The Law of Equivalent Exchange governs the use of alchemy in Fullmetal Alchemist, and with rules come consequences.
In Fullmetal Alchemist: Brotherhood, the practice of alchemy stands at the pinnacle of science. It allows its practitioners to change the composition of matter through the process of transmutation, a skill that is useful both in combat and in everyday life. Despite its many uses, alchemy is a science and as such is subject to the laws of the universe. The principle of alchemy surrounds the law of equivalent exchange.
Although it may seem complicated, the simple concept is absolute: something cannot be created from nothing. In order to produce something, another thing of equal value must be exchanged and then it is lost. The Law of Equivalent Exchange limits alchemy’s infinite potential, and the show explores why that’s actually a good thing.
Alchemy Equivalent Exchange Limits FMA Act
The law of equivalent exchange branches into two basic laws: the conservation of matter and the conservation of providence. The law of conservation of mass dictates that an object cannot be created from nothing, and if it is deconstructed, that object will be reduced to components whose sum is equal in mass. For example, an object with a mass of one gram can only be transformed into an object with a mass equal to one gram. If a one gram object is deconstructed, the process will yield components that add up to 1 gram.
The Law of Natural Providence states that objects composed of a certain material or element can only be transmuted into objects of similar composition. For example, stone objects can be transformed into other stone objects, but not into objects primarily composed of water.
Alchemical Taboos: Human Transmutation, Reflection, and Truth
Alchemy, while capable of performing miraculous feats, is not without limits. Reviving the dead through the process of human transmutation is impossible and considered taboo in the world of alchemy. In order to revive the departed, both their soul and original body must be transmuted, Alphonse Elric states that a wandering soul can only return to its original body and vice versa. This is why his soul begins to reject the armor, as it is not his soul’s own vessel.
Fullmetal Alchemist demonstrates that the value of the human soul is unquantifiable, and since something cannot be created without losing an object of equal value, something of infinite value can never be equally replaced. However, this does not stop alchemists from trying, because sometimes the pain of losing a loved one outweighs logic. If human transmutation is performed, the alchemist in charge pays a high price, as exchanging a soul of infinite value for materials of finite value throws the alchemical equation out of balance and causes a rebound.
Rebounds takes a toll on the taboo offender to rebalance the exchange: Alphonse loses a body and Edward loses a leg when trying to revive their mother, Edward also loses an arm when he attaches Alphonse’s soul to the armor, and Izumi Curtis is robbed of multiple organs after she tried to revive her child. The toll will be taken even if the taboo is committed unintentionally or against his will, as Roy Mustang is robbed of his sight despite being forced by his father and the Homunculus to undergo human transmutation.
Human FMA transmutation is possible with the Philosopher’s Stone
The penalty for human transmutation is severe, not only because it violates the law of equivalent exchange, but also because denying this law means that one has effectively tried to play God, the God in Fullmetal Alchemist being Truth. Anyone who attempts human transmutation is teleported through their own personal Gate of Truth (which allows alchemy to be performed) and brought before the being for whom the gate is named. Truth is God in the sense that He has infinite knowledge, including alchemy, world history, and much, much more. When you break through the Gate of Truth, this infinite knowledge appears to the target alchemist and consumes them. Along with this knowledge, entering the Realm of Truth also allows the alchemist to perform alchemy without the use of a transmutation ring (the basic laws of equivalent exchange still apply).
Using the Philosopher’s Stone is the only way to do human transmutation without rebounding. This is because Philosopher’s Stones are composed of multiple souls, allowing their contents to be exchanged equally in human transmutations. However, even if possible, the morality of the act is questionable, as the creation and use of the Philosopher’s Stone is unethical to begin with.
The only other example of a successful human transmutation is Edward Elric’s final transmutation, in which Truth offers his own Gate of Truth and thus his ability to use alchemy in exchange for Alphonse’s soul and body. Since the values available are incalculable to begin with, whether this is a true equivalent exchange can be left to speculation. However, it is undeniable that in this moment Edward sacrifices absolute power, an idea that, if realized, is of infinite value, in favor of saving his brother. Truth is an omniscient being, just like the alchemist’s mirror image before her, and as such can discern what a person holds most dear. To Edward, alchemy is what he is and was his most prized possession. His willingness to sacrifice what was of greatest value to him was more than enough to satisfy Truth and thus the law of equivalent exchange.