This article has been on my mind for the past few days. It's not that different from any other piece of advice out there on how to make magic systems for fantasy worlds: decide who can use magic, set limitations, think about the mechanisms of spells, and include some sort of cost to using it. It's all quite reasonable, and provides a good set of principles to follow whether you're designing for fiction or for games.
It did, however, get me thinking about historical magic—specifically, the ritual magic of Europe's late Middle Ages and Renaissance—and why it would be terrible for fiction. You'd think that it would be a nice fit for someone who wants a bit of authenticity in their fantasy: the genre is already filled with grimoires, spells in Latin, wands, talismans, Solomonic spirits, and all sorts of similar trappings of historical ritual magic. Why not go all the way?
Well, let me explain.
- Timing is everything. There's an astrological component to most of the spells, which means that they have to be done on the proper day, at the proper hour, under the proper sign. Some are more flexible than others, and might only need one of those conditions to be right. Others (notably rituals involving the conjuration of angels and demons) throw in requirements for the phase of the moon, which can throw off everything until the proper alignment of conditions.
This is all fine if you're building up to some grand "when the stars are right" climax that involves preventing a ritual from being completed, but if your protagonists are magicians themselves? It sucks. Imagine Hermione Granger coming up to a locked door and saying, "Don't worry, Harry, I know a spell for this! We have to come back next Wednesday, in the third or tenth hour after sunset."
- Preparation is boring. Let's say your historically-accurate magician is waiting patiently for the right day to cast the spell that he wants. That doesn't mean that there's nothing to be done in the meantime. In the week or so before a ritual, he'll probably be required to be chaste, to fast, to bathe frequently, and (if Christian) to attend Mass regularly. In other words, all the fun will be drained from his life for several days as he ritually purifies himself.
If it's a spell that requires components that the magician doesn't construct himself—a magic mirror for divinations or a sword with which to threaten demons—then whoever makes them has to abide by the same rules. Good luck persuading them.
- The shopping list is impractical. A spell that was popular in Roman Egypt could require ingredients that could only be found in that part of the world, or that might have become extinct in the intervening centuries. The identities of the necessary stones, plants, or animals might be lost when spells are translated from language to language. In a world without eBay, even a magician with an ancient grimoire of spells might be limited to using only those that can be done with the materials he can find in his neighbourhood. (A corollary to this point: a magician either needs to be rich or to have a rich client. He's going to need a supply of precious metals, gems, rare incenses, oils, perfumes, and various exotic animal parts.)
- Expect to fail. Even if all the preparations are carried out properly, a number of the spells seem to anticipate failure. You can see this in the way that they incorporate instructions on what to do when they don't work, and also by accounts of people being invited to watch a magician perform a conjuration, and describing returning night after night until it's successful.
- That spell might not be a spell. In his excellent book, Forbidden Rites, Richard Kieckhefer suggests that some spells from mediaeval grimoires were meant to be entertaining reading and nothing more. Sadly, it's the more elaborate spells that usually fall into this category, like the ones for making castles, horses, and feasts appear out of thin air. What distinguishes these spells from others is that they're written as a mix of story and instruction, with the emphasis more on the story side. If, in the course of your research into mediaeval collections of spells, you find an invisibility spell that's five lines of instructions followed by a page of amusing anecdotes about apprentice magicians spying on their mentors' wives and daughters, you've probably run into this type of spell.
- Wait, what was that about attending Mass? When you read through the necessary preparations, materials, and incantations that accompany ritual spells in mediaeval Europe, it's hard to avoid the conclusion that the only people with the education and resources to perform them were ones with a clerical education. A few later texts are explicit about the fact that magic is intended to be part of a larger practice whose goals are religious: it's an intermediary step between the study of the natural world and the mystical experience of God, not an end in itself.
Imagine how different the perception of Hogwarts would be if all the students began their days in chapel, and had lessons in Biblical exegesis. I'm sure Rowling's books could have still found an audience, but it would be in a different niche of the young adult market.
All of this isn't to say that you can't make a gripping narrative out of the historical traditions of this kind of magic. What I would ask, though, is whether it's worth all the necessary tweaking and explanation, when you could spend your time and creative energy on devising something wholly new instead.