What is a Mystery?

We were talking on Discord about mystery game campaigns and ended up asking the basic question. What is a mystery? I think a mystery is an epistemic problem. It asks who killed the king, why the people are disappearing at night, or what the monster actually does. There is something about the fictional world that you don't understand and the challenge is figuring out what is true. A mystery isn't a puzzle. A puzzle is a procedural problem. It asks how you open the secret door, how you cross the river, or what order you should kill these enemies in. A mystery might involve procedural problems in its solution, and hidden information may be involved in solving a puzzle, but they are still different kinds of problems. The third thing is investigation, which is related to mystery but not the same thing. An investigation is about acquiring information, while a mystery is about understanding it. You could begin a session by handing the players the witness statements, the map, the autopsy…