From an monograph entitled Ocultus Ocultisimus ("The Deepest Secret") found in the library of the master mage Yurien Gilleni, and presumably written by him: It is practiced in almost every nation, and has many names. The ignorant call it sorcerry, wizardry, or magecraft. To those who study it, it is Occultis Ocultisimus, The Deepest Secret, but is also called the Deep Lore, the Starward Path, or the Great Art. A man who walks the Starward Path gains incredible power: he can impose his Will upon Creation, and can re-order the world according to his desire. Knowledge of the Deep Lore lets a man take a Thought and give it Being. Though the ignorant common folk belive the Great Art can accomplish anything, we who have walked upon the Starward Path know otherwise. No mage has ever succeeded in creating life or restoring it to the dead. And some things that we may accoplish by the Great Art, we do not, for the cost would be exceeding great. Yes, the Great Art could create water to irrigate crops, but doing so would exhaust and probably kill the mage who attempted it: better to fetch water from the river. [Time, water, and insects have destroyed several pages.] Though that arrogant fool would tell you otherwise, there is no special quality that sets the mage apart from mundanes. The Great Art is a skill which anyone can learn it. However, some men are more suited to studying the Deep Lore than others, just as some men are naturally better at carpentry, or painting, or shaping metal than others. The most talented mage, however, will devote more years to the study of his craft than the carpenter, the painter, or blacksmith before he has mastered it. A mage's power comes from Gatae itself. This power, which we call _numen_, can be found everywhere and in everything. There is numen in every grain of sand, every drop of water, in every breath of air, and every blade of grass. When a mage does a working, he draws on numen to give it power, much like the way a fire consumes wood. But by some marvel, the amount of numen never grows any less. Gemstones contain more numen than ought else, adamant most especially. Upon one occasion, I purchased from a jewler a finger ring set with many stones. I found that if I held or wore this ring when I performed a working, the working's power was greatly increased. [...]
Out-of-World info: Numen is a Latin word that litterally means "presence." It's also a synonym for mana (magic energy). Gilleni is wrong about the source of numen. It is not part of the substance of Gatae, but radiates from the sleeping body of the First. Nor are the magic enhancing stones what he he believes. They are not real gems: a phenomenon in which numenic energy condenses and crystalizes into solid form created them. The "arrogant fool" mentioned in the text is one of Gilleni's rivals. The phrase "Starward Path" can also be interpreted as "The Road to Heaven."
What follows has yet to be converted into in-world text.
The early part of a mage's training is spent doing mental exercises. The first exercises are in visualization. In order to produce an effect with magecraft, the practitioner must describe it at accurately and as precisely as possible. Words are too slow and clumsy for the extreme precision required, so a mage deals in images. He must learn to see, in his mind's eye, an image of the result he wants with total clarity and complete to the smallest detail. Many say that this is the most difficult part of magecraft: learning to think in pictures instead of words. When the apprentice has learned to use his mind's eye, he moves on to concentration exercises, so that he can hold onto those mental pictures amidst distractions. This is crucial, because losing one's concentration during a casting can result in an uncontrolled release of magepower, causing random effects which can range from merely embarrasing to fatal or worse. (What could be worse than death, you ask? Consider the case of the mage Kolseizi, who spent the rest of his life in the body of a weasel; or Kesfrel, who became a a living statue— able to think, but unable to act.) The third and final set of exercises develop the ability to manipulate multiple unrelated mental images simultaneously, while maintaing the clarity and detail of them all. Even the simplest parlor tricks require the ability to manipulate two images at once, and the number of images needed only increases with the complexity of the spell. Once the apprentice has completed this mental training, he awakens his secondsight— the ability to see the presence of flow of numen. To secondsight, numen appears as waves of glowing luminous energy. When a mage casts a spell, the first thing he does is to absorb numen from the environment. He does this by creating a mind's eye image of numen flowing into a container, filling it up. The real numen will obligingly follow it's imaginary counterpart. The mage must then hold in his mind the image of the full container while simultaneously creating a second image— the image of the desired result. In order for the spell to be effective, this image must be as complete and as detailed possible. He then imagines the stored-up numen flowing into the image of the spell. The final step is for the mage, while maintaining his mental images of the flowing numen and of his desired spell, is to concentrate on the realness of the image. With a sufficiently strong belief, and a sufficient amount of numen to empower it, the mage's imagined spell gains an independent reality.