This is saying that the obligation of a contract to pay money is not an obligation to pay what both the law and the parties recognize as money, at the time when the contract is made, but only such substitute as congress shall afterwards prescribe, "when the payment is to be made."
This opinion was given by a majority of the court in the year 1870.
In another opinion the court says:
Under the power to coin money, and to regulate its value, congress may issue coins of same denomination [that is, bearing the same name] as those already current by law, but of less intrinsic value than those, by reason of containing a less weight of the precious metals, and thereby enable debtors to discharge their debts by the payment of coins of the less real value. A contract to pay a certain sum of money, without any stipulation as to the kind of money in which it shall be made, may always be satisfied by payment of that sum [that is, that nominal amount] in any currency which is lawful money at the place and time at which payment is to be made.—Juilliard vs. Greenman, 110 U. S. Reports, 449.
This opinion was given by the entire court—save one, Field—at the October term of 1883.
Both these opinions are distinct declarations of the power of congress to alter men's contracts, after they are made, by simply retaining the name, while altering the thing, that is agreed to be paid.
In both these cases, the court means distinctly to say that, after the parties to a contract have agreed upon the number of dollars to be paid, congress has power to reduce the value of the dollar, and authorize all debtors to pay the less valuable dollar, instead of the one agreed on.
In other words, the court means to say that, after a contract has been made for the payment of a certain number of dollars, congress has power to alter the meaning of the word dollar, and thus authorize the debtor to pay in something different from, and less valuable than, the thing he agreed to pay.
Well, if congress has power to alter men's contracts, after they are made, by altering the meaning of the word dollar, and thus reducing the value of the debt, it has a precisely equal power to increase the value of the dollar, and thus compel the debtor to pay more than he agreed to pay.
Congress has evidently just as much right to increase the value of the dollar, after a contract has been made, as it has to reduce its value. It has, therefore, just as much right to cheat debtors, by compelling them to pay more than they agreed to pay, as it has to cheat creditors, by compelling them to accept less than they agreed to accept.