Since they began to be produced in 1914, Federal Reserve notes have always had a promise or obligation printed on their face. But over time this promise has changed. I thought it would be fun to go through the evolution of the promise as an exercise in understanding how the U.S.'s monetary plumbing has changed. The original 1914 series of Federal Reserve notes had the above stipulation printed on it. It's tough to read, so I've reproduced it in full below: "This note is receivable by all national and member banks and Federal Reserve Banks and for all taxes, customs and other public dues. It is redeemable in gold on demand at the Treasury Department of the United States in the city of Washington, District of Columbia or in gold or lawful money at any Federal Reserve Bank." There were really four promises here. The first was that all banks who were members of the Federal Reserve system would accept notes at their counter, as would the Reserve banks themselves—i.e. t...