One of the most defining features of the fantasy genre is magic. It permeates almost every fantasy story, whether in role playing games, novels, or movies. Dealing with the consequences of magic can mean the difference between a compelling narrative and one where your readers are scratching their heads.

If you look at Dungeons and Dragons, or most other role playing games, they have spells like ESP, Detect Thoughts, or even Detect Alignment. The question came to me, why are there any criminals? Couldn’t the local lord just make evil illegal? The spells are 100% accurate, so why is this even a thing? If someone committed a murder, couldn’t they just ask suspects or even just pry the thoughts out of their heads? As the world builder, it’s your job to make sure the readers or players aren’t wondering the same thing.

When building your magic system, consider the effects that system will have on your world. If a wizard can teleport anyone or anything hundreds of miles, why are there still trade caravans? If priests can ask the gods for guidance, why are there wars?

D&D does a lot of this by making these spells high level. If only a really powerful wizard can teleport things, they will likely be rich enough that they don’t need to transport goods, no matter the price. Divine spells don’t give access to the gods directly. Other spells are unbelievably expensive, so it wouldn’t be prudent to use for everyday activities.

For my world, all spells come with side effects. The more powerful the spell, the more difficult the casting and the more severe the consequences for failure. On top of that, my legal system is set up specifically for dealing with magic using investigators. Add into that priesthoods that regulate the magic they teach and what priests are allowed to do with it. It’s hard to find someone who will resurrect someone when the only magic capable of doing that is taught by a priesthood who have an edict against resurrection.

Finally, think about how spells will interact with each other. If the authorities have spells, there will always be people trying to circumvent them. A murderer might learn some Druidic magic to implicate someone else. There will be an arms race, of sorts, just like with the legal system in our world. Our police discover finger prints as a method of identification, criminals not only use gloves, but have been known to put finger pads with other people’s finger prints. Methods of cleaning up crime scenes have progressed. Cyber attacks have been used to corrupt evidence. As one side gains an advantage, the other side will adapt to negate that advantage. Consider how that will change crime, wars, espionage, and daily living.

Then, think about all the interesting stories you have playing with those ideas.