Another suggestion is that the goods returned should represent the same sacrifice as those loaned.

Here again the difficulty is in the lack of a standard applicable to all men.

Whose sacrifice?
That of the lender, who may be rich, or that of the borrower, who may be poor?
Some have supposed that the condition of equal sacrifices was met by the labor standard, according to which the sum returned should purchase the same number of days of labor as when borrowed.

But what kind of labor is to be taken, that of the lender or that of the borrower or that of some one else?
Labor is of many different qualities, which can be exactly compared only through their objective value in terms of some one good.[20] It must be recognized that any possible concrete standard of deferred payments will sometimes work hardship in individual cases.

The best average results for justice and social welfare will be secured by measuring debts in some standard that will change least often, and least rapidly, in relation to the great majority of people of all classes in the community.
Sec.15.