When Demosthenes, in On the Liberty of the Rhodians, distinguished between the equal justice within Athens and the anarchy and amorality among states, he distanced himself from those engaged in critiques of all morality. His argument also implied a rejection of another way of conceiving of internal and interstate relations: they might both be subject to the same moral code. This equivalence is usually due to the application of individual morality to the interaction of states. A central part of the moral code that the Athenians applied to the actions of states was the ideal of reciprocity.

Reciprocity requires that people or states requite the treatment they have received. The requital can be of favors or gifts (positive reciprocity) or of injuries (negative reciprocity, retaliation). Although we shall see significant differences between the roots and consequences of the two types of reciprocity, both require requital for past actions. The use of identical vocabulary for paying back favors and injuries confirms the unity of the Greek concept of reciprocity.

The obligation to pay back good and bad was strong, but was not enforced by law. So, the requirement of requital was on a different plane from the obligation to pay war taxes or not to murder. Its enforcement was not dependent on a central state power. Rather a person's sense of honor, closely linked to his reputation in the community, required reciprocity. It was shameful rather than illegal either to abandon a friend or to allow an injury to remain unavenged.