pity or remorse. But if you're killing dozens, then you don't really put much value on their lives. So, you get less back. It's a vicious circle - if you need to sacrifice MORE of something, you start to think LESS of it and thus decrease its value further and inflate the amount of the sacrifice. $\endgroup$
    – VLAZ
    Feb 6 '20 at 21:52

Because “Truth” is a liar

Never trust a being summoned from a circle, only dark things answer the presumptuous summons of men.

Truth is demon, a hunger from outside the world who intentionally misled you so that way you would end up killing more people.

How would you verify Truth’s claims before you did the sacrifice? You essentially took it on its word without knowing its true motivation, and it tricked you. The monstrous homunculus was actually made with Truth’s otherworldly powers in a method totally different from the Law of Equivalent Exchange, because Truth is from a different world with different laws, or used material from his world, taking part of the sacrificial exchange and keeping it for his own purposes. Truth didn’t even need you to kill for it to work, he just enjoys the act and hopes you kill more, not only because each sacrifice is enjoyable, but because he anxiously awaits you in the next world after you’re damned. He’s already got those other souls

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    $\begingroup$ TLDR: Don’t make deals with anything extradimensional. $\endgroup$
    – Joe Bloggs
    Feb 6 '20 at 8:13
  • $\begingroup$ Truth is not inherently evil as it is a force of nature. You can see that it has no will of its own because it mirrors whoever enters its realm. Its job is to keep balance by making alchemists pay a toll. Not knowing what you're messing with is the cause of all the failed transmutations. $\endgroup$
    – user71341
    Feb 7 '20 at 19:29

a huge behemoth with mental deformities

So there you have it. What it lacks in mind, it makes up for with body.

If you've ever played an RPG (tabletop or videogame) that allows you to min/max characters, you know that you can usually increase one stat by decreasing another. I specially like the S.P.E.C.I.A.L. system from the Fallout series:


They all range from 1 to 10, where 1 means you are a hair width's away from being completely disabled and 10 means you are a superstar in that field. For example, a character with a 1 in Strength can barely support the weight of their own clothes while a 10 in strength means you can carry more than 3x your own body weight.

A template human has a score of five in each attribute. In the game you start just like that, and you can increase a point in an attribute by decreasing a point in another.

So... What you did with your homunculus was getting a template body:

Strength 5
Perception 5
Endurance 5
Charisma 5
Intelligence 5
Agility 5
Luck 5

(total 35 points)

And you probably got this in exchange:

Strength 10
Perception 4
Endurance 10
Charisma 1
Intelligence 1
Agility 4
Luck 5

(total still 35 points)

They're just as min/maxed as average Joe, they are just more specialized towards brawling and gooning. The Law of Equivalence holds true.

  • $\begingroup$ This holds very true for why one might get a brute out of the exchange of one, but not why it takes 1000s of lives to make one that is both smart and strong. Using a system like this, 2-3 people should give you one hell of a homunculus. $\endgroup$
    – Nosajimiki
    Feb 6 '20 at 17:33
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    $\begingroup$ @Nosajimiki-ReinstateMonica well two average bros thinking together don't equal a genius. You have diminishing returns on that. $\endgroup$ Feb 6 '20 at 21:27

The laws were more like guidelines, anyways

The situation you describe reminds me greatly of issues that arise in the philosophy of utilitarianism. In utilitarianism, each thing has a "utility" metric assigned to it, and your goal is to maximize the aggregate utility of Everything with your actions. Thus if an action makes one person happy, and another action makes two people happier, then you elect to do the second action.

It gets famously murky when you try to do the aggregation. How do you go about aggregating happiness? How many unexpected deliveries of flowers is equivalent to curing one person's mother of cancer? 50? 100? 10,000? And how do you equate one person's happiness to others anyways? Critics of utilitarianism point to the possibility of someone being so pleased by the misfortune of others that the entire world feels compelled to comply. For example, if one person was so pleased by the deaths of other human beings that it outweighed the unhappiness of the dying person and everyone who knew them, the entire world would be compelled by utilitarianism to commit suicide. He wouldn't even have to go out and kill them. Likewise, if someone was mostly numbed, or mildly pleased at helping others, he or she would become a "happiness pump," sacrificing everything for the tiniest shred of approval.

Given these issues are not resolved issues in utilitarianism, I would expect the law of equivalent exchange to be similarly incomplete. I would expect that equivalent exchange was a reasonable model fit of reality for the scholars studying magic in this universe, just like how Newtonian gravity was a good fit at the time, even though it was wrong. For all situations the scholars were concerned with, equivalent exchange worked just perfectly.

So if you were exploring taboo magic, it may be taboo for a reason. It may be taboo because those that came before you literally could not model the consequences of your actions with their simplified models. Whether the real model looks more like relativity, more like quantum physics, or more like something that came out of Jeff Goldblum's mouth while the cameras were rolling, that's up to you!


Alchemy is the art of transferring matter.

Intelligence and Soul are not part of Alchemy but of an entirely different discipline. The reason that human transmutation is a forbidden art is because the math of alchemy is straightforward 1:1 ratio. The math of the other one is not entirely known, tried, or tested due to the variable ratio ?:1. (That and the tendency to murder its attemptor and attemptee in the process).

Simply put, Law of Equivalent Exchange is in place. You are combining it with an unexplored discipline.


Alchemy is more like thermodynamics than classical neutonian mechanics. Let's apply Carnot's Rule to magic. You sacrifice the human, which generates a huge blob of magical potential, and then you get magical work done by exploiting the flow of the magic as it winds it's way back to the low-magic reservoir. This results in an efficiency less than 1, naturally, so it isn't that surprising that you got something worse than a human back. And what's worse, you probably want to keep things simple, so you use the room as your low-magic reservoir. Unfortunately you decided to do this experiment in your alchemy lab, where you've already done a bunch of magic, so your "cool" side is actually pretty warm.

And this provides only an upper bound. In a real transmutation, there is always some nonideal loss. You are probably a typical renaissance or medieval alchemist. Your magic vessel is leaky, and it leaks more the more magic you try to jam into it. Human souls have a ton of magic. The practical issues involved in killing 1000 humans makes the process a bit slow, so your magic vessel has plenty of time to leak, and each sacrifice results in a great spout of magic -- it isn't easy to catch it all.

The first documented steam engine was apparently around .5% efficient -- that's right, not 50%, but less than 1%. So you are in the right ballpark with 1000 sacrifices. If you were as bright as Newcomen you could probably get it down to 200.


As it includes magic & ethics (what is "equal"?), I'd say this borders on being opinion based but I still would like to propose two options to resolve this:

1) parts of what you exchanged went somewhere else

2) it actually works as intended, just not how you imagined it to be

The first point covers various possibilities:

"Truth" lied to you and siphoned off some of the sacrifices for its own gains.

The transmutation process is not 100% efficient, the more complex the endproduct the lower the efficiency.

The sacrificed people can resist being used their souls ripped from their body try to flee, slash at you, try to curse you, etc. To your advantage, the transmutation process prohibits them from doing so but that also takes energy.

To lead to the second point, there might just be a universal value to things, beyond any human version/concept of what "equal" is which caused you to misjudge the price required.

The second option is that it actually worked properly.

To create anything with alchemy and equal exchange you need to put in what is required to get the desired output. So if you want to move a rock and sacrifice food, it takes the number of calories that the food contains to move the rock. If you want to create an intelligent, obedient, healthy and overall "perfect" servant you need much more than just a single human life to that. Possibilities range from that the universe just values the creation of new life much more than already existing one to that the whole process just assumes what it would have taken to create such a servant without alchemy. Quite inhuman and to us morally wrong but to get such a servant you would probably have to breed and domesticate a bunch of humans like dogs. You don't get the perfect, completely obedient servant just like that. The exchange does not care that it might be overkill and that your requirements are quite rediculous, any normal loyal servant would have sufficed but that homunculus would do anything for you, even after years of torture it would still serve you to its last breath while also remaining psychologically stable, something that you would not get from a regular normal servant.

Thus the whole process takes way more energy than you thought, its generations worth of work and energy that it takes to get what you want.


you give: 1 +X*500*(body & soul sacrifice) you get: 1 body imprisoning a random compelled demon of X rank

The cost over the original meat prison is (1 soul+X500(sacrifice)) is equal to the energy to summon, imprison and compel the demon. The more intelligent they are the harder they are to summon, imprison & compel.

The resulting physical stats are roughly original body +25% of the demons physical stats in their original dimension. The resulting intelligence & 'magic' stats are roughly 25% of the demons intelligence & 'magic' stats in their original dimension. The original bodies intelligence & 'magic' stats are wiped out.

The biggest gain is health rejuvenation; this is equivalent to the demons original health recovery. This is how a demon can be used to jump start a recently dead body.


The Missing Ingredients

Since your goal is an artificial human, you'll need the appropriate raw materials for a human. Do you have them all? There are 11 you will need in appreciable quantities and several more you will need in trace amounts. If you don't have them, then the transmutation will have to manifest those elements from somewhere with some of the sacrifice's energy.

That does not even go into the idea that if you are creating an artificial human, that the pile of raw materials that you are using need to be rearranged into the correct configuration to function as a human. Sure, your recipe might create a superficial shell of a human, but it probably starts with a pile of stuff. Transmuting that requires energy drawn from the exchange.

Value is Relative

Truth did not lie -- you got a homunculus of equal value. But while one can easily determine the value of physical materials and the cost of rearranging the materials into a homunculus body, what is the value of the metaphysical parts of the body?

A soul is one of those things that science can't quite quantify. How much value does it hold? How much energy can it provide? We just don't know. Likewise, what is the value of the life you are sacrificing? Sure, there is a physical value of it -- the materials, the energy in binding a human together -- but there is something else extra that makes it a life and not a ambulatory mass of chemical reactions.

Other answers have touched on this concept: A random soul and life holds less value than the soul/life you want to create The difference in parameters of the lives in the exchange traded mental stats for physical ones.

And of course, perhaps sacrificing multiple lives has diminishing returns -- each additional life given to your creation now has less individual meaning than the single life you have created.

A Failure to Understand

A third option is that you have taken Truth's words at face value. To make a Homunculus, you need to sacrifice a human. Well, yes, but you have only sacrificed a life. In part this is related to the above point, but more relevantly the soul is not consumed in the transmutation. That you did not understand Truth in this matter is either a failure to communicate or a failure to consider things beyond the physical.

Also, Truth is a troll. Not as big of a troll as that dimension-hopping vampire a couple of universes over, but a troll nonetheless. They have not lied, Truth has just not told you everything.

Also from the question, Truth seems to have not taken anything from you for this knowledge like others that have met Them. It does not sound like you have gained a forbidden insight for a great cost. Or perhaps you did, and Truth is more interesting than I previously thought.


Transmuting the unknown is inefficient

Transmuted matter is only preserved if transmuted properly, if you take lead and reassemble the atoms to get gold you will get an object of equivalent mass, because you have understanding of the structure of atoms. You are fusing nuclei together to get a denser object thus you are not losing mass in the transmutation process.

When transmuting a person what exactly are you transmuting? The body or the life force (soul)? Because of a human beings complexity you cannot visualize every aspect of what you are transmuting thus you lose mass or energy in the process, leading to an inefficient transmutation. If you transmute mere flesh you can get a very buff homunculus with relative ease, whereas if you transmute the soul you're walking into unknown territory. Even with modern science we still do not know what constitutes a consciousness, so how could we manipulate it in the first place?

You're obviously basing this on fullmetal alchemist but you seem to have forgotten that the hundreds of souls required are actually used to make a philosopher's stone not the homunculus itself. The series has already introduced us to homunculi with single souls (the creepy ones with a cyclops eye). They don't possess as much energy as the seven sin homunculi but are still very resilient. The sin homunculi however are philosopher's stones made into homunculi, thus the stone expends its soul energy to rebuild the homunculi when damaged.

Permanent loss has the highest value

When a soul is sacrificed they are lost forever, thus their high value. In FMAB Edward sacrifices his alchemy permanently, which allows him to bring back whatever he desires. This sacrifice was enough to bring back an entire human being back. So using a similar principle sacrificing something permanently could give you something of greater value.

My advice is to use the human reproductive system to create an infinite amount of humans to use in your experiments. With this method you are essentially exploiting the humans ability to produce new souls thus your robbing the money making machine. Using this method your problem of inefficiency won't be a problem anymore because humans are a renewable natural resource. Amoral? Yes, but no one will complain about humans being stolen.


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