The tendency to reciprocate - to return good for good and evil for evil - is a potent force in human life, and the concept of reciprocity is closely connected to fundamental notions of 'justice', 'obligation' or 'duty', 'gratitude' and 'equality'. Lawrence Becker presents a sustained argument about reciprocity, beginning with the strategy for developing a moral theory of the virtues. He considers the concept of reciprocity in detail, contending that it is a basic virtue that provides the basis for parental authority, obligations to future generations, and obedience to law.