Law of similarity/contagion

In numerous works of fantasy, the law of similarity and the law of contagion are magical laws that suggest 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 was written by German ethnographist Richard Andree in Ethnographische Parallelen und Vergleiche (1878), and the law of contagion was similarly codified in The Golden Bough (1890) by Scottish folklorist James George Frazer. Other authors have noted parallels in quantum physics.

Harry Turtledove employs the laws of similarity and 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, the Elabon Series, Every Inch a King, the Videssos Series, and The War Between the Provinces.