The soul is part of every living person, not only mages. It lives almost entirely on the Spiritual plane and holds essence.
- Size matters. A larger soul holds more essence, and carries more weight when reality tallies up how events turn out.
- It grows like a muscle — through use, through hardship survived, and through achievement. Non-mages grow theirs just as much.
- Souls vary in quality from birth, like eye colour: more capacity, better efficiency, and so on. Innate magic is common, and does not make someone a mage.
- Souls protect their bearer against certain magical effects and changes.
- A grown soul may bring longer life, even natural immortality.
Humans and beings like them are assumed to have souls unless stated otherwise. Artificial beings of enough complexity can and do have souls.