How to Create a Rational Magic System

  1. Posted on Mar 30, 2017, 7:45:45 PM UTC
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    How to Create a Rational Magic System

    June 19th, 2015 by Chris Winkle

    Magic systems vary from colorful bears with tummy badges to ritual blood sacrifices. Magic isn’t real, so it can be anything we want. But that doesn’t mean all magic systems work equally well for stories. Some feel cohesive; others feel random. Some are carefully planned; others contradict themselves and lead to plot holes. Creating a rational magic system allows you to add realism and depth to your world while still leaving room for new and interesting changes.

    What Is a Rational Magic System?

    A rational magic system is one where every spell is guided by the same metaphysical laws. To the audience it will feel like every part fits together, even if they’re not precisely sure how.

    Not Rational: Harry Potter

    In the Harry Potter universe, magic works in several different ways:

    1. Wizards cast spells by waving wands and saying incantations. But once characters learn about the spell to disarm and the spell to block, they can’t extrapolate that there’s also a spell to dodge. Students learn all of the spells by memorization, because there’s no logic underpinning how they operate.
    2. Some plants and animals have magic inherently inside them, creating a variety of results. Wizards aren’t included in this; as far as we know, you can’t just simmer a wizard in a pot for a few days and end up with a magic potion. However, you can mix pieces of magic plants and animals in a pot and get powerful effects. While characters can invent some potions, it appears they only do it by trial and error, not through a formula that guides what goes into a potion to create specific effects.
    3. Old magics can occur without any intent. Harry’s mother inadvertently casts a protective spell on him by dying for him. It’s unclear whether there are any other self-casting old magic spells besides this one.

    These three sets of rules don’t appear related to each other. Learning about one doesn’t give a better understanding of another. Even within one category, there’s no way to extrapolate new spells because the rules are so eclectic. That means the stories can’t foreshadow spells prior to their explicit introduction, and when a protagonist has to face a tough problem, they can’t get out of it by inventing new spellwork. The audience has no idea what they can do other than what they’ve been directly told, so if they do anything new in a crisis, it will look like a deus ex machina.

    For instance, the Patronus Charm is a spell that is critical to the plot of multiple Harry Potter books. It worked well, but it had to be named before it became important to the plot. Readers could not have guessed that Harry might create something like a Patronus, so if it hadn’t been explained in depth, using it at pivotal moments would have felt cheap.

    In addition, there are no boundaries on what magic could theoretically do in the Potterverse. That means Rowling doesn’t have any guidelines to keep her from contradicting something she’s already invented or from creating a spell that makes the plot pointless.

    Rational: Avatar

    In the world of Avatar: The Last Airbender, magic (called bending) is embodied by the four elements of air, water, fire, and earth, plus spiritual energy. With the exception of the Avatar, people who cast magic are only attuned to one of the four main elements. By adopting a specific mentality and pairing that with martial art forms, they can move and manipulate their element.

    It’s easy to extrapolate all the basic uses of this magic system. When an earthbender is blocked by a mountain, we know that with enough effort, they could create a tunnel through it. This is true even if we’ve never seen anyone craft a tunnel before. We’ve seen them move and break rock, so it follows that they could make a hole through a mountain.

    In The Last Airbender storyline, Waterbending, Firebending, and Earthbending all have elite applications that not all benders can achieve, while air doesn’t. However, we can only identify that it’s missing because the system is logically consistent as a whole, even if it isn’t perfect in every depiction.

    Almost all of the magic in Avatar: The Last Airbender is clearly linked to the same rules. For instance, some animals can also cast magic, and they do it pretty much the same way people do. The main exception is “the avatar state,” which isn’t clearly linked to bending. It’s no surprise the avatar state causes plot holes during Avatar: The Legend of Korra.

    The Difference

    The magic of Avatar feels like the natural result of a different set of physics, whereas the magic of Harry Potter feels like the arbitrary inventions of an author. Occasionally you may want an arbitrary system – it adds humor and entertainment to Harry Potter. However, in most cases a rational magic system works better.

    Rational Magic Can Still Be Mysterious

    It’s easy to mix up rational magic with what’s often referred to as hard magic. Both Harry Potter and Avatar: The Last Airbender are hard magic systems, because they explain magic and its rules to the audience. The audience must know the rules, because the heroes use magic during the story. While both of these magic systems have mysterious aspects, in general they don’t invoke wonder because they are understood.

    Lord of the Rings and Game of Thrones, on the other hand, use soft magic. Viewpoint characters don’t use magic and the audience doesn’t understand how it operates. It’s mysterious.

    While it’s more difficult to tell whether a soft magic system is rational, I suspect Game of Thrones is using a rational magic system. It’s the subtle way magic leans toward fire or ice.* When Jon Snow kills a white walker with Valyrian steel, it makes sense even though we haven’t been told that could happen. That’s because we know dragon glass can kill them and both weapons were forged by dragon flame. Even without understanding the details, it feels like it all fits together. If George R.R. Martin or the show writers lean hard by revealing how it works, I think they’ll reveal something that’s logically consistent.

    To keep your magic mysterious like in Game of Thrones, hide how it operates. Most often, your audience should see the effects of magic but not the cause. Obscuring the rules is easier if the cause and effect can be separated by space and time or the cause isn’t directly observable. In Game of Thrones, the red woman throws leaches into a fire, and later several lords die far away. The audience isn’t sure if burning the leaches actually caused these deaths, making it mysterious despite having witnessed the magic ritual first-hand.

    Crafting a Basic Framework

    The first step is building a metaphysical framework for how and why magic works. The best frameworks have limitations inherent to the way they operate. For instance, if speaking is an essential part of spellcasting, then characters can’t cast spells if they can’t speak. If you choose a framework that is broader and vaguer, you’ll need to add less obvious limitations to it.

    To craft your framework, just answer these questions.

    What’s the source of magic?

    Pick just one source; I’ll discuss how to add variety to your magic system in the next section. Here are four common categories you can consider.


    Many systems treat magic as energy similar to heat, magnetism, electricity, or movement. In many worlds such as Star Wars, this force is generated by living things. It could also be from astral radiation or human emotion.

    Energy-based magic is easy to use because it comes with limitations. We know it takes more kinetic energy to move a big rock than a small rock, so we can imagine it requires more magical energy too. Spellcasters can’t blow up planets, because obviously that would take too much energy.

    Higher beings

    In some magic systems, gods or other powerful beings are the source of all magic. This is harder to work with, because the divine are technically spellcasters themselves, and incredibly powerful ones. You’ll need to set guidelines for how these beings operate so that you can explain why they do or don’t answer prayers whenever they’re asked. For instance, in Lois McMaster Bujold’s Chalion Series, the divine cannot directly influence the world with their magic. They can only work through people that do their will voluntarily.


    In Dune, those who are exposed to spice develop powers over time. In Brandon Sanderson‘s Mistborn Series, characters acquire magic by imbibing small amounts of metals and burning them once they’re consumed. Substances like these make it easy to put limits on the amount of magic used – just limit the substance. However, set guidelines for how people react to exposure. If one person grows wings and another teleports, your system will feel arbitrary.

    Shifts in reality

    Used by the Matrix and Mage: The Ascension, some magic systems are based on the idea that reality is more malleable than it seems, allowing some to bend it out of shape. If you use this source, decide why reality is so malleable – is everyone in a dream or a virtual reality game? Your answer could have huge ramifications for your world.

    These systems usually adopt limitations from physics, even though physics is no longer a limiting factor. In the Matrix, lifting something huge is harder than lifting something small. Technically, the limitation is actually the mind’s belief that lifting huge objects is difficult. That works for just Neo, but if you have many spellcasters over long periods of time, someone will be able to smash two planets together. Magic that powerful would leave a large fingerprint on the world, and if you don’t avoid ultra-powerful characters, it can also break your plot. Or just feel ridiculous.

    How is it accessed and directed?

    It’s not enough to have a source of magic. That source has to be available to a spellcaster, and that spellcaster needs to direct it to accomplish specific goals. The source should give you an idea for how it might become available. A substance can be traded on the market, gods can be prayed to, and individuals might be sensitive to magical energy – or maybe everyone has machines that do it all for them. Don’t be afraid to try something novel.

    Directing magic can involve a range of activities, but it commonly includes these aspects:

    • Thoughts & will: Character thoughts provide an easy method of directing spells, but unfortunately it comes with few limitations to keep spellcasters from summoning a deus ex machina.
    • Communication: Characters might need to communicate what they want to the gods or program it into a computer. This adds the opportunity for translation errors or for results that technically fit what they said but aren’t what they wanted.
    • Recipes: Perhaps characters almost never ad lib their desires; instead they follow specific directions hoping for specific and hopefully reliable results. Rituals generally fall under this category.

    The more elaborate your direction method is, the harder you’ll need to work to make it feel rational. If a character casts spells with a combination of substances, dance moves, and symbols drawn in charcoal, assign a role to each component. You should understand why some spells have symbols in common but different dance moves. Just knowing how everything works can go a long way.

    What are the constraints of the system?

    Now it’s time to decide why magic can’t do anything and everything the spellcaster wants, whenever they want.

    First, think through what magic is capable of doing in a theoretical best case scenario. It could range from absolutely anything to a single effect such as moving objects or pausing time. In Brandon Sanderson’s Warbreaker, magic is powered by a life force known as “breath.” Sanderson could have made breath do anything, but instead it’s mostly limited to animating objects and improving the caster’s senses. It can’t summon rain or make someone invisible, for instance. Limiting what magic can theoretically do will dramatically cut down the number of plot-breaking scenarios you might have to deal with.

    Second, look through all the essential pieces of spell creation and casting, and think how the casting process might fail at each step. For instance, let’s say magic is powered by a substance found within the soil. Humans access it by eating a special plant that bio-accumulates it. Once eaten, the magical substance builds up in their systems until they focus their will to cast magic. Here’s how this system might break down:

    • Availability of substance: Access to magic requires pairing the magical substance in the ground with specific vegetation. Only some areas would have the substance, and those places could have the wrong climate for the plant, or the ground could have been salted to keep anything from growing.
    • Edibility of plant: Perhaps the plant isn’t good for you. People could get sick by eating a lot of it at once or by eating a lot over the years. It could taste terrible and perish quickly. Drying or pickling could weaken the effect.
    • Amount in system: Before anyone can cast a spell, they need to have eaten the plant previously, building up magic in their system. The power of their spell would be limited by how much of the plant they’d eaten since the last time they did magic. If they run out, they have to eat and then digest the plant before they can do any more.
    • Strength of will: A person’s ability to cast a spell could be compromised if they’re tired, drunk, or simply feel conflicted about their task. To make the spell work, they might have to understand the scientific details of what they want their magic to accomplish instead of giving it vague goals.

    A long list of constraints will make it much easier to craft conflicts in your story. Something as seemingly insignificant as a casting time that’s five seconds longer has a huge impact on whether mages can handle unexpected problems. If spellcasters can run out of magic, it’ll be easy to put them in a tight spot when you need to.

    Adding Variety

    If rational magic systems only had a basic framework, they might get dull. Here’s a couple ways to mix it up while retaining a consistent feel.

    Splitting into categories

    The elemental magic of Avatar is a great example of splitting the same form of magic into different types. Most often, the source of magic itself comes in different types that create different effects. However, you can also experiment with different techniques for accessing and directing the magic, each with upsides and downsides.

    To avoid adding a sense of arbitrariness, your choice of categories must feel natural. Here’s what you need to think about.


    When you look at all your categories together, you shouldn’t find any large gaps where a category should be, and two categories shouldn’t be unusually similar. For instance, if you have chaotic magic, dark magic, and lawful magic, your audience will wonder where the light magic is. If you actually have light magic and you’re just not telling them until later, then great; you’ve foreshadowed without even trying. Otherwise, your categories will feel contrived.

    You can get away with a strange assortment if you have mechanics that explain it. Let’s say powers are granted by a changing lineup of gods, and the ocean goddess has three children that control the wind, waves, and depths. Then it may not feel weird that there isn’t a god specifically of dirt, because the earth goddess hasn’t had children yet.

    If you’re having trouble, you can say there are many more categories but knowledge of them has been lost.


    While your categories wouldn’t be any fun if they were identical, they do need consistency. Generally that means their strengths and weaknesses will be roughly equivalent. You could use a rock-paper-scissors relationship where earth beats air, but air beats water, water beats fire, and fire beats earth. Or you could simply say that air is good for dodging, while earth is good for blocking. You wouldn’t add that fire is good for creative thinking, because that wouldn’t fit.

    Again, you can have variance if there are rules that explain it. Let’s say magic is generated by the vibration of continental plates, and each continental plate vibrates at its own frequency, creating different effects. The size of those continental plates and their placement on the planet would be an arbitrary effect of nature, and so the magic they generate might reflect those arbitrary characteristics.

    If you’re at a loss, take a page from Brandon Sanderson’s Mistborn series. To make an arbitrary assortment of abilities feel like they fit together, he gave them a strong theme. Each ability corresponds with role in a gang of thieves. The list includes a “thug” who burns pewter and becomes stronger; a “tineye” who burns tin and enhances their senses; a “soother” who burns brass and can calm others’ emotions; a “seeker” that burns bronze and can identify other magic works; and a “smoker” that blocks a seeker within a certain radius. Since the main character of the series starts as a member of a gang of thieves, the choice of theme is very appropriate.

    Adding special abilities

    Naturally, you’ll want a few people in your setting with powers that are unusual among magic workers. You can have that, too, while still retaining rationality.


    Start by looking for further implications of what you’ve already established. How might someone with an unusual background or extraordinary dedication take magic either a step further or a step in a new direction? What unusual methods and applications might they attempt?

    In Avatar, most benders can only manipulate pure water, earth, air, and fire. However, a few benders can bend their element when it’s in a different form or less pure. There are Waterbenders that Bloodbend, Firebenders that shoot lightning, and the occasional Earthbender that Metalbends.

    In my example of magic that is acquired by consuming a plant, a clever alchemist might distill and concentrate the plant down to an elixir that is digested more quickly. Someone could gain double the magic in half the time. On the other hand, there could be a group of people allergic to the plant. Eating it makes them very sick, but because of this immune reaction, they can cast more powerful spells.


    Your story may also include a chosen one that’s extra special. To give them an exceptional ability that stands out from the masses, change or break one rule you’ve established for your magic system. Only one. Once you examine all the implications of this change, you’ll discover their powers are different indeed.

    In Avatar, there is one person every generation who violates the rule that people can bend only one element. This person, the Avatar, bends all four plus spirit energy. Because the setting is divided into nations that correspond with the elements, the Avatar is the only person who symbolically belongs to all the nations.

    In my plant-based system, there could be a lineage with the biological adaptation to absorb the magical substance directly, without using the plant as an intermediary. An entire category of limitations would no longer apply to them. Magic would be cheaply acquired from soil the plant can’t grow in, and they wouldn’t have to worry about getting sick from overeating it.

    Further Reading

    For more inspiration and guidance in creating your magic system, I recommend these articles and resources.

    Four Ways to Limit Magic & Technology – Those limits are important! Here are more ideas for them.

    Know How Your Magic Works – Here we discuss considerations outside the scope of this article, such as the effect magic has on society.

    Harry Potter and the Methods of Rationality – This fun fan fiction explores rational explanations for how the Potterverse might work.

    Brandon Sanderson is fantastic at crafting magic systems. He has three great articles on building them, named after what he calls his three laws. You can also read his books to see his systems in action; personally I recommend Elantris.

    Sanderson’s First Law
    Sanderson’s Second Law
    Sanderson’s Third Law

    Last, here’s a fun chart showing the details of magic systems in the most popular works.

    If you think about it, you’ll realize there’s no reason not to have a rational system. You can make it mysterious just by hiding how it operates. While it can be fun to have wacky spells, wouldn’t it be even cooler if you could reveal how your wacky spells all click together? The only downside is that these systems require thought – thought that will make your setting stronger.

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