Alchemy is, as it is understood in the Fullmetal Alchemist series, the ancient metaphysical science/mystical art of manipulating and altering matter by using natural energy. This act is known as "Transmutation" and its sequence is usually described as:
- Comprehension - Understanding the inherent structure and properties of the atomic or molecular makeup of a particular material to be transmuted, including the flow and balance of potential and kinetic energy within.
- Deconstruction - Using energy to break down the physical structure of the identified material into a more malleable state so as to be easily reshaped into a new form.
- Reconstruction - Continuing the flow of energy so as to reform the material into a new shape. The proper application of this craft requires not only a full understanding of chemistry and ancient alchemical theory, but also a sort of natural talent towards recognizing and manipulating the physical objects with energy, which require uncommon levels of intelligence and aptitude. Those remarkable individuals capable of studying and practicing alchemy are known as "Alchemists".
The mystical practice of alchemy to create objects out of raw matter or turn one object into another is widely believed to be capable of anything - indeed alchemy is often viewed as magical or miraculous by those unfamiliar with the craft - but it is a science and as such is subject to certain laws and limitations, all of which fall under the concept of Equivalent Exchange: "In order to obtain or create something, something of equal value must be lost or destroyed." In standard practice, Equivalent Exchange is separated into two parts:
- The Law of Conservation of Mass, which states that energy and matter can neither be created from nothing nor destroyed to the point of elemental nonexistence. In other words, to create an object weighing one kilogram, at least one kilogram of material is necessary and destroying an object weighing one kilogram would reduce it to a set of parts, the sum of which would weigh one kilogram.
- The Law of Natural Providence, which states that an object or material made of a particular substance or element can only be transmuted into another object with the same basic makeup and properties of that initial material. In other words, an object or material made mostly of water can only be transmuted into another object with the attributes of water.
Since the alchemical forces being manipulated are not human in origin, but of the world as a whole, the consequences for attempting to bypass the Law of Equivalent Exchange in transmutation are not merely failure and cessation. When too much is attempted out of too little, what occurs is called a Rebound, in which the alchemical forces that are thrown out of balance on either side of the equation fluctuate wildly of their own accord in order to stabilize themselves - taking or giving more than was intended in often unpredictable and catastrophic ways such as accidental mutation, serious injury or death.
Though no machine or equipment is needed to produce the energy necessary for transmutation, merely understanding the sequence of transmutation and the limitations of Equivalent Exchange is not enough. Just as the processes of "Comprehension, Deconstruction, Reconstruction" and "In order to gain, something of equal value must be lost in return" are cyclical concepts, the circle itself is the foundation of alchemy.
In order to begin an alchemical transmutation, a symbol called a Transmutation Circle is necessary. A Transmutation Circle can either be drawn on the spot when a transmutation is necessary (in chalk, pencil, ink, paint, blood or even traced in dirt) or permanently etched or inscribed beforehand, but without it, transmutation is generally impossible and all Transmutation Circles are made up of two parts:
The circle itself is a conduit which focuses and dictates the flow of power, tapping into the energies that already exist within the earth and matter. It represents the cyclical flow of the world's energies and phenomena and turns that power to manipulable ends.
Inside the circle are specific alchemical runes. These runes vary widely based on ancient alchemical studies, texts and experimentation, but correspond to a different form of energy, allowing the energy that is focused within the circle to be released in the way most conducive to the alchemist's desired effect. In basic alchemy, these runes will often take the form of triangles (which, when positioned differently, can represent the elements of either water, earth, fire or air), but will often be composed of varying polygons built from different triangles. For example: the hexagram is a commonly used base rune in Transmutation Circles because it creates eight multi-directional triangles when inscribed and can therefore represent all four classical elements at once. Other, more esoteric runes (including astrological symbols, symbolic images and varying lines of text) are prevalent and represent a multitude of other, specific functions for the alchemical energy that is released.
A Transmutation Array is similar to a transmutation circle in that it is used to circulate the energy used in a transmutation. However, unlike a transmutation circle, the runes are not confined to the circumference of the circle and may use the circle only as a small aspect of their function. In some instances, a transmutation array may not even be a circle at all, using different concepts to bring about the circulation or release of the energies involved. Transmutation arrays are often found as full body tattoos on alchemists due to the shape of the human body. It is also possible that the non-cyclical nature of transmutation arrays amplifies the 'destruction' stage of alchemy, as they are seen on places such as Scar's right arm and the Grand Arcanum. It is shown in the Fullmetal Alchemist 2009 anime that reconstruction is also augmented by transmutation arrays as shown with both Scar and his brother's other arms.
Over the nearly 400 year history of alchemy in Amestris, great strides in alchemical research have been made by mixing these runes together to augment their power, converge their results and create entirely new pathways of utilization.
Unfortunately, these experiments have given birth to a dark and sinister side of alchemy. Whether out of despair, malice or inquisitive hubris, several alchemists have been known to attempt the application of transmutation to human bodies and souls, in essence, playing god with human lives. But, just as the Law of Equivalent Exchange applies to the transmutation of non-living matter, devastating rebounds can occur in Human Transmutation because human lives and souls are priceless according to the flow of the world.
Attempts to bring deceased human beings back to life are the most common practices to be called Human Transmutation and play a significant role in the Fullmetal Alchemist series. Using various experimental theories and methods, multiple alchemists in the manga and anime have endeavored to resurrect dead loved ones, but such pursuits are always failures, forbidden by the flow of the universe and alchemy itself.
It is determined that resurrective Human Transmutation is impossible because a soul that has left the mortal coil has passed on into the afterlife and can never be called back by human means. The attempt will cause a rebound due to both the inherent lack of any particular substance able to match a human soul in value and the fact that the initiated transmutation is reaching for an unattainable goal. Of the known attempted Human Transmutations, the rebound has been the "taking" of parts of the initiator's body out of the living world and into the void of the flow (in the case of the Elric brothers' attempted transmutation of their mother, Edward's left leg and Alphonse's entire body were taken and in the case of Izumi Curtis' attempt to revive her dead child, several of her internal organs were taken).
In addition, for having trespassed in God's domain with Human Transmutation, the initiating alchemists are essentially called into The Gate of Truth to face God itself. Being pulled through the gate grants alchemists great alchemical and universal knowledge - in exchange for paying a physical toll which usually takes the shape of the body parts "taken" by the rebound - and the ability to perform transmutations without a circle.
The next most referred-to form of Human Transmutation is the concept of an alchemically created human, and artificial human, called a "Homunculus". Though largely considered impossible due to the fact that all recorded and reported attempts to make one have been failures, this act is one of those specifically noted in the Amestrian nationwide prohibition of Human Transmutation.
Another terrible form of Human Transmutation is the manipulation of human souls. Though appearing on no official records, there have been experiments with Human Transmutation involving the extraction of souls from human bodies and the alchemical binding of said souls to inanimate objects usually by way of a rune drawn in blood on the object itself. Though not all the specifics of soul binding have been made clear, it has been explained that the iron in the blood bonds alchemically with the iron in the object (as most instances of soul binding has used metal armor as a vessel) and the blood itself remains bound to the soul of the person from which it was taken. The Blood Runes themselves differ based on the theories and style of whatever alchemist performed the binding, but the three different Blood Runes that have been revealed depict a spark or flame (presumably signifying a soul) hemmed in by other symbols in a blood-drawn Transmutation Circle that suggests a soul trapped within a container. In essence, these souls exist in the mortal plane without their bodies, are able to manipulate the objects to which they are bound and communicate verbally with beings around them but, of course, there are caveats.
Despite the fact that these souls cannot feel pain or die by conventional means, since the "bodies" they now inhabit are not mortal, the act of binding two such different things together is only temporary, as the soul and vessel will eventually reject each other and separate.
Though the manipulated soul is independent of its original body, the issues regarding the storage of knowledge and memory suggest that, for a soul binding to remain intact, the original body must remain alive somewhere. This creates another issue, as the soul and its original body will be inexorably drawn to one another.
The Amestrian government has experimented with soul manipulation and binding under the command of Father, but the case of Alphonse Elric's soul binding is remarkably unique as the only known instance of a particular human soul being purposely called back to the mortal plane from the Gate of Truth. Edward Elric, for performing this brand of Human Transmutation, let his right arm be taken as the toll and drew a rune using his own blood. It has been posited that this was only possible because the two brothers had been pulled into the Gate together and may have had their spirits crossed in the process. Additionally, the body of the soul-binding victim Barry the Chopper was infused with the soul of a lab animal and remains as the only known instance of a soul being bound to a living vessel. It is also unknown whether the act of transmuting the souls of Barry the Chopper and the Slicer Brothers resulted in a rebound or appearance of the Gate of Truth.