"The Congress shall have power ... to make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this Constitution in the government of the United States, or in any department or officer thereof." This necessary and proper clause is used to cover any governmental action not enumerated in the Constitution. Thus, it creates implied powers. These are powers that are not stated in the Constitution, but are implied by the government's need to carry out all of its functions.
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The framers of the Constitution considered the establishment of a single national currency an important function of government. Initially, only gold coins were issued. The charter of the First Bank of the United States (1791) gave it the right to issue bank notes, but the bank notes were not legal tender. In 1863, they were made legal tender, and were called "greenbacks." At first, the Supreme Court stated that the issuing of greenbacks was unconstitutional (Hepurn v. Griswold), since the Constitution spoke only of coining money. In two subsequent cases, Legal Tender of 1871 and Julliar v. Greenman, the Court changed its mind and declared greenbacks constitutional.