Rex Madden

“An IOU which remains for ever a contract between just two parties is nothing more than a loan. It is credit, but it is not money. It is when that IOU can be passed on to a third party—when it is able to be “negotiated” or “endorsed,” in the financial jargon—that credit comes to life and starts to serve as money. Money, in other words, is not just credit—but transferable credit.”
― Felix Martin, Money: The Unauthorized Biography