The Laws of Magic: Control

It seemed that every new room in the Atheneum Arcanum was bigger than the last, or maybe Cedri was simply dreaming. Vaunted, high ceilings--impossibly high--held aloft by numerous columns rising out of the floor like the trunks of trees. The floor itself was a cool, polished granite, shining back the first-year progeny's face as she glanced down at it. Various sounds, sights, tastes, sensations all floated amid the air till it felt charged to burst. The booming voice of the instructor, though, was somehow able to return her to the here and now.
"Magic," he began, "is a will to power." The man, tall, swarthy, and crinkled with age, snapped his fingers. A tiny ball blinked to life above the tips of his thumb and forefinger, shifting through the spectrum of colors, opacity and size flickering as it did, causing the air immediately around it to haze. Even so small a demonstration was enough to draw out a low murmur from the pupils. "It begins--like all things do--with ether. Without it, nothing could be," the magical ball vaporized to punctuate the point, "but without our minds and our will, our art could not be..."

Manifestation

Magic as a concept is a rather vague and nebulous term. There are broad generalizations that are agreed upon as rote fact; magic is at its base the manipulation of ether, any sapient being has the potential to manipulate ether, and all things respond to this manipulation. The hows and whys, though, are a muddier subject.
In essence, there are three broad types of magic user, all of which are differentiated in how they gain the requisite ether to cast their spells, and how they control said energies.
The most common are magi. A mage is able to tap into the pools of ether innate to their own body, and use this to fuel their arcane arts. This is a double-edged sword, for while it allows a practiced mage unparalleled control over the power, extent, and duration of their magic, it is both physically exhausting and potentially lethal. As ether is the lifeblood of all creation, to be sapped of it is to risk death. Therefore, the level of power a mage can exert is limited both by their metanatural constitution, and their concentration. Despite these hurdles, the fundamentals are rather easy to teach and to practice, and as such, most magic users are more than capable of living their lives as a mage without much risk.
Next, there are warlocks and witches. The term is steeped in negative connotation, and (to many) rightly so. Where the mage draws upon themselves to fuel their casting, the warlock takes from without. Generally, this can be easily managed by drawing on the ambient ether present in all places, or pulling from inanimate objects. In more drastic cases, and in most of the powerful rituals and spells that have made warlocks and witches infamous, the amount of ether required demands a living host. Without fear of any harm to themselves, a warlock may freely siphon the life from an animal or person, whether in small amounts or enough to leave behind nothing more than a withered husk, and focus it into their craft. Warlock magic lacks the artistry or control of the magi, but it bleeds raw power, and can reach heights even skilled magi could only dream of.
Lastly, there exists a third type of magic user so uncommon that most aren't even aware of their own power. Ciphers, occasionally known by the terms 'psychic' or 'mentalist,' are far and away the most powerful of magic users. Whether by some immeasurably expansive natural ether pool, or a reality-bending psyche, ciphers are able to force ether to obey their will. This is the most fundamentally basic form of magic, the imposition of will over material things, and it is expressed in its purest, most devastating form by ciphers. The overwhelming majority of ciphers will go their whole lives unaware of their potential, at most sporadically creating outcomes beneficial to themselves from idle daydreams, but easily written off as a string of good luck. In rare cases, a cipher is made aware of their power, and this alone is enough to set them on the level of most other magic users. Should one be found by another, more powerful cipher, and taught how to control their magical ability, though, the cipher in question would become legendarily powerful. Ironically, or perhaps due to the nature of their abilities, more powerful ciphers tend to manifest megalomaniacal personality disorders, believing themselves to be the center of everything. Some of history's most dangerous and hated individuals, such as Zi the Terrible, were this type of cipher.

Localization

Theoretically, any sentient, sapient creature can control magic. In practice, there is a certain level of natural talent required, and even above this a necessity to be trained. A mage without training is like a fire unchecked: it will burn--brightly even--but it will destroy itself. Unable to regulate the flow of their internal ether into proper channels, the untrained magic user is almost guaranteed to overdraw, leaving themselves severely weakened if not outright dead. This is why magical training and the registration of the magically gifted has become mandatory in both the Empire and abroad.

Type

Metaphysical, Arcane