nature of magic

Magic is a supernatural force generated by the human collective consciousness. It's an ambient energy in the world that's usually produced while people are dreaming or engaged in other mental acts of imagination, and it coalesces into natural flows throughout the world called Leylines. Particularly powerful magical constructs such as Portals can only be created at the intersection of leylines, and natural dungeons often occur due to the disruption of leylines.

Mages - people who harness magic - draw upon ambient magic to give them energy in the same way living things draw upon substances in the air like oxygen to power their muscles. Taking in this magical energy is as natural as breathing, but a Mage must still train themselves to turn this energy into specific effects, just as an athlete trains their body.

Due to the nature of Magic, schools of Magic are based on significant concepts in human culture, concepts that have an evocative effect and instant association for most people, or concepts which have been the subject of imagination and creativity for the human race. Funerary rites and contemplation on the afterlife and the dead produced Necromancy, for example. While all humans exude ambient Magic, Mages are able to train the way their consciousness prouces this energy and cultivate an "engine" of sorts in their mind (or soul?) which helps them process ambient magic into specific effects based on the schools they've studied well.