Money or the monetary unit serves not only as a measure of value for the present, but also as a standard for future payments. It is a medium for credit transactions or deferred payments. Most contracts are payable in terms of money and they often run for long periods of time. Justice between borrower and lender requires that the contractual payment shall have the same value at maturity as at the beginning of the contract. It is important, therefore, that the standard shall possess comparative stability of value. But no commodity, not even gold, has perfect stability of value. Since every commodity is subject to changes in the conditions affecting its production, it is impossible to find a perfect standard of deferred payments. And yet some standard must be chosen. Owing to their durability and to the comparatively small annual addition to the world's supply the precious metals are least likely to vary in value on account of changes affecting themselves. Through a long period of evolution the great commercial nations have come to regard gold as the commodity best fitted to serve as a standard. From time to time, however, various proposals have been made to establish a more stable standard of deferred payments. Of these proposals, bimetallism has received most attention.