Editor's note: The following is a slightly cleaned-up partial transcription of pre-publication notes found in Imperial Research Alpha before its destruction in 210 AC. Anything that would allow someone to reconstruct the work has been excised. 

As souls are made of anima, magic can manipulate those souls, consuming them as fuel or transplanting pieces of them into other things. The soul-manipulations described here fall into two broad categories--blood magic and nimbus transplants.

The Resonance Theory of Magic

In my opinion, this model and the resulting theory reconcile RAW and RAI (and answer a whole bunch more questions to boot). Whether or not it is a true model is irrelevant--it's a useful model that allows predictions.

As mentioned in the article Where does magic come from?, the source of all magic is the energy of the soul itself. This article will describe the sources of the patterns ("spells") of each of the traditions of spellcasting ("classes" to use game terms). Although for the sake of the game spells are codified and the same spell cast by casters of different classes have the same effects, in-universe the patterns differ and the effects can be varied. Not all spells in the printed materials can be learned; there are innumerable others that can be cast but are not described in the printed books.

Magic levels--not one-dimensional 

A constant source of disagreement and dissonance is the level of magic in a setting or system. Settings are often described as "low magic" and then have magic items everywhere; systems like D&D 5e are billed as handling "low magic" settings but have spell casters everywhere. So what does it mean to be "low magic" or "high magic"? I suggest that low or high magic isn't a one-dimensional spectrum. Instead, there are many different axes on which to measure the presence of magic.

The energy that fuels magic and other "supernatural" events is the same energy that makes up the souls of living beings. Aether. Aether is formed within a soul when the soul creates new memories, grows, absorbs information--in general, through the process of creation. When a living thing dies, its aether passes into the Shadows (for intelligent beings) or back into the Prime plane (for plants and lower animals). That energy is pumped up into the astral by the Great Mechanism and passed among the gods and used to maintain the universe itself.

Living spell-casters accumulate aether in knots in their souls. These knots come in varying strengths--two lower level "slots" do not equal one higher slot. These knots are used to fuel patterned resonances with the ambient aether--these patterned resonances are spells. Some spells (cantrips) can be cast solely with the caster's mental energy and do not use up these knots. Without special training, these slots reform over time but require a night's rest to be useable again. There are rumors of some who can force energy into their knots faster, but those are not widespread.