Brett Scott’s article, “So you want to invent your own currency” makes for fascinating reading.
If money is an object, it must be an enchanted one, charged up with value by a subtle cultural process. Why else would anyone exchange a box of coffee for a rectangle of paper? Shopkeepers accept the paper because they believe that it has abstract value — because, in turn, they believe that others believe it, too. The value is circular, predicated on each person believing that others believe in it. You hand over your money and claim something from the shopkeeper, almost as if the coffee were owed to you. Then they take the claim that was previously yours and use it to claim something from someone else. We all trust each other to value money — but this still means that every monetary transaction is a leap of faith. And faith has to be carefully maintained.