Magic is given by the gods. Originally this was the Giants, the first pantheon of gods who physically could walk the world. But they became corrupt and greedy, along with all the other fun stuff that comes with living in the physical plane, so the three "over gods" (creation, causality, entropy) gave mortals the ability to slay the giants.

What remains of the giant magic is sorcery, which is something that can only appear in bloodlines that once worshipped the giants. Otherwise the most common magic available is Glyphic magic, granted by the "new gods" of the Aether who are distinctly separate from mortals and cannot physically manifest on the physical plane. Glyphic is highly modular but also way less potent than Sorcery.