SANJIESAN LORE / Knowledge and powers
Decide what a truth-sensing power actually detects
The phrase detects lies can conceal several different abilities. Does a character detect a knowingly false statement, an inaccurate statement or something else? Sanderson’s First Law essay makes reader understanding relevant when magic resolves conflict. For an original mystery, define what the signal means before letting it settle an accusation.
Write three different statements
Choose an invented event, such as a parcel arriving at a workshop. Write one statement by a witness who is correct, one by a person sincerely mistaken and one by someone deliberately concealing what they know. Decide how the ability responds in each case under the rule you intend. Do not use real psychological claims to explain a magical detector; these responses are choices within your fictional system.
Separate the signal from the observer’s conclusion
Choose the visible or felt signal and write what the user believes it means. A signal about sincerity does not automatically identify what actually happened to the parcel. Let a character overinterpret it only if the story recognises that as their inference. The narrator’s wording should not quietly turn a limited ability into an all-knowing authority whenever the investigation reaches a difficult point.
Test the accusation without adding a new rule
Write the confrontation and list what evidence remains necessary after the ability is used. Perhaps the characters still need a location, another witness or an explanation for a mistaken belief. If the ending requires a new signal category, prepare that earlier or revise the solution. The ability can sharpen the mystery by eliminating one kind of uncertainty while leaving another, rather than replacing the whole investigation.