Magic, according to the Cosmology, is the ability of a caster to channel the elements available to him or her on the plane that he or she is on.
There is another interesting theory as to how magic works that I do not want to get into in too much detail, but clearly bears mentioning. Johan Tandrake, of the Institute of Knowledge in Avendale, has put forth a theory stating that there are millions of small particles in the world called Aurons, and that these Aurons, when charged, become the basis of magic. The two basic types of Aurons, Aura Tyrrae and Aura Astrae, are the respective bases for Earth and Celestial magic.
I personally believe that there is much merit both in the elemental explanation and in the Auron explanation. and I consider it reasonable to believe that these two theories may yet be reconciled. For now, though, these are the two theories currently floating around about how magic works.
Concluding for today, there is one specific part of the elemental theory that I want to discuss, which is casting certain spells on hostile planes. Ordinarily, casting a life spell on the plane of death would be impossible. However, certain effects, such as a planar tear, a gate, or something along those lines, might make it possible for this magic to function. Planes of existence, however, would not have this concern, as they have all twelve elements present within them.