According to Credit Theory, money was just an abstract unit to measure debt

Mitchell-Innes was an exponent of what came to be known as the Credit Theory of money, a position that over the course of the nineteenth century had its most avid proponents not in Mitchell-Innes’s native Britain but in the two up-and-coming rival powers of the day, the United States and Germany.

Credit Theorists insisted that money is not a commodity but an accounting tool. In other words, it is not a “thing” at all.

For a Credit Theorist can no more touch a dollar or a deutschmark than you can touch an hour or a cubic centimeter. Units of currency are merely abstract units of measurement, and as the credit theorists correctly noted, historically, such abstract systems of accounting emerged long before the use of any particular token of exchange.

The obvious next question is: If money is a just a yardstick, what then does it measure? The answer was simple: debt.

A coin is, effectively, an IOU. Whereas conventional wisdom holds that a banknote is, or should be, a promise to pay a certain amount of “real money” (gold, silver, whatever that might be taken to mean), Credit Theorists argued that a banknote is simply the promise to pay something of the same value as an ounce of gold. But that’s all that money ever is.

There’s no fundamental difference in this respect between a silver dollar, a Susan B. Anthony dollar coin made of a copper-nickel alloy designed to look vaguely like gold, a green piece of paper with a picture of George Washington on it, or a digital blip on some bank’s computer.

This is one of the many passages and charts Alessandro finds in books and articles on a daily basis. They span many disciplines, including:

Alessandro occasionally adds a personal note to them. The whole collection is available here.