How do I write a magic system?

Decide first whether the magic will solve problems for your protagonist. Brandon Sanderson's First Law is that an author's ability to resolve conflict with magic satisfyingly is proportional to how well the reader understands that magic. Magic that rescues the hero must have rules the reader knows in advance. Magic that only creates problems, sets atmosphere or threatens can stay mysterious.

What is the difference between hard and soft magic?

A hard system has stated rules, costs and limits, and the pleasure is watching characters solve problems cleverly inside them. A soft system is deliberately unexplained and produces awe rather than puzzle-solving — Tolkien is the standard example, and Gandalf's power is never quantified. Neither is better. What fails is soft magic that suddenly resolves a plot, because the reader cannot tell whether the escape was earned.

How much worldbuilding should go in the book?

Far less than you build. The useful image is a hollow iceberg: the visible tip is what the story states, and the mass underneath is what you know and never explain. The invisible part is not wasted, because it is what makes the visible part behave consistently. What ruins books is inverting the ratio and putting the iceberg on the page.

How do I avoid an infodump?

Give the reader information at the moment they need it to understand what is happening, not before. A reader will accept an unexplained term for a long time if the scene around it is clear. The test for a paragraph of history is whether the scene stops while it is delivered; if it does, it is an infodump regardless of how well written it is.

Do I need a map, a glossary and an appendix?

A map if the geography affects the plot and the reader must track movement. A glossary if you use many invented terms a reader may need to look up, which is more common in secondary-world fantasy than elsewhere. Appendices are conventional in epic fantasy and entirely optional. None of them can rescue a story that has not made itself clear in its own prose.

How long is a fantasy novel?

Longer than most genres and often too long in a first novel. Epic fantasy commonly runs 120,000 to 200,000 words, while a debut is easier to sell nearer 100,000 to 120,000. The genre's tolerance for length is real, and it is not an exemption from the requirement that each chapter earn its place.

Should I invent a language?

Almost certainly not a whole one. Tolkien was a professional philologist who built languages first and the story afterwards, which is a working method available to approximately one novelist. What produces the same effect at a fraction of the cost is consistency: names that sound as though they come from the same place, and a handful of words used the same way every time.

How to write a fantasy novel readers believe

Tolkien invented Elvish before he wrote the story, because he was a philologist who wanted somewhere for the language to have come from. Ursula Le Guin built the world of The Left Hand of Darkness out of one biological premise — the inhabitants have no fixed sex — and followed it into their politics, their religion and their conduct of war.

Two methods with nothing in common, both producing worlds people have lived in for decades. What they share is that the invention is not the book. It is the ground the book stands on, and most of it never appears.

The rule about magic

Brandon Sanderson’s First Law is the most useful sentence written about fantasy in fifty years: an author’s ability to solve problems with magic in a satisfying way is directly proportional to how well the reader understands that magic.

It is a statement about payoff, not about system design. If your protagonist is going to escape something using magic, the reader must already know what the magic can do and what it costs. Otherwise the escape is arbitrary, and an arbitrary escape retroactively removes the danger from every threat in the book, because the reader learns that anything can be solved by something they were not told about.

This produces a clean division.

Hard magic has stated rules, costs and limits. The reader is given the system and then watches characters solve problems inside it, and the pleasure is close to that of a puzzle. A hard system can resolve conflicts because the reader can audit the solution.

Soft magic is deliberately unexplained, and exists to produce awe and threat. Tolkien is the model: nobody can tell you the mechanics of what Gandalf does, and the vagueness is a feature — he reads as genuinely other rather than as a man with a skill set. Soft magic can create problems freely. It should not solve them.

The failure mode is a soft system used for a hard job. A wizard whose powers have never been defined suddenly producing the exact ability needed on page 400 is the fantasy equivalent of the detective receiving a confession in the post.

Cost is what makes a hard system dramatic rather than merely mechanical. Magic that is simply available is a tool. Magic that takes something — time, memory, blood, a year of life — is a decision, and decisions are what scenes are made of.

The hollow iceberg

Sanderson’s other useful image: the world is a hollow iceberg. The tip is what the story explains. The mass below is what you know and never state. And it is hollow because you have not built all of it — you have built enough that the visible part behaves as though the rest exists.

The invisible mass is not waste. It is why the visible part is consistent, and readers detect consistency without being able to name it. A currency that behaves the same way in three separate scenes, a religion whose insults derive from its theology, a road network that explains why the army arrives late — these read as depth even though none of the underlying work is on the page.

What kills books is inverting the ratio. The author who has built a beautiful thing wants it seen, and so the reader gets four pages on the succession law of a kingdom the protagonist is about to leave.

The test is mechanical: does the scene stop while the information is delivered? If a character is walking, thinking or fighting and the narration steps aside to explain the guild system, that is an infodump no matter how well the paragraph is written. If the guild system is explained because somebody is being thrown out of a guild, it is a scene.

Confusion is not the same as mystery

New writers over-explain because they fear the reader will be lost. Readers tolerate far more unexplained material than authors expect, on one condition: the scene must be clear even when the world is not.

A reader can meet an unfamiliar word — a rank, a tool, a religious office — and carry it for fifty pages, provided they understand what is happening to whom right now. What they cannot tolerate is not knowing who is in the room, what they want, or what just happened.

Practically: be ruthless about clarity at the level of the sentence and the scene, and relaxed about clarity at the level of the world. That is the ratio readers actually want, and it is the opposite of what a first draft usually does.

Names that came from the same place

Invented languages are a trap, because the one writer who did it properly was a professional philologist working for decades. What Tolkien produced with linguistics, most novels achieve with consistency.

Names from one culture should share sounds and structures. If two of your northern names end in -vek and the third is Jason, the world has a hole in it. Readers do not analyse this; they feel it. The same goes for invented words used inconsistently — a term that means a kind of priest in chapter two and a kind of soldier in chapter nine tells the reader that nobody is keeping track.

Two practical constraints worth adopting: keep names pronounceable, because a reader who cannot say a name will skim it, and keep them distinct from each other. Three characters called Aelin, Aerin and Aleina is a book people put down.

Front matter and the apparatus

Fantasy is the genre most likely to carry a map, a glossary, a dramatis personae and appendices. Each has a real use and none is decorative by default.

A map earns its place when the geography affects the plot and the reader is expected to track movement across it. If your story happens in one city, a map of the continent is an ornament.

A glossary is worth it when invented vocabulary is dense enough that a reader may want to look something up, which is common in secondary-world fantasy. It goes in the back, and nothing in the story should require it — a reader who must flip to the glossary to follow a scene has found a defect in the prose, not a feature of the book.

These affect the physical book more than authors expect. Maps are images and need real resolution at print size, covered in book interior images; a map printed across the gutter loses its middle. Appendices and glossaries are back matter, which is its own set of conventions.

Length, and what it costs

Epic fantasy runs long — 120,000 to 200,000 words is unremarkable in the genre, and a first novel is easier to place nearer 100,000 to 120,000.

The genre’s readers genuinely accept length. The physical book is less forgiving. A 200,000-word novel is roughly 700 printed pages, which raises the print cost per copy, pushes the inside margin wider because a thick book does not open flat, and can run into a printer’s maximum page count. At that size the sensible questions are whether the book is one volume or two, and whether the trim size should be larger to bring the page count down — both covered in trim sizes and print page limits.

Worth knowing before the manuscript is finished, because a book split into two volumes is a different book, not a different export.

The world exists so that the story has consequences. When a reader says a fantasy novel felt real, they almost never mean the appendices were thorough. They mean that things cost what they should have cost, and that the rules held when it would have been convenient to break them.

Sources

Brandon Sanderson, A definitive guide to Sanderson’s Laws of Magic — the First Law, and hard versus soft magic
Brandon Sanderson, Worldbuilding tools — the hollow iceberg

Common questions

How do I write a magic system?: Decide first whether the magic will solve problems for your protagonist. Brandon Sanderson's First Law is that an author's ability to resolve conflict with magic satisfyingly is proportional to how well the reader understands that magic. Magic that rescues the hero must have rules the reader knows in advance. Magic that only creates problems, sets atmosphere or threatens can stay mysterious.
What is the difference between hard and soft magic?: A hard system has stated rules, costs and limits, and the pleasure is watching characters solve problems cleverly inside them. A soft system is deliberately unexplained and produces awe rather than puzzle-solving — Tolkien is the standard example, and Gandalf's power is never quantified. Neither is better. What fails is soft magic that suddenly resolves a plot, because the reader cannot tell whether the escape was earned.
How much worldbuilding should go in the book?: Far less than you build. The useful image is a hollow iceberg: the visible tip is what the story states, and the mass underneath is what you know and never explain. The invisible part is not wasted, because it is what makes the visible part behave consistently. What ruins books is inverting the ratio and putting the iceberg on the page.
How do I avoid an infodump?: Give the reader information at the moment they need it to understand what is happening, not before. A reader will accept an unexplained term for a long time if the scene around it is clear. The test for a paragraph of history is whether the scene stops while it is delivered; if it does, it is an infodump regardless of how well written it is.
Do I need a map, a glossary and an appendix?: A map if the geography affects the plot and the reader must track movement. A glossary if you use many invented terms a reader may need to look up, which is more common in secondary-world fantasy than elsewhere. Appendices are conventional in epic fantasy and entirely optional. None of them can rescue a story that has not made itself clear in its own prose.
How long is a fantasy novel?: Longer than most genres and often too long in a first novel. Epic fantasy commonly runs 120,000 to 200,000 words, while a debut is easier to sell nearer 100,000 to 120,000. The genre's tolerance for length is real, and it is not an exemption from the requirement that each chapter earn its place.
Should I invent a language?: Almost certainly not a whole one. Tolkien was a professional philologist who built languages first and the story afterwards, which is a working method available to approximately one novelist. What produces the same effect at a fraction of the cost is consistency: names that sound as though they come from the same place, and a handful of words used the same way every time.