She talked about "night logic" systems, which create the illusion that there's a working system of magic underneath your story. She asks these questions:
- Who has it?
- What does it do?
- How do you make it happen?
- How is a user affected?
- How is the world affected?
- How are magic users grouped and perceived?
It's an Open Fantasy (as opposed to a Closed Fantasy) in which everyone in the world knows about the magic. It's not a fairyland a person stumbles into. In her world, magic is passed from hand to hand, so people wear gloves. An ungloved hand is like someone coming at you with a knife. She worked through all these details and answered the questions above.
Then she asks additional questions such as these:
- What is the cost of magic? Give it a cost and it automatically feels more real. (Isolation and the weight of responsibility are common costs.)
- What are the limits of magic? All magic needs to be calibrated. You can use the same six questions to define the limits.
- What is a potential model for your magic?
- What do the rules of the magic say about the world? Magic is narrative (and also metaphor).
Dark is Rising by Susan Cooper
Skin Hunger by Kathleen Duey
Sabriel by Garth Nix
Demon's Lexicon by Sarah Rees Brennan
City of Bones by Cassandra Clare
"Once you've created your magic system, the best thing you can do is try and break it," she says. "That is what your readers will do. And to a certain extent, that is what characters will do." (It's good to have friends who are gamers, she adds, because they ask incredibly annoying questions.)