Equivalent Exchange

Equivalent Exchange is an important law of alchemy and a recurring theme throughout the series. The first law of Equivalent Exchange states that, to create, something of equal value must be lost. It is similar to the laws of conservation of mass and conservation of energy.

This alchemical law can, however, be broken by one using a Philosopher's Stone, which allows an alchemist to create without sacrificing something in return.

"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." -Alphonse Elric