Magic is governed by Laws pertaining to the interaction of the Cognitive Realm with the Material and Ethereal realms. These laws are outlined in the Unified Theory of Magic, written over several decades of research by dozens of gifted wizards. Casting magic is accomplished via merging your Cognitive desires with the Material Realm.
The Three Primary Realms of life are detailed as such:
The Cognitive, aka The Source: This is a realm existing purely of thought, unconsciously created by all intelligent beings. The more creatures believe the same things, the more powerful that being/place/thing is in the Cognitive. Enterprising wizards have traveled to this realm by merging their Material presence into their Cognitive presence temporarily. These wizards have found that universally known things such as fire or towns have a very solid presence in the other realm. Many theorize that this is where the Gods reside, but this theory remains unproven due to the expansive nature of the realm.
The Ethereal, aka the Spirit World: The Spirit World is much more difficult to travel to, and a few attempts at traversing the realm have ended in disaster. One notable instance was a small research party of junior wizards led by Researcher Kline in 150 ATC; the party was investigating the effect Material items have in the Ethereal, when they were attacked by… something. The surviving students refused to speak of the creature, only that it was able to completely devour the projected bodies of their teacher and several students, causing their Material bodies to completely, instantly die. Those studentsthat made it back were placed in an Asylum, with only one able to recover his sanity. That student refused to practice any further projection or teleportation spells. To this day, the occasional enterprising wizard or treasure hunter will find a way into the Ethereal, and either die or leave empty handed and forever changed by the experience.
The Material, aka Reality: This is the realm where everything we know and do exists. This realm seems to be the most changeable, and has the most lasting impact on the other Realms. It is currently theorized that the Material has the strongest connections to the Cognitive and Ethereal, and exists in between the two, considering the potency of magic and the ease with which thoughts and spirits are manipulated here.
The second half of the Unified Theory of Magic involves the Three Aspects of Magic, of which at least one is required for all spells. The three Aspects are detailed as such:
Vocal: Vocalizing allows a practitioner to shape their desires. It is a well-documented and known fact that most spells will fizzle and occasionally even backfire without a Vocal component. Oddly, the actual content of the vocalization does not matter, only that the caster speaks what they consider to be their command word or desire. As an example, some less imaginative wizards simply speak the effect, such as Fireball or Hold, while other wizards will make up completely original words known only to them, such as Flangeth or Hillthorp. This is generally considered best practice to keep enemies more in the dark as to what you are casting.
Somatic: Many spells require you to physically shape the effect, such as the Acid Splash cantrip requiring the caster to form a sphere with his hands, allowing the acid to form into a ball there. Many spells that require this Aspect will completely fail or backfire horribly without adequate shaping, due to the formless magic simply going wherever fate determines it should. It has been found that attempting to shape these spells subtly, such as forming a small ring with ones fingers instead of forming one with their arms is possible, though it requires a great degree of skill and focus to do so. Most of those with the instinctual control required to do so are Sorcerers, those born with a Blending and some sort of magical ancestry. Other practitioners have been known to have this ability, though it has always required intense focus and training, and occasionally additional magical energies.
Material: Many spells require an additional focus, usually an item that builds an association with the effect in the casters mind. Diamonds are used in resurrection spells as most associate them with longevity or an immutable form. Most spells require a small item that can be reused, such as a length of iron, representing rigidity, used in Hold Person spells. Some spells will consume their associated materials, usually due to the potency of the spell in question. Interestingly, Arcanium has been found to be an effective stand-in for many reagents, it is as of yet unknown exactly why, though it is attributed to their incredibly complex magical nature. Any spellcaster that requires a valuable gem or some kind of consumable item can use an amount of Arcanium in its place.
Wizards, Arcane Tricksters, Artificers, and Eldritch Knights: you have learned magic through your own intensive studies and practice. It does not come naturally to you, and you must work to control your Cognitive presence in order to produce magical effects.
Clerics and Paladins: your magic is gifted to you via your preferred deity. Your deity gains its power in the Cognitive through the worship of people, literally gaining power through their follower's belief in their power. This magic is a form of faith, and is derived from drawing that entities power from the Cognitive into the Material.
Sorcerers: you were born with a gift. That gift is either a slippery connection to the Cognitive (wild magic) that allows you to easily call forth different magics as easily as another learns to walk, or an inherently powerful bloodline (draconic, celestial, lycanthropic, etc.). Your blood has imbued you with the knowledge to wield magic without training or study.
Warlocks: You gain your magic through some sort of pact, drawing from a potent essence in the Cognitive, one of deep fear, hate, or cunning. This powerful magic comes through in fits and starts, lending you great strength but threatening to destroy you if you draw too on it too deeply.
Bards: Your instrument is an extension of your will, allowing you to focus and shape the thoughts and desires in your mind into magic with the skill that so many wizards strive for years to achieve. When you play, your hands express your desires in a deeper, more subtle way, creating magics through the same Cognitive manipulations as wizards would.
Rangers and Druids: Your magic is obtained from the natural world, bypassing any training or study by drawing on the immutable laws of nature as an anchor for your magic. Instead of training to focus your will and knowledge to shape your desires, you focus on natural processes and effects that are already well shaped in your mind, and draw those forth. In essence, you use nature's own presence in the Material to draw similar effects through the Cognitive.
Monks: Your magic is based in the Spiritual instead of the Cognitive, and is much less prone to interference from Arcanium. Mental focus and discipline is required to keep your Material presence in perfect sync with your Ethereal, making this a very difficult but beneficial type of magic to learn.
In 500 ATC, roughly 500 years after Arcanium was seeded in Sarella, something changed. Magic no longer functioned as it once did. Wizards with decades of study casting high-level spells were suddenly unable to cast more than a barely-seasoned apprentice. Sorcerers lost the ability entirely. Clerics, Warlocks, Bards, and casters of all kind suddenly lost their connections to magic, a few barely able to cast a cantrip here and there. Roughly a day later, people began to notice a shift in the air. They noticed that the air now contained flecks of Arcanium, and only those who had ingested some were able to cast spells, and even then only for a short time. Panic ensued in the magical community. The Academy at Istio shifted almost overnight to simple mundane studies and magical theories, instead of actual magical practice. It would be a year before people figured out what happened.
A year later, the first Blended was born. Someone thought the human child was sickly, as when it was looked at in a certain light, there were small bits of Arcanium reflected in its skin. The child was healthy, though, and completely avoided the small outbreak of illness going on around it at the time. Once the child reached about 15 years old, after a decade and a half of tests and experiments, their abilities surfaced. This child was a Sorcerer, not a weak and sickly one like the ones existing after the Altering, but a full-fledged, powerful sorcerer. No one had seen magical ability like that in almost 20 years. Researchers were frantic in determining why, and the human was paid handsomely for their services in studies and experiments. Eventually, the researchers determined that they were born with a sort of infusion of Arcanium, and the ability to channel magic equivalent to the Pre-Altering sorcerers. This human would be the first Blended.
Once word got out and people knew what to look for, Blended started coming forward all over Feredas: a powerful and resilient Fighter here, an illusion-weaving Bard there, and several understudies at the Academy, who the professors simply assumed were prodigies of some kind. As time went on, these Blended showed to have both more physical resilience and more potent mental faculties than the average person, in addition to being able to weave magic in full Pre-Altering strength.
With a roughly 10% birth rate, these Blended quickly filled the Academy and every odd job in the major cities was being taken up by one aspiring adventurer or another. They formed essentially their own social class, somewhere above the common citizen and below the ruling class. They were treated with jealousy or awe by most, and occasionally fear by the town guards that would have to keep them in line.