Right, right. In my fictional world of fiction. . . Let's call it Earth. There are different types of magic. You have your "Holy" magic, Demonic, Arcane, and a few others that tend to be underused or overshadowed. They don't exactly practice in secret, yet not widely known. Holy magic is what you imagine it to be and Demonic is what you imagine it to be. For those of you with little imagination, think Priests and Clerics from almost any source and warlocks, summoning demons, fire and other things from any source as well. Arcane is sort of a midway between these two and what tends to keep them both in check. The Arcane school is the school that one would consider mages and other things of the sort.

By the way, if you wondered where exactly Witchcraft sat in this type of conflict. . . Well look the equation and take Witchcraft out of it completely. 

Next, curses. . . Curses are fun. Curses stem from adrkness (intentional), like you said, but also require more than that as well. It depends on what kind of curse. Let's say we consider turning someone into a frog is a curse. That would require mastery over Darkness and Alteration.

More questions?