|Magic Circle by J.W.W. Waterhouse|
By laws, I mean the factual kind that recur in nature. You can jump upwards as many times as you want to, but as long as you’re dealing with a g of gravity, you will always come back down. You can do your darndest to stop the ocean tides, but as long as the earth keeps spinning and the moon keeps pulling, there will be tides.
The same thing has to happen with magic. There must be laws to any magical universe, and to create them, a writer must ask herself things like
* Who can use magic and who can’t? Only people who are trained? Only people who have certain genes? Only people of a certain gender or race or culture? Why only those people? Must the power be awakened, or is it there from birth?
* What is magic? Where does it come from? Is it a force of nature, neither good nor evil, or is it a spiritual or eschatological kind of power only angels or demons can grant?
* How is magic used? Must the user cast spells, or is magic more of a generalized energy? Must he rely on herbs, or blood, or eye of newt, or are spell components obsolete in your world? Are sigils, runes, or incantations used?
* What price must be paid? If you fight gravity by jumping, eventually you’re going to wear yourself out. That’s the price. So what happens when one uses magic? And are the consequences the same for any kind of magic, or do they vary with the kind of spell?
* What are the limits on magic? If your character can do anything and everything, there’s no tension in the story, so what can’t she do with magic?
* Are there different types of magicians with specialized powers -- like necromancers and alchemists and prophets -- or are they all the same?
Your answers can’t be random, either. They have to make sense, just like the laws of our universe do. And you can’t be whimsically changing them because your character suddenly needs to be able to do this or that kind of magic. You should write your rules down and pretend they're set in stone.
One more thought: It's challenging to come up with new rules if you write in multiple fantasy universes. When you have a logical, well-defined set of rules that you carefully abide by, it can be hard to think beyond them for another story. This is part of the reason many authors set different stories in the same universe. If you have trouble coming up with multiple sets of rules and keeping them straight, don't feel bad about setting things in the same universe!
Carolyn Kaufman, PsyD's book, THE WRITER'S GUIDE TO PSYCHOLOGY: How to Write Accurately About Psychological Disorders, Clinical Treatment, and Human Behavior helps writers avoid common misconceptions and inaccuracies and "get the psych right" in their stories. You can learn more about The Writer's Guide to Psychology, check out Dr. K's blog on Psychology Today, or follow her on Facebook or Google+!