The Magic is a force of nature– the nature of the unseen world, which underlies the world of sense and experience. Ancient natural philosophers were the first to conclusively demonstrate the existence of the unseen world, but the Magic has been practiced by humans for longer. Humans should not be able to use the Magic any more than they should be able to light controlled fires or sow grain. The Magic would otherwise only impact the world in two ways: first, through powerful storms defying the mere explanations of physics, and second, through daemons who either influence or possess living creatures.
But this is not the case. Humans have used the Magic in some form since their first intercessions with daemons, although these daemons were no more potent than mere blessings or curses. The basic capacities of the Magic are as follows: the practices which step into the real world are the manipulation of storms, the generation of physical energy, the distortion of spaces, the empowering of spirits to affect the physical world, and the manipulation of living flesh. It is not possible to affect inert matter by Magic directly. Classically considered to be more important, the practices which exist solely within the unseen world are the manipulation of spirits, astral projection, and the warding of places, things, and ideas beyond sense or thought. Practices like alchemy and radiometry are also considered to be magical techniques, because it relies on laws of nature that exist wholly within the unseen. However, they not require any use of the Magic, so they are not always thought of as such.
The unseen world is not merely invisible, it actively defies understanding. In other words, its properties are not consistent in a way that makes sense to mortal perspective when observed. Fortunately, or unfortunately, the unseen is very difficult to observe. The best existing methods rely on its effects in the physical, the most obvious of which is radio interference. In fact, the distinction between storms of magical origin and those solely driven by wind is interference. Specialized devices, however, can be used to attempt to detect spellcasting, and even demons. Studies in the field of radiometry have even attempted to diagnose sicknesses of the soul.