Because it is a debt. In the U.S. all debts, public or private, may be paid in "cash" with Federal Reserve Notes (fiat currency). You'd need to have your contr

Because it is a debt. In the U.S. all debts, public or private, may be paid in "cash" with Federal Reserve Notes (fiat currency). You'd need to have your contract signed and agreed upon prior to rendering services or goods.