This is an outline of the code of magic that we would try to establish. It would be based upon a fictional "lost work" of Aristotle where he establishes the principles of magic. The primary mythic model I want to establish is that of Chiron: a hermit in the wilderness who will teach exceptional students and produce magnificent effects.
A note here about what constitutes "magic"... Several people in the game have made a distinction between magic (i.e. what we do) and superstition (i.e. what the "mundanes" do). While this is built into the game to some extent, I think it is *extremely* artificial in the medieval worldview.
For example, in my opinion having a candlelit ceremony where we walk around the house to ward off evil magic is not in the slightest a cause for prejudice against us as "sorcerers". I don't have definite documentation, but I will bet that other folk do this sort of thing all the time: there are rituals for establishing a new home or building, at harvest-time, upon planting of seeds I'm sure there is a ceremony for a good crop.
Many or most of these are holdovers from pagan beliefs -- but in an era where actual pagans are rampant, the Church does not particularly complain about harmless ceremonies of this sort -- especially if some nod towards Christianity is given. That is, some chanting over a sick person is probably expected in barbarian society -- which the Church doesn't particularly approve of, but doesn't count as heresy, either. However, if instead they say a special prayer over the victim, the "magic" is often actively approved of.
As long as the magic is Christian in name, many virtually identical practices are approved of by the Church. Thus, pagan charms are looked down on, but wearing saints bones for particular effects is approved of.
Sorry about the rant, but this is vital to my point. The published work not going to talk about magic as a secret way to fling fireballs, but rather will be read as a systemization of practices which are already going on in public: astrology, ritual ceremonies, etc. It will further talk about greater magics in the abstract, but they are not the sole focus of the work.
To Aristotle, change of any sort reflects impurity. In his terminology, the "efficient" cause of change is the agent of that change. Thus, if I get tired, the efficient change is my exertion. However, in his philosophy Aristotle explains that ultimately the cause of change in the mortal sphere is the motion of the Sun around the Earth.
To Aristotle, magic in general is essentially the process of calling down celestial influences. In short, it is sort of like cutting out the middleman -- you might say that a stone building is worn down by rain -- but in fact this rain is just the proximate cause. The real cause is the motion of the Sun, which makes the rain and also wears down the building. Magic, as he puts it, is proof that the proximate cause (i.e. the rain) is unneccessary -- all change comes directly from the motion of heavenly bodies, and the proximate cause is merely a symptom. By magic, you can wear down the building without rain.
Under this theory, our "hermetic" magic is almost exclusively solar magic -- magic of the sun (although there are sometimes lunar influences). Note how this effects how long spells last: of 360 spells in ArM, only 12 have moon-based durations, and the majority have durations involving Sun or Year.
Moon Duration Spells:
MuAu35,Rit: Heat of Hell's Impending Doom (Conc/Moon)
CrCo5: Charm against Putrefaction (Moon/Perm)
MuCo30: Mists of Change (Moon/Perm)
CrHe45,Rit: Calling the Council of Trees (Moon)
InIg20: Vision of Heat's Light (Sun/Moon)
CrMe15: Panic of the Trembling Heart (Sun/Moon)
CrMe15: Rising Ire (Sun/Moon)
CrMe20: Pains of Perpetual Worry (Moon/Year)
CrMe20: Weight of a Thousand Hells (Moon/Year)
MuMe10: Subtle Shift of Heart (Sun/Moon)
MuMe25: Emotion of Reversed Intentions (Sun/Moon)
ReMe20: Aura of Rightful Authority (Sun/Moon)
The power of solar magic is emphasized in Aristotle's work, but he does not confine himself solely to it. Solar magic is powerful and dangerous, he says, but not so dangerous as lunar magic.
Solar magic is primarily magic of the sublunary elements, and can have enormously powerful effects. Mental magic is a bit different because the human mind is not sublunary -- it often involves lunar or other influences.
Magi teach, that is their primary function within the Republic. They will advise rulers, and educate students. Lesser magi (those without mastery) will teach mundane topics within society, while the more skilled masters will be in the wilderness and teach arcane lore.
This is not apprenticeship, but rather scholastic tutelage. Poor students may pay their way by work, but this is not neccessary. They may pay in other ways, for example. This is a huge difference from the view in the 12th century Order of Hermes. Students are not bonded slaves.
Vis as we know it is literally an amalgam of mortal elements and quintessence (or ether). That is, there are bits of Celestial matter which are scattered around the mortal globe, and strong concentrations of these are called pawns of vis. These represent links to the Celestial sphere, and can thus aid magic.
However, as a mixture of Sublunary and Celestial elements, vis is impure. It is a volatile mixture and must be handled with great care. "Pure" vis is simply quintessence, and is only contained in the heavens. "Vim vis" is vis with the least admixture to mortal elements (i.e. the most pure, and thus with the weakest connection to the Earth).
The process of extracting vis from the aura is simply going around and picking up plants or rocks or such which seems special. By doing various ceremonies over them, you can move minute bits of quintessence into a central container. Sort of by definition, the vis which is can be extracted in this way is the sort which has the least ties to the mortal substance it is in -- i.e. "Vim vis" by definition can be moved from one mortal container to another, while other sorts of vis are more tightly bound to their mortal elements.
The Gift is simply having a strong link to the Sun. In theory it can be predicted by astrology, but like eclipses it is extremely hard to nail down.
The Gift does not make magic possible -- but it enhances it to an incredible degree. Thus, a mundane could go through the same rituals as a magus and see some small benefit (i.e. minor bonuses), but nothing like the spell a magus would cast.
Magic in general is established by physical ritual -- not by thought, and it is made more powerful by having connections to the Celestial: i.e. Aura, Gift, or Vis. Magic can be cast by subvocalizing, which is the "no words, no gestures" version of spells -- but it is the act which does it, not the will.
In addition, magic is affected by other celestial influences. Aristotle naturally doesn't talk about the Dominion, but he does talk about the shifting nature of how lands have different connections to the Celestial. "Hermetic" magic is based upon a solar or (sometimes) lunar influence, and thus can be adversely affected by other influences.