This post is about something I don't understand.
Let's start out simple. There are two parallel imaginary worlds: the green world and the red world.
In the green world people use positively-valued green money as the medium of exchange. If I buy something I give the seller my green money in exchange. Green money flows in the opposite direction from all other goods and financial assets. I am not allowed to take green money from someone without their consent. Only the issuer of green money is allowed to create green money. The borrower of green money undertakes an obligation to give green money to the lender at some future date.
In the red world people use negatively-valued red money as the medium of exchange. If I buy something the seller gives me his red money in exchange. Red money flows in the same direction as goods and financial assets. I am not allowed to give red money to someone without their consent. Only the issuer of red money is allowed to destroy red money. The lender of red money undertakes an obligation to accept red money from the borrower at some future date.
There is a symmetry between the red and green worlds; one is the negative mirror-image of the other. But there is also one asymmetry: the red world has a fundamental problem. Each individual can increase his utility by buying more goods and selling less goods, thereby accumulating an infinitely large stock of red money. The bank that issues the red money needs to put some limit on each customer's holdings of red money, to ensure this does not happen. This is not a problem in the green world, because having zero stock of green money sets a natural limit that stops an individual buying, and the individual is fully aware of that limit.
The real world is a red/green world. It has both green money and red money. A positive balance in a chequing account is green money. A negative balance in a chequing account is red money. If I sell my car to Andy, who gives me a cheque for $1,000, the bank reduces my overdraft by $1,000 and increases Andy's overdraft by $1,000. The bank has transferred $1,000 of red money from me to Andy. IIRC my father nearly always used red money. He nearly always ran an overdraft, paying it off once a year when he sold the harvest, to keep the bank manager happy.
In a red/green world, we can define the stock of "gross money" as the absolute sum of red money plus green money, and we can define the stock of "net money" as green money minus red money.
The Bank of Canada.
Canadian commercial banks have chequing accounts at the Bank of Canada. It's a red/green system. If I bank at BMO, and Andy banks at TD, and I sell my car to Andy who pays by cheque, BMO now has a positive balance of $1,000 at the Bank of Canada, and TD now has a negative balance of $1,000 at the Bank of Canada.
But the Bank of Canada sets a 50 basis point spread between the interest it charges TD on red money and the interest it pays BMO on green money. So BMO and TD can both gain if BMO lends TD $1,000 to eliminate both balances, at a rate of interest that splits the spread between the Bank of Canada's two rates of interest. Which is what Canadian commercial banks normally do. So the gross money stock is small, and normally the same as the equally small net money stock, by the end of each day.
- If the Bank of Canada acted differently, and set the same rate of interest on both red and green money, so the spread is zero, then there would be no incentive for BMO and TD to trade in the overnight market. If BMO's customers always sold more to TD customers than vice versa, BMO's chequing account at the Bank of Canada would become more and more positive, and TD's chequing account at the Bank of Canada would get more and more negative. The gross money stock would rise without limit, though the net money stock would not change.
- Or if TD were a risky bank, and if that risk were bigger than a 50 basis point compensation would warrant, there would be no rate of interest at which BMO would lend to TD that TD would accept. Again it is possible for BMO's account at the Bank of Canada to become increasingly positive, and TD's account increasingly negative.
A red/green world faces the same fundamental problem as the red world. A commercial bank will put a limit on each customer's overdraft. Similarly, the Bank of Canada must, at least implicitly, place a limit on commercial banks' overdrafts.
The European Central Bank.
Eurozone national banks have chequing accounts at the European Central Bank. It's a red/green system. They call it TARGET2. But unlike the Bank of Canada's red/green system, there doesn't seem to be any functioning equivalent to the overnight market that eliminates negative balances every evening. The ECB can hold the net money stock fixed, but the gross money stock can rise without limit. Here is the recent data (pdf).
I think you can see where this is going. I don't understand how it is supposed to work.