Law of contagion

In numerous works of fantasy, the law of contagion is a magical law that suggests that once two people or objects have been in contact a magical link persists between them unless or until a formal cleansing, consecration, exorcism, or other act of banishing breaks the non-material bond. The first description of the law of contagion appeared in The Golden Bough by James George Frazer. Other authors have noted parallels in quantum physics.

Harry Turtledove employs the law of contagion as a daily fact of life, and/or a normal part of the landscape, in numerous fantasy works of his, including but not limited to Darkness, Elabon, Videssos, and The War Between the Provinces.