The common folk are continually singing as they work. Why? What effect does this have? Why do they spend the energy? And why are they singing similar songs across the land? Because those songs are actually chants, special songs that induce magical effects. These chants gain strength from massed voices--the choir is greater than the sum of its voices. Each chant is simple, but blending voices requires effort and trust. Only the most disciplined groups can reach the full strength of a chant, even though most societies use chants on a smaller scale.

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.

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 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.