The FLUBA Committee on Dealing With the Uneducable notes this exchange from Russell Roberts' interview with Milton Friedman:
Russ Roberts: Focusing on the central bank role, going back again to the '70s when I was in school and shortly after your book came out, the focus was on the money supply—the quantity of money, counting it, controlling it through open market operations.
Something changed in the last 25 or 30 years. That's not what Alan Greenspan or Ben Bernanke talk about. They talk about other things and they play with that short-term interest rate, not the so-called stock of money that you focused on so intensely in the book.
Milton Friedman: That's what the talk about but that's not what they do.
Russ Roberts: What do they do?
Milton Friedman: They use the short-term interest rate as a way of controlling the quantity of money. ....
The Fed says the short-term interest rate should be 4.5 percent. How do they keep it there? By buying and selling securities on the open market. Now you're Mr. Bernanke; you're Mr. Greenspan. You're watching that. And with the current short-term interest rate, you find that the quantity of money is starting to creep up more rapidly than you really want. Well, then you will tend to be favorable to raising to a higher rate of interest.
At that higher rate of interest, the demand for money is less and so the supply of money under that phenomenon, instead of having to sell government bonds to keep it there, they have to buy government bonds to keep it there or vice versa. Maybe I'm getting it mixed up. But in any event, the short-term interest rate is a tool with which you can control the quantity of money.
Russ Roberts: But they don't talk about it that way.
Milton Friedman: No, they don't talk about it that way.