Norm of reciprocity

The norm of reciprocity requires that people repay in kind what others have done for them.^[1] It can be understood as the expectation that people will respond to each other by returning benefits for benefits, and with either indifference or hostility to harms. The social norm of reciprocity may take different forms in different areas of social life, or in different societies. This is distinct from related ideas such as gratitude, the Golden Rule, or mutual goodwill. See reciprocity (social and political philosophy) for an analysis of the concepts involved.

The norm of reciprocity mirrors the concept of reciprocal altruism in evolutionary biology. However, evolutionary theory and therefore sociobiology was not well-received by mainstream psychologists. This led to reciprocal altruism being studied instead under a new social-psychological concept: the norm of reciprocity. Reciprocal altruism has been applied to various species, including humans, while mainstream psychologists use the norm of reciprocity only to explain humans.^{[citation needed]}

A norm of reciprocity motivates, creates, sustains, and regulates the cooperative behavior required for self-sustaining social organizations. It limits the damage done by unscrupulous people, and contributes to social system stability.^[2] For more details, see the discussions in tit for tat and reciprocity (social psychology). The power and ubiquity of the norm of reciprocity can be used against the unwary, however, and is the basis for the success of many malicious confidence games, advertising and marketing campaigns, and varieties of propaganda in which a small gift of some kind is proffered with the expectation of producing in the recipient an eagerness to reciprocate (by purchasing a product, making a donation, or becoming more receptive to a line of argument).

For some legal scholars, reciprocity underpins international law "and the law of war specifically".^[3] Until well after World War II ended in 1945, the norm of reciprocity provided a justification for conduct in armed conflict.^[4] British jurist Hersch Lauterpacht noted in 1953 that "it is impossible to visualize the conduct of hostilities in which one side would be bound by rules of warfare without benefiting from them and the other side would benefit from rules of warfare without being bound by them."^[5]