As a random thing that came to me as I was laying in bed and thinking about magic (what, world building is what I do for fun, hehe) I had a potential idea for how things might have looked and progressed in an alternate Ars Magica world.
Originally magic was learned piecemeal - every spell was learned as its own 'Ability'. Wizards might have a really good understanding of what a particular spell could do but that didn't translate into knowledge of theory.
A later generation created the Magic Skills and the Magic Lores. The Magic Skills are learned individually for each Magic Lore. So like if the Magic Skills are Sense, Control, Alter, Destroy, and Create (the order representing how hard it is to learn) and some of the Magic Lores are Air, Earth, Fire, Water, Plant, Animal, Body, ... you would have to learn Sense Air, Control Air, Alter Air, Destroy Air, and Create Air but also if you wanted to know some water magics you would have to repeat learning the same skills just with Water instead of Air - so Sense Water, Control Water, etc.
You no longer have to learn individual spells as abilities but are still limited by the themes you know. Having Sense Air would do nothing to help one cast Sense Fire spells, no overlaps here.
The final generation, which represents something like current Hermetic Magic, is that you learn the Magic Skills in a general sense and the Lores in a general sense and you can combine any of your Magic Skills with any of your Lores with no need to repeat your studies. Your Sense Skill will apply to Fire and Earth and Body and Illusion equally.
So yeah, that's the idea. It was random but I had it and I think it is kind of fun. I mean I don't really expect to do anything with this idea but I figured that its close enough to Ars Magica that it might be somewhat interested to those reading this forum.