I’m going to try adapting EN Publishing’s Elements of Magic (revised edition) to my purpose. It contains a spell construction system reminiscent of Ars Magica, with each spell list being a pairing of action and subject (abjure fire, compel dragon, and so on). There are 11 actions and 22 subjects (elements, energies, and creatures). Spells are constructed by combining one or more lists with general modifiers such as range and duration. Spells are fueled with magic points (which I might or might not keep; it might be good to see if I can adapt this to Godbound‘s effort mechanic instead).
There is functionally no spell level, but you cannot cast a spell with a higher cost than your caster level.
I expect to extend the list of modifiers based on ideas from Drop Dead Studios’ Spheres of Magic system, from Hero System’s power advantages and limitations, and from BASH’s power advantages and limitations. While I might use these in constructing specific spells, I suspect I’ll get more mileage out of them in constructing my magical traditions.
In some ways this is similar to the words of power system presented in Pathfinder Ultimate Magic, but words of power works with slightly bigger pieces. Where Elements of Magic has a baseline (‘cantrip’, 0-point) effect that you can buy up, individual words of power can already be built up. That is, an ‘evoke fire 0’ spell might do 1d6 points of damage as a touch attack, and you can buy up more damage, range, area of effect, and so on, but the fire blast word of power might be a level 3 power that does more damage at range.
I am not certain if I will have the full dynamic casting presented in Elements of Magic, where a player can make up spells as needed from their known spell lists (assign points to lists and modifiers on the spot), or if characters will need to prepare spells (decide on the configuration) ahead of time. I don’t think I’ll use this as just a framework for spell design and casters need to pick their spells as they do today. If I were going that route I’d just use the existing spell definitions.
I think I might even be able to bend this into a ‘martial powers’ framework as well, with ‘casting traditions’ that work better for martial characters…
Okay, a necromancer often uses rituals that call for the ritualist to sacrifice a living creature for power. A martial necromancer has learned to do this really fast on a successful killing blow in combat. She perhaps can’t do as much with it (smaller time constraints, doesn’t need the victim helpless, etc.) but can make use of death magic in combat… seems like an appropriate and should-be-viable tradeoff to me.