From Introduction in [The Elemental Dimension of Magic]:
It is easy to point out fire as an element. We see it about us every day, just as we see water, or the blowing wind and most certainly earth. Magic warps and twists and follows the commands of those who call upon it.
Yet, at the same time, it works upon the world. Magic seems to know what it is doing, yet has no direct mind of its own. It transcends definition and limitation. Attempts to bottle it and place boundaries upon it, saying "Here then lie the boundaries of what is the Arcane," fail time and again. Indeed, with magic, more often than not, the only consistent rule is that whatever rules you establish will eventually be broken.
This is the manifestation of magic. It breaks rules. It binds logic and forces it through a tiny mesh of human understanding. It pretends to follow pattern and format, but in the end those who use it end up dust and it continues flowing. Gods die; mortals fade; entire races become extinct and, yet, the magic remains. This, then, is how one defines an element. Magic is a fundamental building block of the universe, as basic a part of existence as anything else.
What is it? Ultimately, magic is whatever you want it to be, literally. On the sunken world of Deris‐bar, magic only works in proper conjunction with the stars. On the world of Lykra‐han, magic works only by patient blood sacrifice of a willing subject. In the world of the Throne of the Emerald Dawn, magic flows as freely as air, and all wield it to one degree or another. Each realm has separate rules that govern its magic, generally regulated through the will of powerful minds manifested as gods. And yet leave them, and quite often their rules cease to apply. Paradoxically, despite having different rules governing its nature from realm to realm, magic often produces identical effects in each, such as fireballs and lightning bolts.