In every edition of D&D, you can gain the ability to cast spells of powerful magic. Nowadays, most classes are spellcasters. Back in ye olden times, there was "the Magic-User" class. They have always carried three assumptions:
- You acquire the ability to cast spells by enrolling in a spellcasting class.
- You acquire more spells (both spells known and spells you can cast per day) automatically from leveling up.
- You get access to better and better spells as you level.
But the system I'm using does not agree with those three basic assumptions. There's about a billion and a half ways to do magic systems in fantasy fiction gaming. One of my favorites in the system found in Ben Milton's Knave, which is one of many reasons it forms the basis of my own game. And out of all stuff I'm changing, this is one of the few things I want kept the same. I'll summarize:
- There are no classes. Rather, spells come in the form of books. One spell per book, and each book can be cast once per day. Thus, the spells you "know" are just the spells you own, and the number you can cast per day is the number of books you have on you.
- Like all other items and magic artifacts and treasure, you acquire them by adventuring for them. They have to be put into the world itself by the referee and then fought for by the PCs. There is no automated system for gaining spells.
- There are no spell levels. They're all of "equal" power. Now, many spells will have built-in numerical variables that are keyed to the level of the person casting them, so that they can scale in power. For example, Sleep targets a number of creatures equal to your level when you cast it. But many other spells don't scale at all. Read Mind lets you hear the surface thoughts of all nearby creatures and that's it.
How do you mechanically create options for "improving" at spellcasting or somehow allow for a PC to "invest" in the magic system without breaking the current assumptions in place?