How to create a magic system: costs, limits and rules

To create a magic system, decide what job magic does in your story, choose how much the reader will be told about it, then write down what it can do, where its power comes from, who can use it and, above all, what it costs and where it fails. Brandon Sanderson puts the priority in a formula: limitations are more important than powers. He adds that a brilliant magic system is more often one with relatively few powers that the author has considered in depth than one with a thousand.

Start with the job magic does in your story

Hannah Kate Kelley, a developmental editor writing on Jane Friedman's site, begins before any rules. Magic should serve the tale you plan to tell. She asks two sets of questions. For society: how does each culture regard magic, who uses it, and does it change who holds power? For plot: how does magic directly and indirectly influence the main character, and would the story work without it?

If the story runs fine without magic, you may be building a system because it is fun to build. Sanderson's Third Law essay warns about "worldbuilder's disease", which he says is a problem only for writers aiming at a professional career in books. If you enjoy the building for its own sake, enjoy it, and know that is what you are doing.

Decide how much the reader will know

Sanderson's First Law says an author's ability to solve conflict with magic is directly proportional to how well the reader understands it. He describes a scale. At the soft end, magic creates wonder and the heroes rarely understand it. At the hard end, the rules are explicit and the characters solve problems by using them cleverly. Most books sit between.

The sources do not agree on which end is better. Sanderson recalls a Worldcon panel early in his career where every other panelist disagreed violently with him, saying rules destroy wonder, and he realised there was another complete school of thought. He puts his own systems at perhaps 80% hard. Kelley matches the choice to genre: hard systems suit epic and urban fantasy with large casts, and soft systems suit gothic horror and magical realism, where ambiguity is part of the mood. She also notes that soft systems are trickier because you must balance mystery with consistency.

A working test from Sanderson: in a soft system, ask how the characters can solve the problem without magic, or how trying to use magic could make things worse. In a hard system, ask how they could use only what they already know.

Write limitations, weaknesses and costs

Sanderson's Second Law gives three different tools, and it helps to keep them apart.

He gives three reasons limits help the writer. They create struggle, because characters must work and be clever. They create tension: Superman against a villain is not very tense, and Superman against a villain with kryptonite is. And they add depth, because a limit like "she can only fly when she is happy" ties her mood to the plot.

Two cautions from the same essay. Costs that are too drastic lock you in: if casting a spell kills one of your grandparents, readers will not see it cast often. And limits should have real effects. Special implements that never matter and are never missing do nothing.

Sanderson also lists questions that push you past first answers: how does someone gain access (born with it, taught, or both), what powers it, how often can it be used, and what does it require, such as an implement or a state of mind. His advice is to avoid the standard answer to each.

Kelley adds source and method. Magic can come from an object, a bloodline, the elements, a deity, the stars or a bargain, and each source needs a way to use it, such as incantations, gestures or rituals. Her key point is that the method has to stay the same. Her example of a break: early in a story a character needs a specific incantation, and later casts the same spell with a thought and no explanation.

A worked example: the knotwrights

Take a small system built the way the sources suggest. In a mountain country, knotwrights tie spoken wishes into linen cord.

• Power: one knot holds one small effect, such as a door that will not open, a fever that breaks or a lamp that stays lit for a night.
• Access: learned in a guild over seven years. Nobody is born able.
• Limitation: the effect reaches only what the cord touches. A knot cannot be tied for something the knotwright has not seen.
• Cost: every knot takes an hour of the knotwright's sleep, permanently. Old knotwrights sleep three hours a night and call the rest of the day the grey hours.
• Weakness: wet linen. A soaked cord goes slack and the effect ends.

Already the scenes suggest themselves. A knotwright defending a siege runs out of sleep and judgement together. A rival cuts the cord with a knife. A poor family sells its children's sleep to a rich buyer, and that raises a law, a guild and a black market.

That last step is Sanderson's Third Law: expand what you already have before you add something new. He suggests three directions. Extrapolate, by asking what happens when. Interconnect, by tying powers to the society's culture and the book's themes. Streamline, by combining where you can, so that one distinctive thing magic does is used differently by each culture instead of inventing ten systems for ten kingdoms. The knotwrights need no second magic. They need more consequences.

Test the system in scenes

Three tests show whether the system holds.

1. The shortcut test. Ask what happens if the hero uses magic right now. If the answer is that the problem is solved, add a limit or a cost until it is not.
2. The shared rule test. Kelley points out that a good system is simple and gets richer when the same principle applies to different characters. If two abilities serve the same plot purpose, consider merging them.
3. The reader test. She suggests asking beta readers. If they are confused or keep flipping back to earlier chapters, simplify.

Introduce rules in waves. Kelley notes that J.K. Rowling holds back the horcrux magic until the later books while seeding clues earlier.

Keep the rules consistent as you draft

Most magic problems appear in the draft, not in the plan. A cost forgotten in chapter twelve, a limit softened to rescue a scene, a spell that worked at night and is cast at noon: all of these are continuity errors, and continuity errors in novels are easy for readers to remember. Keep one page that states each rule in a sentence and the scene where it was shown. Update the page when you change a rule on purpose, and then fix the earlier scenes.

For the wider setting around your magic, see the worldbuilding guide and how to write a fantasy novel.

Common mistakes

• Powers without prices. If nothing is spent, nothing is at stake.
• The convenient new rule. Sanderson warns against writing laws into your system just to use them in one situation, which can make magic seem flimsy and convenient even if you set the ability up earlier.
• Complexity for its own sake. Kelley suggests that if one part is complex, simplify the others.
• Weaknesses as props. Sanderson calls kryptonite-style weaknesses a cliché of easy storytelling and finds weaknesses harder to build in without seeming simplistic.

Frequently asked questions

What is a magic system in a novel?

A magic system is the set of rules for how magic works in your story: where it comes from, who can use it, what it can and cannot do, and what it costs. Kelley calls it a map of where magic comes from and how it works.

What is the difference between hard and soft magic?

In hard magic, the rules are clear to the reader and characters solve problems by using them. In soft magic, the rules stay mysterious and the magic mostly creates wonder or problems. Sanderson describes it as a continuum and says most writers sit somewhere in the middle.

Do I need to explain how my magic works?

You need to know it. Whether you explain it depends on how you want to use it. Sanderson's First Law suggests that the more you want magic to solve problems, the more the reader should understand it.

How many rules should a magic system have?

Few. Sanderson argues for depth over width, and Kelley says complex should not mean complicated. A few powers considered in depth, with limits that have real consequences, beat a long list the reader cannot hold.

How do I keep a magic system consistent across a series?

Write each rule in one sentence, record where it was first shown, and check new scenes against that list. Change a rule only on purpose, and revise the scenes that depended on it.

Where Musael fits

A magic system only works if it is still true in chapter forty. In Musael you can record the rules of your magic as entries in the world and characters codex, see where each one appears in your scenes, and set continuity rules that are checked against your manuscript, with the sentence that breaks one and the scene it came from. The checks do not write or change your prose. You write the book, and Musael helps you keep it true to its own rules.

Sources

• Brandon Sanderson, "Sanderson's First Law": brandonsanderson.com
• Brandon Sanderson, "Sanderson's Second Law": brandonsanderson.com
• Brandon Sanderson, "Sanderson's Third Law of Magic": brandonsanderson.com
• Hannah Kate Kelley, "How to Create a Believable Magic System in Your Fantasy Story", Jane Friedman: janefriedman.com