Formal feud or vendetta under the rules of the Great Convention carried on according to the strictest limitations. (See Judge of the Change.) Originally the rules were designed to protect innocent bystanders.

Kanly was the enactment of a formal feud or vendetta in a manner that complied with the Great Convention. It often resulted in an official war of attrition between two opponents, usually Great Houses during the days of the Old Imperium.

The act of kanly was originally created as a way of allowing bitter disputes to be resolved without any harm being brought upon innocent bystanders. It was similar in many ways to the ancient duels made on Earth, although it usually had much broader ramifications. Kanly (kanli) is a Turkish word meaning sworn enemy (bloody, from the stem kan, blood). This animosity continued from father to son, until the last child was dead or the two families made peace.

Kanly has occurred most famously between House Atreides and House Harkonnen, and between House Moritani and House Ecaz. In both situations, Kanly resulted in the dramatic success of the former party over the latter.

Kanly required that certain forms of conflict were permitted, while others were not. The use of nuclear weapons was forbidden, for example. Usage of nuclear weapons usually meant a sentence of exile.