Article One of the United States Constitution
States may not exercise certain powers reserved for the federal government: they may not enter into treaties, alliances or confederations, grant letters of marque or reprisal, coin money or issue bills of credit (such as currency). Furthermore, no state may make anything but gold and silver coin a tender in payment of debts, which expressly forbids any state government (but not the federal government) from "making a tender" (i.e., authorizing something that may be offered in payment) of any type or form of money to meet any financial obligation, unless that form of money is coins made of gold or silver (or a medium of exchange backed by and redeemable in gold or silver coins, as noted in Farmers & Merchants Bank v. Federal Reserve Bank). Much of this clause is devoted to preventing the States from using or creating any currency other than that created by Congress. In Federalist no. 44, Madison explains that "... it may be observed that the same reasons which shew the necessity of denying to the States the power of regulating coin, prove with equal force that they ought not to be at liberty to substitute a paper medium in the place of coin. Had every State a right to regulate the value of its coin, there might be as many different currencies as States; and thus the intercourse among them would be impeded." Moreover, the states may not pass bills of attainder, enact ex post facto laws, impair the obligation of contracts, or grant titles of nobility.