Authority can be classified in many different ways. However, the most widely accepted type of classification in the literature is the classification by source. The source -that authority holders draw energy from to cast their wills- can be internal or external. An internal source is usually the physical, mental, or spiritual being of the authority holder, meaning the body, the mind, and the soul respectively. The amount of energy that could be drawn from an internal source is determined by the quality and the quantity of the source itself called the vessel. Access to a vessel is direct, complete, unbounded, and can't be blocked. On the other hand, an external source is simply an external vessel, meaning any animate or inanimate entity from which the authority holder can directly or indirectly draw power. The amount of energy that could be drawn from an external source is determined by the quality and the flow rate of the channel which is used to draw power called the vein. Access to a vein, whether direct or indirect, is incomplete, bounded, and can be blocked.
The basis of all anti-will efforts is to prevent, complicate or delay the authority holder’s interaction with the source. However, if this can't be done, preventing, delaying, or directing the effect is the second option, also known as counter-will. This requires accurate and precise information about the effect to be countered, which is always difficult and more than often practically impossible for fast-acting wills. For this reason, anti-will efforts are always considered superior to counter-will efforts, and therefore, classification according to the source is accepted as the most basic and important classification type. Or it would. At least that's how it was where I came from.
The authority holders of this place divide the sources of their authorities into two distinct domains, named divine and arcane, and I can honestly say that I have absolutely no idea what purpose this classification serves. Although I sincerely believe that they have no idea too, this should be a subject for another discussion.
They have chapters, called okuls, and use these as their basic classification system, which I think is not much different than classification according to the observed effect. Considering that they name the wills they use according to their observed effects too, makes such a classification only a shallow approach to the simplest of terms.
But by no means, no one doubts what you mean when you mention the famous, or rather infamous, Fireball: A ranged fire orb of attack, the size of which is proportional to the amount of energy spent, spreads out on contact or trigger, releasing flames into the area of effect. However, no one cares how you achieve this result. As long as your orb of fire spreads out and causes fire damage to the designed area, it doesn't matter whether you summon this orb from the primary plane of fire or create it using elements from your own plane. However, the difference between these two approaches is enormous. Especially in this place, where the external source's density is much higher than where I came from.
Ah… Erk… That was the first thing I noticed about this place when I thought about it. But even before, that woman…
Agâh H. Ates
571 AR + 003 AA