|OK give me a minute, and I'll tell you if you are a toad.|
However, most fantasy settings will have magic in the form of spells and spell-casters; wizards, witches, and sorcerers. And to write about this, these days its all about the system. With book series such as the Dresden Files and books by Patrick Rothfuss, the magic system was so fascinating and central that fantasy authors and readers have begun to strongly identify with the system as a critical part of having magic at all.
A magic system is how and why magic works; what it can and cannot do, what its limitations are and how the magic is used. For example, in Dresden's world you have to store up power and can channel it either in explosive sudden effects or with time and equipment more powerful, subtle effects. In the Harry Potter books magic requires (unless the plot demands otherwise) a wand, and cannot create objects.
This systemization of magic has become the standard for fantasy writing, and in some ways it is quite interesting. The system its self can become a sort of character for the story, creating complications and challenges the mage has to overcome.
And for the author, remembering how everything works and keeping it under control is a very valuable tool. If your mage cannot do something one book then can later, readers are going to notice and complain. As Brandon Sanderson wrote famously, its the limitations and what magic cannot do that makes it most interesting and useful for an author.
However, there's a problem with this trend that writers should keep in mind. There is a temptation to turn magic system building (like world building) into a fixation, where this ends up being the primary focus and interest for the writer rather than storytelling, characterization, plotting, description, and character development. Ultimately, fantasy writing is just writing, and it should be the story that matters most, not your perfect system.
Overthinking your system is a serious temptation, as you work out how exactly every minute aspect of magic works and why, what can and cannot be done, and how, and every possible permutation of that system. In fact, I've seen burgeoning new writers trying to write a story starting with the magic system. "I have this cool magic system, I want to write a book about it!" Well nobody wants to read a textbook about a fictitious magical system. They want to read a story.
|With this simple test we can show how far Lucas has jumped the shark!|
Another concern is that people tend to think almost scientifically about magic, breaking everything down into physics and scientific terms and categories. This energy can only produce this much force, and the chemistry of this can only produce that effect, and so on. Instead of being magic, it ends up a science fiction story with guys in robes. Remember when in The Phantom Menace Qui Jon whips out the blood testing kit and starts going on about Midichlorians? The whole audience groaned and said "what the ($@)*???" in the theater when I was watching.
Lucas took something mystical and fascinating and tried to reduce it to science, almost an infection. Now instead of it being magical and spiritual, the force was some scientific process and the wonder was lost. If you do that with your magic, the same thing will happen with readers. Now it doesn't feel magical any longer.
There's a real tendency of modern westerners to define all of reality in terms of science, and that doesn't mix well with fantasy because by definition fantasy transcends science. That's why Arthur C Clarke famously said that sufficiently advanced tech is indistinguishable from magic. Not because they are equivalent like Thor quips in the film, but because at a certain point, technology becomes inscrutable and incomprehensible, it stops being something you can explain and understand, and becomes mystical and unknowable.
Clark's point wasn't that magic is simply advanced tech, but that tech eventually seems magical because it is so amazing and advanced beyond our comprehension. And if you lose that and magic becomes so systematized and scientific and measurable, you lose that sense of wonder and amazement. It stops being magical.
Magic should, ultimately, be mysterious. Even its greatest practitioners shouldn't be totally sure and confident in how it works. Magic should at some point just be too magical to know, too mystical to pin down. At some point you as the designer should either say "it just does" or make sure the characters and readers are unclear on it, not out of confusion but out of a sense of wonder and mysticism.
The thing is, you'll never know enough details to have it all perfectly defined and wrapped up. Whatever you come up with may be comprehensive enough, but until hundreds of people over scores of years have tinkered with it, tried to break it, and kept pushing the limits, you will not even have half of it understood. So stop trying to get it exactly perfect anyway.
The best thing a writer can do with a magic system is, unless the story or characters immediately call for it, to keep it in the background. It should be demonstrated through activity, but not explained or called out. Nobody really wants to read the perfect magic system as explained by Joe the Sorcerer. They enjoy seeing it played out through the story.
So go ahead and work on that ultimate magic system, just don't obsess over it, keep it magical, and remember that your book is about a story, not a system.