In the SR4 rulebooks, magical traditions have listings of which spirits a character of that tradition can summon.
The Aztec Tradition
Each of the above equates a spell category with a type of spirit. The spirits don't cast spells (other than the ones with Innate Spell power)... do they? It seems to me like the spirit has whatever powers it has, regardless of what spell category it goes with. What does the spell category mean?