My vision for magic in the world of Renaissance Asiyah is that it would be free of a set spell-list; players could make up spells on the fly, as suited the given situation.
However, magic needed some constraints. A given mage shouldn’t be able to just cast any sort of spell. Thus, the concept of paths and subpaths came into play. A mage’s paths would act as essentially the “school of magic” the mage has access to, and thus place some limits on their magic. Thus, one mage might be able to cast spells dealing with beasts while another manipulates the force of life itself.
The concept of improvisational magic is nothing new, but it is my hope that this system turns out exceptionally fun for the Fate RPG.
However, I didn’t just want this magic system to be improvisational within some constraints. I wanted mages to be something people would fear, and for a reason; thus, magic also had to have a cost, a cost which would make it and those who wield it potentially dangerous. That cost has been worked in, and thus if you use this system unmodified, it works best in a darker-edged fantasy setting.