Five Tips for Using an Arbitrary Magic System

Rational magic systems powered by consistent metaphysical laws are cool and useful, but they aren’t the right choice for every project. Whether you want spells to feel hilariously random or your magic is too complex and variable to explain, sometimes it’s more practical to invent individual spells on a case-by-case basis. However, these arbitrary magic systems have some liabilities. Keep them from catching you unaware with these five tips.

1. Avoid Power Creep

Time and time again, storytellers invent spells because they’ll be convenient for a scene or two, but neglect to consider how many plot holes they’ll create later. When you’re not using robust rules as guardrails to prevent you from inventing a spell that’s too powerful, you have to think through the implications of a spell every time you create one.

That’s because every spell you create could be cast again. Some spells solve an overwhelming number of story problems, and allowing a protagonist to cast those will get you into big trouble.

  • Mind reading makes social conflicts impossible by giving characters lie detection. Almost every story relies on lying at some point.
  • Teleportation means characters can easily escape when they’re in trouble or drop into an enemy’s bedroom and assassinate them while they’re sleeping.
  • Large-scale destruction means characters can win fights even when they’re greatly outmatched or outnumbered.

You don’t want to write yourself into a corner by making threats too easy for protagonists to deal with. Plus, even when a powerful spell doesn’t turn solving problems into a cakewalk, it can make conflicts less interesting. If your character can shoot fireballs to a location one hundred feet away, they’ll keep their distance instead of getting into close quarters with enemies.

So when you’re choosing what spell your protagonist might cast, look for the weakest power that could do the trick. Instead of dispersing a whole storm so a ship at sea won’t sink, maybe redirect the wind around the ship or slow it down a little. Your magic doesn’t have to be powerful to feel wondrous; it’s magic. You just have to describe it in a way that makes it feel wondrous rather than mundane.

When characters other than the hero cast magic to establish the world or set the atmosphere, avoid making it look like something your protagonist could replicate. Maybe no one knows how the master wizard is able to summon a stairway of light.

2. Set Flexible Limits

Limits are helpful with every type of magic system, but some kinds of limits are especially useful for arbitrary systems. With rational magic systems, limits are often created by examining the basic operation of magic to find ways that spellcasting could be prevented. For instance, if a wizard needs a staff, that staff could be taken away. If casters need to do martial arts moves, tying them up could keep them from using their abilities.

Those limits are still useful in an arbitrary system. However, arbitrary systems often include so many different magical effects that the issue is not whether characters can cast magic at all, but which spells they can use. If your protagonist previously dispersed a storm to save a ship, and now the big bad is using a storm to threaten characters on a mountain, you need to ban that storm dispersal spell. Otherwise, it will be too easy to rescue those characters.

Storytellers often try to fix this by explaining how this new storm is different. If the protagonist is taking on a challenge that is obviously more difficult than what they did previously, that can work okay. But, in many cases, declaring that a previous spell won’t work in the current situation feels contrived. The more times you use it, the worse it will sound.

Instead, you can create a few rules for your magic system that makes replicating a previous spell harder.

  • If every spell uses up a rare and expensive ingredient, then what spells a mage can cast will depend on what they have on hand.
  • Your protagonist might have to cast what they’ll need in advance. Anytime they get in a fix that’s time sensitive, they’ll have a limited list of spells to work from.
  • Fickle spirits that grant magic can also be used to explain why a spell can’t be repeated. Maybe a different spirit is available every time, or the spirits get bored if they’re asked to repeat the same favor.

Using these kinds of limits, you’ll be able to declare what spells your protagonists have access to for each conflict.

Another common way to limit magic is to give it a significant cost. Spells that make the caster sick or require them to destroy something valuable can be fun additions to a story. However, these costs don’t really fix overpowered spells. In many stories, casting a spell is a matter of life or death. If the whole city is about to go up in smoke, even severe consequences are no longer a deterrent.

3. Keep Track of Everything

As stated above, the spells you invent don’t evaporate afterward; they become a permanent part of your magic system. Once you’ve established that a witch can smoke a catnip joint to summon a horde of cats, your readers will know they can do that for the rest of the story. If you only wanted to create a swarm of cats for one scene, it’ll be easy to forget the catnip spell when it comes time to defeat the plague rats. But while you may have forgotten it, not all your readers will have.

This is why I recommend rigorous note-taking. Every time a character does magic, put it on a big list. Write down its effect and any methods the character uses to get that effect, such as speaking incantations or waving their wand. Be as specific as you can. Once your witch summoned all those cats, did they do her bidding or did they act like they were stopping by of their own free will? You might also want to include the chapter title to make it easier to go back and read the scene the spell is in.

Keeping track of spells will help you in several ways.

  • You can only fix plot holes if you know they’re there. When your characters get in a fix, you can run through your list to see if there are any spells that would get them out of it too easily. Then you can look for a way to change the spell or the situation so that it’s no longer true.
  • You can identify spells to reuse. While new spells have more novelty, reusing a spell once in a while will make your magic system feel more real. Lower-stakes conflicts are the best time to reuse a spell you invented from an earlier scene. If your notes aren’t detailed, read through the scenes where it was last used to make sure it works the same way.
  • You’ll have a great place to start if you want to tweak the rules of your system. For instance, by looking at your spell list, you might find that most spells involve speaking incantations, but two don’t. To give your spellcasting a more consistent feel, you might add incantations to those two spells. You might even find that converting your spell list to a rational system isn’t as hard as you thought.

4. Introduce Spells Before They Matter

If your magic system is rational enough that readers can extrapolate what magic can do even if they’ve never seen it, then you have built-in foreshadowing. That means if your protagonist pulls out a badass new spell at the climax, that will probably qualify as a clever deduction turning point, creating a satisfying ending. But if the protagonist defeats the villain with an unheard of spell in an arbitrary system, it’s a deus ex machina. No one likes those.

This doesn’t mean that the protagonist can’t use magic to defeat the big bad or surmount other obstacles, but it takes some setup. If you’re discovery writing, you’ll need to go back and make revisions to earlier scenes.

Generally, your audience needs to know about a spell and its effects before a protagonist uses it to win a conflict. If your protagonist uses a spell in an early scene, they can pull out that same spell later to defeat a villain. You’ll still need a turning point, of course, but the spell itself won’t feel contrived. It may seem like this takes the fun out of it, but you can spice things up so that using a known spell doesn’t feel perfunctory.

  • Surprise the audience with which spell you use. It’s really satisfying to watch protagonists use an insignificant spell in a clever way to create a big effect. Perhaps the character worked hard on a basic spell that seemed useless until the big moment, creating a prior achievement turning point.
  • Have the character cast the spell successfully for the first time. Introduce a really cool spell that the character hasn’t been able to cast. Be specific about what’s holding them back; you’ll need that to justify why they have a breakthrough at a critical moment. Maybe the spell requires a strong sense of purpose, and they don’t have that until it’s up to them to save the day.
  • Make the protagonist piece together clues to figure out how to cast it. Perhaps a legendary mage opened a magical gateway centuries ago, and no one knows how they did it or how to close it. Plant clues so that your protagonist can figure it out in the nick of time. It’ll be easier to make this reveal click together if you narrow down your spellcasting options. Perhaps the gateway spell is in an ancient book, but it hasn’t worked for anyone who’s tried it. Then the protagonist can figure out the one thing that has to be done differently for it to work.

If a protagonist isn’t solving an important problem, you don’t need to be as cautious. Foreshadowing isn’t required before they cast a spell to make the fruit in their breakfast ripen or craft a mild protective charm to trade for goods at the market.

5. Theme It

I know I say this every time I mention worldbuilding. It’s still true, especially for an arbitrary magic system. Rational magic feels believable not only because the audience understands how it works but also because the rules force all the spellwork to be somewhat consistent. When your magic system is a collection of spells and effects you created when you needed one, you’re likely to end up with an eclectic set. To your audience, some of your spells may feel, well, arbitrary. You want spells to feel natural, not like you made them up on the spot. Even if you did.

Spells are likely to feel contrived rather than believable when they’re different from what you’ve previously established. If the first three spells you pull out are all elemental spells and then your character waves their wand and a smashed piano snaps back into perfect condition, that will draw scrutiny.

Using a theme for your magic system helps protect against this.

  • What atmosphere do you want to create? Should magic be ancient and wondrous, a dark temptation, or wacky high jinks?
  • What is the origin of magic? Does it come from the blood of the old gods, calling their descendants to heroism? Is it cosmic energy that’s only perceived by those who are psychically sensitive?
  • How should magic look aesthetically? Do you see your mages doing fluid dance moves, burying their noses in books, or dropping an eye of newt into a bubbling cauldron?

Using an arbitrary system means you have complete freedom in describing your magic. Unlike in a rational system, in an arbitrary system you don’t have to justify why characters are chanting or holding hands in a circle. If you’re not using that freedom to make spells feel mystical, dangerous, hilarious, or something else, what’s the point?

While you may want to keep your options open, you can also narrow down the breadth of what spells can do. That will help you create a matching set, adding credibility. For more on this, see Creating a Magic System for Superpowers.

I’ve been hard on arbitrary systems because they’re more likely to be used by storytellers who haven’t thought their magic through. Examples abound of stories where the protagonist pulled out a godlike spell only to forget about it in the next scene. However, in the hands of the right storyteller, arbitrary magic systems can be used to great effect.

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  1. Cay Reet

    I do have a rather arbitrary (read: I make it up as I go along) magic system for two of my stories (and two more I have not yet written but am plotting might have one, too) and I’m very careful to write down what my characters do in that aspect. I also try to keep it fitting together (not hard to theme necromancy, of couse) and I do try to figure out what they could all be doing with their powers as they are defined.

    My necromancers are limited by having to use ingredients, rituals, and their own life force. The life force regenerates over time (or can be restored with potions), but if it goes down too far, they will die. Just raising a large number of the dead at once is impossible that way. When Isadora raises an army of skeletons to fight her brother, for instance, she prepares that well in advance, so she only needs some energy for directing and repairing the army during the fight. When Gabrielle calls up the spirit of a dead burglar to learn who killed him, she’s so exhausted afterwards that she almost gets caught by an inquisitor while buying ingredients for the potion – which serves as a lesson to her to do such things in advance the next time.
    I also try to throw in some problems which magic can’t solve, so it’s not only about waving a wand. Or problems which will only be solvable with magic after a more complex solution is figured out, which means it’s going to take the character some thinking and some work.

    I’m not quite sure how to limit my fallen angel, but they might just arbitrarily decided to use or not use what they have… They’re not the viewpoint character for most of the story (a regular human will be), so it’s not as if I have to explain their motives.
    Colin, on the other hand, has no magical powers himself, so any kind of creature he faces can have other magical properties (I’ll still write it all down, of course).

    • Luke Slater

      Where does the Fallen Angel’s power come from? If it’s a residual connection to Heaven, each use could spend from an irreplaceable pool. Heal a gunshot, smite a fool; one more feather drops from their wings – metaphorically or literally – and they feel a little bit further from what they’ve left behind, a little more distant – metaphorically or literally – from the Throne. Alternatively, for more immediate stakes, if the power they now use comes from downstairs, each use could forge another link in the chains that will eventually bind them to Hell’s service.

      • Cay Reet

        Its part of their being – the more they are invested in a situation, the more powers they draw, the more seriously they take everything. Of course, angels don’t have god-like powers, they’re on a lower level than that.

        It’s not fully clear for me at this point, but I’m not actually looking that much for a limit. Raziel is going to be a lot of fun to write. They (angels don’t have a sex, so fallen angels don’t, either) have decided not to join Lucifer in Hell when they fell, but have chosen to live among humans. They’re often bored and do what they want when they want to. The focus is on the human they hang out with, so I don’t need to replain their motives much. I think, to a degree, I’m looking for someone like Alucard from the “Hellsing” series – limiting their own powers because they want a challenge, sort of.

        • Cay Reet

          ‘explain their motives much’ … geez

  2. Dave L

    Not really germane to your point…

    But those are some really cool pics accompanying this post

  3. Sam Victors

    Can it alright to have more than one magic system?

    For example, in one of my story ideas, there are two types of witches; Mortal Witches and Fay Witches.

    Mortal Witches’ magic is given to them by a Cosmic source, and it doesn’t pass on like hereditary. Mortal magic isn’t powerful (though it is strong), as its restricted to things like magical devices, rituals, incantations, potions, poppets, flying ointments, dates, time of the year, etc.

    Fay Witches are mortal magicians with fairy blood in their veins. Their magic is hereditary but can fade away in seven generations if they continue to marry humans. Fay Magic is whimsical, involving colored smokes, tinkling sparks and glitters. It also has a flair for the dramatic, with incantations done in rhymes and couplets or nonsensical words, flying on broomsticks or cloudy ships, and magical ingredients taken from mystical creatures. And yes, some wacky high jinks involved.

    • Cay Reet

      There’s no reason why those two types of magic shouldn’t go together – I don’t see anything which should make one impossible in a world which has the other.

    • Kit

      My thoughts with that would be that it might be a little much for readers to take in and remember if you go into a lot of detail with them both, and that they don’t seem too clearly themed within themselves. You say Mortal magic is ‘restricted’, but the things it’s restricted to seems like a randomly-selected list – I can’t see what any of those elements have in common. As for Fay magic, I don’t know that magical ingredients or flight would necessarily constitute ‘dramatic’. And though the root causes of the two kinds of magic are distinct, the ways they’re cast seems to have some overlap, like ‘potions’ versus ‘magical ingredients’, and ‘incantations’ versus, er, ‘incantations’. Are they not effectively the same magic, just granted to the user by different means and with maybe different cultural aspects regarding casting?

      I don’t see an issue with having multiple systems, but if you want a reader to remember the gist of them, I think they’ll benefit from being tidy, strongly-themed and distinct, even if they are arbitrary.

      • Sam Victors

        I have worked it out.

        Mortal witches tend to be up to date; using regular electronics, chemistry sets, and kitchen appliances such as blenders, microwaves, cooking pots and saucepans. Disguising their potions as perfumes, moisturizers, ointments, and wine bottles. Using Flying Ointment instead of brooms (they just rub the ointment on themselves and they can fly). Though they would still use crystals and horseshoes as talismans and for aesthetics. They also still use poppet dolls and familiars. They also use guns and other modern weapons.

        Fay Witches tend to be traditional, using cauldrons, brooms, spinning wheels, distaffs, hourglasses, elaborate robes, etc. They’re old-fashioned.

  4. Star of Hope

    A question I asked myself lately regards mind-reading is the following: How would Mind reading even affect the person having this skill or even society for that matter?

    To almost all humans the inner machinations of their minds are an enigma to many and having a skill that penetrates that enigma would reveal a lot about humans we never have seen before and could even change the character from the person having this power. Would they be less disgusted by the way people act, if they can see the inner thoughts of their fellow people or just becoming more uncomfortable with human companionship? I wish more people would exploit this type of thinking and we could have a sensible discussion about how minds work. I bet psychologist would greatly benefit from this skill and we might even make more advanced on that field, as this field is relatively young in comparison to older sciences like chemistry and physics. Here is my idea for a podcast: Mind reading!

    Regarding power creep, Mind reading can work if the person has to put effort in order to read their minds by making their brains do it. Also Mind reading can also create conflicts through revealing bad things someone has done or lead to a misunderstanding if the thought has been mispresented. I think the ability is best used with intent and only when someone from the good guys keeps a suspicious secret or if we want to interrogate the villians.
    If you made it too powerful as the article suggests, it would make all conflicts disappear at bet and at worst creates a more creepy and awful conflict through the pain of reading too many thoughts at once, similarly with Superman’s increased senses in the terrible Zack Snyder movie “Man of Steel”(unless you made it like with sounds and they can safely ignore some thoughts they hear).

    • Gwen

      I think Mind “syncing” might be a good low power mind reading. Like in Dracula, they have to hypnotize Mina and she doesn’t get thoughts but impressions and senses. It is very useful but has the negative side effect of working both ways.

      I wish more stories used that instead of just as a bonding element to an ally.

  5. Julia M.

    One solution is to have the mind reading character not be present at the places a spymight be. Perhaps they’re a peasant or lower ranked and not allowed in the castle. Perhaps they’re out fighting, and they can’t get to the spy anytime soon. Perhaps they have a specific set of skills that are needed elsewhere. (They’re a shapeshifter, too, for example, and they need to use their powers to communicate with a dragon.)

    Or, have everybody powerful enough have at least a slight mind block. Mind reading is still good for consensual and secret communication, and it senses feelings with the block, but it’s not clear enough to make out.

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