Equivalent Exchange

Lore & Background

In Amestris, alchemists draw patterns called Transmutation Circles to create or form almost anything from existing physical substances. However, the Law of Equivalent Exchange ensures that no matter can be created from nothing. The one absolute taboo is Human Transmutation, which attempts to create a human from body substances; this inevitably fails because no natural physical substance equals a human soul. When alchemists attempt this forbidden act, they are confronted by Truth, a pantheistic godlike being who appears as their reflection. To rectify the non-equivalent exchange, Truth takes a part of the alchemist's physical body as punishment. These lost flesh parts are often symbolic of what the alchemist values most or what they attempted to acquire. Additionally, these individuals see the Gate of Truth, gaining simultaneous knowledge of all information in the universe—a experience that frequently drives survivors mad but allows them to transmute without a circle.

In Their Own Story

Edward and Alphonse Elric lived in Resembool with their mother Trisha until she died from an illness. After training under Izumi Curtis, the brothers attempted human transmutation to resurrect her. The backfire resulted in Edward losing his left leg while Alphonse lost his entire body. To retrieve Alphonse's soul, Edward sacrificed his right arm to bind it to a suit of armor. Later, Dr. Marcoh revealed that philosopher's stones are created by trapping thousands of human souls to bypass the Law for human transmutation. These stones fuel Homunculi, granting them regeneration and immortality until their power is exhausted. While Father founded Amestris to amass a population large enough to create a massive philosopher's stone on the Promised Day, the Elrics learned that even this method relies on the ultimate price: the lives of thousands.

Reader's Guide

State Alchemists are government-recruited experts given code names based on their unique areas of expertise. They operate under the strict understanding that transmutation follows scientific rules. The only way to bypass the Law for human transmutation is using a philosopher's stone, which acts as a substitute for a soul. However, this substance is made by trapping thousands of souls through alchemy. Homunculi created from these stones possess superhuman abilities like regeneration but do not age and can only be killed by destroying or exhausting their stone's power. The narrative follows the Elrics over three years searching for such a stone to restore their bodies, navigating a world where the law is absolute: any attempt to create something without all parts present results in failure and severe physical tolls enforced by Truth.

Did You Know?

• Truth appears as a reflection of the alchemist themselves and takes flesh parts that are often symbolic to what the alchemist values most.
• Survivors who maintain their minds after seeing the Gate of Truth gain the knowledge to transmute without using a circle.
• Homunculi can only be killed by destroying or exhausting the power of the philosopher's stone inside them, as they typically do not age.
• The Law of Equivalent Exchange is a natural law that states transmutation cannot be successful if used to attempt to create something without all parts present.