Spheres of Magic
]While there is alot of confusion about the Subgroups of magic.. Almost all magicians consider the 15 Spheres, (and the element of magic itself.. RAW magic) to be the basis of all magic.
The Spheres of Magic ARE:
* Elemental Magic
* Protection magic
*Spirit Plane magic
These ‘groups’ of magic are considered so, due to their complexity and difficulty, the original spells were written down in the great book, but over time they all gained power and the book became sentient.. threatening to destroy.. well, everyone.. the book was torn apart, the pages separated and schools of each magic were built up in separate cities.
Since then, Some of the schools have been destroyed.. but many of the spells have been copied down, re-copied and distributed, but with caution See the Carnigene Theory on exploding spellbooks.
All in all. the 15 spheres remains a stable construction of spells that most magi would go to in case of need.