Andy Kessler has a clear explaination of what the money supply is and why we’re in for a whole lot of hurt if it just keeps getting bigger.
I like to think of the economy as a giant bucket filled with money (money supply) sloshing around the bucket (velocity). We all hope the bucket is filled to the rim. But, in normal times, the economy grows every year. Population increases, too, so the size of the bucket has to grow to handle the transactions of more people who like to eat and drink. So more money needs to be created to fill the bigger bucket. That’s pretty straightforward.
But now the hard part. Someone is out there inventing something useful, refrigeration, steamships, ATM machines (sic)–something productive that increases the output per worker hour. Productivity increases the size and wealth of the economy above and beyond population growth. How much? Who knows? Still, more money needs to be created to fill the bigger bucket/economy. And to make matters worse, since no one knows what the velocity of money is, no one really knows how much money supply is needed so the economy will work just right. It’s virtually impossible to fill the bucket up just to the rim. The Fed has to guess.