This familiar game has really made me think deeply about the way magic works in existing games, and how I should best make it work in a game of my own.
I think of the spells used by magic users in D&D, each divided into different schools of magic, using a random assortment of game mechanisms. In that game paradigm (incorporating the OSR), there are also different classes that are capable of granting certain similar spells...for the purposes of game mechanisms the same spell appears in both lists, but the trappings might be slightly different. A sorceror might cast the spell instinctively, a cleric might call on their god to cast it, and a wizard might read a specific incantation and use ingredients to get the effect. Rifts does the same thing (but it's basically hipster OSR anyway... OSR before it was cool).
I think of the Disciplines of Vampire: the Masquerade, each of which manifests in a different way, but basically accumulate in power along certain themes... Where the basic powers often allow minor manipulation of the story, while the higher powers often offer a method to avoid character elimination in certain circumstances (by mind control, physical transformation, or spiritual transcendence).
I started working on specific paths of magic with specific spell outcomes common to them. Alchemy creating potions, Craftwork creating artefacts and relics, Maleficia creating curses, Theurgy creating blessings, Shamanism channeling the spirits... But then I realised that these outcomes were simply means to an end in themselves. The actual outcome of magic shouldn't be limited by the trappings used to reach it. This is a game about transcending barriers, or not even understanding whether the barriers are there for familiars in the same way that they apply to humans.
My new version of the magic rules sees each branch of magic provide new tools to gain power, but the power gained is spent to achieve the same effects.
I don't know how much sense this makes, but in my head it was an epiphany.