There actually isnt. It just sounds the most boring so people wont chose that.
Well... we do only sell crappy liquorice...
Primal Conundrum said
The idea with it is that the power doesn't come from the caster so much as the spirits that they invoke, and a caster being 'powerful' really just means that more spirits listen to them.
Xzayler said
Spirit summoning is also possible with the Ancient Language. Some Magic users call on the spirits to obey them and make them do what they want. This doesn't drain the power of the Magician but it is very hard to control the spirits, and things can go very wrong, like losing control and giving birth to a Shade.