In Propp's morphology, a warning or prohibition given to a character, which is typically violated to advance the plot.
Interdiction is the second of Vladimir Propp's 31 narrative functions, following Absentation (a family member leaves home). An interdiction is a command or warning: 'Don't go into the forest,' 'Don't open that door,' 'Don't speak for seven years.' In nearly all cases, the interdiction is violated, either by the hero or by another character, which sets the plot in motion. Common examples include: Little Red Riding Hood's mother telling her to stay on the path, Bluebeard's prohibition against opening the forbidden room, and Beauty's promise not to leave the Beast's castle. The interdiction-violation pattern reflects a universal narrative logic: rules exist to be broken, and transgression drives story.