The essential idea of "legal tender" is that quality given to money by law which obliges the creditor to receive it in full satisfaction of a past debt when expressed in general terms of the money of a country. A debt is a sum of money due by contract, express or implied. When our laws, for instance, declare that United States notes are legal tender--and this is the only complete designation of a legal-tender money--for "all debts public and private," it must be understood that this provision does not cover any operations not arising from contract. Current buying and selling do not make a situation calling for legal tender; a purchaser cannot compel the delivery of goods over a counter by offering legal-tender money for them, because, as yet, no debt has been created.[6] Contracts made in general terms of the money units of the country must necessarily often be interpreted by the courts. The existence of contracts calling for a given sum of dollars and the necessity of adjudicating and enforcing such contracts, require that there should be an accurate legal interpretation of what a dollar is. As every one knows, the name, or unit of account, is affixed to a given number of grains of a specified fineness of a certain metal. This being the standard, and this having been chosen by the concurring habits of the business world, it is fit that the law should designate that, when only dollars are mentioned in a contract, it should be satisfied only by the payment of that which is the standard money of the community.