Reciprocity

Second, the reciprocal performances of the parties must in some sense be equal in value…. We cannot here speak of an exact identity, for it makes no sense at all to exchange, say, a book or idea in return for exactly the same book or idea. The bond of reciprocity unites men, not simply in spite of their differences but because of their differences….

Source: Lon L. Fuller, The Morality of Law, pp. 23–24, 1964
Taken From: Bruce Benson, The Enterprise of Customary Law, 6/29/2007