Definition: The art and science of manipulating the properties of various substances through the addition, subtraction and/or alteration of magical fields. The typical application of these efforts being toward creating potions, elixirs, and other items. It is a traditional province of Zebras and can be similarly mastered by Earth Ponies but, without specialized tools, no other species can typically progress in the craft beyond that of basic chemical combination.

Explanation: Considered a compliment to the more contemporary science of chemistry, alchemy can be stated to involve the same basic applications in many ways in that it, too, is the study of composition, structure, properties and change of matter. Where the two sciences differ, however, is in the focus of the science. While chemistry involves itself exclusively in the inner workings of matter, alchemy is the study of its fields.

Through extensive study all substances, organic or not, of sufficient complexity have been determined to maintain some level of magical field, being an area of ambient magical activity within some radius of the substance which, while having its own properties and behaviors, is intrinsically linked to the substance's state and composition. These fields, in many ways, define the properties and role of the substance within the world at large. In fact, studies have shown that powerful mages have been capable of engendering substances strictly through the creation of their accompanying magical fields, not unlike how the encouragement of certain electromagnetic fields engenders the presence of flowing electrons within a wire.

From an alchemical perspective, substances can be defined as a set of properties and roles. Properties being, generally, the physical attributes that describe a substance’s composition. Roles being the substance’s relative "purpose" within the world at large.

Roles, in this context, are by far the more abstract defining trait of a given substance. Water exists to hydrate essentially every living organism on the earth, to provide an hospitable environment within aquatic life can thrive, to keep the earth cool in maintaining a habitable environment for all living things, etc. As an aside, when the role of a substance correlates with their actual attributes, it is considered to be “in balance”. When it is not, it is considered “out of balance”. It is not, generally, unusual for a substance’s role and its actual attributes to “disagree”, but it is worth considering as it is always easier to bring a substance in balance through alchemy than it is to take it out of balance.

In any case alchemy, in all its forms, involves itself in the manipulation of these roles. It is the skewing, diminishing and exaggerating of the properties, purposes and balance of a substance. At the lowest levels of alchemy, this is essentially indistinguishable from the practice of chemistry, with the exception of a typical preference for particularly potent magical substances over the mundane. To those adept or higher in skill, however, this becomes a very powerful and dynamic craft, the alchemist in question utilizing their own magical energy to saturate and manipulate the magical fields of a substance or substances, aligning their roles somewhat like how one might magnetize a piece of metal to align the substance to behave in a certain way that would. Through various methods of preparation, the substance then becomes exaggerated or diminished in tune with the alchemist's purpose.

As an example, if a seasoned alchemist wished to craft an explosive, they would have to look no farther than the earth itself. Grinding soil in their hooves, they could quickly refine the soil's innate energy from barren, to fertile, to fertilizer, to fuel. The result of which's properties, depending on the time devoted to refinement and the skill of the alchemist, could potentially match or surpass that of gunpowder. Steel can become rust or vice versa, become malleable, even melt away. Water can take on any number of states and properties. Even become a poison or sludge. All of this due to the realignment, or outright establishment, of the substance's magical field.

Disambiguation: In the most basic of laypony terms, if something could be described with an adjective (luminous, hard, life-giving, pleasant, warm, sharp, translucent) a skilled alchemist can amplify it (brilliant, impregnable, rejuvenating, wondrous, searing, razor-sharp, almost-invisible) or rebuff it (dark, soft, deadly, horrible, cool, blunt, opaque). In addition, if something is capable of doing something through the addition or subtraction of energy to create or reverse a change to its makeup, an alchemist can induce such changes (IE inducing, delaying or reversing a chemical reaction, as well as state changes).

All of this aside, while it might be possible for a powerful alchemist to, essentially, create substances from nothing, as well as skew other substances to take on fantastical properties, all of this involves some degree of instability. The realignment of magical fields is a delicate process and a lack of balance between a substance’s roles and the attributes being manipulated creates a strain on its magical field. Simply put, it is always better to start with a substance having as close a role to one’s intended purpose as possible. If not, the alchemist risks either a subpar result or a potentially toxic byproduct or side-effect as the strained magical field begins, itself, affecting the fields of the substances around it.

Many an alchemist has been driven mad by the unforeseen, poisonous effects of attempting too much with too little. Such is the danger of the science.

In any case it is no small surprise, giving the combination of both the complexity and the potential applications of the craft, that there are few large population centers without at least one alchemist in service to some capacity.