This article by N.K. Jemisin seems to have caused a minor kerfuffle. Some people agree: “Yes, it’s fercrissakes magic. It’s supposed to be all about wonder and stuff, not logic.” Some disagree: “Magic is energy and energy is physics and physics requires logical rules. Also, you can’t have a plot and character development without rules and logic.”
Clearly there are two very different schools of thought here. Both have good points, both are missing a point or two.
Jemisin makes some good points; magic is, well, magic. It’s anti-logic. That’s what makes it magic. (She’s dead wrong about the need some people have for rules and logic in magic coming from D&D; D&D got its magic system mostly from Jack Vance’s short stories. The plot-puzzle type of story, where each spell is a key that fits in a particular plot-keyhole predates D&D by decades.)
The other side has good arguments as well; if magic can do anything, how do you construct a plot that makes sense to the reader?
What a puzzle, eh? Perhaps an example will (magically) illuminate the subject.
The magic in LoTR is almost completely unexplained. What powers does Gandalf have? Elrond? The Nazgul? How does their magic work? We don’t know. It doesn’t matter. All we really know–all we need to know–is that Sauron’s power is tied to the One Ring, and the only way to destroy the Ring (and Sauron) is by tossing it into the fire where it was forged.
But Frodo doesn’t use magic to solve that problem. The magic in the Lord of The Rings is almost entirely in the background, not used to resolve plot problems, so it doesn’t need to be explained.
Here’s the real Important Rule of Fictional Magic Systems: The magic in your story-world requires rules and explanation in direct proportion to how much you’ll be using magic to solve plot problems.
This is a subset of a larger rule; the reader must be able to follow the plot-threads that you use to resolve the story conflicts. If you use magic to resolve the conflicts, the reader must be able to understand how magic works well enough to follow along, just as she would the science in a science fiction story, or the law in a legal thriller.
As with everything else in your story world, explain as much as the reader needs to know to follow along and don’t worry about the rest. No magic; just the basic rules of storytelling.