Ok, so I've been reading the forums for a few weeks now and, while I'm still protective of my magic system, I think its time I put it out there to get thoughts from fellow fantasy writers/readers. So, here goes...
It all begins in one place; the Auganum, a realm of uncontrolled energy that sits just beyond the real world. From there, all the power to create magic is drawn. It is not aspected; there is no fire corner or ice area. There are areas controlled by certain gods, though this doesn't change the Auganum. It's like earth in that way, oblivious to whatever it placed on top of it. It's inhabitants, aside from powerful beings like the gods, are entities of energy, referred to by humans as sprites or demons.
Humanity is not a magical race. Of course, their blood contains traces of magic, enough to keep them young and help them grow until that magic slowly fades away and they age. But unlike several of the other races that inhabit the world, they have no natural ability to tap into the Auganum. So how do they wield magic? By binding those sprites or demons to their souls and using them as a doorway into that realm.
There are drawbacks, of course. Namely that, should the doorway be opened too far, the demon itself can come through and claim the mages body for its own. Normally this is only fatal to the mage; the demon unconsciously attempts to reform the body into its own shape which inevitably leaves the mage a barely recognisable sack of flesh. But if the demon is powerful enough it might just be able to drag itself through this reforming, and then it wreaks havoc on anyone and everything. This is a secret kept among the mages, as they all know no one would trust them if it got out. This also manifests during the use of magic, the mages feeling a tugging of sorts as the demons try to tear themselves loose of their chains, and the mages also taking on steadily more demonic characteristics the wider they open this door. Sharpened teeth, black eyes, ghost of clawed hands/horns, etc.
Further, the magic is naturally unpredictable/uncontrollable, so it takes dedication to master it. This mastering comes from an understanding of what you're trying to do, i.e. creating flames or healing flesh. For example, a healer could try to create and control fire, but the results would be completely unpredictable. Some mages can master several different fields with enough time and effort, but most will stick to one field or mutually beneficial fields (i.e. a fire mage might study how to manipulate certain parts of the air to increase the effectiveness of his flames).
The second kind of magic used by humans is blood magic. As previously said, a human body contains magic in the blood, and the younger a person is the more magic their blood will contain. A mage, after under going the proper rituals, can harness this magic by drinking it. This allows them to draw on energy not linked to the Auganum, which means its no longer chaotic; a blood mage, with the right amount of blood, can do anything they wish without having to master it the traditional way.
However, there are drawbacks to this as well. Firstly, most people look down on this kind of mage, at least in "civilised" lands, barring the Vald kingdom who are more or less ruled by a group of blood mages parading as priests. Secondly, continued drinking of blood, and in large doses, will make the person addicted. And finally, blood mages tend to age faster, as their spells inevitably take some of the magic from their own blood, no matter how little. There are also rumours, unconfirmed of course, that it can cause madness if one lives long enough. Most don't though, so who knows?
The final type of magic used by humans was actually created by another race; the Senomaal, machinists who sought to harness the power of magic to use as fuel for their machines. They were successful through the use of runes, carved with figures that no one understands anymore. The Senomaal themselves are all long dead and, while the occasional working rune is found in their ruins, their only real legacy in this regard is a rune that sucks up magic. It was originally just one part of a larger machine, designed to absorb and then refine magic into a usable resource, but it works just as fine on its own, negating magic in any form. The rune, when fully charged, will be hot to the touch, eventually being hot enough to burn through rocks and steel, finally exploding if the magic isn't used in some way. This is difficult, however, as any attempt to use the magic would be sucked up by the stone again, so most are just cast aside, tossed into the ocean or buried in caverns under the ground.
So, if you've made it this far, this is my magic system (or a small part of it, anyway). What do you think?