Evocation is direct, immediate, line-of-sight magical-effect. It is a fast-cast kind of thing, done with little or no preparation. It is limited to those rare individuals who may channel raw energy.
System: Depending on your setting, this may require an Aspect giving permission to use Evocation, or may involve the existence of a whole separate Mana stress-track.
Evocation is most notably used for direct magical attacks.
But it can be so much more!
Calling a fireball is the most obvious and direct expression of such elemental forces. However, there are almost an unlimited number of ways “elemental forces” can be applied. This provides the narrative justification to perform actions “with magic” and would be performed as a standard roll without further mechanical alteration.
- freeze the top of the lake (the energy's gotta come from somewhere)
- burn your name in a piece of wood
- incinerate the arrows before they reach you
- cauterize a wound
- light a torch
So... No meta-game spell-lists?
The effect you're going for isn't codified. It's a direct expression of what you want to accomplish. But your character has to be able to envision what he wants and describe it, so he can channel the magic involved. In this way, there aren't spell-lists for your character to learn (or, if there are, they're narrative elements, not game-mechanics).
I say “elemental” magics because Evocation, in this setting is literally a fast-cast magic. More complex workings simply can't be envisioned all at once and therefore can't be cast all at once. Take for instance, a tracking ritual that uses a dowsing rod and a person's hair to find the person (embue dowsing rod to point to the person with who's hair it is). I'm hard-pressed to figure out how to fast-cast this… I don't see the spell working without the ritual components. Not to say it can't be done. I just can't envision it. So, it's Ritual magic only.
Would you use air or earth? You could argue that air seems the most logical choice, but you could also argue that earth gives you access to electromagnetism, which would let you direct and divert electricity. So which is it? Both. Or, rather, either. Figuring out how to creatively apply your command of the elements fundamental.